DRV8711_15 Datasheet, PDF (12/44 Pages) Texas Instruments – DRV8711 Stepper Motor Controller IC

DRV8711
SLVSC40E – JUNE 2013 – REVISED MARCH 2015
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Feature Description (continued)
7.3.2 Direct PWM Input Mode
Direct PWM mode is selected by setting the PWMMODE bit in the OFF register. In direct PWM input mode, the
AIN1, AIN2, BIN1, and BIN2 directly control the state of the output drivers. This allows for driving up to two
brushed DC motors. The logic is shown in Table 2:
Table 2. Direct PWM Input Mode Logic
xIN1
0
0
1
1
xIN2
0
1
0
1
xOUT1
Z
L
H
L
xOUT2
Z
H
L
L
OPERATION
Asynchronous Fast Decay
Reverse Drive
Forward Drive
Slow Decay
If mixed or auto-mixed decay modes are used, they will apply to every cycle, because current change information
is not available.
In direct PWM mode, the current control circuitry is still active. The full-scale VREF is set to 2.75 V. The
TORQUE register may be used to scale this value, and the ISEN sense amp gain may still be set using the
ISGAIN bits of the CTRL register.
xIN1
xIN2
PWM
logic
Gate
Drive
&
OCP
Gate
Drive
&
OCP
VM
x1HS
xOUT1
x1LS
VM
x2HS
xOUT2
x2LS
Comp
Comp
ISEN
amp
xISENP
xISENN
R_ISENSE
VREF
X
1V
TORQUE
Torque
DAC
ISGAIN
Figure 7. Direct PWM Input Mode
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.
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