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LTC1282 3V 140ksps 12-Bit Sampling A/D Converter with Reference
FEATURES
s s s s s s s s s s s s
DESCRIPTIO
Single Supply 3V or 3V Operation 140ksps Throughput Rate 12mW (Typ) Power Dissipation On-Chip 25ppm/C Reference Internal Synchronized Clock; No Clock Required High Impedance Analog Input 69dB S/(N + D) and 77dB THD at Nyquist 1/2LSB INL and 3/4LSB DNL Max (A Grade) 2.7V Guaranteed Minimum Supply Voltage ESD Protected On All Pins 24-Pin Narrow DIP and SOL Packages 0V to 2.5V or 1.25V Input Ranges
The LTC1282 is a 6s, 140ksps, sampling 12-bit A/D converter which draws only 12mW from a single 3V or dual 3V supply. This easy-to-use device comes complete with 1.0s sample-and-hold, precision reference and internally trimmed clock. Unipolar and bipolar conversion modes provide flexibility for various applications. They are built with LTBiCMOSTM switched capacitor technology. The LTC1282 has a 25ppm/C (max) internal reference and converts 0V to 2.5V unipolar inputs from a single 3V supply. With 3V supplies its input range is 1.25V with two's complement output format. Maximum DC specifications include 1/2LSB INL, 3/4LSB DNL and 25ppm/C full scale drift over temperature. Outstanding AC performance includes 69dB S/(N + D) and 77dB THD at the Nyquist input frequency of 70kHz. The internal clock is trimmed for 6s maximum conversion time. The clock automatically synchronizes to each sample command eliminating problems with asynchronous clock noise found in competitive devices. A high speed parallel interface eases connections to FIFOs, DSPs and microprocessors.
LTBiCMOSTM is a trademark of Linear Technology Corporation
APPLICATI
s s s s s s
S
3V Powered Systems High Speed Data Acquisition Digital Signal Processing Multiplexed Data Acquisition Systems Audio and Telecom Processing Spectrum Analysis
TYPICAL APPLICATI
1.20V VREF OUTPUT
Single 3V Supply, 140ksps, 12-Bit Sampling A/D Converter
LTC1282 ANALOG INPUT 1 A VDD (0V TO 2.5V) 2 IN VREF VSS 3 AGND BUSY 0.1F 4 D11(MSB) CS 5 D10 RD 6 D9 HBEN 7 D8 NC 8 D7 NC 9 D6 D0/8 10 8- OR 12-BIT D5 D1/9 PARALLEL BUS 11 D4 D2/10 12 DGND D3/11 3V 24 23 22 21 20 19 18 17 16 15 14 13 10F P CONTROL LINES 0.1F
Effective Bits and Signal-to-(Noise + Distortion) vs Input Frequency
12 74 68 62 NYQUIST FREQUENCY 56 50
ENOBs (EFFECTIVE NUMBER OF BITS)
+
11 10 9 8 7 6 5 4 3 2 1 0 1k 10k INPUT FREQUENCY (Hz) 100k
LTC1282 * TA02
+
10F
fSAMPLE = 140kHz
LTC1282 * TA01
U
S/(N + D) (dB)
UO
UO
1
LTC1282 ABSOLUTE
(Notes 1 and 2)
TOP VIEW
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
AIN VREF AGND D11(MSB) D10 D9 D8 D7 D6 1 2 3 4 5 6 7 8 9 24 VDD 23 VSS 22 BUSY 21 CS 20 RD 19 HBEN 18 NC 17 NC 16 D0/8 15 D1/9 14 D2/10 13 D3/11
Supply Voltage (VDD) .............................................. 12V Negative Supply Voltage (VSS)................... - 6V to GND Total Supply Voltage (VDD to VSS) .......................... 12V Analog Input Voltage (Note 3) .............................. VSS - 0.3V to VDD + 0.3V Digital Input Voltage (Note 4) ........... VSS - 0.3V to 12V Digital Output Voltage (Note 3) .............................. VSS - 0.3V to VDD + 0.3V Power Dissipation............................................. 500mW Specified Temperature Range (Note 14) ..... 0C to 70C Operating Temperature Range LTC1282AC, LTC1282BC ......................... 0C to 70C Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec)................. 300C
ORDER PART NUMBER LTC1282ACN LTC1282BCN LTC1282ACS LTC1282BCS
D5 10 D4 11 DGND 12
N PACKAGE S PACKAGE 24-LEAD PLASTIC DIP 24-LEAD PLASTIC SOL
TJMAX = 110C, JA = 100C/W (N) TJMAX = 110C, JA = 130C/W (S)
Consult factory for Industrial and Military grade parts (Note 14).
CO VERTER CHARACTERISTICS
PARAMETER Resolution (No Missing Codes) Integral Linearity Error (Note 7) Commercial Military Commercial Military (Note 8)
q
With Internal Reference (Notes 5 and 6)
MIN LTC1282A TYP MAX 1/2 1/2 3/4 3/4 1 3 4 10 5 0.3 0.1 25 10 0.3 0.1 MIN 12 1 1 1 1 1 4 6 15 45 LTC1282B TYP MAX UNITS Bits LSB LSB LSB LSB LSB LSB LSB LSB ppm/C LSB LSB
CONDITIONS
q q q q q
12
Differential Linearity Error Offset Error Full Scale Error Full Scale Tempco Power Supply Rejection
IOUT(REF) = 0 (Note 9) VDD 10% (Note 10) VSS 10%
q
DY A IC ACCURACY
SYMBOL S/(N + D) THD IMD PARAMETER
(Note 5)
CONDITIONS 10kHz/70kHz Input Signal 10kHz/70kHz Input Signal, Up to 5th Harmonic 10kHz/70kHz Input Signal fIN1 = 19.0kHz, fIN2 = 20.6kHz LTC1282A/LTC1282B MIN TYP MAX 71/69 - 82/- 77 - 82/- 77 - 78 4 200 UNITS dB dB dB dB MHz kHz
Signal-to-Noise Plus Distortion Ratio Total Harmonic Distortion Peak Harmonic or Spurious Noise Intermodulation Distortion Full Power Bandwidth Full Linear Bandwidth (S/(N + D) 68dB)
2
U
W
U
U
WW
W
WU
U
LTC1282
A ALOG I PUT (Note 5)
SYMBOL PARAMETER VIN IIN CIN tACQ Analog Input Range (Note 11) Analog Input Leakage Current Analog Input Capacitance Sample-and-Hold Acquisition Time CONDITIONS 2.7V VDD 3.6V (Unipolar Mode) 2.7V VDD 3.6V, - 3.3V VSS - 2.5V (Bipolar Mode) CS = High Between Conversions (Sample Mode) During Conversions (Hold Mode) Commercial Military
q q q q q
I TER AL REFERE CE CHARACTERISTICS (Note 5)
PARAMETER VREF Output Voltage VREF Output Tempco VREF Line Regulation VREF Load Regulation CONDITIONS IOUT = 0 IOUT = 0 2.7V VDD 3.6V - 3.6V VSS - 2.7V 0V |IOUT| 1mA
q
DIGITAL I PUTS A D DIGITAL OUTPUTS (Note 5)
SYMBOL PARAMETER VIH VIL IIN CIN VOH High Level Input Voltage Low Level Input Voltage Digital Input Current Digital Input Capacitance High Level Output Voltage VDD = 2.7V IO = - 10A IO = - 200A VDD = 2.7V IO = 160A IO = 1.6mA VOUT = 0V to VDD, CS High CS High (Note 12 ) VOUT = 0V VOUT = VDD CONDITIONS VDD = 3.6V VDD = 2.7V VIN = 0V to VDD
q q q
VOL
Low Level Output Voltage
IOZ COZ ISOURCE ISINK
High Z Output Leakage D11-D0/8 High Z Output Capacitance D11-D0/8 Output Source Current Output Sink Current
POWER REQUIRE E TS (Note 5)
SYMBOL PARAMETER VDD VSS IDD ISS PD Positive Supply Voltage Negative Supply Voltage Positive Supply Current Negative Supply Current Power Dissipation CONDITIONS (Note 13) Bipolar Operation (Note 13) fSAMPLE = 140ksps fSAMPLE = 140ksps fSAMPLE = 140ksps
q q q
UW
U
U
U
U
U
U
LTC1282A/LTC1282B MIN TYP MAX 0 to 2.5 1.25 1 63 5 0.45 1.00 1.50
UNITS V V A pF pF s s
U
MIN 1.1900
LTC1282A TYP 1.200 5 0.55 0.02 3
MAX 1.210 25
MIN 1.190
LTC1282B TYP 1.200 10 0.55 0.02 3
MAX 1.210 45
UNITS V ppm/C LSB/V LSB/V LSB/mA
LTC1282A/LTC1282B MIN TYP MAX 1.9 0.45 10 5 2.6
q
UNITS V V A pF V V V V A pF mA mA
2.3 0.05 0.10
q q q
0.4 10 15
- 4.5 4.5
LTC1282A/LTC1282B MIN TYP MAX 2.70 - 2.50 4 0.03 12 3.60 - 3.60 7.8 0.15 24
UNITS V V mA mA mW
3
LTC1282
TI I G CHARACTERISTICS (Note 5)
SYMBOL fSAMPLE(MAX) tCONV t1 t2 PARAMETER Maximum Sampling Frequency Conversion Time CS to RD Setup Time RD to BUSY Delay CL = 50pF Commercial Military CL = 20pF (Note 13) Commercial Military CL = 100pF (Note 13) Commercial Military t4 t5 t6 RD Pulse Width CS to RD Hold Time Data Setup Time After BUSY (Note 13) (Note 13) (Note 13) Commercial Military (Note 13) Commercial Military (Note 13) (Note 13) Commercial (Note 13) Military (Note 13) CONDITIONS Commercial (Note 13) Military (Note 13) Commercial Military
q q q q q q q
t3
t7
t8 t9 t10 t11 t12
The q indicates specifications which apply over the full operating temperature range; all other limits and typicals TA = 25C. Note 1: Absolute maximum ratings are those values beyond which the life of a device may be impaired. Note 2: All voltage values are with respect to ground with DGND and AGND wired together (unless otherwise noted). Note 3: When these pin voltages are taken below VSS or above VDD, they will be clamped by internal diodes. This product can handle input currents greater than 60mA below VSS or above VDD without latchup. Note 4: When these pin voltages are taken below VSS they will be clamped by internal diodes. This product can handle input currents greater than 60mA below VSS without latchup. These pins are not clamped to VDD. Note 5: VDD = 3V, VSS = 0V for unipolar mode and VSS = - 3V for bipolar mode, fSAMPLE = 140kHz, tr = tf = 5ns unless otherwise specified. Note 6: Linearity, offset and full scale specifications apply for unipolar and bipolar modes. Note 7: Integral nonlinearity is defined as the deviation of a code from a straight line passing through the actual endpoints of the transfer curve. The deviation is measured from the center of the quantization band.
4
UW
LTC1282A/LTC1282B MIN TYP MAX 140 120 6.0 6.5 0 140 200 230 260 180 200 220 200 240 260
UNITS kHz kHz s s ns ns ns ns ns ns ns ns ns ns ns ns
Data Access Time After RD
100
q q
110
q q q q q q q q q q q q q
t3 0 60 85 110 120 120 130 150
ns ns ns ns ns ns ns ns ns
Bus Relinquish Time
40 40 40 0 0 40 1000 1500
60
HBEN to RD Setup Time HBEN to RD Hold Time Delay Between RD Operations Delay Between Conversions Aperture Delay of Sample-and-Hold
450 30
ns ns ns
Note 8: Bipolar offset is the different voltage measured from - 1/2LSB when the output code flickers between 0000 0000 0000 and 1111 1111 1111. Note 9: Full scale change when VSS = 0V (Unipolar Mode) or - 3V (Bipolar Mode). Note 10: Full scale change when VDD = 3V. Note 11: The LTC1282 can perform unipolar and bipolar conversions. When VSS is grounded (i.e. - 0.1V VSS), the ADC will convert in unipolar mode with input voltage of 0V to 2.5V. When VSS is taken negative (i.e. VSS - 2.5V), the ADC will convert in bipolar mode with an input voltage of 1.25V. AIN must not exceed VDD or fall below VSS by more than 50mV for specified accuracy. Note 12: Guaranteed by design, not subject to test. Note 13: Recommended operating conditions. Note 14: Commercial grade parts are designed to operate over the temperature range of - 40C to 85C but are neither tested nor guaranteed beyond 0C to 70C. Industrial grade parts specified and tested over - 40C to 85C are available on special request. Consult factory.
LTC1282
TI I G CHARACTERISTICS (Note 5)
Slow Memory Mode, Parallel Read Timing Diagram
CS t1 RD t2 BUSY t3 DATA HOLD TRACK t12 OLD DATA DB11 TO DB0 t6 t7 NEW DATA DB11 TO DB0 tCONV t11 t10 t5 t1
UW
ROM Mode, Parallel Read Timing Diagram
CS t1 RD t2 BUSY t3 DATA HOLD
LTC1282 * TC01
t4
t5 t11 tCONV t7
t1
t4 t2
t5
tCONV t7 NEW DATA DB11 TO DB0
t3
OLD DATA DB11 TO DB0 t12 t12
TRACK
LTC1282 * TC02
Slow Memory Mode, Two Byte Read Timing Diagram
HBEN t8 CS t1 RD t2 BUSY t3 DATA HOLD TRACK t12 OLD DATA DB7 TO DB0 t6 t7 NEW DATA DB7 TO DB0 t3 t7 NEW DATA DB11 TO DB8 t12 t10 tCONV t11 t10 t5 t1 t4 t5 t9 t8 t9
LTC1282 * TC03
ROM Mode, Two Byte Read Timing Diagram
HBEN t8 CS t1 RD t2 BUSY t3 DATA HOLD TRACK t12 t7 OLD DATA DB7 TO DB0 t3 t7 NEW DATA DB11 TO DB8 t12
LTC1282 * TC04
t9
t8
t9
t8
t9
t4
t5
t1
t4 t11
t5 t10
t1
t4 t2
t5
tCONV
t3
t7 NEW DATA DB7 TO DB0
5
LTC1282
TYPICAL PERFOR A CE CHARACTERISTICS
Integral Nonlinearity
DIFFERENTIAL NONLINEARITY ERROR (LSBs) 1 INTEGRAL NONLINEARITY ERROR (LSBs)
SUPPLY CURRENT (mA)
0.5
0
-0.5
-1 0 512 1024 1536 2048 2560 3072 3584 4096 CODE
LTC1282 * TPC01
Supply Current (IDD) vs Supply Voltage
20
EFFECTIVE NUMBER OF BITS (ENOBs)
18 16
fSAMPLE = 160kHz TA = 25C
11 10 9 8 7 6 5 4 3 2 1 0 1k fSAMPLE = 160kHz VS = 2.7V BIPOLAR VS = 3V UNIPOLAR UNIPOLAR (0V - 2.5V INPUT)
BIPOLAR (1.25V INPUT)
AMPLITUDE (dB BELOW THE FUNDAMENTAL)
SUPPLY CURRENT (mA)
14 12 10 8 6 4 2 0 2.5 3 4 4.5 3.5 SUPPLY VOLTAGE (V) 5 DUAL SUPPLIES SINGLE SUPPLY
Distortion vs Input Frequency (Bipolar)
AMPLITUDE (dB BELOW THE FUNDAMENTAL)
0
AMPLITUDE OF POWER SUPPLY FEEDTHROUGH (dB)
-10 -20 -30 -40 -50 -60 -70 -80 -90 -100 1k
fSAMPLE = 140kHz 3V SUPPLIES BIPOLAR
-40 -50 -60 -70 -80 -90 -100 1k 10k 100k RIPPLE FREQUENCY (Hz) 1M
AMPLITUDE (dB)
THD
3rd HARMONIC 2nd HARMONIC
100k 1M 10k INPUT FREQUENCY (Hz)
6
UW
LTC1282 * TPC04
LTC1282 * TPC07
Differential Nonlinearity
1
10 9
Supply Current (IDD) vs Temperature
fSAMPLE = 160kHz VDD = 3V
0.5
8 7 6 5 4 3 2 1
0
-0.5
-1 0 512 1024 1536 2048 2560 3072 3584 4096 CODE
LTC1282 * TPC02
0 -50 -25
50 25 0 75 TEMPERATURE (C)
100
125
LTC1282 * TPC03
ENOBs and S/(N + D) vs Input Frequency
12 74 68 62 56 50
0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100
Distortion vs Input Frequency (Unipolar)
S/(N + D) (dB)
fSAMPLE = 160kHz 3V SUPPLY UNIPOLAR
THD 3rd HARMONIC 2nd HARMONIC
10k 100k 1M INPUT FREQUENCY (Hz)
10M
1k
100k 1M 10k INPUT FREQUENCY (Hz)
10M
LTC1282 * TPC05
LTC1282 * TPC06
Power Supply Feedthrough vs Ripple Frequency
0 -10 -20 -30 fSAMPLE = 140kHz VDD (VRIPPLE = 2.5mV) VSS (VRIPPLE = 2.5mV) DGND (VRIPPLE = 250mV)
Intermodulation Distortion Plot
0 -20 -40 -60 -80 fSAMPLE = 160kHz fIN1 = 19.0kHz fIN2 = 20.6kHz VDD = 3V UNIPOLAR
-100 -120 0 10k
10M
20k 30k 40k 50k 60k 70k FREQUENCY (Hz)
80k
LTC1282 * TPC08
LTC1282 * TPC09
LTC1282
TYPICAL PERFOR A CE CHARACTERISTICS
S/(N + D) vs Input Frequency and Amplitude (Unipolar, VDD = 3V)
80 VIN = 0dB 80
SIGNAL/(NOISE + DISTORTION) (dB)
SIGNAL/(NOISE + DISTORTION) (dB)
70 60 VIN = -20dB 50 40 30 20 10 0 1k VIN = -60dB
fSAMPLE = 160kHz UNIPOLAR
50 40 30 20 10 0 1k 100k 1M 10k INPUT FREQUENCY (Hz) 10M VIN = -60dB
AMPLITUDE (dB)
100k 1M 10k INPUT FREQUENCY (Hz)
Reference Voltage vs Load Current
1.220
SIGNAL/(NOISE + DISTORTION) (dB)
80
MAGNITUDE OF OFFSET VOLTAGE CHANGE (LSBs)
1.215
REFERENCE VOLTAGE (V)
VDD = 3V
1.210 1.205 1.200 1.195 1.190 1.185 1.180 1.175 1.170 -5 -4 -2 -1 -3 LOAD CURRENT (mA) 0 1
Change in Gain Error vs Temperature
MAGNITUDE OF GAIN ERROR CHANGE (LSBs)
MAGNITUDE OF DIFFERENTIAL NONLINEARITY CHANGE (LSBs)
5
MAGNITUDE OF INTEGRAL NONLINEARITY CHANGE (LSBs)
fSAMPLE = 140kHz VDD = 2.7V 4
3
2
1
0 -50 -25
50 25 0 75 TEMPERATURE (C)
UW
LTC1282 * TPC10
S/(N + D) vs Input Frequency and Amplitude (Bipolar, 3V Supplies)
0
Spurious Free Dynamic Range vs Input Frequency
-10 -20 fSAMPLE = 160kHz VDD = 3V UNIPOLAR
VIN = 0dB 70 60 VIN = -20dB
fSAMPLE = 160kHz
-30 -40 -50 -60 -70 -80 -90
10M
-100 100
1k 10k 100k INPUT FREQUENCY (Hz)
1M
LTC1282 * TPC10
LTC1282 * TPC12
S/(N +D) vs Input Frequency vs Source Resistance (Bipolar)
5
Change in Offset Voltage vs Temperature
fSAMPLE = 140kHz VDD = 2.7V 4
70 60 50 40 30 20 10 0 1k VDD = 3V VSS = -3V BIPOLAR
RS = 50 RS = 500 RS = 1k RS = 5k
3
2
1
100k 1M 10k INPUT FREQUENCY (Hz)
10M
0 -50 -25
50 25 0 75 TEMPERATURE (C)
100
125
LTC1282 * TPC13
LTC1282 * TPC14
LTC1282 * TPC15
Change in Integral Nonlinearity (INL) vs Temperature
0.5 fSAMPLE = 140kHz VDD = 2.7V 0.4
Change in Differential Nonlinearity (DNL) vs Temperature
0.5 fSAMPLE = 140kHz VDD = 2.7V 0.4
0.3
0.3
0.2
0.2
0.1
0.1
100
125
0 -50 -25
50 25 0 75 TEMPERATURE (C)
100
125
0 -50 -25
50 25 0 75 TEMPERATURE (C)
100
125
LTC1282 * TPC16
LTC1282 * TPC17
LTC1282 * TPC18
7
LTC1282
TYPICAL PERFOR A CE CHARACTERISTICS
Change in Offset Voltage vs Supply Voltage
MAGNITUDE OF OFFSET VOLTAGE CHANGE (LSBs)
0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 2 2.5 3.5 4 3 SUPPLY VOLTAGE (V) 4.5 5 fSAMPLE = 140kHz
MAGNITUDE OF GAIN ERROR CHANGE (LSBs)
1
Change in Integral Nonlinearity (INL) vs Supply Current
fSAMPLE = 140kHz 0.4
MAGNITUDE OF DIFFERENTIAL NONLINEARITY CHANGE (LSBs)
0.5
MAGNITUDE OF INTEGRAL NONLINEARITY CHANGE (LSBs)
0.3
0.2
0.1
0
2
2.5
8
UW
Change in Gain Error vs Supply Voltage
5 fSAMPLE = 140kHz 4
3
2
1
0
2
2.5
3 3.5 4 SUPPLY VOLTAGE (V)
4.5
5
LTC1282 * TPC19
LTC1282 * TPC20
Change in Differential Nonlinearity (DNL) vs Supply Current
0.5 fSAMPLE = 140kHz 0.4
0.3
0.2
0.1
3 3.5 4 SUPPLY VOLTAGE (V)
4.5
5
0
2
2.5
3 3.5 4 SUPPLY VOLTAGE (V)
4.5
5
LTC1282 * TPC21
LTC1282 * TPC22
LTC1282
PI FU CTIO S
AIN (Pin 1): Analog Input. 0V to 2.5V (Unipolar), 1.25V (Bipolar). VREF (Pin 2): +1.20V Reference Output. Bypass to AGND (10F tantalum in parallel with 0.1F ceramic). AGND (Pin 3): Analog Ground. D11-D4 (Pins 4 to 11): Three-State Data Outputs. D11 is the Most Significant Bit. DGND (Pin 12): Digital Ground. D3/11-D0/8 (Pins 13 to 16): Three-State Data Outputs. NC (Pins 17 and 18): No Connection. HBEN (Pin 19): High Byte Enable Input. This pin is used to multiplex the internal 12-bit conversion result into the lower bit outputs (D7 and D0/8). See Table 1. HBEN also disables conversion start when HIGH.
Table 1. Data Bus Output, CS and RD = LOW
Pin 4 MNEMONIC* HBEN = LOW HBEN = HIGH D11 DB11 DB11 Pin 5 D10 DB10 DB10 Pin 6 D9 DB9 DB9 Pin 7 D8 DB8 DB8 Pin 8 D7 DB7 LOW Pin 9 D6 DB6 LOW Pin 10 D5 DB5 LOW Pin 11 D4 DB4 LOW Pin 13 D3/11 DB3 DB11 Pin 14 D2/10 DB2 DB10 Pin 15 D1/9 DB1 DB9 Pin 16 D0/8 DB0 DB8
*D11...D0/8 are the ADC data output pins. DB11...DB0 are the 12-bit conversion results, DB11 is the MSB.
TEST CIRCUITS
Load Circuits for Access Time
5V 3k DBN 3k DGND A) HIGH-Z TO VOH (t3) AND VOL TO VOH (t6) CL DBN CL DGND B) HIGH-Z TO VOL (t3) AND VOH TO VOL (t6)
1282 * F05
U
U
U
RD (Pin 20): READ Input. This active low signal starts a conversion when CS and HBEN are low. RD also enables the output drivers when CS is low. CS (Pin 21): The CHIP SELECT Input must be low for the ADC to recognize RD and HBEN inputs. BUSY (Pin 22): The BUSY Output shows the converter status. It is low when a conversion is in progress. VSS (Pin 23): Bipolar Mode -- Negative Supply, - 3V. Bypass to AGND with 0.1F ceramic. Unipolar Mode -- Tie to DGND. VDD (Pin 24): Positive Supply, 3V. Bypass to AGND (10F tantalum in parallel with 0.1F ceramic).
Load Circuits for Output Float Delay
5V 3k DBN 3k DGND A) VOH TO HIGH-Z 10pF DBN 10pF DGND B) VOL TO HIGH-Z
1282 * F06
9
LTC1282
FU TIO AL BLOCK DIAGRA
SAMPLE AIN HOLD
CSAMPLE
VREF(OUT)
12-BIT CAPACITIVE DAC 1.2V REFERENCE AGND DGND
INTERNAL CLOCK
APPLICATI
S I FOR ATIO
CONVERSION DETAILS The LTC1282 uses a successive approximation and an internal sample-and-hold circuitry to convert an analog signal to a 12-bit parallel or 2-byte output. The ADC is complete with a precision reference and an internal clock. The control logic provides easy interface to microprocessors and DSPs. Please refer to the Digital Interface section for the data format. Conversion start is controlled by the CS, RD and HBEN inputs. At the start of conversion the successive approximation register (SAR) is reset and the three-state data outputs are enabled. Once a conversion cycle has begun it cannot be restarted. During conversion, the internal 12-bit capacitive DAC output is sequenced by the SAR from the most significant bit (MSB) to the least significant bit (LSB). Referring to Figure 1, the AIN input connects to the sample-and-hold capacitor during the sample phase, and the comparator offset is nulled by the feedback switch. In this sample phase, a minimum delay of 1.0s will provide enough time for the sample-and-hold capacitor to acquire the analog signal. During the convert phase, the comparator feed-
10
+
-
W
SAMPLE VDD COMPARATOR VSS (-3V FOR BIPOLAR MODE, AGND FOR UNIPOLAR MODE) D11 12 SUCCESSIVE APPROXIMATION REGISTER 12 OUTPUT LATCHES * * * D0/8 BUSY CONTROL LOGIC CS RD HBEN
LTC1282 * FBD
U
W
U
UO
U
U
back switch opens, putting the comparator into the compare mode. The input switch switches CSAMPLE to ground, injecting the analog input charge to the summing junction. This input charge is successively compared with the binary-weighted charges supplied by the capacitive DAC. Bit decisions are made by the high speed comparator. At the end of a conversion, the DAC output balances the AIN input charge. The SAR contents (a 12-bit data word) which represent the AIN are loaded into the 12-bit latch.
SAMPLE CSAMPLE SI
SAMPLE AIN HOLD
- +
COMPARATOR DAC VDAC S A R
CDAC
LTC1282 * F01
12-BIT LATCH
Figure 1. AIN Input
LTC1282
APPLICATI S I FOR ATIO U
12
EFFECTIVE NUMBER OF BITS (ENOBs)
DYNAMIC PERFORMANCE The LTC1282 has exceptionally high speed sampling capability. FFT (Fast Fourier Transform) test techniques are used to characterize the ADC's frequency response, distortion and noise at the rated throughput. By applying a low distortion sine wave and analyzing the digital output using an FFT algorithm, the ADC's spectral content can be examined for frequencies outside the fundamental. Figure 2 shows a typical LTC1282 FFT plot. Signal-to-(Noise + Distortion) Ratio The Signal-to-Noise plus Distortion Ratio [S/(N + D)] is the ratio between the RMS amplitude of the fundamental input frequency to the RMS amplitude of all other frequency components at the A/D output. The output is band limited to frequencies from above DC and below half the sampling frequency. Figure 2 shows a typical LTC1282 FFT plot.
0 -20 fSAMPLE = 160kHz VDD = 3V UNIPOLAR
AMPLITUDE (dB)
-40 - 60 -80
-100 -120 0 10 20
30 40 50 60 FREQUENCY (kHz)
AMPLITUDE (dB BELOW THE FUNDAMENTAL)
Figure 2. LTC1282 Nonaveraged, 1024 Point FFT Plot
Effective Number of Bits The Effective Number of Bits (ENOBs) is a measurement of the resolution of an ADC and is directly related to S/(N + D) by the equation: N = [S/(N + D) - 1.76]/6.02 where N is the Effective Number of Bits of resolution and S/(N + D) is expressed in dB. At the maximum sampling rate of 140kHz the LTC1282 maintains 11.3 ENOBs at 70kHz input frequency. Refer to Figure 3.
W
U
UO
74 BIPOLAR (1.25V INPUT) 68 62 56 50
S/(N + D) (dB)
11 10 9 8 7 6 5 4 3 2 1 0 1k fSAMPLE = 160kHz VS = 2.7V BIPOLAR
10k 100k 1M INPUT FREQUENCY (Hz)
10M
LTC1282 * F03
Figure 3. ENOBs and S/(N + D) vs Input Frequency
Total Harmonic Distortion Total Harmonic Distortion (THD) is the ratio of the RMS sum of all harmonics of the input signal to the fundamental itself. The out-of-band harmonics alias into the frequency band between DC and half the sampling frequency. THD is expressed as:
THD = 20log
V22 + V32 + V42 ... + VN2 V1
70
80
where V1 is the RMS amplitude of the fundamental frequency and V2 through VN are the amplitudes of the second through Nth harmonics. The typical THD specification in the Dynamic Accuracy table includes the 2nd through 5th harmonics. With a 70kHz input signal, the LTC1282 has a typical - 82dB THD as shown in Figure 4.
0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 1k 100k 1M 10k INPUT FREQUENCY (Hz) 10M
LTC1282 * F04
LTC1282 * F07
fSAMPLE = 140kHz 3V SUPPLIES BIPOLAR
THD
3rd HARMONIC 2nd HARMONIC
Figure 4. Distortion vs Input Frequency (Bipolar)
11
LTC1282 APPLICATI S I FOR ATIO U
Full Power and Full Linear Bandwidth The full power bandwidth is that input frequency at which the amplitude of the reconstructed fundamental is reduced by 3dB for a full scale input signal. The full linear bandwidth is the input frequency at which the S/(N + D) has dropped to 68dB (11 effective bits). The LTC1282 has been designed to optimize input bandwidth, allowing the ADC to undersample input signals with frequencies above the converter's Nyquist Frequency. Driving the Analog Input The analog input of the LTC1282 is easy to drive. It draws only one small current spike while charging the sampleand-hold capacitor at the end of conversion. During conversion the analog input draws no current. The only requirement is that the amplifier driving the analog input must settle after the small current spike before the next conversion starts. Any op amp that settles in 1.0s to small current transients will allow maximum speed operation. If slower op amps are used, more settling time can be provided by increasing the time between conversions. Suitable devices capable of driving the ADC's AIN input include the LT1190/LT1191, LT1007, LT1220, LT1223 and LT1224 op amps. The analog input tolerates source resistance very well. Here again, the only requirement is that the analog input must settle before the next conversion starts. For larger source resistance, full accuracy can be obtained if more time is allowed between conversions. Internal Reference
0 10k 20k 30k 40k 50k 60k 70k FREQUENCY (Hz) 80k
Intermodulation Distortion If the ADC input signal consists of more than one spectral component, the ADC transfer function nonlinearity can produce intermodulation distortion (IMD) in addition to THD. IMD is the change in one sinusoidal input caused by the presence of another sinusoidal input at a different frequency. If two pure sine waves of frequencies fa and fb are applied to the ADC input, nonlinearities in the ADC transfer function can create distortion products at sum and difference frequencies of mfa nfb, where m and n = 0, 1, 2, 3, etc. For example, the 2nd order IMD terms include (fa + fb) and (fa - fb) while the 3rd order IMD terms include (2fa + fb), (2fa - fb), (fa + 2fb), and (fa - 2fb) if the two input sine waves are equal in magnitude, the value (in decibels) of the 2nd order. IMD products can be expressed by the following formula: IMD (fa fb) = 20log Amplitude at (fa fb) Amplitude at fa
Figure 5 shows the IMD performance at a 20kHz input.
0 -20 fSAMPLE = 160kHz fIN1 = 19.0kHz fIN2 = 20.6kHz VDD = 3V UNIPOLAR
AMPLITUDE (dB)
-40 -60 -80
-100 -120
Figure 5. Intermodulation Distortion Plot
Peak Harmonic or Spurious Noise The peak harmonic or spurious noise is the largest spectral component excluding the input signal and DC. This value is expressed in decibels relative to the RMS value of a full scale input signal.
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LTC1282 * F05
The LTC1282 has an on-chip, temperature compensated, curvature corrected, bandgap reference which is factory trimmed to 1.20V. It is internally connected to the DAC and is available at pin 2 to provide up to 0.3mA current to an external load. For minimum code transition noise the reference output should be decoupled with a capacitor to filter wideband noise from the reference (10F tantalum in parallel with a 0.1F ceramic).
LTC1282
APPLICATI S I FOR ATIO U
is natural binary with 1LSB = FS/4096 = 2.5V/4096 = 0.61mV. Figure 9 shows the input/output transfer characteristics for the LTC1282 in bipolar operation. The full scale for LTC1282 in bipolar mode is still 2.5V and 1LSB = 0.61mV.
111...111 111...110 111...101 FS = 2.5V 1LSB = FS/4096
Overdriving the Internal Reference The VREF pin can be driven above its normal value with a DAC or other means to provide input span adjustment. Figure 6 shows an LT1006 op amp driving the reference pin. The VREF pin must be driven to at least 1.25V to prevent conflict with the internal reference. The reference should be driven to no more than 1.44V in unipolar mode or 2.88V for bipolar mode to keep the input span within the single 3V or 3V supplies.
INPUT RANGE 1.033VREF(OUT) AIN VDD 3V
OUTPUT CODE
+
LT1006
VREF(OUT) 1.25V 3 10F
-
Figure 6. Driving the VREF with the LT1006 Op Amp
OUTPUT CODE
Figure 7 shows a typical reference, the LT1019A-2.5 connected to the LTC1282 operating in bipolar mode. This will provide an improved drift (due to the 5ppm/C of the LT1019A-2.5) and a 2.604V full scale.
INPUT RANGE 2.60V 5V VIN VOUT LT1019A-2.5 GND VREF 3 AIN VDD 3V
+
10F
Figure 7. Supplying a 2.5V Reference Voltage to the LTC1282 with the LT1019A-2.5
UNIPOLAR/BIPOLAR OPERATION AND ADJUSTMENT Figure 8 shows the ideal input/output characteristics for the LTC1282. The code transitions occur midway between successive integer LSB values (i.e., 1/2LSB, 1 1/2LSBs, 2 1/2LSBs, FS - 1 1/2LSBs). The output code
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111...100
LTC1282 VREF
000...011 000...010 000...001 000...000 0V
UNIPOLAR ZERO
AGND VSS
LTC1282 * F06
-3V
1 LSB INPUT VOLTAGE (V)
FS - 1LSB
LTC1282 * F8
Figure 8. LTC1282 Unipolar Transfer Characteristic
011...111 011...110 BIPOLAR ZERO
000...001 000...000 111...111 111...110 100...010 100...001 100...000 -FS/2 FS = 2.5V 1LSB = FS/4096 -1 0V 1 LSB LSB INPUT VOLTAGE (V) FS/2 - 1LSB
LTC1282 * F09
LTC1282
AGND VSS
LTC1282 * F07
-3V
Figure 9. LTC1282 Bipolar Transfer Characteristic
Unipolar Offset and Full Scale Adjustment In applications where absolute accuracy is important, offset and full scale errors can be adjusted to zero. Figure 10 shows the extra components required for full scale error adjustment. If both offset and full scale adjustments are needed, the circuit in Figure 11 can be used. Offset should be adjusted before full scale. To adjust offset,
13
LTC1282
APPLICATI
S I FOR ATIO
apply 0.305mV (i.e., 1/2LSB) at V1 and adjust the op amp offset voltage until the LTC1282 output code flickers between 0000 0000 0000 and 0000 0000 0001. For zero full scale error, apply an analog input of 2.49909V (i.e., FS - 1 1/2LSBs or last code transition) at the input and adjust the full scale trim until the LTC1282 output code flickers between 1111 1111 1110 and 1111 1111 1111.
R1 50 V1
+
A1 AIN R4 100 LTC1282 R5 10k FULL SCALE ADJUST AGND ADDITIONAL PINS OMITTED FOR CLARITY 20LSB TRIM RANGE
LTC1282 * F10
-
R2 10k
Figure 10. Full Scale Adjust Circuit
R1 10k R2 10k
ANALOG INPUT 0V TO 2.5V 5V
+
AIN
10k
-
R9 20
R4 100k R5 4.3k FULL SCALE ADJUST R3 100k R7 100k R6 400 LTC1282
5V R8 10k OFFSET ADJUST
LTC1282 * F11
Figure 11. Unipolar Offset and Full Scale Adjust Circuit
Bipolar Offset and Full Scale Adjustment Bipolar offset and full scale errors are adjusted in a similar fashion to the unipolar case. Figure 10 shows the extra components required for full scale error adjustment. If both offset and full scale adjustments are needed, the circuit in Figure 12 can be used. Again, bipolar offset must be adjusted before full scale error. Bipolar offset error adjustment is
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ANALOG INPUT 1.25V R1 10k R2 10k
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AIN
-
R4 100k R5 4.3k FULL SCALE ADJUST R3 100k R7 100k R6 200 LTC1282
5V R8 20k OFFSET ADJUST -5V
LTC1282 * F12
Figure 12. Bipolar Offset and Full Scale Adjust Circuit
achieved by trimming the offset adjustment of Figure 12 while the input voltage is 1/2LSB below ground. This is done by applying an input voltage of - 0.305mV (- 1/2LSB for LTC1282) to the input in Figure 12 and adjusting R8 until the ADC output code flickers between 0000 0000 0000 and 1111 1111 1111. For full scale adjustment, an input voltage of 1.24909V (FS - 3/2LSBs for LTC1282) is applied to the input and R5 is adjusted until the output code flickers between 0111 1111 1110 and 0111 1111 1111. BOARD LAYOUT AND BYPASSING The LTC1282 is easy to use. To obtain the best performance from the device, a printed circuit board is recommended. Layout for the printed circuit board should ensure that digital and analog signal lines are separated as much as possible. In particular, care should be taken not to run any digital track alongside an analog signal track or underneath the ADC. The analog input should be screened by AGND. High quality tantalum and ceramic bypass capacitors should be used at the VDD and VREF pins as shown in Figure 13. In bipolar mode, a 0.1F ceramic provides adequate bypassing for the VSS pin. The capacitors must be located as close to the pins as possible. The traces connecting the pins and the bypass capacitors must be kept short and should be made as wide as possible.
LTC1282
APPLICATI
S I FOR ATIO
1 AIN AGND 3
ANALOG INPUT CIRCUITRY
+ -
VREF 2 10F 0.1F 10F
ANALOG GROUND PLANE
LTC1282 * F13
Figure 13. Power Supply Grounding Practice
Noise: Input signal leads to AIN and signal return leads from AGND (Pin 3) should be kept as short as possible to minimize input noise coupling. In applications where this is not possible, a shielded cable between source and ADC is recommended. Also, since any potential difference in grounds between the signal source and ADC appears as an error voltage in series with the input signal, attention should be paid to reducing the ground circuit impedances as much as possible. A single point analog ground separate from the logic system ground should be established with an analog ground plane at pin 3 (AGND) or as close as possible to the ADC, as shown in Figure 13. Pin 12 ( DGND) and all other analog grounds should be connected to this single analog ground point. No other digital grounds should be connected to this analog ground point. Low impedance analog and digital power supply common returns are essential to low noise operation of the ADC and the foil width for these tracks should be as wide as possible. In applications where the ADC data outputs and control signals are connected to a continuously active microprocessor bus, it is possible to get errors in conversion results. These errors are due to feedthrough from the microprocessor to the successive approximation comparator. The problem can be eliminated by forcing the microprocessor into a WAIT state during conversion or by using three-state buffers to isolate the ADC data bus.
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LTC1282 VDD 24 0.1F DGND 12 GROUND CONNECTION TO DIGITAL CIRCUITRY DIGITAL SYSTEM
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DIGITAL INTERFACE The ADC is designed to interface with microprocessors as a memory mapped device. The CS and RD control inputs are common to all peripheral memory interfacing. The HBEN input serves as a data byte select for 8-bit processors and is normally either connected to the microprocessor address bus or grounded. Connecting to 5V Logic Systems The LTC1282 interfaces well to 5V logic because the ESD clamps on the inputs do not clamp to the positive supply (see Figure 14). Inputs of 0V to 5V do not bother the ADC at all. In addition, the 0V to 3V outputs of the 3V ADC are more than adequate to meet TTL input levels in the 5V logic. (5V logic with CMOS input levels requires a level shift.)
3V ADC OUTPUTS 0V TO 3V LTC1282 3V ADC LTC ESD CLAMP ADC INPUTS 0V TO 5V TTL INPUT LEVELS CMOS OUTPUT LEVELS 5V
5V LOGIC
LTC1282 * F14
Figure 14. 3V ADC ESD Protection Handles 0V to 5V Swings Easily
15
LTC1282
APPLICATI
Internal Clock The LTC1282 has an internal clock that eliminates the need for synchronization between the external clock and the CS and RD signals found in other ADCs. The internal clock is factory trimmed to achieve a typical conversion time of 5.5s, and a maximum conversion time over the full operating temperature range of 6.0s. No external adjustments are required and, with the guaranteed maximum acquisition time of 1.0s, throughput performance of 140ksps is assured. Timing and Control Conversion start and data read operations are controlled by three digital inputs: HBEN, CS and RD. Figure 15 shows the logic structure associated with these inputs. The three signals are internally gated so that a logic "0" is required on all three inputs to initiate a conversion. Once initiated it cannot be restarted until the conversion is complete. Converter status is indicated by the BUSY output, and this is low while conversion is in progress.
LTC1282 HBEN 19 CS 21 D FLIP FLOP CLEAR Q
S I FOR ATIO
BUSY CONVERSION START (RISING EDGE TRIGGER)
RD 20
ACTIVE HIGH ACTIVE HIGH
ENABLE THREE-STATE OUTPUTS D11....D0/8 = DB11....DB0 ENABLE THREE-STATE OUTPUTS D11....D8 = DB11....DB8 D7....D4 = LOW D3/11....D0/8 = DB11....DB8
LTC1282 * F15
* D11....D0/8 ARE THE ADC DATA OUTPUT PINS DB11....DB0 ARE THE 12-BIT CONVERSION RESULTS
Figure 15. Internal Logic for Control Inputs CS, RD and HBEN
There are two modes of operation as outlined by the timing diagrams of Figures 16 to 19. Slow Memory Mode is designed for microprocessors which can be driven into a WAIT state. A READ operation brings CS and RD low which
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initiates a conversion and data is read when conversion is complete. The second is the ROM Mode which does not require microprocessor WAIT states. A READ operation brings CS and RD low which initiates a conversion and reads the previous conversion result. Data Format The output format can be either a complete parallel load for 16-bit microprocessors or a two byte load for 8-bit microprocessors. Data is always right justified (i.e., LSB is the most right-hand bit in a 16-bit word). For a two byte read, only data outputs D7...D0/8 are used. Byte selection is governed by the HBEN input which controls an internal digital multiplexer. This multiplexes the 12-bits of conversion data onto the lower D7...D0/8 outputs (4MSBs or 8MSBs) where it can be read in two read cycles. The 4MSBs always appear on D11...D8 whenever the threestate output drivers are turned on. Slow Memory Mode, Parallel Read (HBEN = LOW) Figure 16 and Table 2 show the timing diagram and data bus status for Slow Memory Mode, Parallel Read. CS and RD going low trigger a conversion and the ADC acknowledges by taking BUSY low. Data from the previous conversion appears on the three-state data outputs. BUSY returns high at the end of conversion when the output latches have been updated and the conversion result is placed on data outputs D11...D0/8. Slow Memory Mode, Two Byte Read For a two byte read, only 8 data outputs D7...D0/8 are used. Conversion start procedure and data output status for the first read operation are identical to Slow Memory Mode, Parallel Read. See Figure 17 timing diagram and Table 3 data bus status. At the end of the conversion, the low data byte (D7...D0/8) is read from the ADC. A second READ operation with the HBEN high, places the high byte on data outputs D3/11...D0/8 and disables conversion start. Note the 4MSBs appear on data output D11...D8 during the two READ operations.
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LTC1282
APPLICATI
S I FOR ATIO
CS t1 RD t2 BUSY t3 DATA HOLD TRACK t12 tCONV
OLD DATA DB11-DB0
Figure 16. Slow Memory Mode, Parallel Read Timing Diagram
Table 2. Slow Memory Mode, Parallel Read Data Bus Status
Data Outputs Read D11 DB11 D10 DB10 D9 DB9 D8 DB8 D7 DB7 D6 DB6 D5 DB5 D4 DB4 D3/11 DB3 D2/10 DB2 D1/9 DB1 D0/8 DB0
HBEN t8 CS t1 RD t2 BUSY t3 DATA HOLD TRACK
LTC1282 * F17
t CONV t6 OLD DATA DB7-DB0 t7 NEW DATA DB7-DB0
t12
Figure 17. Slow Memory Mode, Two Byte Read Timing Diagram Table 3. Slow Memory Mode, Two Byte Read Data Bus Status
Data Outputs First Read Second Read D7 DB7 Low D6 DB6 Low D5 DB5 Low D4 DB4 Low D3/11 DB3 DB11 D2/10 DB2 DB10 D1/9 DB1 DB9 D0/8 DB0 DB8
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t5 t10 t1 t11 t6 t7 NEW DATA DB11-DB0
LTC1282 * F16
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t9
t8
t9
t5
t1
t4
t5
t10
t11
t10
t3 NEW DATA DB11-DB8
t7
t12
17
LTC1282
APPLICATI
S I FOR ATIO
CS t1 RD t2 BUSY t3 DATA HOLD TRACK OLD DATA DB11-DB0 t12 t4
Figure 18. ROM Mode, Parallel Read Timing Diagram (HBEN = LOW) Table 4. ROM Mode, Parallel Read Data Bus Status
Data Outputs First Read (Old Data) Second Read D11 DB11 DB11 D10 DB10 DB10 D9 DB9 DB9 D8 DB8 DB8 D7 DB7 DB7 D6 DB6 DB6 D5 DB5 DB5 D4 DB4 DB4 D3/11 DB3 DB3 D2/10 DB2 DB2 D1/9 DB1 DB1 D0/8 DB0 DB0
ROM Mode, Parallel Read (HBEN = LOW) The ROM Mode avoids placing a microprocessor into a WAIT state. A conversion is started with a READ operation, and the 12 bits of data from the previous conversion are available on data outputs D11...D0/8 (see Figure 18 and Table 4). This data may be disregarded if not required. A second READ operation reads the new data (DB11...DB0) and starts another conversion. A delay at least as long as the ADC's conversion time plus the 1.0s minimum delay between conversions must be allowed between READ operations. ROM Mode, Two Byte Read As previously mentioned for a two byte read, only data outputs D7...D0/8 are used. Conversion is started in the normal way with a READ operation and the data output status is the same as the ROM mode, Parallel Read (see Figure 19 timing diagram and Table 5 data bus status). Two more READ operations are required to access the new conversion result. A delay equal to the ADC's conversion
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t5 t1 t4 t5 t11 t CONV t7 t2 t CONV t3 NEW DATA DB11-DB0 t12 t7
LTC1282 * F18
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time must be allowed between conversion start and the second data READ operation. The second READ operation with HBEN high disables conversion start and places the high byte (4MSBs) on data outputs D3/11...D0/8. A third read operation accesses the low data byte (DB7...DB0) and starts another conversion. The 4MSBs appear on data outputs D11...D8 during all three read operations. MICROPROCESSOR INTERFACING The LTC1282 allows easy interfacing to digital signal processors as well as modern high speed, 8-bit or 16bit microprocessors. Here are several examples. TMS320C25 Figure 20 shows an interface between the LTC1282 and the TMS320C25. The R/W signal of the DSP initiates a conversion and conversion results are read from the LTC1282 using the following instruction: IN D, PA
LTC1282
APPLICATI
HBEN
S I FOR ATIO
t8 t9
CS t1 RD t2 BUSY t3 DATA HOLD TRACK t12 OLD DATA DB7-DB0 t7 t3 NEW DATA DB11-DB8 t12 t7 t3 t7 NEW DATA DB7-DB0 t11 tCONV t4 t5 t1 t4 t5 t10 t2 t1 t4 t5
Figure 19. ROM Mode Two Byte Read Timing Diagram Table 5. ROM Mode, Two Byte Read Data Bus Status
Data Outputs First Read (Old Data) Second Read (New Data) Third Read (New Data) D7 DB7 Low DB7 D6 DB6 Low DB6 D5 DB5 Low DB5 D4 DB4 Low DB4 D3/11 DB3 DB11 DB3 D2/10 DB2 DB10 DB2 D1/9 DB1 DB9 DB1 D0/8 DB0 DB8 DB0
A16 A1
ADDRESS BUS
IS TMS320C25 READY R/W D16 D0
EN
ADDRESS DECODE LTC1282 CS BUSY RD
DATA BUS
D11 D0/8 HBEN
ADDITIONAL PINS OMITTED FOR CLARITY
LTC1282 * F20
Figure 20. TMS320C25 Interface
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t8 t9 t8 t9
LTC1282 * F19
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where D is Data Memory Address and PA is the PORT ADDRESS. MC68000 Microprocessor Figure 21 shows a typical interface for the MC68000. The LTC1282 is operating in the Slow Memory Mode. Assuming the LTC1282 is located at address C000, then the following single 16-bit MOVE instruction both starts a conversion and reads the conversion result: Move.W $C000,D0 At the beginning of the instruction cycle when the ADC address is selected, BUSY and CS assert DTACK so that the MC68000 is forced into a WAIT state. At the end of conversion, BUSY returns high and the conversion result is placed in the D0 register of the microprocessor.
19
LTC1282
APPLICATI
A23 A1
S I FOR ATIO
ADDRESS BUS
AS MC68000 DTACK R/W D11 D0
EN
ADDRESS DECODE LTC1282 CS BUSY RD
DATA BUS
D11 D0/8 HBEN
ADDITIONAL PINS OMITTED FOR CLARITY
LTC1282 * F21
Figure 21. MC68000 Interface
8085A/Z80 Microprocessor Figure 22 shows an LTC1282 interface for the Z80 and 8085A. The LTC1282 is operating in the Slow Memory Mode and a two byte read is required. Not shown in the figure is the 8-bit latch required to demultiplex the 8085A common address/data bus. A0 is used to assert HBEN so that an even address (HBEN = LOW) to the LTC1282 will start a conversion and read the low data byte. An odd address (HBEN = HIGH) will read the high data byte. This is accomplished with the single 16-bit LOAD instruction below. For the 8085A For the Z80
A15 A0
LHLD (B000) LDHL, (B000)
ADDRESS BUS
A0
RD D11 D11 D0/8 HBEN
MREQ Z80 8085A WAIT RD D7 D0
EN
ADDRESS DECODE
HBEN CS BUSY LTC1282 RD
LINEAR CIRCUITRY OMITTED FOR CLARITY
DATA BUS
D7 D0/8
LINEAR CIRCUITRY OMITTED FOR CLARITY
LTC1282 * F22
Figure 22. 8085A and Z80 Interface
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This is a two byte read instruction which loads the ADC data (address B000) into the HL register pair. During the first read operation, BUSY forces the microprocessor to WAIT for the LTC1282 conversion. No WAIT states are inserted during the second read operation when the microprocessor is reading the high data byte. TMS32010 Microcomputer Figure 23 shows an LTC1282/TMS32010 interface. The LTC1282 is operating in the ROM Mode. The interface is designed for a maximum TMS32010 clock frequency of 18MHz but will typically work over the full TMS32010 clock frequency range. The LTC1282 is mapped at a port address. The following I/O instruction starts a conversion and reads the previous conversion result into data memory. IN A,PA (PA = PORT ADDRESS) When conversion is complete, a second I/O instruction reads the up-to-date data into memory and starts another conversion. A delay at least as long as the ADC conversion time must be allowed between I/O instructions.
PA2 PA0 PORT ADDRESS BUS DEN TMS32010 CS EN ADDRESS DECODE LTC1282 D0 DATA BUS
LTC1282 * F23
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Figure 23. TMS32010 Interface
LTC1282
APPLICATI S I FOR ATIO U
events. The LTC1282 digitizes this final value and outputs the digital data.
3V CD4051 NO BUFFER REQUIRED D11 AIN LTC1282 8 INPUT CHANNELS 1.25V INPUT VARIES CS RD BUSY -3V
* * *
MUXing with CD4051 The high input impedance of the LTC1282 provides an easy, cheap, fast, and accurate way to multiplex many channels of data through one converter. Figure 24 shows a low cost CD4051, one of the most common multiplexers connected to the LTC1282. The LTC1282's input draws no DC input current so it can be accurately driven by the unbuffered MUX. The CD4520 counter increments the MUX channel after each sample is taken. 100ps Resolution Time Measurement with LTC1282 Figure 25 shows a circuit that precisely measures the difference in time between two events. It has a 400ns full scale and 100ps resolution. The start signal releases the ramp generator made up of the PNP current source and the 500pF capacitor. The circuit ramps until the stop signal shuts off the current source. The final value of the ramp represents the time between the start and stop
65 1N457
LM134 45.3 74HC03 1N457 45.3 5V START D CLK CLR 74HC74 Q Q 1k 1N4148 10k 5V STOP D CLK CLR Q 5V Q 1k 100k 0.001F 1N4148 100pF 250pF POLYSTYRENE
1k 5V 10k 10pF
LTC1282 * F25
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D0
P OR DSP
LTC1282 * F24
VSS A BC ENABLE CD4520 COUNTER Q0 RESET Q2 Q1
Figure 24. MUXing the LTC1282 with CD4051
3.3V 10F 10F 20k AIN REFOUT LTC1282 CS VSS GND RD BUSY VDD 12-BIT DATA OUTPUT
65 200k 2N5771
2N2369
2N2369
430
DATA LATCH SIGNAL
Figure 25. Time Measurement with the LTC1282
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Comparison of Specifications and Features
DEVICE TYPE LTC1272 LTC1273 LTC1275 LTC1276 LTC1278 LTC1282 SAMPLING S/(N + D) INPUT FREQ @ NYQUIST RANGE 250kHz 300kHz 300kHz 300kHz 520kHz 140kHz 65dB 70dB 70dB 70dB 70dB 68dB 0V-5V 0V-5V 2.5V 5V 0V-5V or 2.5V POWER POWER SUPPLY DISSIPATION 5V 5V 5V 5V 5V or 5V 75mW 75mW 75mW 75mW 75mW 6mW* 12mW 0V-2.5V 3V or 1.25V or 3V *6mW power shutdown with instant wake up
Other High Speed A/D Converters LTC makes a family of high speed sampling ADCs for a variety of applications. Both single 5V and 5V supply devices are available at high speeds. The high speed 12-bit family is summarized below.
300ksps and 500ksps 12-Bit Sampling A/D Converters
2.7s Conversion Time Built-In Sample & Hold
2.42V VREF OUTPUT ANALOG INPUT
Reference On Board
5V
LTC1273/5/6
AIN VREF AGND D11 (MSB) D10 D9 D8 D7 D6 D5 D4 DGND D0/8 D1/9 D2/10 D3/11 VDD NC BUSY CS RD HBEN P CONTROL LINES 10F
+
0.1F 10F
Reference Output For System Use
8- OR 12-BIT PARALLEL BUS
Parallel Outputs For The Fastest Data Transfer Rates
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0.1F
Only 75mW Power Consumption
No Negative Supply Required for Unipolar Operation Internal Clock No Crystal Required
LTC1282
PACKAGE DESCRIPTIO
0.300 - 0.325 (7.620 - 8.255)
0.009 - 0.015 (0.229 - 0.381)
(
+0.025 0.325 -0.015 +0.635 8.255 -0.381
)
0.005 (0.127) RAD MIN
0.291 - 0.299 (7.391 - 7.595) (NOTE 2) 0.010 - 0.029 x 45 (0.254 - 0.737)
0.009 - 0.013 (0.229 - 0.330)
NOTE 1 0.016 - 0.050 (0.406 - 1.270)
NOTE: 1. PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS. THE PART MAY BE SUPPLIED WITH OR WITHOUT ANY OF THE OPTIONS. 2. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006 INCH (0.15mm).
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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0.015 (0.381) MIN
Dimensions in inches (millimeters) unless otherwise noted. N Package 24-Lead Plastic DIP
1.265 (32.131) 24 23 22 21 20 19 18 17 16 15 14 13
0.260 0.010 (6.604 0.254)
1
2
3
4
5
6
7
8
9
10
11
12
0.130 0.005 (3.302 0.127)
0.045 - 0.065 (1.143 - 1.651)
0.065 (1.651) TYP
0.125 (3.175) MIN
0.050 - 0.085 (1.27 - 2.159) 0.100 0.010 (2.540 0.254)
0.018 0.003 (0.457 0.076)
S Package 24-Lead Plastic SOL
0.598 - 0.614 (15.190 - 15.600) (NOTE 2) 20 19 18 17 16
24
23
22
21
15
14
13
NOTE 1
0.394 - 0.419 (10.007 - 10.643)
1
2
3
4
5
6
7
8
9
10
11
12
0.093 - 0.104 (2.362 - 2.642)
0.037 - 0.045 (0.940 - 1.143)
0 - 8 TYP 0.050 (1.270) TYP
0.004 - 0.012 (0.102 - 0.305)
0.014 - 0.019 (0.356 - 0.482)
23
LTC1282
U.S. Area Sales Offices
NORTHEAST REGION Linear Technology Corporation One Oxford Valley 2300 E. Lincoln Hwy.,Suite 306 Langhorne, PA 19047 Phone: (215) 757-8578 FAX: (215) 757-5631 Linear Technology Corporation 266 Lowell St., Suite B-8 Wilmington, MA 01887 Phone: (508) 658-3881 FAX: (508) 658-2701 SOUTHEAST REGION Linear Technology Corporation 17060 Dallas Parkway Suite 208 Dallas, TX 75248 Phone: (214) 733-3071 FAX: (214) 380-5138 CENTRAL REGION Linear Technology Corporation Chesapeake Square 229 Mitchell Court, Suite A-25 Addison, IL 60101 Phone: (708) 620-6910 FAX: (708) 620-6977 SOUTHWEST REGION Linear Technology Corporation 22141 Ventura Blvd. Suite 206 Woodland Hills, CA 91364 Phone: (818) 703-0835 FAX: (818) 703-0517 NORTHWEST REGION Linear Technology Corporation 782 Sycamore Dr. Milpitas, CA 95035 Phone: (408) 428-2050 FAX: (408) 432-6331
International Sales Offices
FRANCE Linear Technology S.A.R.L. Immeuble "Le Quartz" 58 Chemin de la Justice 92290 Chatenay Malabry France Phone: 33-1-41079555 FAX: 33-1-46314613 GERMANY Linear Techonolgy GMBH Untere Hauptstr. 9 D-85386 Eching Germany Phone: 49-89-3197410 FAX: 49-89-3194821 JAPAN Linear Technology KK 5F YZ Bldg. 4-4-12 Iidabashi, Chiyoda-Ku Tokyo, 102 Japan Phone: 81-3-3237-7891 FAX: 81-3-3237-8010 KOREA Linear Technology Korea Branch Namsong Building, #505 Itaewon-Dong 260-199 Yongsan-Ku, Seoul Korea Phone: 82-2-792-1617 FAX: 82-2-792-1619 SINGAPORE Linear Technology Pte. Ltd. 101 Boon Keng Road #02-15 Kallang Ind. Estates Singapore 1233 Phone: 65-293-5322 FAX: 65-292-0398 TAIWAN Linear Technology Corporation Rm. 801, No. 46, Sec. 2 Chung Shan N. Rd. Taipei, Taiwan, R.O.C. Phone: 886-2-521-7575 FAX: 886-2-562-2285 UNITED KINGDOM Linear Technology (UK) Ltd. The Coliseum, Riverside Way Camberley, Surrey GU15 3YL United Kingdom Phone: 44-276-677676 FAX: 44-276-64851
World Headquarters
Linear Technology Corporation 1630 McCarthy Blvd. Milpitas, CA 95035-7487 Phone: (408) 432-1900 FAX: (408) 434-0507
08/16/93
24
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977
LT/GP 0893 10K REV 0 * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1993

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