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3962 DUAL FULL-BRIDGE PWM MOTOR DRIVER
3962
Designed for pulse-width modulated (PWM) current control of bipolar stepper motors, the A3962SLB is capable of continuous output currents to 800 mA and operating voltages to 30 V. Internal fixed off-time PWM current-control circuitry can be used to regulate the maximum load current to a desired value. An internal precision voltage reference is provided to improve motor peak-current control accuracy. The peak load current limit is set by the user's selection of an external resistor divider and current-sensing resistors. The fixed off-time pulse duration is set by user-selected external RC timing networks. The capacitor in the RC timing network also determines a user-selectable blanking window that prevents false triggering of the PWM current control circuitry during switching transitions. This eliminates the need for two external RC filter networks on the current-sensing comparator inputs. For each bridge the PHASE input controls load current polarity by selecting the appropriate source and sink driver pair. For each bridge the ENABLE input, when held high, disables the output drivers. Special power-up sequencing is not required. Internal circuit protection includes thermal shutdown with hysteresis, transient-suppression diodes, and crossover-current protection. The A3962SLB is supplied in a 20-lead plastic SOIC with copper heat sink tabs. The power tab is at ground potential and needs no electrical isolation.
Data Sheet 29319.27
DUAL FULL-BRIDGE PWM MOTOR DRIVER
SENSE 1 OUT 1A
LOAD SUPPLY
GROUND GROUND V REF(IN)
PHASE 1 ENABLE 1
ABSOLUTE MAXIMUM RATINGS
Load Supply Voltage, VBB . . . . . . . . . 30 V Output Current, IOUT . . . . . . . . . . 800 mA* Logic Supply Voltage, VCC . . . . . . . . . 7.0 V Logic Input Voltage Range, VIN . . . . . . . . . . . -0.3 V to VCC + 0.3 V Sense Voltage, VSENSE . . . . . . . . . . . . 1.0 V Reference Output Current, IREF OUT . . . . . . . . . . . . . . . . . . . 1.0 mA Package Power Dissipation, PD . . . . . . . . . . . . . . . . . . . . See Graph Operating Temperature Range, TA . . . . . . . . . . . . . . . . -20C to +85C Junction Temperature, TJ . . . . . . . +150C Storage Temperature Range, TS . . . . . . . . . . . . . . . -55C to +150C
* Output current rating may be limited by duty cycle, ambient temperature, and heat sinking. Under any set of conditions, do not exceed the specified current rating or a junction tempera ture of 150C.
T C U D LY ON RO P D CE B E N SL UE 4 IN R 96 TE3 NFA O Ee C Re IS R S DO-- F
2 3 4 5 1 2 19 18 SENSE 2 OUT 2A VBB V CC 17 LOGIC SUPPLY 16 GROUND 6 15 GROUND 7 14 13 12 11 V REF(OUT) RC 2 RC 1 9 8 9
PWM 1 PWM 2
OUT 1B
1
20
OUT 2B
1
2
PHASE 2
10
ENABLE 2
Dwg. PP-047-1
FEATURES
s s s s s s s s
800 mA Continuous Output Current Rating 30 V Output Voltage Rating Internal PWM Current Control, Saturated Sink Drivers Internally Generated Precision 2.5 V Reference Internal Transient-Suppression Diodes Internal Thermal-Shutdown Circuitry Crossover-Current Protection, UVLO Protection Automotive Capable
Fault conditions that produce excessive junction temperature will activate the device's thermal shutdown circuitry. These conditions can be tolerated but should be avoided.
Always order by complete part number: A3962SLB .
3962 DUAL FULL-BRIDGE PWM MOTOR DRIVER
ALLOWABLE PACKAGE POWER DISSIPATION in WATTS
2.5
TRUTH TABLE
RJT = 6C/W
2.0
ENABLE H L
PHASE X H L
OUTA Off H L
OUTB Off L H
1.5
1.0
RJA = 60C/W
L
0.5
X = Irrelevant
0 25 50 75 100 125 150 TEMPERATURE in C
Dwg. GP-019-1
FUNCTIONAL BLOCK DIAGRAM AND TYPICAL BIPOLAR STEPPER MOTOR APPLICATION
MOTOR SUPPLY C BB V BB V CC C CC LOGIC SUPPLY
OUT 1A OUT 1B
OUT 2A OUT 2B
ENABLE 1 PHASE 1 CONTROL LOGIC AND LEVEL SHIFT BLANKING TIME AND SOURCE DRIVER T OFF CONTROL UVLO AND TSD VOLTAGE REFERENCE CONTROL LOGIC AND LEVEL SHIFT BLANKING TIME AND SOURCE DRIVER T OFF CONTROL
ENABLE 2 PHASE 2
+ _
+ _
RC1
SENSE 1 GND
REF OUT R1
REF IN
SENSE 2
RC 2
RT1
C T1
RS1
R2
RS2
CT2
RT2
115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 Copyright (c) 1995 Allegro MicroSystems, Inc.
3962 DUAL FULL-BRIDGE PWM MOTOR DRIVER
ELECTRICAL CHARACTERISTICS at TA = +25C, VBB = 30 V, VCC = 4.75 V to 5.25 V, VSENSE = 0 V, 30 k & 1000 pF RC to Ground (unless noted otherwise)
Limits Characteristic Symbol Test Conditions Min. Typ. Max. Units
Output Drivers
Load Supply Voltage Range Output Sustaining Voltage Output Leakage Current V BB VCE(sus) ICEX Operating, IOUT = 800 mA, L = 3 mH IOUT = 800 mA, L = 3 mH VOUT = VBB VOUT = 0 V Output Saturation Voltage VCE(SAT) Source Driver, IOUT = -500 mA Source Driver, IOUT = -750 mA Source Driver, IOUT = -800 mA Sink Driver, IOUT = +500 mA Sink Driver, IOUT = +750 mA Sink Driver, IOUT = +800 mA Clamp Diode Forward Voltage (Sink or Source) VF IF = 500 mA IF = 750 mA IF = 800 mA Motor Supply Current (No Load) IBB(ON) IBB(OFF) VENABLE = 0.8 V VENABLE = 2.4 V 5.0 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- <1.0 <1.0 1.0 1.1 -- 0.3 0.5 -- 1.1 1.3 -- 5.0 5.0 30 30 +VF 50 -50 1.2 1.5 1.7 0.6 1.2 1.5 1.4 1.6 1.7 7.0 7.0 V V A A V V V V V V V V V mA mA
Control Logic
Logic Supply Voltage Range Logic Input Voltage VCC VIN(1) VIN(0) Logic Input Current IIN(1) IIN(0) VIN = 2.4 V VIN = 0.8 V Operating 4.75 2.4 -- -- -- -- -- -- <1.0 <-2.0 5.25 -- 0.8 20 -200 V V V A A
Continued next page...
3962 DUAL FULL-BRIDGE PWM MOTOR DRIVER
ELECTRICAL CHARACTERISTICS at TA = +25C, VBB = 30 V, VCC = 4.75 V to 5.25 V, VSENSE = 0 V, 30 k & 1000 pF RC to Ground (unless noted otherwise) (cont.)
Limits Characteristic Symbol Test Conditions Min. Typ. Max. Units
Control Logic (Continued)
Reference Output Voltage Reference Output Current Ref. Input Offset Current Comparator Input Offset Volt. Comparator Input Volt. Range PWM RC Fixed Off-time PWM Propagation Delay Time PWM Minimum On Time Propagation Delay Times VREF OUT I REF OUT IOS VIO VREF tOFF RC tPWM t ON (min) tpd VCC = 5.0 V, IREF OUT = 90 to 900 A 3 k R D = R1 + R2 15 k VREF IN = 1 V VREF = 0 V Operating CT = 1000 pF, R T = 30 k Comparator Trip to Source OFF CT = 1000 pF 5%, RT 15 k, VCC = 5 V IOUT = 800 mA, 50% to 90%: ENABLE ON to Source ON ENABLE OFF to Source OFF ENABLE ON to Sink ON ENABLE OFF to Sink OFF PHASE Change to Sink ON PHASE Change to Source ON PHASE Change to Sink OFF PHASE Change to Source OFF Thermal Shutdown Temp. Thermal Shutdown Hysteresis UVLO Disable Threshold UVLO Hysteresis Logic Supply Current ICC(ON) ICC(OFF) Logic Supply Current Temperature Coefficient ICC(ON) VENABLE1 = VENABLE2 = 0.8 V VENABLE1 = VENABLE2 = 2.4 V VENABLE 1 = VENABLE 2 = 0.8 V TJ TJ -- -- -- -- -- -- -- -- -- -- 2.5 0.7 -- -- -- 3.2 1.2 3.2 0.7 3.2 3.2 0.7 1.2 165 15 2.7 0.9 60 11 0.18 -- -- -- -- -- -- -- -- -- -- 2.9 1.1 85 17 -- s s s s s s s s C C V V mA mA mA/C 2.45 150 -2.5 -6.0 -0.3 27 -- -- 2.50 -- 0 0 -- 30 1.2 2.5 2.55 900 1.0 6.0 1.0 33 2.0 3.6 V A A mV V s s s
NOTES: 1. Typical Data is for design information only. 2. Negative current is defined as coming out of (sourcing) the specified device terminal.
115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000
3962 DUAL FULL-BRIDGE PWM MOTOR DRIVER
FUNCTIONAL DESCRIPTION
Internal PWM Current Control. The A3962SLB contains a fixed off-time pulse-width modulated (PWM) currentcontrol circuit that can be used to limit the load current to a desired value. The peak value of the current limiting (ITRIP) is set by the selection of an external current-sensing resistor (RS ) and reference input voltage (VREF IN). The internal circuitry compares the voltage across the external sense resistor to the voltage on the reference input terminal (VREF IN) resulting in a transconductance function approximated by: ITRIP V REF IN RS internal current-control circuitry (or by the PHASE or ENABLE inputs). The comparator output is blanked to prevent false over-current detections due to reverserecovery currents of the clamp diodes, and/or switching transients related to distributed capacitance in the load. During internal PWM operation, at the end of the tOFF time, the comparator's output is blanked and CT begins to be charged from approximately 1.1 volts by an internal current source of approximately 1 mA. The comparator output remains blanked until the voltage on CT reaches approximately 3.0 volts. When a transition of the PHASE input occurs, CT is discharged to near ground during the crossover delay time (the crossover delay time is present to prevent simultaneous conduction of the source and sink drivers). After the crossover delay, CT is charged by an internal current source of approximately 1 mA. The comparator output remains blanked until the voltage on CT reaches approximately 3.0 volts. When the device is disabled, via the ENABLE input, CT is discharged to near ground. When the device is re-enabled, CT is charged by an internal current source of approximately 1 mA. The comparator output remains blanked until the voltage on CT reaches approximately 3.0 volts. The minimum recommended value for CT is 1000 pF. This value ensures that the blanking time is sufficient to avoid false trips of the comparator under normal operating conditions. For optimal regulation of the load current, the above value for CT is recommended and the value of RT can be sized to determine tOFF. For more information regarding load current regulation, see below. Load Current Regulation. Because the device operates in a slow decay mode (2-quadrant PWM mode), there is a limit to the lowest level that the PWM current control circuitry can regulate load current. The limitation is due to the minimum PWM duty cycle, which is a function of the user-selected value of tOFF and the minimum on-time pulse tON(min)max that occurs each time the PWM latch is reset. If the motor is not rotating, as in the case of a stepper motor in hold/detent mode, a brush dc motor when stalled or at startup, the worst case value of current regulation can be approximated by:
The reference input voltage is typically set with a resistor divider from VREF OUT. To ensure proper operation of the voltage reference, the resistor divider (RD = R1+R2) should have an impedance of 3 k to 15 k. Within this range, a low impedance will minimize the effect of the REF IN input offset current. The current-control circuitry limits the load current as follows: when the load current reaches ITRIP, the comparator resets a latch that turns off the selected source driver. The load inductance causes the current to recirculate through the sink driver and flyback diode. For each bridge, the user selects an external resistor (RT) and capacitor (CT) to determine the time period (tOFF = RTCT) during which the source driver remains disabled (see "RC Fixed Off-time" below). The range of recommended values for CT and RT are 1000 pF to 1500 pF and 15 k to 100 k respectively. For optimal load current regulation, CT is normally set to 1000 pF (see "Load Current Regulation" below). At the end of the RC interval, the source driver is enabled allowing the load current to increase again. The PWM cycle repeats, maintaining the peak load current at the desired value. RC Blanking. In addition to determining the fixed off-time of the PWM control circuit, the CT component sets the comparator blanking time. This function blanks the output of the comparator when the outputs are switched by the
I AVG
[(VBB - VSAT(SOURCE+SINK) ) tON(min)max] - (1.05 (VSAT(SINK) + VF) tOFF) 1.05 (tON(min)max + tOFF) RLOAD
3962 DUAL FULL-BRIDGE PWM MOTOR DRIVER
where tOFF = RTCT, RLOAD is the series resistance of the load, VBB is the motor supply voltage and t ON(min)max is specified in the electrical characteristics table. When the motor is rotating, the back EMF generated will influence the above relationship. For brush dc motor applications, the current regulation is improved. For stepper motor applications when the motor is rotating, the effect is dependent on the polarity and magnitude of the motor's back EMF. The following procedure can be used to evaluate the worst case internal PWM load current regulation in the system: Set VREF to 0 volts. With the load connected and the PWM current control operating in slow decay mode, use an oscilloscope to measure the time the output is low (sink ON) for the output that is chopping. This is the typical minimum on time (tON(min)typ) for the device. The CT then should be increased until the measured value of tON(min) is equal to tON(min)max as specified in the electrical characteristics table. When the new value of CT has been set, the value of RT should be decreased so the value for tOFF = R TCT (with the artificially increased value of CT) is equal to the nominal design value. The worst-case loadcurrent regulation then can be measured in the system under operating conditions. PWM of the Phase and Enable Inputs. The PHASE and ENABLE inputs can be pulse width modulated to regulate load current. Typical propagation delays from the PHASE and ENABLE inputs to transitions of the power outputs are specified in the electrical characteristics table. If the internal PWM current control is used, the comparator blanking function is active during phase and enable transitions. This eliminates false tripping of the overcurrent comparator caused by switching transients (see "RC Blanking" above). Enable PWM. Toggling the ENABLE input turns ON and OFF the selected source and sink drivers. The corresponding pair of flyback and ground clamp diodes conduct after the drivers are disabled, resulting in fast current decay. When the device is enabled the internal current control circuitry will be active and can be used to limit the load current in a slow decay mode. Phase PWM. Toggling the PHASE terminal selects which sink/source pair is enabled, producing a load current that varies with the duty cycle and remains continuous at all times. This can have added benefits in bidirectional brush dc servo motor applications as the transfer function between the duty cycle on the PHASE input and the average voltage applied to the motor is more linear than in the case of ENABLE PWM control (which produces a discontinuous current at low current levels). Miscellaneous Information. An internally generated dead time prevents crossover currents that can occur when switching phase. Thermal protection circuitry turns OFF all drivers should the junction temperature reach 165C (typical). This is intended only to protect the device from failures due to excessive junction temperatures and should not imply that output short circuits are permitted. The hysteresis of the thermal shutdown circuit is approximately 15C.
APPLICATION NOTES
Current Sensing. The actual peak load current (IPEAK) will be above the calculated value of ITRIP due to delays in the turn off of the drivers. The amount of overshoot can be approximated by: IOS (VBB - [(ITRIP * RLOAD) + VBEMF]) tPWM LLOAD
where VBB is the motor supply voltage, VBEMF is the backEMF voltage of the load, RLOAD and LLOAD are the resistance and inductance of the load respectively, and t PWM is specified in the electrical characteristics table. To minimize current sensing inaccuracies caused by ground trace IR drops, each current-sensing resistor should have a separate return to the ground terminal of the device. For low-value sense resistors, the IR drops in the PCB can be significant and should be taken into account. The use of sockets should be avoided as their contact resistance can cause variations in the effective value of RS . Generally, larger values of RS reduce the aforementioned effects but can result in excessive heating and power loss in the sense resistor. The selected value of RS should not cause the absolute maximum voltage rating of 1.0 V, for the SENSE terminal, to be exceeded. The recommended value of RS is in the range of: RS 0.5 ITRIPmax 50%
115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000
3962 DUAL FULL-BRIDGE PWM MOTOR DRIVER
If desired, the reference input voltage can be filtered by placing a capacitor from REFIN to ground. The ground return for this capacitor as well as R2 should be independent from the high-current power-ground trace to avoid changes in REFIN due to I*R drops. Thermal Considerations. For reliable operation it is recommended that the maximum junction temperature be kept below 110 to 125C. The junction temperature can be measured best by attaching a thermocouple to the power tab/batwing of the device and measuring the tab temperature, TTAB . The junction temperature can then be approximated by using the formula: TJ TTAB + (ILOAD 2 V F RJT) where VF can be chosen from the electrical specification table for the given level of ILOAD. The value for RJT is given in the package thermal resistance table for the appropriate package. The power dissipation of the batwing packages can be improved by 20 to 30% by adding a section of printed circuit board copper (typically 6 to 18 square centimeters) connected to the batwing terminals of the device. The thermal performance in applications that run at high load currents and/or high duty cycles can be improved by adding external diodes from each output to ground in parallel with the internal diodes. Fast recovery (200 ns) diodes should be used to minimize switching losses. The load supply terminal, VBB, should be decoupled with an electrolytic capacitor (47 F is recommended) placed as close to the device as is physically practical. To minimize the effect of system ground I*R drops on the logic and reference input signals the system ground should have a low-resistance return to the motor supply voltage. See also "Current Sensing" and "Thermal Considerations" above. Fixed Off-Time Selection. With increasing values of tOFF, switching losses will decrease, low-level load current regulation will improve, EMI will be reduced, the PWM frequency will decrease, and ripple current will increase. The value of tOFF can be chosen for optimization of these parameters. For applications where audible noise is a concern, typical values of tOFF are chosen to be in the range of 15 to 35 ms.
3962 DUAL FULL-BRIDGE PWM MOTOR DRIVER
Dimensions in Inches (for reference only)
20 11 0.0125 0.0091
0.2992 0.2914
0.419 0.394
0.050 0.016 0.020 0.013
1
2
3 0.5118 0.4961
0.050
BSC NOTE 1 NOTE 3
0 TO 8
0.0926 0.1043 0.0040 MIN.
Dwg. MA-008-21A in
Dimensions in Millimeters (controlling dimensions)
20 11 0.32 0.23
7.60 7.40
10.65 10.00
1.27 0.40 0.51 0.33
1
2
3 13.00 12.60
1.27
BSC NOTE 1 NOTE 3
0 TO 8
2.65 2.35 0.10 MIN.
Allegro MicroSystems, Inc. reserves the right to make, from Dwg. MA-008-21A mm time to time, such departures from the detail specifications as may be required to permit improvements in the design of its products. The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringements of patents or other rights of third parties which may result from its use.
NOTES: 1. Webbed lead frame. Leads 5, 6, 15, and 16 are internally one piece. 2. Lead spacing tolerance is non-cumulative. 3. Exact body and lead configuration at vendor's option within limits shown.
115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000

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