If you design products that incorporate a bipolar stepper or brushed-DC motor, Texas Instruments has some new driver integrated circuits (ICs) that might simplify your driver circuits. Eight devices in the new DRV8x family offer low-cost alternatives to do-it-yourself drive circuits or complicated commercial motor-control devices.
The new integrated circuits offer a low RDSon (100 milliohms) in their H bridges and can handle either 2.5 or 5 amperes of motor-drive current. The stepper-motor drive ICs give you the option of as many as 256 microsteps if you use an external microcontroller or as many as 32 microsteps when you use the on-chip indexer in the DRV8825 IC. You can select 1/2-, 1/4-, 1/8-, or 1/16-step operations, too, via three logic inputs. For complete information, visit: www.ti.com/drv8x-pr. The new DRV8x motor drivers come in a 9.7-by-6.4-mm PowerPAD HTSSOP package. For quantities of 1000, the ICs cost $US 2.25 each, except for the DRV8825 that costs $US 2.40 each for 1000 ICs.
TI has an evaluation package for each of the eight new motor-drive ICs for $US 149 each. The package includes a board (shown below) with the driver IC and an MSP430 MCU, and you can use a graphical user interface to set up the board. When I tried the order links on Web site noted above, several of the “Order” links for the evaluation modules (EVMs) did not work, but TI knows and should have those links “connected” now. TI also provides schematics, Gerber files, and additional software.
The chips have one or more H bridge circuits that control motor windings and built-in protection circuits detect and prevent damage from over-temperature, over-current, shoot-through, and under-voltage conditions. A logic-level output pin supplies a fault-indicator signal so your MCU can handle recovery operations. As far as I can tell, though, the driver ICs cannot indicate the type of fault experienced. Each driver can go into a low-power sleep mode that reduces current demands and saves power. One input pin controls the sleep operation.
Note: Mike Firth at Texas Instruments added the following information about the fault pin, “The fault pin is shared by overtemp and overcurrent events, which means on either of these two faults, the fault pin will be driven low. But note that the overcurrent fault is latched and the overtemp fault is auto-retry. So once the device cools down it will resume normal operation where as with an overcurrent fault, the device must either be reset of power removed/reapplied in order to start it back up. So there is a way to determine which fault condition triggered the fault pin.” Thanks, Mike.
And according to TI, “The portfolio offers different interfaces to suit your implementation. Phase-enable is a widely used interface where the duty cycle of a PWM signal can determine the speed and direction of a DC motor, for example. The indexer interface can be used for easy implementation of microstepping of a stepper motor. The PWM interface allows flexible control over each half bridge. Details for h-bridge control logic, decay modes and current regulation can be found in the product datasheets.”
I won’t repeat the technical specs and details you can find in the data sheet for each IC. Happy motoring. –Jon Titus