DRV8711 Datasheet, PDF (11/34 Pages) Texas Instruments – STEPPER MOTOR CONTROLLER IC

DRV8711
www.ti.com
SLVSC40 – JUNE 2013
The current through the motor windings is regulated by an adjustable fixed-off-time PWM current regulation
circuit. When an H-bridge is enabled, current rises through the winding at a rate dependent on the DC voltage
and inductance of the winding and the magnitude of the back EMF present. Once the current hits the current
chopping threshold, the bridge disables the current for a fixed period of time, which is programmable between
500 nS and 128 µS by writing to the TOFF bits in the OFF register. After the off time expires, the bridge is re-
enabled, starting another PWM cycle.
The chopping current is set by a comparator which compares the voltage across a current sense resistor
connected to the xISENx pins, multiplied by the gain of the current sense amplifier, with a reference voltage. The
current sense amplifier is programmable in the CTRL register.
When driving in PWM mode, the chopping current is calculated as follows:
ICHOP
=
2.75V · TORQUE
256 · ISGAIN · RISENSE
(1)
Where TORQUE is the setting of the TORQUE bits, and ISGAIN is the programmed gain of the ISENSE
amplifiers (5, 10, 20, or 40).
Microstepping Indexer
Built-in indexer logic in the DRV8711 allows a number of different stepping configurations. The MODE bits in the
CTRL register are used to configure the stepping format as shown in the table below:
MODE3
0
0
0
0
0
0
0
0
1
Table 2. Microstepping Indexer Logic
MODE2
0
0
0
0
1
1
1
1
0
MODE1
0
0
1
1
0
0
1
1
0
MODE0
0
1
0
1
0
1
0
1
0
STEP MODE
Full step (2-phase excitation)
with 71% current
1/2 step
1/4 step
1/8 step
1/16 step
1/32 step
1/64 step
1/128 step
1/256 step
Copyright © 2013, Texas Instruments Incorporated
Product Folder Links: DRV8711
Submit Documentation Feedback
11