View A8904_8355103.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

description the A8904 is a 3-phase brushless dc motor controller/driver designed for applications where accurate control of high-speed motors is required. the three half-bridge outputs are low on-resistance, n-channel dmos devices capable of driving up to 1.2 a. the A8904 provides complete, reliable, self-contained back emf sensing, motor start-up, and running algorithms. a programmable digital frequency-locked loop speed control circuit together with the linear current control circuitry provides precise motor speed regulation. a serial port allows the user to program various features and modes of operation, such as the speed control parameters, start-up current limit, sleep mode, direction, and diagnostic modes. the A8904 is fabricated in the allegro ? bcd (bipolar cmos dmos) process, an advanced mixed-signal technology that combines bipolar, analog, and digital cmos, with dmos power devices. the device is provided in a 24-pin wide-body soic package, with 4 internally-fused leads for enhanced thermal dissipation (package lb), and a thin (<1.2 mm overall height), 28-pin tssop package with an exposed thermal pad package lp). both packages are lead (pb) free, with 100% matte tin leadframe plating. 26301.5h features and benefits ? pin-for-pin replacement for a8902clba ? start-up commutation circuitry ? sensorless commutation circuitry ? option of external sector data tachometer signal ? option of external speed control ? oscillator operation up to 20 mhz ? programmable overcurrent limit ? transconductance gain options: 500 ma/v or 250 ma/v ? programmable watchdog timer ? directional control ? serial port interface ? ttl-compatible inputs ? system diagnostics data-out ported in real time ? dynamic braking through serial port or external terminal 3-phase brushless dc motor controller/driver with back emf sensing packages: functional block diagram not to scale A8904 24-pin soicw with internally fused pins (lb package) 28-pin tssop with exposed thermal pad (package lp) current control centertap c wd osc sector data filter c st c res brake out a out b out c commutation delay commutation logic c d1 c d2 watchdog timer blank fcom out a out b out c load supply v bb charge pump frequency- locked loop serial port mux data in tsd r s v dd logic supply start-up osc. boost charge pump brake ground ground sequence logic chip select clock reset data out
3-phase brushless dc motor controller/driver with back emf sensing A8904 2 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com absolute maximum ratings characteristic symbol notes rating units load supply voltage v bb 15 v logic supply voltage v dd 7v logic input voltage range v in continuous ?0.3 to v dd + 0.3 v t w < 30 ns ?1.0 to v dd + 1.0 v output current i out output current rating may be restricted to a val- ue determined by system concerns and factors. these include: system duty cycle and timing, ambient temperature, and use of any heatsink- ing and/or forced cooling. for reliable operation, the speci ed maximum junction temperature should not be exceeded. 1.4 a peak output current (brake) i out(brk) 3.0 a i out(brk) period t fiout(brk) fall of i out(brk) from 3.0 a to 1.4 a peak output current is a transient condition that occurs during braking when the motor acts as a generator. the 3 a level is based on the maxi- mum peak of a sine wave that is damped. the maximum period between the initial brake being applied and the current through the drivers fall- ing to 1.4 a should not exceed 800 ms. see the braking section for more information. 800 a operating ambient temperature t a range s ?20 to 85 oc maximum junction temperature t j (max) fault conditions that produce excessive junc- tion temperature will activate device thermal shutdown circuitry. these conditions can be tolerated, but should be avoided. 150 oc storage temperature t stg ?55 to 150 oc selection guide part number package packing A8904slbtr-t 24-pin soic 450 per reel A8904slptr-t 28-pin tssop 4000 per reel
3-phase brushless dc motor controller/driver with back emf sensing A8904 3 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com copyright ? 2003 allegro microsystems, inc. 1 2 3 4 5 6 7 8 9 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 brake filter data in logic supply ground chip select clock reset ground ground ground dd v c st out a out b out c c d1 bb v load supply c wd c d2 data out index centertap oscillator c res fll mux commutation delay serial port boost charge pump pin-out diagrams lp package lb package
3-phase brushless dc motor controller/driver with back emf sensing A8904 4 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com lb (soic) package lp (tssop) package thermal characteristics characteristic symbol test conditions* value units package thermal resistance r ja package lb, 4-layer pcb based on jedec standard 35 oc/w package lb, 2-layer pcb with 1 in. 2 of copper area each side 50 oc/w package lp, 4-layer pcb based on jedec standard 28 oc/w package lp, 2-layer pcb with 3.8 in 2 of copper area each side 36 oc/w *additional thermal information available on the allegro website
3-phase brushless dc motor controller/driver with back emf sensing A8904 5 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com electrical characteristics at t a = +25c, v dd = 5.0 v limits characteristic symbol test conditions min. typ. max. units logic supply voltage v dd operating 4.5 5.0 5.5 v logic supply current i dd operating ? 7.5 10 ma sleep mode ? 250 500 a undervoltage threshold uvlo decreasing v dd ? 3.6 ? v increasing v dd ? 3.9 ? v load supply voltage v bb operating 4.0 ? 14 v load supply current i bb operating ? 4.0 8.0 ma sleep mode ? 20 30 a thermal shutdown t j ? 165 ? c thermal shutdown hysteresis ? t j ? 20 ? c output drivers output leakage current i dsx v bb = 14 v, v out = 14 v, sleep mode ? 200 300 a v bb = 14 v, v out = 0 v ? -2.0 -15 a total output on resistance r ds(on) i out = 600 ma ? 1.0 1.4 ? (source + sink + r s ) output sustaining voltage v ds(sus) v bb = 14 v, i out = i out (max), l = 3 mh 14 ? ? v clamp diode forward voltage v f i f = 1.0 a ? 1.25 1.5 v control logic logic input voltage v in(0) sector data, reset, clk, ? ? 0.8 v v in(1) chip select, osc 2.0 ? ? v logic input current i in(0) v in = 0 v ? ? -0.5 a i in(1) v in = 5.0 v ? ? 1.0 a brake threshold v brk 1.5 1.75 2.0 v brake hysteresis current i brkl v brk = 750 mv ? 4.0 ? a brake current i brk brake set, d2 = 1, i brk = 750 mv ? 20 ? a data output voltage v out(0) i out = 500 a ? ? 1.5 v v out(1) i out = -500 a 3.5 ? ? v c st current i cst charging -9.0 -10 -11 a discharging, v cst = 2.5 v ? 500 ? a c st threshold v csth high 2.25 2.5 2.75 v v cstl low 0.85 1.0 1.15 v filter current i filter charging -9.0 -10 -11 a discharging 9.0 10 11 a leakage, v filter = 2.5 v ? ? 5.0 na filter threshold v filterth 1.57 1.85 2.13 v c d current i cd charging -18 -20 -22 a (c d1 or c d2 ) discharging 32 40 48 a c d current matching ? i cd(dischrg) /i cd(chrg) 1.8 2.0 2.2 ? c d threshold v cdth 2.25 2.5 2.75 v c d input leakage i cdil ? ? 1.0 a continued next page ?
3-phase brushless dc motor controller/driver with back emf sensing A8904 6 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com limits characteristic symbol test conditions min. typ. max. units c wd current i cwd charging, d26 = 0, d27 = 0 -9.0 -10 -11 a charging, d26 = 0, d27 =1 -18 -20 -22 a charging, d26 = 1 d27 = 0 -27 -30 -33 a charging, d26 = 1, d27 =1 -36 -40 -44 a c wd threshold voltage v tl 0.22 0.25 0.28 v v th 2.25 2.5 2.75 v max. fll oscillator frequency f osc 20* ? ? mhz oscillator high duration ton 20 ? ? ns oscillator low duration toff 20 ? ? ns maximum output current i out (max) d3 = 0, d4 = 0, d28 = 0 1.0 1.2 1.4 a d3 = 0, d4 = 1, d28 = 0 0.9 1.0 1.1 a d3 = 1, d4 = 0, d28 = 0 500 600 700 ma d3 = 1, d4 = 1, d28 = 0 ? 250 ? ma d3 = 0, d4 = 0, d28 = 1 500 600 700 ma d3 = 0, d4 = 1, d28 = 1 415 500 585 ma d3 = 1, d4 = 0, d28 = 1 ? 300 ? ma d3 = 1, d4 = 1, d28 = 1 ? 125 ? ma transconductance gain g m d28 = 1 210 250 290 ma/v d28 = 0 420 500 580 ma/v centertap resistors r ct 5.0 10 13 k ? back-emf threshold with respect ? 5.0 20 37 mv to v ctap at fcom transition -5.0 -20 -37 mv electrical characteristics (continued) at t a = +25c, v dd = 5.0 v negative current is de ned as coming out of (sourcing) the speci ed device terminal. * operation at an oscillator frequency greater than the speci ed minimum value is possible but not waranteed.
3-phase brushless dc motor controller/driver with back emf sensing A8904 7 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com serial port timing conditions a. minimum chip select setup time before clock rising edge ........... 100 ns b. minimum chip select hold time after clock rising edge ................ 150 ns c. minimum data setup time before clock rising edge .......................... 150 ns d. minimum data hold time after clock rising edge ............................... 150 ns e. minimum clock low time before chip select ................................... 50 ns f. maximum clock frequency ................................................................ 3.3 mhz g. minimum chip select high time ........................................................ 500 ns note: the A8904 can be directly used in an existing a8902?a application, as the ve most signi cant bits are reset to zero, which is the default condition for a8902?a operation. the only consideration when using the A8904 in an a8902-a application, is to ensure the mini- mum chip select high time is at least 500 ns.
3-phase brushless dc motor controller/driver with back emf sensing A8904 8 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com terminal functions lb lp terminal name function (soic) (tssop) load supply v bb ; the 5 v or 12 v motor supply. 1 15 c d2 one of two capacitors used to generate the ideal commutation points from 2 16 the back-emf zero crossing points. c wd timing capacitor used by the watchdog circuit to blank out the back-emf 3 17 comparators during commutation transients, and to detect incorrect motor position. c st start-up oscillator timing capacitor. 4 18 nc no( internal) connection. ? 19 out a power ampli er a output to motor. 5 20 nc no (internal) connection. ? 21 ground power and logic ground and thermal heat sink. 6-7 ? power ground power ground. ? 22* nc no (internal) connection. ? 23 out b power ampli er b output to motor. 8 24 out c power ampli er c output to motor. 9 25 centertap motor centertap connection for back-emf detection circuitry. 10 26 brake active low turns on all three sink drivers shorting the motor windings to 11 27 ground. external capacitor and resistor at b rake provide brake delay. the brake function can also be controlled via the serial port. c res external reservoir capacitor used to hold charge to drive the source drivers? 12 28 gates. also provides power for brake circuit. analog ground analog ground. ? 1* filter analog voltage input/output to control motor current. also, compensation node for internal speed control loop. 13 2 sector data external tachometer input. can use sector or index pulses from disk to 14 3 provide precise motor speed feedback to internal frequency-locked loop. logic supply v dd ; the 5 v logic supply. 15 4 oscillator clock input for the speed reference counter. 16 5 data out thermal shutdown indicator, fcom, tach, or sync signals available in 17 6 real time, controlled by 2-bit multiplexer via serial port. nc no (internal) connection. ? 7 ground power and logic ground and thermal heat sink. 18-19 ? digital ground logic ground. ? 8* reset when pulled low forces the chip into sleep mode; clears all serial port bits. 20 9 nc no (internal) connection. ? 10 chip select strobe input (active low) for data word. 21 11 clock clock input for serial port. 22 12 data in sequential data input for the serial port. 23 13 c d1 one of two capacitors used to generate the ideal commutation points from 24 14 the back-emf zero crossing points. * for the lp package, ground terminals 1, 8, and 22 must be connected together externally.
3-phase brushless dc motor controller/driver with back emf sensing A8904 9 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com functional description overview of operation. each electrical revolution contains six states that control the three half-bridge outputs. optimized switching from state to state is achieved through the adaptive commutation circuitry. during any state, one output is high, one is low and the other is high impedance. the back-emf at the high-impedance output is sensed and compared to the voltage of the centertap and when the two signals are equivalent, the fcom signal toggles. a controlled delay is then introduced before the sequencer commutates into the next state. linear current-mode control is employed to provide preci- sion control of the motor speed while maintaining extremely low electrical noise emissions. the speed control is realized through a frequency-locked loop that processes the sensed back-emf signals from the stator phases to eventually produce a tach signal. the tach signal is then compared to the desired programmed speed, to produce an error. the error signal is then used to linearly control the current through the low-side dmos power devices to obtain the correct speed. alternative control schemes can be introduced, giving the user maximum exibility and optimization for each application. an external tachometer signal applied to the sector data input, along with the internal speed reference can be used for high-precision speed control. as another alternative, the user can introduce external speed control by driving the filter terminal directly. start-up routines are inherent in the solution to guarantee reliable start-up. during start-up, a yank feature allows rapid transition to the nominal operating condition on the filter terminal. this feature is also available when the external speed control is used. dynamic braking can be introduced by either the external brake terminal or through the brake bit in the serial port. a serial port allows the user to program various features and modes of operation, such as motor speed, internal or external speed control, internal or external speed reference, current limit, sleep mode, direction, charge current (for blanking pulse), motor poles, transconductance gain, and various diagnostic outputs. full device protection is incorporated, including program- mable overcurrent limit, thermal shutdown, and undervoltage shutdown on the logic supply. power outputs. the power outputs of the A8904 are n-channel dmos transistors with a total source plus sink r ds(on) of typically 1 ? . an internal charge pump provides a voltage rail above the load supply for driving the high-side dmos gates. intrinsic ground clamp and yback diodes provide protection when switching inductive loads. these diodes will also rectify the motor back-emf during power-down conditions. if neces- sary, a transient voltage supply can be provided, by connecting an external schottky power diode or pass fet in series, between the power source and the load supply (v bb ). this fet or diode effectively isolates the low impedance path through the power source. a lter capacitor is also required to ?hold up? the recti ed signal, and is connected between the load supply and ground. back-emf sensing motor start-up and running algorithm. the A8904 provides a complete self-contained back-emf sensing, start-up and running commutation scheme. a state machine with six states, (shown in the tables below for both forward and reverse direction) controls the three half-bridge outputs. in each state, one output is high (sourcing current), one low (sinking current), and one is off (high impedance or ?z?). motor back-emf is sensed at the output that is off. sequencer state (forward direction) out a out b out c 1 high z low 2 high low z 3 z low high 4 low z high 5 low high z 6 z high low sequencer state (reverse direction) out a out b out c 1 high z low 6 z high low 5 low high z 4 low z high 3 z low high 2 high low z at start-up, the outputs are always enabled in state 1. the back-emf is examined at the off output by comparing the out- put voltage to the motor centertap voltage at centertap. the motor will then either step forward, step backward or remain stationary (if in a null-torque position). if the motor does not move during the initial start-up state, the outputs are commutated automatically by the start-up oscil- lator. when suitable back-emf signals are detected, the start-up oscillator is overridden and the corresponding timing clock is generated, providing synchronous back-emf commutation. the start-up oscillator period is determined by t cst = (v csth - v cstl ) x c st / i st(charge) where c st is the start-up capacitor. if the motor moves, the back-emf detection and direction circuit waits for the correct polarity of back-emf zero crossing
3-phase brushless dc motor controller/driver with back emf sensing A8904 10 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com (output crossing through centertap). if the correct polarity of back-emf is not detected, a watchdog circuit commutates the output until the correct back-emf is detected. correct back- emf sensing is indicated by the fcom signal, which toggles every time the back-emf completes a zero crossing (see wave- forms below). fcom is available at the data out terminal. true back-emf zero crossings are used by the adaptive commutation delay circuit to advance the state sequencer (com- mutate) at the proper time to synchronously run the motor. see next section. adaptive commutation delay. the adaptive commuta- tion delay circuit uses the back-emf zero-crossing indicator signal (fcom) to determine an optimal commutation time for ef cient synchronous switching of the output drivers. when the fcom signal changes state, one of the delay capacitors (c d1 or c d2 ) is discharged at approximately twice the rate of the charging current. when the capacitor reaches the 2.5 v thresh- old, a commutation occurs. during this discharge period, the other delay capacitor is being charged in anticipation of the next fcom state change. in addition, there is an interruption to the charging, which is set by the blanking duration (see waveform below, v cwd, and next section). this additional charging delay causes the commutation to occur at slightly less than 50% of the fcom on or off duration, to compensate for delays caused by winding inductance. the typical delta voltage change during normal operation in the commutation capacitors (c d1 & c d2 ), will range between 1.5 v and 2.0 v. the commutation capacitor values can be deter- mined from: c dx = i cd x t / v cd where v cd = 1.5 v, i cd = 20 a, and t = (60/rpm)/(#motor poles x 3), duration of each state. functional description (cont?d) to avoid the capacitors charging to the supply rail, the value selected should provide adequate margin, taking into account the effects of capacitor tolerance, charging current, etc. blanking and watchdog timing functions. the blank- ing and watchdog timing functions are derived from one timing capacitor c wd . during normal commutation, at the beginning of each new sequencer state, a blanking signal is created until the watchdog capacitor c wd is charged to the threshold v tl (see waveforms below). this blanking signal prohibits the back-emf compara- tors from tripping due to the discharging of inductive energy and voltage settling transients during sequence state transitions. the duration of this blanking signal depends on the size of the c wd capacitor and the programmed charge current, i cwd (via d26- 27). this blanking pulse also interrupts the commutation delay capacitors c d1 and c d2 from charging (see previous section). the ability to select the minimum charge current for c wd is particularly useful during start-up, where the duration of the diode recirculation current is highest. in applications where high motor speeds are experienced, the charge current can be increased so that the blanking period does not encroach signi - cantly into the period of each sequencer state and does not cause unbalance in the commutation points. it is recommended to select the value of c wd in the actual application circuit with the A8904 put into step mode. c st should be reselected (only for this test), to be between 4.7 f and 10 f, so that the motor comes to rest between steps and the maximum diode conduction time can be measured. the value of c wd can be determined as: c wd = i cwd x t d / v tl where t d = measured diode conduction, i cwd = charge current at start-up, and v tl = 250 mv.
3-phase brushless dc motor controller/driver with back emf sensing A8904 11 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com after the watchdog capacitor c wd charges to the v tl threshold, and if the correct polarity of back-emf signal is detected, the back-emf detection circuit discharges c wd to zero volts (see waveform above) and the circuit is ready to detect the next back- emf zero crossing. if the correct polarity of back-emf is not detected between the blanking period, t blank, and the watchdog period, t wd , then the back-emf detection circuit does not allow the watch- dog capacitor c wd to be discharged and the watchdog circuit commutates the outputs to the next sequencer state (see wave- form above). this mode of operation continues until a suitable back-emf signal is detected. this function is useful in prevent- ing excessive reverse rotation, and helps in resynchronising (or starting) with a moving spindle. the duration of the watchdog-triggered commutation is determined by: t wd = v th x c wd / i cwd where i cwd = normal charge current. speed control . the actual speed of the motor is measured by either internally sensing the back-emfs or by an external scheme via the sector data terminal. a tach signal is produced from these signals, which is then compared against the desired speed, which is programmed into a 14-bit counter (see diagram and waveforms below - assumes internal scheme used). the resulting error signal, error, is then used to charge or discharge the filter terminal capacitor depending on whether the motor is running too slow or too fast. the filter terminal voltage is used to linearly drive the low-side mosfets to match the desired speed. each back-emf signal detected causes the state of the fcom signal to change. the number of fcom transitions per mechanical revolution is equal to the number of poles times 3. for example, with a 4-pole motor (as shown on next page), the number of fcom transitions will equal 12 per mechanical revo- lution. the number of poles are programmed via serial port bits d20 and d21. there are six electrical states per electrical revolu- tion, therefore, for this example, there are 12 commutations or two electrical revolutions per mechanical revolution. the tach signal changes state once per mechanical revolu- tion and as well as providing information on the actual motor speed is also used to trigger the ref counter which contains the information on the desired motor speed. alternatively an external tach signal can be used, an explanation of which is presented in the sector mode section. the duration of ref is set by programming the counter to count the desired number of oscillator cycles, according to the following: total count = 60 x f osc / desired motor speed (rpm) where the total count (number of oscillator cycles) is equal to the sum of the count numbers selected through bits d5 to d18 in the serial port and f osc corresponds to the oscillator frequency. functional description (cont?d) watchdog-triggered commutation
3-phase brushless dc motor controller/driver with back emf sensing A8904 12 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com a speed error signal is created by integrating the differences between the tach and ref signal. if the tach signal goes low before the ref signal then an error fast is produced and if the tach signal goes low after the ref signal then an error slow is produced. the error signal generated enables the ap- propriate current source (see diagram next page) to either charge or discharge the lter components on the filter terminal. the filter voltage is then used to provide linear cur- rent control in the windings via the transconductance stage (see diagram next page). the output current is sensed through an internal sense resistor, r s . the voltage across the sense resistor is compared to the lowest of either one-tenth of the voltage at the filter terminal, minus the lter threshold voltage, or to the maximum current limit reference. alternatively, external control of the filter terminal can be introduced by disabling the frequency-lock loop circuitry (d24 = 1). the transconductance function is de ned as: i out = (v filter ? v filterth ) / (10 x r s x g) where r s is nominally 200 m ? , v filterth is approximately 1.85 v, g = 1, when d28 = 0 and gain = 500 ma/v or g = 2, when d28 = 1 and gain = 250 ma/v. the closed loop control response of the overall system is shaped via the lter components that are introduced at the fil- ter terminal. clamping the current to a level de ned by the serial port (d3 & d4) provides output current limit protection. this feature is particularly useful where high transient currents are experi- enced, e.g., during start-up. once normal running conditions are reached, the current limit can be appropriately reduced. note that the current limit is scaled according to the g m value selected. sector mode. an external tachometer signal, such as sec- tor or index pulses, can be used to create the tach signal, rather than the internally generated once-around scheme. the external signal is applied to the sector data terminal and the serial port bit (d19 = 1) must be programmed to enable this feature. functional description (cont?d) speed error signals
3-phase brushless dc motor controller/driver with back emf sensing A8904 13 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com in applications where both internal and external tach sig- nals are used, it is important to only switch between modes when the sync signal on data out is low. this ensures the speed control information that is being processed during the transition, is not corrupted. sync is accessed through the data out multiplexer, which is controlled by d22 & d23. data out. the data out terminal is the output of a 2-bit input multiplexer controlled by d22 & d23 of the serial port. data available are tach signal (internally or externally generated), sync signal, fcom signal, and thermal shutdown (low = A8904 operating within thermal limits, high = thermal shutdown has occurred). speed loop initialization (yank). to ensure rapid transition from start-up to the normal operating condition, the filter terminal is pulled up to the lter threshold voltage, v filterth , by the internal yank command and the initial output current will be set to the maximum selected current limit. this condition is maintained until the motor reaches the correct speed and the rst error fast signal is produced which removes the yank and allows linear current control. the yank feature is also activated when an external speed control scheme is used (d24 = 1). to ensure the yank is functional description (cont?d) released at start-up by the internal speed control, it is important to ensure the speed reference is set at a lower speed than what the motor is designed to run at. note that when the serial port is programmed to run initially, the default condition for the speed is set for the slowest condition so this will guarantee the yank to be released. it is important when using external speed control that, as a minimum, the number of poles, speed control mode, and speed reference are programmed in the serial port. forward/reverse. directional control is managed through d25 in the serial port. serial port. control features and diagnostic data selection are communicated to the A8904 through the 29-bit serial port. see serial port timing diagrams on page 6. when chip select is low, data is written to the serial port on the positive edge of the clock with the msb (d28) fed in rst. at the end of the write cycle, the chip select goes high, the serial port is disabled and no more data can be transferred. in addition, the data written to the serial port is latched and becomes active. if a word of less than 29 bits is sent, the unused most sig- ni cant bits that are not programmed, are reset to zero. there are no compatibility issues when using the A8904 in an existing a8902-a application as the ve msbs are reset to zero, which is speed and current control
3-phase brushless dc motor controller/driver with back emf sensing A8904 14 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com the default condition for a8902-a operation. the only consid- eration when using the A8904 in an a8902-a application is to ensure the minimum chip select high time is at least 500 ns. d0 - sleep/run mode; low = sleep, high = run. this bit allows the device to be powered down when not in use. d1 - step mode; low = normal operation, high = step only. when in the step-only mode the back-emf commutation circuitry is disabled and the start-up oscillator commutates the power outputs. this mode is intended for device and system testing. d2 - brake; low = run, high = brake. d3, d4, and d28 - the output current limit is set by d3 & d4; d28 sets the transconductance gain. current limit transconductance d3 d4 d28 (typical) gain 0 0 0 1.2 a 500 ma/v 0 1 0 1.0 a 500 ma/v 1 0 0 600 ma 500 ma/v 1 1 0 250 ma 500 ma/v 0 0 1 600 ma 250 ma/v 0 1 1 500 ma 250 ma/v 1 0 1 300 ma 250 ma/v 1 1 1 125 ma 250 ma/v d5 to d18 - 14-bit word, active low. programs the count number to produce the corresponding ref signal, which indi- cates the desired motor speed. bit number count number d5 16 d6 32 d7 64 d8 128 d9 256 d10 512 d11 1,024 d12 2,048 d13 4,096 d14 8,192 d15 16,384 d16 32,768 d17 65,536 d18 131,072 d19 - speed control mode; low = internal, once-around speed signal, high = external sector data. d20 and d21 - programs the number of motor poles for the once-around fcom counter. d20 d21 motor poles 0 0 8 0 1 4 1 0 16 1 1 12 d22 and d23 - controls the multiplexer for data out. see data out section for status de nitions. d22 d23 data out 0 0 tach (once around or sector) signal 0 1 thermal shutdown 1 0 sync signal 1 1 fcom signal d24 - speed reference. low = internal, using back-emf technique, high = external (internal control disabled). d25 - direction. low = forward, high = reverse. d26 and d27 - programs the charging current for the watch- dog capacitor. this function is used for adjusting the blanking duration and also the watchdog commutation period. d26 d27 watchdog charge current (typical) 0 0 -10 a 0 1 -20 a 1 0 -30 a 1 1 -40 a d28 - programs the transconductance gain. low = 500 ma/v, high = 250 ma/v. reset. when the reset terminal is pulled low, all the serial port bits are reset to low and the part operates in sleep mode. undervoltage lockout, v dd . when an undervoltage condition occurs, all the serial port bits are reset to low and the part operates in sleep mode. charge pump. the charge pump is required to provide a voltage rail above the load supply for driving the high-side dmos gates. in addition the charge pump supply capacitor, c res, also powers the brake control circuit during power-down conditions. c res should be 220 nf. functional description (cont?d)
3-phase brushless dc motor controller/driver with back emf sensing A8904 15 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com braking. a dynamic braking feature of the A8904 shorts the three motor windings to ground. this is accomplished by turning the three source drivers off and the three sink drivers on. activation of the brake can be implemented through the brake input or through the d2 bit in the serial port. during braking, the motor is effectively acting as three sine-wave voltage generators, 120 out of phase, where the voltage developed by each of the windings is proportional to the motor speed and constant. the current through any sink driver is simply the generated voltage divided by the center tap to out resistance plus the sink driver resistance. as the motor tends to slow during the braking process, both the generated voltage and the corresponding current decreases. when selecting a motor to use where braking will be ap- plied, it is important to characterize the application to ensure that when braking is applied, the peak current in the sink drivers does not exceed 3a and the period from the peak current to the maximum current limit of the drivers does not exceed 800 ms. another consideration is the thermals of the solution, where repeated spin-up followed by brake cycles could cause excessive junction temperatures. the supply voltage for the brake circuit is derived from the charge pump supply capacitor, c res . with c res chosen to be 220 nf, the brake circuit will function for at least 100 ms after a power failure. in certain applications such as disk drives, it is desirable to include a brake delay to allow sensitive circuitry such as the disk head to retract before activating the spindle motor brake. the brake delay can be simply implemented by using an external rc and diode to control the brake terminal. the brake delay can be set using the equation: t brk = ?r b c b x ln (v brk / [v fault ? v d ]). once the brake is activated, the three sink drivers will re- main active until the supply rails fall below the operating range. it is recommended that the part is reset before restarting. centertap. it is recommended that the centertap connec- tion of the motor be connected to the centertap terminal. if the centertap of the motor is not connected to the centertap terminal, the A8904 internally emulates the centertap voltage of functional description (cont?d) the motor through a series of 10 k ? resistors connected between each output and centertap. this technique does not provide ideal commutation points. external component selection. all capacitors should be rated to at least 25 v and the dielectric should be x7r, apart from the start-up capacitor c st , which can be z5u dielectric or equivalent and the input capacitor c lter , which should be an electrolytic type of value greater than 100 f, 35 v, i ripple > 100 ma. if the solution experiences ambient temperatures of greater than 70c then c lter should be rated for 105c. all resistors are at least 1/8 w and have a tolerance of 5%. in noise-sensitive systems where electromagnetic interfer- ence is an issue, or to stabilize the current waveforms with cer- tain motors, it may be necessary to add rc snubbers across the motor windings as shown in the application circuit on the next page. the A8904 solution should be relatively noise immune from the effects of switching voltage spikes etc. if the correct watchdog capacitor has been selected for optimum blanking and good layout practices are implemented. at the range of operating frequencies that the current pulses are drawn out of the load supply, it is the capacitance reactance as opposed to the esr that dominates the overall impedance of the input lter, c lter . therefore, it is possible to reduce conduct- ed electromagnetic emissions further, by simply increasing the value of c lter. in extremely sensitive systems, it may be neces- sary to introduce a differential mode inductor in series with the load supply line. layout considerations. the tssop part (A8904slp) has three separate ground connections, analog, digital, and pow- er that must be connected together externally. a ground plane should be used to provide heat sinking for the power switches and the reduction of potential noise pick-up through inductive loops and radiated emissions. the ground plane should cover the area beneath the A8904 and extend beyond the outline to form a plane around all the external components. the exposed thermal pad of the tssop part should be connected to the ground plane. filter components, especially c lter , timing, and delay capacitors should be positioned as close as possible to the device terminals. it is also imperative that the traces to the serial port and oscillator are as short and as wide as possible to reduce stray inductance and prevent potential data corruption. in addition, these traces should be positioned well away from any noisy signals.
3-phase brushless dc motor controller/driver with back emf sensing A8904 16 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com typical application (lb package)
3-phase brushless dc motor controller/driver with back emf sensing A8904 17 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com lb package, 24-pin soicw 1.27 0.25 b reference pad layout (reference ipc soic127p1030x265-24m) all pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary to meet application process requirements and pcb layout tolerances b 0.20 0.10 0.41 0.10 2.20 0.65 9.60 1.27 2 1 24 a 15.400.20 2.65 max 10.300.33 7.500.10 c seating plane c 0.10 24x for reference only pins 6 and 7, and 18 and 19 internally fused dimensions in millimeters (reference jedec ms-013 ad) dimensions exclusive of mold flash, gate burrs, and dambar protrusions exact case and lead configuration at supplier discretion within limits shown a terminal #1 mark area gauge plane seating plane pcb layout reference view 4 4 0.27 +0.07 ?0.06 0.84 +0.44 ?0.43 2 1 24 lp package, 28-pin tssop with exposed thermal pad 1.20 max 0.10 max c seating plane c 0.10 28x 6.10 0.65 0.45 1.65 3.00 3.00 5.00 5.00 0.25 0.65 2 1 28 gauge plane seating plane b a 28 2 1 a terminal #1 mark area b for reference only (reference jedec mo-153 aet) dimensions in millimeters dimensions exclusive of mold flash, gate burrs, and dambar protrusions exact case and lead configuration at supplier discretion within limits shown reference land pattern layout (reference ipc7351 sop65p640x120-29cm); all pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary to meet application process requirements and pcb layout tolerances; when mounting on a multilayer pcb, thermal vias at the exposed thermal pad land can improve thermal dissipation (reference eia/jedec standard jesd51-5) pcb layout reference view exposed thermal pad (bottom surface) 4.40 0.10 6.40 0.20 (1.00) 9.70 0.10 c c 0.60 0.15 4 4 0.15 +0.05 ?0.06 0.25 +0.05 ?0.06
3-phase brushless dc motor controller/driver with back emf sensing A8904 18 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com for the latest version of this document, visit our website: www.allegromicro.com copyright ?2003-2008, allegro microsystems, inc. the products described here are manufactured under one or more u.s. patents or u.s. patents pending. allegro microsystems, inc. reserves the right to make, from time to time, such de par tures from the detail spec i fi ca tions as may be required to per- mit improvements in the per for mance, reliability, or manufacturability of its products. before placing an order, the user is cautioned to verify that the information being relied upon is current. allegro?s products are not to be used in life support devices or systems, if a failure of an allegro product can reasonably be expected to cause the failure of that life support device or system, or to affect the safety or effectiveness of that device or system. the in for ma tion in clud ed herein is believed to be ac cu rate and reliable. how ev er, allegro microsystems, inc. assumes n o re spon si bil i ty for its use; nor for any in fringe ment of patents or other rights of third parties which may result from its use.

▲Up To Search▲

Price & Availability of A8904

	To Download A8904 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .