A3982 Frequently Asked Questions

Thermal shutdown (TSD) 

Undervoltage lockout (UVLO) 

Crossover current protection 

VREG and charge pump monitors 

The value ±2 A defines the maximum current that each phase of the driver can support continuously. This is independent of temperature rise. 

Caution should be taken to never exceed a junction temperature of 150°C when running the device. 

The following components are required for correct operation of the A3982/83/84: 

RSENSE1 and RSENSE2, the external sense resistors required for the PWM current control circuit. These should be noninductive type resistors. The value for RS can be calculated using the formula: ITRIP(max) = VREF / (8 x RS). When selecting a value for RS it is very important not to exceed the 0.5 V limit on the SENSE pin over the full expected current range. For very short time durations during switching, transient voltages larger than 0.5 V may be observed. Using a reasonably smaller value for RS will dissipate less power in RS and provide headroom. 

A 0.1 µF mono/ceramic capacitor must be placed between the CP1 and CP2 pins. 

The VREG pin should be decoupled with a 0.22 µF capacitor to ground. 

A logic supply decoupling capacitor; a 10 µF ceramic capacitor is recommended. 

A load supply decoupling capacitor; a value of > 47 µF electrolytic capacitor is recommended. In addition, a 0.1 µF ceramic capacitor should be placed in parallel. 

A 0.1 µF capacitor is required on the VREF pin. 

By using the formula: 

where: 

RS is the sense resistor, 

0.5 is the absolute maximum allowable voltage on the SENSE pin, and 

ITRIP(max) is the maximum expected current. 

This will ensure that the 0.5 V limit on the SENSE pin is never exceeded.

Yes. The printed circuit board should use a heavy groundplane. For optimum electrical and thermal performance, the exposed pad on the underside of the device provides a path for enhanced thermal dissipation. The thermal pad should be soldered directly to an exposed surface on the PCB. Thermal vias are used to transfer heat to other layers of the PCB.
 

In order to minimize the effects of ground bounce and offset issues, it is important to have a low impedance singlepoint ground, known as a star ground, located very close to the device. By making the connection between the exposed thermal pad and the groundplane directly under the device, that area becomes an ideal location for a star ground point. 

The two input capacitors (electrolytic and ceramic) should be placed in parallel, and as close to the device supply pins as possible. The ceramic capacitor should be closer to the pins than the bulk capacitor. This is necessary because the ceramic capacitor will be responsible for delivering the high frequency current components. 

The sense resistors, RSx, should have a very low impedance path to ground, because they must carry a large current while supporting very accurate voltage measurements by the current sense comparators. Long ground traces will cause additional voltage drops, adversely affecting the ability of the comparators to accurately measure the current in the windings. 

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 Package Thermal Characteristics. 

NOTE: The datasheet also defines RθJA with various copper areas. See page 4 of the datasheet. 

Yes, as long as the timing requirements are met. The easiest way to change sequencing modes, to higher or lower resolution, is to do it at the HOME position (HOME is low). Otherwise, when going from a lower resolution to a higher resolution mode (half-step to quarter-step, etc.) both sequences have identical output currents. (Both sequences fall on the same row of table 2 in the datasheet.) The translator will keep the output current levels unchanged until the next step, at which time it will begin the smaller steps. 

To keep the motor moving at a constant speed while changing sequencing modes, the step frequency must be multiplied by 2, 4, or 8, depending on the modes you jump from and to. Going from a higher-resolution mode to a lower-resolution mode should only be done when both modes appear on the same row of table 2 from the datasheet (Eighth Step #5 and Full Step #1, etc.). This is only important if position must be maintained or if there is no position control loop. 

It should be mentioned that changing the MSx pins at any time will not cause damage to the device. To keep the motor moving at a constant speed while changing sequencing modes, the step frequency must be divided by 2, 4, or 8, depending on the modes you jump from and to. If you go from a higher resolution mode to a lower resolution mode and do it at a position that is not a valid possibility for the lower resolution mode in table 2 of the datasheet, then the sequencer will advance to first possibility without actually changing the output currents. When the next step arrives, the device will go from the position the translator was at before the sequencing mode was changed, to the next position of the new sequencing mode. For example, with direction low, if you changed from Eighth Step mode to Full Step mode when you were at Eighth Step #2, the translator will advance to Full Step #2 (but not change the output currents). When the next step occurs, the position will go to Full Step #3. The effect would be that the motor would move by 11 eighth-steps. This would make keeping the motor at constant speed very tricky.