A3972 Dual DMOS Full-Bridge Microstepping PWM Motor Driver Features and Benefits Description ▪ ±1.5 A, 50 V Continuous Output Rating ▪ Low RDS(on) DMOS Output Drivers ▪ Optimized Microstepping via 6-Bit Linear DACs ▪ Programmable Mixed, Fast, and Slow Current-Decay Modes ▪ 4 MHz Internal Oscillator for Digital Timing ▪ Serial-Interface Controls Chip Functions ▪ Synchronous Rectification for Low Power Dissipation ▪ Internal UVLO and Thermal Shutdown Circuitry ▪ Crossover-Current Protection ▪ Precision 2 V Reference ▪ Inputs Compatible with 3.3 or 5 V Control Signals ▪ Sleep and Idle Modes Designed for pulse-width modulated (PWM) current control of bipolar microstepping stepper motors, the A3972 is capable of continuous output currents to ±1.5 A and operating voltages to 50 V. Internal fixed off-time PWM current-control timing circuitry can be programmed via a serial interface to operate in slow, fast, and mixed current-decay modes. Package: 24-pin DIP with 4 fused leads (suffix B) The desired load-current level is set via the serial port with two 6-bit linear DACs in conjunction with a reference voltage. The six bits of control allow maximum flexibility in torque control for a variety of step methods, from microstepping to full-step drive. Load current is set in 1.56% increments of the maximum value. Synchronous rectification circuitry allows the load current to flow through the low RDS(on) of the DMOS output driver during the current decay. This feature will eliminate the need for external clamp diodes in most applications, saving cost and external component count, while minimizing power dissipation. Internal circuit protection includes thermal shutdown with hysteresis, transient-suppression diodes, and crossover-current protection. Special power-up sequencing is not required. Not to scale The A3972SB is supplied in a 24-pin plastic DIP with two batwing power tabs (suffix ‘B’). The power tabs are at ground potential and need no electrical isolation. The device is lead (Pb) free with 100% matte tin leadframe plating. Pin-out Diagram 29319.33, Rev. D Dual DMOS Full-Bridge Microstepping PWM Motor Driver A3972 Selection Guide Part Number A3972SB-T Packing 15 pieces/tube Absolute Maximum Ratings Rating Units Load Supply Voltage Characteristic VBB 50 V Output Current* IOUT ±1.5 A Logic Supply Voltage VDD 7.0 V Logic Input Voltage Range VIN –0.3 to VDD + 0.3 V Reference Voltage Symbol Notes VREF 3 V Sense Voltage (DC) VS 500 mV Package Power Dissipation PD Operating Ambient Temperature TA Range S 3.1 W –20 to 85 ºC Junction Temperature TJ 150 ºC Storage Temperature Tstg –55 to 150 ºC *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 temperature of 150°C. Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 2 Dual DMOS Full-Bridge Microstepping PWM Motor Driver A3972 FUNCTIONAL BLOCK DIAGRAM 0.22 μF 0.22 μF 22 LOGIC SUPPLY VREG CP2 3 CP1 2 2V UVLO AND FAULT DETECT 15 VDD REGULATOR CHARGE PUMP LOAD SUPPLY VCP 1 BANDGAP 0.22 μF VBB1 5 MUX 14 DMOS H-BRIDGE 6-BIT LINEAR DAC SENSE1 + VCP OUT1A 6 9 OSC 24 OSCILATOR PROGRAMMABLE PWM TIMER OSC SELECT/ DIVIDER FIXED-OFF BLANK MIXED DECAY OUT1B 4 8 SENSE1 CLOCK 11 CONTROL LOGIC SERIAL PORT DATA 12 GATE DRIVE PHASE 1/2 SYNC. RECT. MODE SYNC. RECT. DISABLE MODE 1/2 STROBE 10 DMOS H-BRIDGE 0.1 μF 20 VBB2 SLEEP 23 OUT2A 16 PROGRAMMABLE PWM TIMER 2V 6 REF 13 OUT2B 21 FIXED-OFF BLANK MIXED DECAY BUFFER + - 6-BIT LINEAR DAC 17 SENSE2 0.1 μF 6 GROUND 7 18 19 Dwg. FP-050-1 Copyright © 2000, Allegro MicroSystems, Inc. Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 3 Dual DMOS Full-Bridge Microstepping PWM Motor Driver A3972 ELECTRICAL CHARACTERISTICS at TA = +25°C, VBB = 50 V, VDD = 5.0 V, VS = 0.5 V, fPWM < 50 kHz (unless otherwise noted). Limits Characteristic Load Supply Voltage Range Symbol VBB Test Conditions Min. Typ. Max. Units Operating 15 — 50 V During sleep mode 0 — 50 V Logic Supply Voltage Range VDD Operating 4.5 5.0 5.5 V Load Supply Current IBB fPWM < 50 kHz — — 8.0 mA Operating, outputs disabled — — 6.0 mA Sleep or idle mode — — 20 μA fPWM < 50 kHz — — 12 mA Outputs off — — 10 mA Idle mode (D0 = 1, D18 = 0) — — 1.5 mA Sleep mode — — 100 μA VOUT = VBB — <1.0 50 μA VOUT = 0 V — <-1.0 -50 μA Source driver, IOUT = –1.5 A — 0.5 0.55 Ω Sink driver, IOUT = 1.5 A — 0.315 0.35 Ω Source diode, IF = 1.5 A — — 1.2 V Sink diode, IF = 1.5 A — — 1.2 V VIN(1) 2.0 — — V VIN(0) — — 0.8 V Logic Supply Current IDD Output Drivers Output Leakage Current Output On Resistance Body Diode Forward Voltage IDSS rDS(on) VF Control Logic Logic Input Voltage Logic Input Current IIN(1) VIN = 2.0 V — <1.0 20 μA OSC Input Frequency Range IIN(0) fOSC VIN = 0.8 V Divide by one — 2.5 <-2.0 — -20 6.0 μA MHz — 40 — 60 % ΔVIN 0.20 — 0.40 V (D0 =1, D13 = 0, D14 = 1) OSC Input Duty Cycle Input Hysterisis continued next page ... Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 4 Dual DMOS Full-Bridge Microstepping PWM Motor Driver A3972 ELECTRICAL CHARACTERISTICS at TA = +25°C, VBB = 50 V, VDD = 5.0 V, VS = 0.5 V, fPWM < 50 kHz (unless otherwise noted). Limits Characteristics Symbol Test Conditions Min. Typ. Max. Units OSC shorted to ground 3.0 4.0 5.0 MHz ROSC = 51 kΩ 3.4 4.0 4.6 MHz Relative to DAC reference buffer — ±1/2 — LSB VREF(EXT) 0.5 — 2.6 V Reference Buffer Offset VOS — ±10 — mV Reference Divider Ratio VREF/VS D0 = 0, D18 = 0 — 8.0 — — D0 = 0, D18 = 1 — 4.0 — — VREF = 2.0 V — — ±0.5 μA 1.94 2.0 2.06 V D0 = 0, D17 = 0, D18 = 0, DAC = 63 D18 = 0, DAC = 31 D18 = 1, DAC = 63 — — — 0 0 0 ±6 ±9 ±6 % % % D18 = 1, DAC = 15 — 0 ±10 % — ±5.0 — mV Control Logic (continued) Internal Oscillator DAC Accuracy (total error) fOSC ET output, D0 = 0, D17 = 0 Reference Input Voltage Range Reference Input Current Internal Reference Voltage Gain (Gm) Error (note 3) IREF VREF(INT) EG Comparator Input Offset Voltage VIO VREF = 0 V Propagation Delay Times tpd 50% to 90%: PWM change to source on PWM change to source off PWM change to sink on 500 50 500 800 150 800 1200 350 1200 ns ns ns PWM change to sink off 50 150 350 ns Crossover Dead Time tdt 300 700 900 ns Thermal Shutdown Temperature TJ — 165 — °C ΔTJ — 15 — °C 3.9 4.2 4.45 V 0.05 0.10 — V Thermal Shutdown Hysteresis UVLO Enable Threshold UVLO Hysteresis VUVLO ΔVUVLO Increasing VDD NOTES: 1. Typical Data is for design information only. 2. Negative current is defined as coming out of (sourcing) the specified device terminal. 3. EG = [(VREF/Range) – VS]/(VREF/Range). Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 5 Dual DMOS Full-Bridge Microstepping PWM Motor Driver A3972 FUNCTIONAL DESCRIPTION Serial Interface. The A3972SB is controlled via a 3-wire (clock, data, strobe) serial port. The programmable functions allow maximum flexibility in configuring the PWM to the motor drive requirements. The serial data is written as two 19-bit words: 1 bit to select the word and 18 bits of data. The serial data is clocked in starting with D18. D13 Bridge 1 Phase. This bit controls the direction of output current for Load 1. OUT1B D13 OUT1A Word 0 Bit Assignments D14 Bridge 2 Phase. This bit controls the direction of output current for Load 2. D14 OUT2A OUT2B Bit D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14 D15 D16 D17 D18 Function Word select = 0 Bridge 1, DAC, LSB Bridge 1, DAC, bit 2 Bridge 1, DAC, bit 3 Bridge 1, DAC, bit 4 Bridge 1, DAC, bit 5 Bridge 1, DAC, MSB Bridge 2, DAC, LSB Bridge 2, DAC, bit 2 Bridge 2, DAC, bit 3 Bridge 2, DAC, bit 4 Bridge 2, DAC, bit 5 Bridge 2, DAC, MSB Bridge 1 phase Bridge 2 phase Bridge 1 mode Bridge 2 mode REF select Range select D1 – D6 Bridge 1 Linear DAC. Six-bit word sets desired current level for Bridge 1. Setting all six bits to zero disables Bridge 1, with all drivers off (See current regulation section of functional description). D7 – D12 Bridge 2 Linear DAC. Six-bit word sets desired current level for Bridge 2. Setting all six bits to zero disables Bridge 2, with all drivers off (See current regulation section of functional description). 0 1 L H 0 1 L H H L H L D15 Bridge 1 Mode. D15 Mode 0 1 Mixed-decay Slow-decay D16 Bridge 2 Mode. D16 Mode 0 1 Mixed-decay Slow-decay D17 REF Select. This bit determines the reference input for the 6-bit linear DACs. D17 Reference Voltage 0 1 Internal 2 V External (3 V max) D18 Gm Range Select. This bit determines the scaling factor (4 or 8) used. D18 Divider 0 1 1/8 1/4 Load Current ITRIP = VDAC/8RS ITRIP = VDAC/4RS continued next page ... Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 6 Dual DMOS Full-Bridge Microstepping PWM Motor Driver A3972 FUNCTIONAL DESCRIPTION (continued) Word 1 Bit Assignments Bit D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14 D15 D16 D17 D18 Function Word select = 1 Blank-time LSB Blank-time MSB Off-time LSB Off-time bit 1 Off-time bit 2 Off-time bit 3 Off-time MSB Fast-decay time LSB Fast-decay time bit 1 Fast-decay time bit 2 Fast-decay time MSB C0 oscillator control C1 oscillator control SR control bit 1 SR control bit 2 Reserved for testing Reserved for testing Idle mode D1 – D2 Blank Time. These two bits set the blank time for the current-sense comparator. When a source driver turns on, a current spike occurs due to the reverse-recovery currents of the clamp diodes and/or switching transients related to distributed capacitance in the load. To prevent this current spike from erroneously resetting the source-enable latch, the sense comparator is blanked. The blank timer runs after the off-time counter to provide the programmable blanking function. The blank timer is reset when PHASE is changed. D2 0 0 1 D1 0 1 0 Time 4/fOSC 6/fOSC 8/fOSC 1 1 12/fOSC D3 – D7 Fixed Off Time. These five bits set the fixed off-time for the internal PWM control circuitry. Fixed off-time is defined by: toff = [(1 + N) x 8/fOSC] - 1/fOSC where N = 0….31 For example, with a master oscillator frequency of 4 MHz, the fixed off-time will be adjustable from 1.75 μs to 63.75 μs in increments of 2 μs. D8 – D11 Fast Decay Time. These four bits set the fastdecay portion of fixed off-time for the internal PWM control circuitry. The fast-decay portion is defined by: tfd = [(1 + N) x 8/fOSC] - 1/fOSC where N = 0….15 For example, with an oscillator frequency of 4 MHz, the fastdecay time will be adjustable from 1.75 μs to 31.75 μs in increments of 2 μs. For tfd > toff , the device will effectively operate in fast-decay mode. D12 – D13 Oscillator Control. A 4 MHz internal oscillator is used for the timing functions and charge-pump clock. If more precise control is required, an external oscillator can be input to the OSC terminal. To accommodate a wider range of system clocks, an internal divider is provided to generate the desired MO frequency according to the following table: D13 0 0 1 1 D12 0 1 0 1 OSC 4 MHz internal clock External clock External clock/2 External clock/4 D14 – D15 Synchronous Rectification. D15 0 0 1 1 D14 0 1 0 1 Synchronous Rectifier Active Disabled Passive Low side only The different modes of operation are in the synchronous rectification section of the functional description. D16, D17. These bits are reserved for testing and should be programmed to zero during normal operation. D18 Idle Mode. The device can be placed in a low power “idle” mode by writing a “0” to D18. The outputs will be disabled, the charge pump will be turned off, and the device will draw a lower load supply currrent. The undervoltage monitor circuit will remain active. D18 should be programmed high for 1 ms before attempting to enable any output driver. continued next page ... Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 7 A3972 Dual DMOS Full-Bridge Microstepping PWM Motor Driver FUNCTIONAL DESCRIPTION (continued) VREG. This internally generated supply voltage is used to run the sink-side DMOS outputs. VREG is internally monitored and in the case of a fault condition, the outputs of the device are disabled. The VREG pin should be decoupled with a 0.22 μF capacitor to ground. Shutdown. In the event of a fault due to excessive junction temperature, or low voltage on VCP or VREG, the outputs of the device are disabled until the fault condition is removed. At power up, or in the event of low VDD, the UVLO circuit disables the drivers and resets the data in the serial port to zeros. Current Regulation. The reference voltage can be set by analog input to the REF terminal, or via the internal 2 V precision reference. The choice of reference voltage and sense resistor set the maximum trip current. ITRIPMAX = VREF/(Range x RS) Synchronous Rectification. When a PWM off-cycle is triggered, either by a bridge disable command or internal fixed off-time cycle, the load current will recirculate according to the decay mode selected by the control logic. The A3972SB synchronous rectification feature will turn on the appropriate MOSFET(s) during the current decay and effectively short out the body diodes with the low rDS(on) driver. This will lower power dissipation significantly and can eliminate the need for external Schottky diodes for most applications. Microstepping current levels are set according to the following equations: ITRIP = VDAC/(Range x RS) VDAC = [(1 + DAC) x VREF]/64 where DAC input code equals 1 to 63 and Range is 4 or 8 as selected by Word 0, D18. Programming the DAC input code to zero disables the bridge, and results in minimum load current. Four distinct modes of operation can be configured with the two serial port control bits: PWM Timer Function. The PWM timer is programmable via the serial port to provide fixed off-time PWM signals to the control block. In mixed-decay mode, the first portion of the off time operates in fast decay, until the fast-decay time count is reached, followed by slow decay for the rest of the fixed off-time period. If the fast-decay time is set longer than the off-time, the device effectively operates in fast-decay mode. 2. Passive Mode. Allows reversal of current but will turn off the synchronous rectifier circuit if the load current inversion ramps up to the current limit. Oscillator. The PWM timer is based on an oscillator input, typically 4 MHz. The A3972SB can be configured to select either a 4 MHz internal oscillator or, if more precision is required, an external clock can be connected to the OSC terminal. If an external clock is used, three internal divider choices are selectable via the serial port to allow flexibility in choosing fOSC, based on available system clocks. If the internal oscillator option is used, the absolute accuracy is dependent on the process variation of resistance and capacitance. A precision resistor can be connected from the OSC terminal to VDD to further improve the tolerance. The frequency will be: fOSC = 204 x 109/ROSC If the internal oscillator is used without the external resistor, the OSC terminal should be connected to ground. Sleep Mode. The input terminal SLEEP is dedicated to putting the device into a minimum current draw mode. When pulled low, the serial port will be reset to all zeros and all circuits will be disabled. 1. Active Mode. Prevents reversal of load current by turning off synchronous rectification when a zero current level is detected. 3. Disabled. MOSFET switching will not occur during load recirculation. This setting would only be used with four external clamp diodes per bridge. 4. Low Side Only. The low-side MOSFETs will switch on during the off time to short out the current path through the MOSFET body diode. With this setting, the high-side MOSFETs will not synchronously rectify so four external diodes from output to supply are recommended. This mode is intended for use with high-power applications where it is desired to save the expense of two external diodes per bridge. In this mode, the sink-side MOSFETs are chopped during the PWM off time. In all other cases, the source-side MOSFETs are chopped in response to a PWM off command. continued next page ... Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 8 Dual DMOS Full-Bridge Microstepping PWM Motor Driver A3972 APPLICATIONS INFORMATION Current Sensing. To minimize inaccuracies in sensing the IPEAK current level caused by ground-trace IR drops, the sense resistor should have an independent ground return to the ground terminal of the device. For low-value sense resistors, the IR drops in the sense resistor’s PCB traces can be significant and should be taken into account. The use of sockets should be avoided as they can introduce variation in RS due to their contact resistance. Thermal Protection. Circuitry turns off all drivers when the junction temperature reaches 165°C typically. It is intended only to protect the device from failures due to excessive junction temperature and should not imply that output short circuits are permitted. Thermal shutdown has a hysteresis of approximately 15°C. Layout. The printed wiring board should use a heavy ground plane. For optimum electrical and thermal performance, the driver should be soldered directly onto the board. The ground side of RS should have an individual path to the ground pin(s) of the driver. This path should be as short as physically possible and should not have any other components connected to it. The load supply pin, VBB, should be decoupled with an electrolytic capacitor (>47 μF is recommended) placed as close to the driver as is possible. Serial Port Write Timing Operation. Data is clocked into a shift register on the rising edge of CLOCK signal. Normally, STROBE will be held high, and only will be brought low to initiate a write cycle. The data is written MSB first, followed by the word-select bit. Refer to serial port diagram for timing requirements. SLEEP H STROBE C D E F G CLOCK A DATA B D18 D17 D0 Dwg. WP-038-1 A. Minimum Data Setup Time .......................................15 ns B. Minimum Data Hold Time ........................................10 ns C. Minimum Setup Strobe to Clock Rising Edge ........150 ns D. Minimum Clock High Pulse Width ...........................40 ns E. Minimum Clock Low Pulse Width ............................40 ns F. Minimum Setup Clock Rising Edge to Strobe ...........50 ns G. Minimum Strobe Pulse Width .................................150 ns H. Minimum Setup Sleep to Strobe Falling ...................50 μs Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 9 Dual DMOS Full-Bridge Microstepping PWM Motor Driver A3972 B Package, 24-Pin DIP 1.185 24 0.010 0.250 0.430 0.300 A 1 2 0.210 0.130 0.100 0.005 All dimensions nominal, not for tooling use (reference JEDEC MS-001 BE) Dimensions in inches Pins 6, 7, 18 and 19 internally fused 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 0.060 0.018 Copyright ©2000-2007, 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 departures from the detail specifications as may be required to permit improvements in the performance, 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 information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringement of patents or other rights of third parties which may result from its use. For the latest version of this document, visit our website: www.allegromicro.com Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 10