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| rev. b information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of analog devices. a lc 2 mos complete, 8-bit analog i/0 systems ad7569/ad7669 one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 617/329-4700 world wide web site: http://www.analog.com fax: 617/326-8703 ? analog devices, inc., 1996 features 2 m s adc with track/hold 1 m s dac with output amplifier ad7569, single dac output ad7669, dual dac output on-chip bandgap reference fast bus interface single or dual 5 v supplies general description the ad7569/ad7669 is a complete, 8-bit, analog i/o system on a single monolithic chip. the ad7569 contains a high speed successive approximation adc with 2 m s conversion time, a track/ hold with 200 khz bandwidth, a dac and an output buffer ampli- fier with 1 m s settling time. a temperature-compensated 1.25 v bandgap reference provides a precision reference voltage for the adc and the dac. the ad7669 is similar, but contains two dacs with output buffer amplifiers. a choice of analog input/output ranges is available. using a sup- ply voltage of +5 v, input and output ranges of zero to 1.25 v and zero to 2.5 volts may be programmed using the range in- put pin. using a 5 v supply, bipolar ranges of 1.25 v or 2.5 v may be programmed. digital interfacing is via an 8-bit i/o port and standard micro- processor control lines. bus interface timing is extremely fast, al- lowing easy connection to all popular 8-bit microprocessors. a separate start convert line controls the track/hold and adc to give precise control of the sampling period. the ad7569/ad7669 is fabricated in linear-compatible cmos (lc 2 mos), an advanced, mixed technology process combining precision bipolar circuits with low power cmos logic. the ad7569 is packaged in a 24-pin, 0.3" wide skinny dip, a 24-terminal soic and 28-terminal plcc and lccc packages. the ad7669 is available in a 28-pin, 0.6" plastic dip, 28-terminal soic and 28-terminal plcc package. ad7569 functional block diagram ad7669 functional block diagram product highlights 1. complete analog i/o on a single chip. the ad7569/ad7669 provides everything necessary to interface a microprocessor to the analog world. no external components or user trims are required and the overall accu- racy of the system is tightly specified, eliminating the need to calculate error budgets from individual component specifications. 2. dynamic specifications for dsp users. in addition to the traditional adc and dac specifications, the ad7569/ad7669 is specified for ac parameters, includ- ing signal-to-noise ratio, distortion and input bandwidth. 3. fast microprocessor interface. the ad7569/ad7669 has bus interface timing compatible with all modern microprocessors, with bus access and relin- quish times less than 75 ns and write pulse width less than 80 ns.
dac specifications 1 ad7569 j, a versions 3 ad7569 ad7669 k, b ad7569 ad7569 parameter j version versions s version t version units conditions/comments static performance resolution 4 8 8 8 8 bits total unadjusted error 5 2 2 3 3 lsb typ relative accuracy 5 1 1/2 1 1/2 lsb max differential nonlinearity 5 1 3/4 1 3/4 lsb max guaranteed monotonic unipolar offset error dac data is all 0s; v ss = 0 v @ +25 c 2 1.5 2 1.5 lsb max typical tempco is 10 m v/ c for +1.25 v range t min to t max 2.5 2 2.5 2 lsb max bipolar zero offset error dac data is all 0s; v ss = C5 v @ +25 c 2 1 5 2 1.5 lsb max typical tempco is 20 m v/ c for 1.25 v range t min to t max 2.5 2 2.5 2 lsb max full-scale error 6 (ad7569 only) v dd = 5 v @ +25 c 2 1 2 1 lsb max t min to t max 3 2 4 3 lsb max full-scale error 6 (ad7669 only) v dd = 5 v @ +25 c 3 lsb max t min to t max 4.5 lsb max daca/dacb full-scale error match 6 (ad7669 only) 2.5 lsb max v dd = 5 v d full scale/ d v dd , t a = +25 c 0.5 0.5 0.5 0.5 lsb max v out = 2.5 v; d v dd = 5% d full scale/ d v ss , t a = +25 c 0.5 0.5 0.5 0.5 lsb max v out = C2.5 v; d v ss = 5% load regulation at full scale 0.2 0.2 0.2 0.2 lsb max r l = 2 k w to /c dynamic performance signal-to-noise ratio 5 (snr) 44 46 44 46 db min v out = 20 khz full-scale sine wave with f sampling = 400 khz total harmonic distortion 5 (thd) 48 48 48 48 db max v out = 20 khz full-scale sine wave with f sampling = 400 khz intermodulation distortion 5 (imd) 55 55 55 55 db typ fa = 18.4 khz, fb = 14.5 khz with f sampling = 400 khz analog output output voltage ranges unipolar 0 to +1.25/2.5 volts v dd = +5 v, v ss = 0 v bipolar 1.25/ 2.5 volts v dd = +5 v, v ss = C5 v logic inputs cs , x /b, wr , range, reset , db0Cdb7 input low voltage, v inl 0.8 0.8 0.8 0.8 v max input high voltage, v inh 2.4 2.4 2.4 2.4 v min input leakage current 10 10 10 10 m a max v in = 0 to v dd input capacitance 7 10 10 10 10 pf max db0Cdb7 input coding (single supply) binary input coding (dual supply) 2s complement ac characterlstics 7 voltage output settling time settling time to within 1/2 lsb of final value positive full-scale change 2 2 2 2 m s max typically 1 m s negative full-scale change (single supply) 4 4 4 4 m s max typically 2 m s negative full-scale change (dual supply) 2 2 2 2 m s max typically 1 m s digital-to-analog glitch impulse 5 15 15 15 15 nv secs typ digital feedthrough 5 1 1 1 1 nv secs typ v in to v out isolation 60 60 60 60 db typ v in = 2.5 v, 50 khz sine wave dac to dac crosstalk 5 (ad7669 only) 1 nv secs typ daca to dacb isolation 5 (ad7669 only) C70 db max power requirements v dd range 4.75/5.25 4.75/5.25 4.75/5.25 4.75/5.25 v min/v max for specified performance v ss range (dual supplies) C4.75/C5.25 C4.75/C5.25 C4.75/C5.25 C4.75/C5.25 v min/v max specified performance also applies to v ss = 0 v for unipolar ranges. i dd v out = v in = 2.5 v; logic inputs = 2.4 v; clk = 0.8 v (ad7569) 13 13 13 13 ma max output unloaded (ad7669) 18 ma max outputs unloaded i ss (dual supplies) v out = v in = C2.5 v; logic inputs = 2.4 v; clk = 0.8 v (ad7569) 4 4 4 4 ma max output unloaded (ad7669) 6 ma max outputs unloaded dac/adc matching gain matching 6 v in to v out match with v in = 2.5 v, @ +25 c 1 111% typ20 khz sine wave t min to t max 1 111% typ notes 1 specifications apply to both dacs in the ad7669. v out applies to both v out a and v out b of the ad7669. 2 except where noted, specifications apply for all output ranges including bipolar ranges with dual supply operation. 3 temperature ranges as follows: j, k versions; 0 c to +70 c a, b versions; C40 c to +85 c s, t versions; C55 c to +125 c 4 1 lsb = 4.88 mv for 0 v to +1.25 v output range, 9.76 mv for 0 v to +2.5 v and 1.25 v ranges and 19.5 mv for 2.5 v range. 5 see terminology. 6 includes internal voltage reference error and is calculated after offset error has been adjusted out. ideal unipolar full-scale voltage is (fs C 1 lsb); ideal bipolar positive full-scale voltage is (fs/2 C 1 lsb) and ideal bipolar negative full-scale voltage is Cfs/2. 7 sample tested at +25 c to ensure compliance. specifications subject to change without notice. C2C rev. b ad7569/ad7669Cspecifications (v dd = +5 v 6 5%; v ss 2 = range = agnd dac = agnd adc = dgnd = 0 v; r l = 2 k v , c l = 100 pf to agnd dac unless otherwise noted. all specifications t min to t max unless otherwise noted.) adc specifications ad7569 j, a versions 3 ad7569 ad7669 k, b ad7569 ad7569 parameter j version versions s version t version units conditions/comments dc accuracy resolution 3 8 8 8 8 bits total unadjusted error 4 3 3 4 4 lsb typ relative accuracy 4 1 1/2 1 1/2 lsb max differential nonlinearity 4 1 3/4 1 3/4 lsb max no missing codes unipolar offset error typical tempco is 10 m v/ c for +1.25 v range; v ss = 0 v @ +25 c 2 1.5 2 1.5 lsb max t min to t max 3 2.5 3 2.5 lsb max bipolar zero offset error typical tempco is 20 m v/ c for + 1.25 v range; v ss = C5 v @ +25 c 3 2.5 3 2.5 lsb max t min to t max 3.5 3 4 3.5 lsb max full-scale error 5 v dd = 5 v @ +25 c C4, +0 C4, +0 C4, +0 C4, +0 lsb max t min to t max C5.5, +1.5 C5.5, +1.5 C7.5, +2 C7.5, +2 lsb max d full scale/ d v dd , t a = +25 c 0.5 0.5 0.5 0.5 lsb max v in = +2.5 v; d v dd = 5% d full scale/ d v ss , t a = +25 c 0.5 0.5 0.5 0.5 lsb max v in = C2.5 v; d v ss = 5% dynamic performance signal-to-noise ratio 4 (snr) 44 46 44 45 db min v in = 100 khz full-scale sine wave with f sampling = 400 khz 6 total harmonic distortion 4 (thd) 48 48 48 48 db max v in = 100 khz full-scale sine wave with f sampling = 400 khz 6 intermodulation distortion 4 (imd) 60 60 60 60 db typ fa = 99 khz, fb = 96.7 khz with f sampling = 400 khz frequency response 0.1 0.1 0.1 0.1 db typ v in = 2.5 v, dc to 200 khz sine wave track/hold acquisition time 7 200 200 300 300 ns typ analog input input voltage ranges unipolar 0 to +1.25/ +2.5 volts v dd = +5 v; v ss = 0 v bipolar 1.25/ 2.5 volts v dd = +5 v; v ss = C5 v input current 300 300 300 300 m a max see equivalent circuit figure 5 input capacitance 10 10 10 10 pf typ logic inputs cs , rd , st , clk, reset , range input low voltage, v inl 0.8 0.8 0.8 0.8 v max input high voltage, v inh 2.4 2.4 2.4 2.4 v min input capacitance 8 10 10 10 10 pf max cs , rd , st , range, reset input leakage current 10 10 10 10 m a max v in = 0 to v dd clk input current i inl C1.6 C1.6 C1.6 C1.6 ma max v in = 0 v i inh 40 40 40 40 m a max v in = v dd logic outputs db0Cdb7, int , busy v ol , output low voltage 0.4 0.4 0.4 0.4 v max i sink = 1.6 ma v oh , output high voltage 4.0 4.0 4.0 4.0 v min i source = 200 m a db0Cdb7 floating state leakage current 10 10 10 10 m a max floating state output capacitance 8 10 10 10 10 pf max output coding (single supply) binary output coding (dual supply) 2s complement conversion time with external clock 2 2 2 2 m s max f clk = 5 mhz with internal clock, t a = +25 c 1.6 1.6 1.6 1.6 m s min using recommended clock components shown in figure 21. 2.6 2.6 2.6 2.6 m s max clock frequency can be adjusted by varying r clk . power requirements as per dac specifications notes 1 except where noted, specifications apply for all ranges including bipolar ranges with dual supply operation. 2 temperature ranges are as follows: j, k versions; 0 c to +70 c a, b versions; C40 c to +85 c s, t versions; C55 c to +125 c 3 1 lsb = 4.88 mv for 0 v to +1.25 v range, 9.76 mv for 0 v to +2.5 v and 1.25 v ranges and 19.5 mv for +2.5 v range. 4 see terminology. 5 includes in ternal voltage reference error and is calculated after offset error has been adjusted out. ideal unipolar last code transition occurs at (fs C 3/2 lsb). ideal bipolar last code transition occurs at (fs/2 C 3/2 lsb). 6 exact frequencies are 101 khz and 384 khz to avoid harmonics coinciding with sampling frequency. 7 rising edge of busy to falling edge of st . the time given refers to the acquisition time, which gives a 3 db degradation in snr from the tested figure. 8 sample tested at +25 c to ensure compliance. specifications subject to change without notice. (v dd = +5 v 6 5%; v ss 1 = range = agnd dac = agnd dac = dgnd = 0 v; f clk = 5 mhz external unless other- wise noted. all specifications t min to t max unless otherwise noted.) specifications apply to mode 1 interface. ad7569/ad7669 C3C rev. b ad7569/ad7669Ctiming characteristics 1 limit at limit at limit at t min , t max t min , t max parameter 25 8 c (all grades) (j, k, a, b grades) (s, t grades) units test conditions/comments dac timing t 1 80 80 90 ns min wr pulse width t 2 0 0 0 ns min cs , a /b to wr setup time t 3 0 0 0 ns min cs , a /b to wr hold time t 4 60 70 80 ns min data valid to wr setup time t 5 10 10 10 ns min data valid to wr hold time adc timing t 6 50 50 50 ns min st pulse width t 7 110 130 150 ns max st to busy delay t 8 20 30 30 ns max busy to int delay t 9 0 0 0 ns min busy to cs delay t 10 0 0 0 ns min cs to rd setup time t 11 60 75 90 ns min rd pulse width determined by t 13 . t 12 0 0 0 ns min cs to rd hold time t 13 2 60 75 90 ns max data access time after rd ; c l = 20 pf 95 120 135 ns max data access time after rd ; c l = 100 pf t 14 3 10 10 10 ns min bus relinquish time after rd 60 75 85 ns max t 15 65 75 85 ns max rd to int delay t 16 120 140 160 ns max rd to busy delay t 17 2 60 75 90 ns max data valid time after busy ; c l = 20 pf 90 115 135 ns max data valid time after busy ; c l = 100 pf notes 1 sample tested at +25 c to ensure compliance. all input control signals are specified with t r = t f = 5 ns (10% to 90% of +5 v) and timed from a voltage level of 1.6 v. 2 t 13 and t 17 are measured with the load circuits of figure 1 and defined as the time required for an output to cross either 0.8 v or 2.4 v. 3 t l4 is defined as the time required for the data line to change 0.5 v when loaded with the circuit of figure 2. specifications subject to change without notice. rev. b C4C warning! esd sensitive device caution esd (electrostatic discharge) sensitive device. electrostatic charges as high as 4000 v readily accumulate on the human body and test equipment and can discharge without detection. although the ad7569/ad7669 features proprietary esd protection circuitry, permanent dam- age may occur on devices subjected to high energy electrostatic discharges. therefore, proper esd precautions are recommended to avoid performance degradation or loss of functionality. absolute maximum ratings v dd to agnd dac or agnd adc . . . . . . . . . . . . . C0.3 v, +7 v v dd to dgnd . . . . . . . . . . . . . . . . . . . . . . . . . . . C0.3 v, +7 v v dd to v ss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C0.3 v, +14 v agnd dac or agnd adc to dgnd . . . . C0.3 v, v dd + 0.3 v agnd dac to agnd adc . . . . . . . . . . . . . . . . . . . . . . . . . 5 v logic voltage to dgnd . . . . . . . . . . . . . C0.3 v, v dd + 0.3 v clk input voltage to dgnd . . . . . . . . . C0.3 v, v dd + 0.3 v v out (v out a, v out b) to agnd 1 dac . . . . . . . . . . . . . . . . . v ss C 0.3 v, v dd + 0.3 v v in to agnd adc . . . . . . . . . . . . . . . v ss C 0.3 v, v dd + 0.3 v note 1 output may be shorted to any voltage in the range v ss to v dd provided that the power dissipation of the package is not exceeded. typical short circuit current for a short to agnd or v ss is 50 ma. figure 1. load circuits for data access time test a. high-z to v oh figure 2. load circuits for bus relinquish time test b. high-z to v ol a. v oh to high-z b. v ol to high-z power dissipation (any package) to +75 c . . . . . . . . 450 mw derates above 75 c by . . . . . . . . . . . . . . . . . . . . . 6 mw/ c operating temperature range commercial (j, k) . . . . . . . . . . . . . . . . . . . . . . 0 c to +70 c industrial (a, b) . . . . . . . . . . . . . . . . . . . . . C40 c to +85 c extended (s, t) . . . . . . . . . . . . . . . . . . . . C55 c to +125 c storage temperature range . . . . . . . . . . . . C65 c to +150 c lead temperature (soldering, 10 secs) . . . . . . . . . . . +300 c *stresses above those listed under absolute maximum ratings may cause permanent damage to the device. this is a stress rating only; functional operation of the device at these or any other condition above those indicated in the operational sections of this specification is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. (see figures 8, 10, 12; v dd = 5 v 6 5%; v ss = 0 v or C5 v 6 5%) ad7569/ad7669 C5C rev. b note: the term dac (digital-to-analog converter) throughout the data sheet applies equally to the dual dacs in the ad7669 as well as to the single dac of the ad7569 unless otherwise stated. it follows that the term v out applies to both v out a and v out b of the ad7669 also. terminology total unadjusted error total unadjusted error is a comprehensive specification that in- cludes internal voltage reference error, relative accuracy, gain and offset errors. relative accuracy (dac) relative accuracy or endpoint nonlinearity is a measure of the maximum deviation from a straight line passing through the endpoints of the dac transfer function. it is measured after al- lowing for offset and gain errors. for the bipolar output ranges, the endpoints of the dac transfer function are defined as those voltages that correspond to negative full-scale and positive full- scale codes. for the unipolar output ranges, the endpoints are code 1 and code 255. code 1 is chosen because the amplifier is now working in single supply and, in cases where the true offset of the amplifier is negative, it cannot be seen at code 0. if the relative accuracy were calculated between code 0 and code 255, the negative offset would appear as a linearity error. if the off- set is negative and less than 1 lsb, it will appear at code 1, and hence the true linearity of the converter is seen between code 1 and code 255. relative accuracy (adc) relative accuracy is the deviation of the adcs actual code transition points from a straight line drawn between the end- points of the adc transfer function. for the bipolar input ranges, these points are the measured, negative, full-scale transi- tion point and the measured, positive, full-scale transition point. for the unipolar ranges, the straight line is drawn between the measured first lsb transition point and the measured full-scale transition point. differential nonlinearity differential nonlinearity is the difference between the measured change and an ideal 1 lsb change between any two adjacent codes. a specified differential nonlinearity of 1 lsb max en- sures monotonicity (dac) or no missed codes (adc). a differ- ential nonlinearity of 3/4 lsb max ensures that the minimum step size (dac) or code width (adc) is 1/4 lsb, and the maxi- mum step size or code width is 3/4 lsb. digital-to-analog glitch impulse digital-to-analog glitch impulse is the impulse injected into the analog output when the digital inputs change state with the dac selected. it is normally specified as the area of the glitch in nv secs and is measured when the digital input code is changed by 1 lsb at the major carry transition. digital feedthrough digital feedthrough is also a measure of the impulse injected to the analog output from the digital inputs, but is measured when the dac is not selected. it is essentially feedthrough across the die and package. it is also a measure of the glitch impulse trans- ferred to the analog output when data is read from the internal adc. it is specified in nv secs and is measured with wr high and a digital code change from all 0s to all 1s. dac-to-dac crosstalk (ad7669 only) the glitch energy transferred to the output of one dac due to an update at the output of the second dac. the figure given is the worst case and is expressed in nv secs. it is measured with an update voltage of full scale. dac-to-dac isolation (ad7669 only) dac-to-dac isolation is the proportion of a digitized sine wave from the output of one dac, which appears at the output of the second dac (loaded with all 1s). the figure given is the worst case for the second dac output and is expressed as a ra- tio in dbs. it is measured with a digitized sine wave (f sampling = 100 khz) of 20 khz at 2.5 v pk-pk. signal-to-noise ratio signal-to-noise ratio (snr) is the measured signal to noise at the output of the converter. the signal is the rms magnitude of the fundamental. noise is the rms sum of all the nonfundamen- tal signals (excluding dc) up to half the sampling frequency. snr is dependent on the number of quantization levels used in the digitization process; the more levels, the smaller the quanti- zation noise. the theoretical snr for a sine wave is given by snr = (6.02 n + 1.76) db where n is the number of bits. thus for an ideal 8-bit converter, snr = 50 db. harmonic distortion harmonic distortion is the ratio of the rms sum of harmonics to the fundamental. for the ad7569/ad7669, total harmonic distortion (thd) is defined as 20 log v 2 2 + v 3 2 + v 4 2 + v 5 2 + v 6 2 v 1 where v 1 is the rms amplitude of the fundamental and v 2 , v 3 , v 4 , v 5 and v 6 are the rms amplitudes of the individual harmonics. intermodulation distortion with inputs consisting of sine waves at two frequencies, fa and fb, any active device with nonlinearities will create distortion products, of order (m + n), at sum and difference frequencies of mfa nfb where m, n = 0, l, 2, 3, . intermodulation terms are those for which m or n is not equal to zero. for example, the second order terms include (fa + fb) and (fa C fb) and the third order terms include (2fa + fb), (2fa C fb), (fa + 2fb) and (fa C 2fb). C6C rev. b ad7569/ad7669 ordering guide relative temperature accuracy package model range t min Ct max option 1 ad7569jn 0 c to +70 c 1 lsb n-24 ad7569jr 0 c to +70 c 1 lsb r-24 ad7569aq C40 c to +85 c 1 lsb q-24 ad7569sq 2 C55 c to +125 c 1 lsb q-24 ad7569bn C40 c to +85 c 0.5 lsb n-24 ad7569kn 0 c to +70 c 0.5 lsb n-24 ad7569br C40 c to +85 c 0.5 lsb r-24 ad7569bq C40 c to +85 c 0.5 lsb q-24 ad7569tq 2 C55 c to +125 c 1/2 lsb q-24 ad7569jp 0 c to +70 c 1 lsb p-28a ad7569se 2 C55 c to +125 c 1 lsb e-28a ad7569kp 0 c to +70 c 1/2 lsb p-28a ad7569te 2 C55 c to +125 c 1/2 lsb e-28a ad7669an C40 c to +85 c 1 lsb n-28 ad7669jn 0 c to +70 c 1 lsb n-28 ad7669jp 0 c to +70 c 1 lsb p-28a ad7669ar C40 c to +85 c 1 lsb r-28 ad7669jr 0 c to +70 c 1 lsb r-28 notes 1 e = leadless ceramic chip carrier; n = plastic dip; p = plastic leaded chip carrier; q = cerdip; r = small outline soic. 2 to order mil-std-883, class b processed parts, add /883b to part number. contact your local sales office for military data sheet. ad7569 pin configurations dip, soic plcc lccc ad7669 pin configurations dip, soic plcc ad7569/ad7669 C7C rev. b pin function description (applies to the ad7569 and ad7669 unless otherwise stated.) pin mnemonic description agnd dac analog ground for the dac(s). separate ground return paths are provided for the dac(s) and adc to minimize crosstalk. v out output voltage. v out is the buffered output (v out a, v out b) voltage from the ad7569 dac. v out a and v out b are the buffered dac output voltages from the ad7669. four different output volt- age ranges can be achieved (see table i). v ss negative supply voltage (C5 v for dual sup- ply or 0 v for single supply). this pin is also used with the range pin to select the differ- ent input/output ranges and changes the data format from binary (v ss = 0 v) to 2s comple- ment (v ss = C5 v) (see table i). range range selection input. this is used with the v ss input to select the different ranges as per table i. the range selected applies to both the analog input voltage of the adc and the output voltage from the dac(s). reset reset input (active low). this is an asyn- chronous system reset that clears the dac register(s) to all 0s and clears the int line of the adc (i.e., makes the adc ready for new conversion). in unipolar operation, this input sets the output voltage to 0 v; in bipolar operation, it sets the output to negative full scale. db7 data bit 7. most significant bit (msb). db6Cdb2 data bit 6 to data bit 2. dgnd digital ground. db1 data bit 1. db0 data bit 0. least significant bit (lsb). wr write input (edge triggered). this is used in conjunction with cs to write data into the ad7569 dac register. it is used in conjunc- tion with cs and a /b to write data into the selected dac register of the ad7669. data is transferred on the rising edge of wr . pin mnemonic description cs chip select input (active low). the device is selected when this input is active. rd read input (active low). this input must be active to access data from the part. in the mode 2 interface, rd going low starts con- version. it is used in conjunction with the cs input (see digital interface section). st start conversion (edge triggered). this is used when precise sampling is required. the falling edge of st starts conversion and drives busy low. the st signal is not gated with cs . busy busy status output (active low). when this pin is active, the adc is performing a conversion. the input signal is held prior to the falling edge of busy (see digital inter- face section). int interrupt output (active low). int go- ing low indicates that the conversion is com- plete. int goes high on the rising edge of cs or rd and is also set high by a low pulse on reset (see digital interface section). a /b (ad7669 dac select input. this input selects which only) dac register data is written to under control of cs and wr . with this input low, data is written to the daca register; with this input high, data is written to the dacb register. clk a ttl compatible clock signal may be used to determine the adc conversion time. inter- nal clock operation is achieved by connecting a resistor and capacitor to ground. agnd adc analog ground for the adc. v in analog input. various input ranges can be se- lected (see table i). v dd positive supply voltage (+5 v). table i. input/output ranges input/output db0Cdb7 range v ss voltage range data format 0 0 v 0 v to +1.25 v binary 1 0 v 0 v to +2.5 v binary 0 C5 v 1.25 v 2s complement 1 C5 v 2.5 v 2s complement noise spectral density vs. frequency positive-going settling time ( 2.5 v range) dac/adc full-scale temperature coefficient ad7569/ad7669typical performance graphs power supply rejection ratio vs. frequency negative-going settling time ( 2.5 v range) imd plot for adc C8C rev. b ad7569/ad7669 C9C rev. b circuit description d/a section the ad7569 contains an 8-bit, voltage-mode, d/a converter that uses eight equally weighted current sources switched into an r-2r ladder network to give a direct but unbuffered 0 v to +1.25 v output range. the ad7669 is similar, but contains two d/a converters. the current sources are fabricated using pnp transistors. these transistors allow current sources that are driven from positive voltage logic and give a zero-based output range. the output voltage from the voltage switching r-2r lad- der network has the same positive polarity as the reference; therefore, the d/a converter can be operated from a single power supply rail. the pnp current sources are generated using the on-chip bandgap reference and a control amplifier. the current sources are switched to either the ladder or agnd dac by high speed p-channel switches. these high-speed switches ensure a fast set- tling time for the output voltage of the dac. the r-2r ladder network of the dac consists of highly stable, thin-film resistors. a simplified circuit diagram for the d/a converter section is shown in figure 3. an identical d/a converter is used as part of the a/d converter, which is discussed later. figure 3. dac simplified circuit diagram op amp section the output from the d/a converter is buffered by a high speed, noninverting op amp. this op amp is capable of developing 2.5 v across a 2 k w and 100 pf load to agnd dac . the am- plifier can be operated from a single +5 v supply to give two unipolar output ranges, or from dual supplies ( 5 v) to allow two bipolar output ranges. the feedback path of the amplifier contains a gain/offset net- work that provides four voltage ranges at the output of the op amp. the output voltage range is determined by the range and v ss inputs. (see table i in the pin function description section.) the four possible output ranges are: 0 v to +1.25 v, 0 v to +2.5 v, 1.25 v and 2.5 v. it should be noted that whichever range is selected for the output amplifier also applies to the input voltage range of the a/d converter. the output amplifier settles to within 1/2 lsb of its final value in typically less than 500 ns. operating the part from single or dual supplies has no effect on the positive-going settling time. however, the negative-going output settling time to voltages near 0 v in single supply will be slightly longer than the settling time to negative full scale for dual supply operation. addition- ally, to ensure that the output voltage can go to 0 v in single supply, a transistor on the output acts as a passive pull-down with output voltages near 0 v with v ss = 0 v. this means that the sink capability of the amplifier is reduced as the output volt- age nears 0 v in single supply. in dual supply operation the full sink capability of 1.25 ma is maintained over the entire output voltage range. for all other parameters, the single and dual supply perfor- mances of the amplifier are essentially identical. the output noise from the amplifier, with full scale on the dac, is 200 m v peak-to-peak. the spot noise at 1 khz is 35 nv/ ? hz with all 0s on the dac. a noise spectral density versus frequency plot for the amplifier is shown in the typical performance graphs. voltage reference the ad7569/ad7669 contains an on-chip bandgap reference that provides a low noise, temperature compensated reference voltage for both the dac and the adc. the reference is trimmed for absolute accuracy and temperature coefficient. the bandgap reference is generated with respect to v dd . it is buff- ered by a separate control amplifier for both the dac and the adc reference. this can be seen in the dac ladder network configuration in figure 3. digital section the data pins on the ad7569/ad7669 provide a connection between the external bus and dac data inputs and adc data outputs. the threshold levels of all digital inputs and outputs are compatible with either ttl or 5 v cmos levels. internal input protection of all digital pins is achieved by on-chip distrib- uted diodes. the data format is straight binary when the part is used in single supply (v ss = 0 v). however, when a v ss of C5 v is applied, the data format becomes twos complement. this data format ap- plies to the digital inputs of the dac and the digital outputs of the adc. adc section the analog-to-digital converter on the ad7569/ad7669 uses the successive approximation technique to achieve a fast conver- sion time of 2 m s and provides an 8-bit parallel digital output. the reference for the adc is provided by the on-chip bandgap reference. conversion start is controlled by st or by cs and rd . once a conversion has been started, another conversion start should not be attempted until the conversion in progress is completed. exercising the reset input does not affect conversion; the reset input resets the int line high, which is useful in inter- rupt driven systems where a read has not been performed at the end of the previous conversion. the int line does not have to be cleared at the end of conversion. the adc will continue to convert correctly, but the function of the int line will be affected. figure 4 shows the operating waveforms for a conversion cycle. the analog input voltage, v in , is held 50 ns typical after the fall- ing edge of st or ( cs & rd ). the msb decision is made ap- proximately 50 ns after the second falling edge of the input clk following a conversion start. if t 1 in figure 4 is greater than 50 ns, then the falling edge of the input clk will be seen as the first falling clock edge. if t 1 is less than 50 ns, the first fall- ing clock edge of the conversion will not occur until one clock cycle later. the succeeding bit decisions are made approxi- mately 50 ns after a clk edge until conversion is complete. C10C rev. b ad7569/ad7669 internal clock clock pulses are generated by the action of an internal current source charging the external capacitor (c clk ) and this external capacitor discharging through the external resistor (r clk ). when a conversion is complete, this internal clock stops operat- ing and the clk pin goes to the dgnd potential. connections for r clk and c clk are shown in the operating diagram of fig- ure 21. the nominal conversion time versus temperature for the recommended r clk and c clk combination is shown in figure 6. the internal clock provides a convenient clock source for the ad7569/ad7669. due to process variations, the actual operat- ing frequency for this r clk /c clk combination can vary from device to device by up to 25%. figure 6. conversion time vs. temperature for internal clock operation digital interface dac timing and controlad7569 table ii shows the truth table for dac operation for the ad7569. the part contains an 8-bit dac register, which is loaded from the data bus under control of cs and wr . the data contained in the dac register determines the analog out- put from the dac. the wr input is an edge-triggered input, and data is transferred into the dac register on the rising edge of wr . holding cs and wr low does not make the dac regis- ter transparent. table ii. ad7569 dac truth table cs wr reset dac function h h h dac register unaffected l l h dac register unaffected l g h dac register updated g l h dac register updated x x l dac register loaded with all zeros l = low state, h = high state, x = dont care the contents of the dac register are reset to all 0s by an active low pulse on the reset line, and for the unipolar output ranges, the output remains at 0 v after reset returns high. for the bi- polar output ranges, a low pulse on reset causes the output to go to negative full scale. in unipolar applications, the reset line can be used to ensure power-up to 0 v on the ad7569 dac out- put and is also useful when used as a zero override in system cali- bration cycles. if the reset input is connected to the system at the end of conversion, the sar contents are transferred to the output latch, and the sar is reset in readiness for a new conversion. a single conversion lasts for 8 input clock cycles. figure 4. operating waveforms using external clock analog input the analog input of the ad7569/ad7669 feeds into an on-chip track-and-hold amplifier. to accommodate different full-scale ranges, the analog input signal is conditioned by a gain/offset network that conditions all input ranges so the internal adc al- ways works with a 0 v to +1.25 v signal. as a result, the input current on the v in input varies with the input range selected as shown in figure 5. figure 5. equivalent v in circuit track-and-hold the track-and-hold (t/h) amplifier on the analog input of the ad7569/ad7669 allows the adc to accurately convert an in- put sine wave of 2.5 v peak-to-peak amplitude up to a fre- quency of 200 khz, the nyquist frequency of the adc when operated at its maximum throughput rate of 400 khz. this maximum rate of conversion includes conversion time and time between conversions. because the input bandwidth of the t/h amplifier is much larger than 200 khz, the input signal should be band-limited to avoid converting high-frequency noise components. the operation of this t/h amplifier is essentially transparent to the user. the t/h amplifier goes from its tracking mode to its hold mode at the start of conversion. this occurs when the adc receives a conversion start command from either st or cs & rd . at the end of conversion ( busy going high), the t/h reverts back to tracking the input signal. external clock the ad7569/ad7669 adc can be used with its on-chip clock or with an externally applied clock. when using an external clock, the clk input of the ad7569/ad7669 may be driven directly from 74hc, 4000b series buffers (such as 4049) or from ttl buffers. when conversion is complete, the internal clock is disabled. the external clock can continue to run be- tween conversions without being disabled. the mark/space ratio of the external clock can vary from 70/30 to 30/70. ad7569/ad7669 C11C rev. b reset line, the dac output resets to 0 v when the entire system is reset. figure 7 shows the input control logic for the ad7569 dac; the write cycle timing diagram is shown in figure 8. figure 7. ad7569 dac input control logic figure 8. ad7569/ad7669 write cycle timing diagram dac timing and controlad7669 table iii shows the truth table for the dual dac operation of the ad7669. the part contains two 8-bit dac registers that are loaded from the data bus under the control of cs , a /b and wr . address line a /b selects which dac register the data is loaded to. the data contained in the dac registers determines the analog output from the respective dacs. the wr input is an edge-triggered input, and data is transferred into the selected dac register on the rising edge of wr . holding cs and wr low does not make the selected dac register transparent. the a /b input should not be changed while cs and wr are low. table iii. ad7669 dac truth table cs wr a /b reset dac function h h x h dac registers unaffected l g l h daca register updated g l l h daca register updated l g h h dacb register updated g l h h dacb register updated x x x l dac registers loaded with all zeros l = low state, h = high state, x = dont care the contents of the dac registers are reset to all 0s by an active low pulse on the reset line, and for the unipolar output ranges, the outputs remain at 0 v after reset returns high. for the bipolar output ranges, a low pulse on reset causes the outputs to go to negative full scale. in unipolar applications, the reset line can be used to ensure power-up to 0 v on the ad7669 dac outputs and is also useful when used as a zero override in system calibration cycles. if the reset input is con- nected to the system reset line, then the dac outputs reset to 0 v when the entire system is reset. figure 9 shows the dac input control logic for the ad7669, and the write cycle timing diagram is shown in figure 8. figure 9. ad7669 dac control logic adc timing and control the adc on the ad7569/ad7669 is capable of two basic oper- ating modes. in the first mode, the st line is used to start con- version and drive the track-and-hold into hold mode. at the end of conversion, the track-and-hold returns to its tracking mode. the second mode is achieved by hard-wiring the st line high. in this case, cs and rd start conversion, and the microproces- sor is driven into a wait state for the duration of conversion by busy . figure 10. adc mode 1 interface timing C12C rev. b ad7569/ad7669 mode 1 interface the timing diagram for the first mode is shown in figure 10. it can be used in digital signal processing and other applications where precise sampling in time is required. in these applica- tions, it is important that the signal sampling occurs at exactly equal intervals to minimize errors due to sampling uncertainty or jitter. in these cases, the st line is driven by a timer or some precise clock source. the falling edge of the st pulse starts conversion and drives the ad7569/ad7669 track-and-hold amplifier into its hold mode. busy stays low for the duration of conversion and returns high at the end of conversion and the track-and hold amplifier reverts to its tracking mode on this rising edge of busy . the int line can be used to interrupt the microprocessor. a read to the ad7569/ad7669 address accesses the data, and the int line is reset on the rising edge of cs or rd . alternatively, the int can be used to trigger a pulse that drives the cs and rd and places the data into a fifo or buffer memory. the microprocessor can then read a batch of data from the fifo or buffer memory at some convenient time. the st input should not be high when rd is brought low; otherwise, the part will not operate correctly in this mode. it is important, especially in systems where the conversion start ( st pulse) is asynchronous to the microprocessor, that a read does not occur during a conversion. trying to read data from the device during a conversion can cause errors to the conver- sion in progress. also, pulsing the st line a second time before conversion ends should be avoided since it too can cause errors in the conversion result. in applications where precise sampling is not critical, the st pulse can be generated from a micropro- cessor wr or rd line gated with a decoded address (different from ad7569/ad7669 cs address). figure 11. multichannel inputs this interface mode is also useful in applications where a num- ber of input channels are required to be converted by the adc. figure 11 shows the circuit configuration for such an applica- tion. the signal that drives the st input of the ad7569/ ad7669 is also used to drive the enable input of the multi- plexer. the multiplexer is enabled on the rising edge of the st pulse while the input signal is held on the falling edge; therefore, the signal must have settled to within 8 bits over the duration of this st pulse. the settling time, including t on (enable) of the multiplexer plus the t/h acquisition time (typically 200 ns), thus determines the width of the st pulse. this is suited to ap- plications where a number of input channels needs to be succes- sively sampled or scanned. mode 2 interface the second interface mode is intended for use with micropro- cessors, which can be forced into a wait state for at least 2 m s. the st line of the ad7569/ad7669 must be hardwired high to achieve this mode. the microprocessor starts a conversion and is halted until the result of the conversion is read from the con- verter. conversion is initiated by executing a memory read to the ad7569/ad7669 address, bringing cs and rd low. busy subsequently goes low (forcing the microprocessor ready or wait input low), placing the microprocessor into a wait state. the input signal is held on the falling edge of rd (assum- ing cs is already low or is coincident with rd ). when the con- version is complete ( busy goes high), the processor completes the memory read and acquires the newly converted data. while conversion is in progress, the adc places old data (from the previous conversion) on the data bus. the timing diagram for this interface is shown in figure 12. figure 12. adc mode 2 interface timing the major advantage of this interface is that it allows the micro- processor to start conversion, wait, and then read data with a single read instruction. the user does not have to worry about servicing interrupts or ensuring that software delays are long enough to avoid reading during conversion. the fast con- version time of the adc ensures that for many microprocessors, the processor is not placed in a wait state for an excessive amount of time. digital signal processing applications in digital signal processing (dsp) application areas such as voice recognition, echo cancellation and adaptive filtering, the dynamic characteristics (snr, harmonic distortion, intermod- ulation distortion) of both the adc and dac are critical. the ad7569/ad7669 is specified dynamically as well as with stan- dard dc specifications. because the track/hold amplifier has a wide bandwidth, an antialiasing filter should be placed on the v in input to avoid aliasing of high-frequency noise back into the band of interest. the dynamic performance of the adc is evaluated by applying a sine-wave signal of very low distortion to the v in input, which is sampled at a 409.6 khz sampling rate. a fast fourier transform (fft) plot or histogram plot is then generated from which snr, harmonic distortion and dynamic differential nonlinearity data can be obtained. for the dac, the codes for an ideal sine wave are stored in prom and loaded down to the dac. the output spectrum is analyzed, using a spectrum analyzer to evaluate snr ad7569/ad7669 C13C rev. b figure 15. dac output spectrum histogram plot when a sine wave of specified frequency is applied to the v in in- put of the ad7569/ad7669 and several thousand samples are taken, it is possible to plot a histogram showing the frequency of occurrence of each of the 256 adc codes. if a particular step is wider than the ideal 1 lsb width, the code associated with that step will accumulate more counts than for the code for an ideal step. likewise, a step narrower than ideal width will have fewer counts. missing codes are easily seen because a missing code means zero counts for a particular code. the absence of large spikes in the plot indicates small differential nonlinearity. figure 16 shows a histogram plot for the adc indicating very small differential nonlinearity and no missing codes for an input frequency of 204 khz. for a sine-wave input, a perfect adc would produce a cusp probability density function described by the equation p ( v ) = 1 p ( a 2 - v 2 ) 1/ 2 where a is the peak amplitude of the sine wave and p ( v ) the probability of occurrence at a voltage v . the histogram plot of figure 16 corresponds very well with this cusp shape. further typical plots of the performance of the ad7569/ad7669 are shown in the typical performance graphs section of the data sheet. figure 16. adc histogram plot and harmonic distortion performance. similarly, for inter- modulation distortion, an input (either to v in or dac code) consisting of pure sine waves at two frequencies is applied to the ad7569/ad7669. figure 13. adc fft plot figure 13 shows a 2048 point fft plot of the adc with an in- put signal of 130 khz. the snr is 48.4 db. it can be seen that most of the harmonics are buried in the noise floor. it should be noted that the harmonics are taken into account when calculat- ing the snr. the relationship between snr and resolution (n) is expressed by the following equation: snr = (6.02 n + 1.76) db this is for an ideal part with no differential or integral linearity errors. these errors will cause a degradation in snr. by work- ing backward from the above equation, it is possible to get a measure of adc performance expressed in effective number of bits (n). this effective number of bits is plotted versus fre- quency in figure 14. the effective number of bits typically falls between 7.7 and 7.8, corresponding to snr figures of 48.1 db and 48.7 db. figure 15 shows a spectrum analyzer plot of the output spec- trum from the dac with an ideal sine-wave table loaded to the data inputs of the dac. in this case, the snr is 46 db. figure 14. effective number of bits vs. frequency C14C rev. b ad7569/ad7669 ad7569/ad7669adsp-2100 interface figure 19 shows a typical interface to the dsp processor, the adsp-2100. the adc is in the mode 2 interface mode, which means that the adsp-2100 is halted during conversion. this is achieved using the decoded address output. this is gated with dmwr to ensure that it halts the processor for read instruc- tions only. int going low at the end of conversion releases the processor and allows it to finish off the read instruction. figure 19. ad7569/ad7669 to adsp-2100 interface because the instruction cycle of the adsp-2100 is so fast (125 ns cycle), the dmwr pulse also has to be stretched also for write cycles. this is achieved using the 74121, which gener- ates a pulse that is fed back to dmack. the duration of this pulse determines how long the adsp-2100 write cycle is stretched. the buffers driving the dmack line must have open-collector outputs. writing data to the relevant ad7569/ ad7669 dac is achieved using a single instruction, ad7569/ad7669 C15C rev. b an rd pulse for the ad7569/ad7669. this rd pulse accesses data from the adc and places the conversion result into a regis- ter on the 74646. the rising edge of this pulse generates an in- terrupt request to the processor. the conversion result is read from the 74646 register by performing an i/o read to the decoded address of the 74646. writing data to the relevant ad7569/ad7669 dac involves an i/o write to the 74646, which transfers the data to the data inputs of the ad7569/ ad7669. data is latched into the selected dac register on the rising edge of iow . applying the ad7569/ad7669 dac an internal gain/offset network on the ad7569/ad7669 allows several output voltage ranges. the part can produce unipolar output ranges of 0 v to +1.25 v or 0 v to +2.5 v and bipolar output ranges of C1.25 v to +1.25 v or C2.5 v to +2.5 v. con- nections for these various output ranges are outlined below. unipolar (0 v to +1.25 v) configuration the first of the configurations provides an output voltage range of 0 v to +1.25 v. this is achieved by tying the v ss and range inputs to agnd dac (= 0 v). figure 21 shows the con- figuration of the ad7569 to achieve this output range. a similar configuration of the ad7669 gives the same output range. the table for output voltage versus the digital code in the dac regis- ter is shown in table iv. figure 21. ad7569 unipolar (0 v to +1.25 v) operation table iv. unipolar (0 v to +1.25 v) code table dac register contents msb lsb analog output, v out 1111 1111 +v ref 255 256 ? ? ? ? 1000 0001 +v ref 129 256 ? ? ? ? 1000 0000 +v ref 128 256 ? ? ? ? = +v ref /2 0111 1111 +v ref 127 256 ? ? ? ? 0000 0001 +v ref 1 256 ? ? ? ? 0000 0000 0 v note: 1 lsb = (v ref ) (2 C8 ) = v ref (1/256); v ref = +1.25 v nominal unipolar (0 v to +2.5 v) configuration the 0 v to +2.5 v output voltage range is achieved by tying v ss to agnd dac (= 0 v) and the range input to v dd . the table for output voltage versus digital code is as in table iv with 2.v ref replacing v ref . note that for this range 1 lsb = 2. v ref (2 - 8 ) = v ref 1 128 bipolar (C1.25 v to +1.25 v) configuration the first of the bipolar configurations is achieved by tying the range input to agnd dac (= 0 v) and v ss to C5 v. the v ss voltage level at which the ad7569/ad7669 changes to bipolar operation is approximately C1 v. when the part is configured for bipolar outputs, the input coding becomes twos comple- ment. the table for output voltage versus the digital code in the dac register is shown in table v. note as with the unipolar configuration, a digital input code of all 0s produces an output of 0 v. it should be noted, however, that a low pulse on the reset line for the bipolar ranges sets the output voltage to negative full scale. table v. bipolar (C1.25 v to +1.25 v) code table dac register contents msb lsb analog output, v out 0111 1111 +v ref 127 128 ? ? ? ? 0000 0001 +v ref 1 128 ? ? ? ? 0000 0000 0 v 1111 1111 Cv ref 1 128 ? ? ? ? 1000 0001 Cv ref 127 128 ? ? ? ? 1000 0000 Cv ref 128 128 ? ? ? ? = Cv ref note: 1 lsb = (v ref )(2 C7 ) = v ref (1/128) bipolar (C2.5 v to +2.5 v) configuration the C2.5 v to +2.5 v bipolar output range is achieved by tying the range input to v dd and the v ss input to C5 v. once again, the input coding is 2s complement. the table for output voltage versus digital code is as in table v with 2.v ref replacing v ref . note that for this range 1 lsb = 4. v ref (2 - 8 ) = v ref 1 64 C16C rev. b ad7569/ad7669 applying the ad7569/ad7669 adc the analog input on the ad7569/ad7669 accepts the same four input ranges as the output ranges on the dac. whatever output range is selected for the dac also applies to the input range of the adc. although separate agnds exist for both the dac and adc to minimize crosstalk, writing data to the dac while the adc is performing a conversion may result in an incorrect conversion from the adc due to an interaction of currents between the dac and adc. therefore, to ensure correct operation of the adc, the dac register should not be updated while the adc is converting. unipolar operation the circuit of figure 21 shows the ad7569 configured for both an input and output range of 0 v to +1.25 v (the ad7669 con- figuration is similar). the nominal transfer characteristic for this range is shown in figure 22. the output code is natural binary with 1 lsb = (1.25/256)v = 4.88 mv. as before, to achieve the unipolar 0 v to +2.5 v input range, v ss is connected to 0 v, and the range input is tied to a logic high. the nominal transfer characteristic is as in figure 22 but, in this case, 1 lsb = (2.5/256)v = 9.76 mv. figure 22. nominal transfer characteristic for unipolar (0 v to +1.25 v) operation bipolar operation the analog input of the ad7569/ad7669 adc is configured for bipolar inputs when v ss = C5 v. the output code provided by the part is twos complement. figure 23 shows the transfer function for bipolar (C1.25 v to +1.25 v) operation. the lsb size for this range is (2.5/256)v = 9.76 mv. the transfer function for the C2.5 v to +2.5 v range is identical to that of figure 23, but now fs = 5 v and the lsb size is (5/256)v = 19.5 mv. adc offset and full-scale error adjustment in most digital signal processing (dsp) applications, offset and full-scale error have little or no effect on system performance. a figure 23. nominal transfer characteristic for bipolar (C1.25 v to +1.25 v) operation typical example is a digital filter where an ac analog signal is quantized by the adc, digitally processed and recreated using the dac. in these types of applications, the offset error can be eliminated by ac coupling the recreated signal. full-scale error effect is linear and does not cause problems as long as the input signal is within the full dynamic range of the adc. an impor- tant parameter in dsp applications is differential nonlinearity, and this is not affected by either offset or full-scale error. in applications where absolute accuracy is important adc off- set and full-scale error can be adjusted to zero. figure 24 shows the additional components required for offset and full-scale er- ror adjustment. offset error must be adjusted before full-scale error. zero offset is achieved by adjusting the offset of the op amp driving v in (i.e., a1 in figure 23). in unipolar applica- tions, for zero offset error, apply 1/2 lsb at the analog input and adjust the op amp offset voltage until the adc output code flickers between 0000 0000 and 0000 0001. for zero full-scale error, apply an analog input of fs C 3/2 lsbs and adjust r1 un- til the adc output code flickers between 1111 1110 and 1111 1111. in bipolar applications, to adjust for bipolar zero offset, apply C1/2 lsb at the analog input and adjust the op amp offset volt- age until the output code flickers between 1111 1111 and 0000 0000. for zero full-scale error, apply +fs/2 C 3/2 lsb at the analog input and adjust r1 until the adc output code flickers between 0111 1110 and 0111 1111. figure 24. adc error adjust circuit ad7569/ad7669 C17C rev. b figure 25. peak-reading a/d converter head (or motor) is monitored. the closed-loop system allows an error between the desired position and the actual position to be monitored and corrected. the correction is achieved by adjust- ing the ratio of the phase currents in the motor windings until the required head position is reached. the ad7669 is ideally suited for the closed-loop microstepping technique with its on-chip dual dacs for positioning the disk drive head, and onboard adc for monitoring the position of the head. a generalized circuit for a closed-loop microstepping sys- tem is shown in figure 26. the dac waveforms are shown in figure 27, along with the direction information for clockwise ro- tation supplied by the controller. figure 26. typical closed-loop microstepping circuit with the ad7669 the ad7669 is used in the unipolar 0 v to +2.5 v configura- tion. this allows the circuit of figure 26 to be completely uni- polar (+5 v, +12 v supplies); no negative power supplies are required. the power output stage is a dual h-bridge device such as the udn-2998w from sprague electric. the phase currents in both windings are detected by means of the small value sense resistors, r s a and r s b, in series with the windings. the voltage developed across these resistors is amplified and compared with the respective dac output voltage. the com- parators in turn chop the phase winding current. the adc completes the feedback path by converting information from a suitable transducer for analysis by the controller. peak detectionad7569 the circuit of figure 25 shows a peak-reading a/d converter, which is useful in such applications as monitoring flow rates, temperature, pressure, etc. the circuit ensures that a peak will not be missed while at the same time does not require the mi- croprocessor to frequently monitor the data. the peak value is stored in the a/d converter and can be read at any time. the gain on the ad524 is adjusted to yield a 0 v to +2.5 v out- put. when the input signal exceeds the current stored value, the output of the tl311 goes low, triggering the q output of the 74121. this low-going pulse starts a conversion on the ad7569 adc, and at the end of conversion latches the result into the dac. this pulse must be at least 120 ns greater than the con- version time of the adc. the q output is used to drive the strobe input of the tl311, resetting the tl311 output high in readiness for another conversion. the additional gates on the rd and wr inputs are to allow the data to be read by the microprocessor while at the same time ensuring that the dac is not updated when the microprocessor reads the data. it may be necessary to monitor the ad7569 busy line to ensure that a processor read is not attempted while the ad7569 is in the middle of a conversion. the read pulse width from the processor must be less than 1 m s to ensure correct data is read from the adc. a low-going pulse on the r eset line resets the dac output to 0 v and starts a new peak- detection period. this reset pulse must also be less than 1 m s. disk drive applicationad7669 closed-loop microstepping microstepping is a popular technique in low density disk drives (both floppy and hard disk) that allows higher positional resolu- tion of the disk drive head over that obtainable from a full- step driven stepper motor. typically, a two-phase stepper motor has its phase currents driven with a sine-cosine relationship. these cosinusoidal signals are generated by two dacs driven with the appropriate data. the resolution of the dacs determines the number of microsteps into which each full step can be divided. for example, with a 1.8 full-step motor and a 4-bit dac, a microstep size of 0.11 (1.8 /(2 n )) is obtainable. the microstepping technique improves the positioning resolu- tion possible in any control application; however, the positional accuracy can be significantly worse than that offered by the original full-step accuracy specification due to l oad torque effects. to ensure that the increased resolution is usable, it is necessary to use a closed-loop system where the position of the disk drive C18C rev. b ad7569/ad7669 figure 27. typical dac output voltages for microstepping and direction signals for clockwise rotation with the udn-2998w analog delay linead7569 in many applications, especially in audio systems, it is necessary to provide a delay on the input signal. the circuit of figure 28 shows how a simple analog delay line can be implemented, based on the ad7569. the input signal is sampled using the ad7569 adc, and converted data is loaded into the 6116 (2k 3 8 static ram). the inverted input clock drives a counter that selects the address for the 6116. the delay is selected by choos- ing one of the output lines of the hct4040 counter to reset the coun-ter. this can be done using a simple switch in a manual system or by a multiplexer in a programmable delay application. data is written to the dac using the inverted input clock signal. figure 28. analog delay line on initial start-up, the output voltage, v o , will be invalid until the length of the delay is reached (i.e., until the counter is re- set). from this point forward, the delayed data is read from the 6116 and loaded to the dac before the newly converted data is written into the same memory location. the input clock to the system can be a square wave of maximum input frequency 200 khz (assuming 2 m s conversion time for the adc). the mark/space ratio of the input clock can be varied to maximize the sampling frequency if required. the clock low time has to be equal to the conversion time and access time of the adc plus the setup time required for the 6116. the clock high time has only to be equal to the setup time for the dac plus the delay time through the counter and the access time of the 6116. the amount of memory used, as well as the sampling frequency, determines the maximum possible delay. using the hct4040, and the 6116 with an input clock frequency of 200 khz, the maximum delay is 5 ms on a maximum input frequency of 100 khz. using 64k memory, with an 8 khz input clock fre- quency, the maximum delay is 8 seconds on a maximum input frequency of 4 khz. transient recorderad7569 the scheme just outlined can also form the basis for a transient recorder. in this case, transients on the input signal are con- verted and stored in memory. the transient can then be recalled from memory at a later time, and the transient waveform can be recreated using the ad7569 dac. infinite sample-and-holdad7569 the ad7569 is ideal for implementing a single-chip infinite sample-and-hold function. basically, the adc samples and con- verts the input signal into an 8-bit digital word. the 8 bits of data are then loaded to the dac and the sampled value is re- stored to analog form. the sampled value is held until the dac register is updated. the full-scale matching between the adc and the dac on the ad7569 ensures a typical error of less than 1% between the analog input voltage and the held output voltage. figure 29 shows the connections required on the ad7569 to achieve this infinite sample-and-hold function. figure 29. infinite sample-and-hold ad7569/ad7669 C19C rev. b tare function for weigh scalead7569 the infinite sample-and-hold just outlined can also form the ba- sis of a circuit to provide a tare function for a weigh scale sys- tem. figure 30 shows a circuit for a weigh scale system. it incorporates a tare function using a simple circuit based on the ad7569. the ad587, along with the 2n6285, provides a buffered +10 v reference to supply the low impedance load cell transducer. the load cell output is amplified by the ad624 precision instrumen- tation amplifier with gain adjustment provided by r1. the out- put of the ad624 is applied to the noninverting input of a unity gain differential summing amplifier that uses the ad707, a high precision op amp with low drift. the ad707 feeds a 3 1/2 digit panel meter module that converts the signal for digital readout. the input signal to the panel meter is also applied to the analog input of the ad7569 for the tare function. when the tare switch (s1) is closed, a tare cycle commences and v in is sampled and held infinitely at v out until the next tare cycle. v out drives the inverting input of the differential amplifier and forces its output to zero. thus, the tare function is used to give a readout of zero for any undesired weight, such as a box, when only the item placed in it is to be weighed. the tare function can also be used in calibrating the system, to cancel out offset errors due to the load cell, ad624 and differential amplifier. the ad7569 offers many advantages in the system outlined, such as: simple, low cost circuitno need for microprocessor, software, etc.and low power consumption. figure 30. weigh scale system with tare function C20C rev. b ad7569/ad7669 c1214C10C8/88 printed in u.s.a. outline dimensions dimensions shown in inches and (mm). 24-pin plastic (n-24) 28-terminal leadless ceramic chip carrier (e-28a) 24-pin cerdip (q-24) 28-terminal plastic leaded chip carrier (p-28a) 28-pin plastic dip (n-28) 28-lead small outline (so) (r-28) |
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