A3972: Dual DMOS Full-Bridge Microstepping PWM Motor Driver

This part is discontinued. Samples are no longer available. Date of status change: June 1, 2016.

Recommended substitution: A3992SLPTR-T.

Designed for pulse-width modulated (PWM) current control of bipolar microstepping stepper motors, the A3972SB 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.

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.

DATASHEETS
SAMPLE & BUY

Astrorep Inc. (Allegro and Sanken Semiconductors, Sanken Power Supplies)
141 John Street, Suite 300
Babylon, NY 11702
Phone: (631)422-2500
Fax: (631)422-2504
Web: www.astrorepinc.com
Email: donna.tweedy@astrorepinc.com

If this is not your local representative, find your local sales rep here.

RECEIVE PRODUCT ALERTS
We'll notify you when there are updates to this product. Sign Up
  • Features and BenefitsFeatures and Benefits
  • PackagingPackaging
  • Technical DocsTechnical Docs
  • NewsNews
  • ±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 V or 5 V Control Signals
  • Sleep and Idle Modes
Pinout Diagram

Frequently Asked Questions


Q1: What step sequencing options exist for the A3972?

Q2: What is the function of the MUX pin? (pin 14)

Q3: Is the A3972 available in a surface-mount package?

Q4: What is the difference between the "Sleep" and "Idle" modes?

Q5: Are there applications tools available for this device?

Q6: What is the maximum allowable motor supply voltage?

Q7: Do I need any external components?

Q8: What protection features come with the A3972?

Q9: Are there layout concerns that I should be aware of?

Q10: Is this a constant-current or constant-voltage controlled device?

Q11: Are there special techniques to reduce the package power dissipation when running at high currents?

Q11.1: Is there an application note on the use of external diodes?

Q11.2: Do you have a recommended Schottky diode?

Q12: What is the recommended minimum copper ground plane area for taking heat away from the device?

Q13: Is there an applications note for the A3972?

Q14: If more than 19 bits are clocked into the serial port, what happens to the "excess" bits?

Q15: Can Word 0 bit assignments overwrite Word 1 bit assignments?

Q16: If I use the external oscillator, what do I do with the internal oscillator pin?

Q17: If the internal VREF is used, what do I do with the external VREF?

Q18: Is the A3972 capable of being used in portable applications?

Q19: Are there recommended setup functions for Word 0 and Word 1?


Q1: What step sequencing options exist for the A3972?

Full, half, quarter, one-eighth, one-sixteenth, and one-thirty-second step modes are possible. In addition, the onboard linear DAC allows current to be programmed in 1.56% increments of the maximum value 100%/64.


Q2: What is the function of the MUX pin? (pin 14)


It is used by Allegro for testing during production. It should NOT be used in actual applications.


Q3: Is the A3972 available in a surface-mount package?

This device is currently available only in a 24-lead plastic "batwing" DIP package. However, the A3992, the next generation version of the A3972, will be released in January 2006. That will be available in a 24-pin TSSOP package with exposed thermal pad.


Q4: What is the difference between the "Sleep" and "Idle" modes?

Sleep mode disables all circuits, including UVLO, and resets the serial port to all zeros. Idle mode disables all circuits except UVLO.


Q5: Are there applications tools available for this device?

The APEK3972 demo board is no longer available.


Q6: What is the maximum allowable motor supply voltage?

50 V. This must not be exceeded.


Q7: Do I need any external components?

Yes. The following components are required:

  1. Sense1 & Sense2 - the external sense resistors. These should be
    non-inductive. There also needs to be a 0.1 µF ceramic capacitor in
    parallel with each of these resistors.
  2. A 0.22 µF ceramic capacitor must be placed between the CP1 and CP2 pins.
  3. VREG - This should be decoupled with a 0.22 µF capacitor to ground.
  4. Decoupling capacitor - logic supply. A 0.01 µF ceramic capacitor is recommended.
  5. Decoupling capacitor - load supply. A 47 µF electrolytic capacitor is recommended. In addition, a 0.1 µF ceramic capacitor should be placed in parallel with this decoupling cap.

Q8: What protection features come with the A3972?

  1. Thermal shutdown (TSD)
  2. Crossover current protection
  3. Under-voltage lockout (UVLO)
  4. Charge pump undervoltage monitor

Q9: Are there layout concerns that I should be aware of?

Yes. Power ground for the sense resistor, Rs, should be connected as close to the device as possible. The ground side of the sense resistor should return on a separate trace to the ground pin(s) of thes device. Also, Rs should be non-inductive, and the circuit board ground run should be as large as physically possible. Finally, a 47 µF electrolytic decoupling capacitor should be placed between the load supply pins and ground. For further layout considerations, please refer to application note 29501.5A, "Improving Batwing Power Dissipation".


Q10: Is this a constant-current or constant-voltage controlled device?

Constant-current. Motor winding current is controlled by internal fixed-offtime, PWM current-control circuitry.



Q11: Are there special techniques to reduce the package power dissipation when running at high currents?

Use of external Schottky diodes with low Vforward to clamp the outputs to VBB and ground will help to reduce the power dissipation in the A3972. Heat sinks are also a possibility, but not as efficient. Note: When using external diodes, synchronous rectification should be disabled to achieve maximum results. For additional information, please refer to the application note AN29504.8, "Power Drive Circuits".

Q11.1: Is there an application note on the use of external diodes?

There is no application note about using external diodes for the A3972. In most applications, each of the outputs should have one Schottky diode connected to VBB (cathode to VBB), and also one Schottky diode connected to ground (anode to ground, not to the sense pins).

Q11.2: Do you have a recommended Schottky diode?

We typically don't recommend a specific diode due to the range of voltages and currents that can be used. The V/I rating of the diode should be greater than or equal to the application requirements.



Q12: What is the recommended minimum copper ground plane area for taking heat away from the device?

A ground plane area at least two times larger than the package outline is a good place to start. For further layout considerations, please refer to application note 29501.5A, "Improving Batwing Power Dissipation".  



Q13: Is there an applications note for the A3972?

Not at this time, but one is planned for the future.



Q14: If more than 19 bits are clocked into the serial port, what happens to the "excess" bits?

Like typical shift registers, the most recent bits are the ones that are retained. As an example, if 24 bits are clocked in , the last 19 are the ones that will be used.



Q15: Can Word 0 bit assignments overwrite Word 1 bit assignments?

No. Since Word 0 and Word 1 are separate, they cannot write to each other or over each other. The appropriate word has to be selected to be overwritten.



Q16: If I use the internal oscillator what do I do with the external oscillator pin?

Pull it up to VDD through a 51 kW resistor or ground it. It should be noted that accuracy will be improved if the 51 kW resistor to VDD is used.


Q17: If the internal VREF is used, what do I do with the external VREF?

Let it float.


Q18: Is the A3972 capable of being used in portable applications?

Yes. The A3972 has Sleep mode, which minimizes power consumption when the device is not in use. During Sleep mode, the device only draws a maximum of 100 µA. The logic supply voltage range of 3.3 to 5.5 V makes it compatible with some battery operated equipment.


Q19: Are there recommended setup functions for Word 0 and Word 1?

Each application is different. For this reason, there isn’t a recommended setup. However, when evaluating the A3972, care should be taken to ensure that the motor will start up and run. This can be achieved by choosing (addressing) the Word 0 and Word 1 bit assigments for a mid-range setting. Specifically, set the following bits initially:

Word 0 Word 1
D1 through D6
D7 through D12
D1 and D2
D3 through D7
D8 through D12

This configuration allows the motor to start and run. After it is running, adjust the bit assignments slightly for optimum performance.

There are no news items available for this product.

Click the image to view larger
Functional Block Diagram Pinout Diagram

Part Number Specifications and Availability

Part Number Package Type Temperature RoHS
Compliant
Part Composition /
RoHS Data
Comments Samples Check
Distributor Stock
A3972SB-T 24-lead DIP -20°C to 85°C Yes View Data Discontinued Contact your
local sales rep
Check Stock

Allegro’s products are not to be used in any devices or systems, including but not limited to life support devices or systems, in which a failure of Allegro’s product can reasonably be expected to cause bodily harm.

Copyright © 2017 Allegro MicroSystems, LLC

Sitemap  |  Privacy Policy  |  Contact Webmaster

Follow us on: LinkedIn YouTube Google+ Follow Allegro on Twitter

Careers   |   Contact Sales   |   Home   |   Legal   |   Quality & Environment   |   Request Samples