DRV8841_15 Datasheet, PDF (11/28 Pages) Texas Instruments – Dual H-Bridge Driver IC

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DRV8841
SLVSAC0F – MAY 2010 – REVISED DECEMBER 2015
Feature Description (continued)
7.3.2 Blanking Time
After the current is enabled in an H-bridge, the voltage on the xISEN pin is ignored for a fixed period of time
before enabling the current sense circuitry. This blanking time is fixed at 3.75 μs. Note that the blanking time also
sets the minimum on time of the PWM.
7.3.3 Bridge Control
The AIN1 and AIN2 input pins directly control the state of the AOUT1 and AOUT2 outputs; similarly, the BIN1
and BIN2 input pins directly control the state of the BOUT1 and BOUT2 outputs. Either input can also be used
for PWM control of the load. Table 1 shows the logic.
Table 1. H-Bridge Logic
xIN1
0
0
1
1
xIN2
0
1
0
1
xOUT1
L
L
H
H
xOUT2
L
H
L
H
The control inputs have internal pulldown resistors of approximately 100 kΩ.
7.3.4 Current Regulation
The current through the motor windings is regulated by a fixed-frequency PWM current regulation, or current
chopping. When an H-bridge is enabled, current rises through the winding at a rate dependent on the DC voltage
and inductance of the winding. Once the current hits the current chopping threshold, the bridge disables the
current until the beginning of the next PWM cycle.
For stepping motors, current regulation is normally used at all times, and can changing the current can be used
to microstep the motor. For DC motors, current regulation is used to limit the start-up and stall current of the
motor.
If the current regulation feature is not needed, it can be disabled by connecting the xISENSE pins directly to
ground and the xVREF pins to V3P3.
The PWM chopping current is set by a comparator which compares the voltage across a current sense resistor
connected to the xISEN pins, multiplied by a factor of 5, with a reference voltage. The reference voltage is input
from the xVREF pins, and is scaled by a 2-bit DAC that allows current settings of 100%, 71%, 38% of full-scale,
plus zero.
The full-scale (100%) chopping current is calculated in Equation 1.
I_CHOP
V_REFX
5 u R_ISENSE
(1)
Example:
If a 0.25-Ω sense resistor is used and the VREFx pin is 2.5 V, the full-scale (100%) chopping current will be
2.5 V / (5 × 0.25 Ω) = 2 A.
Two input pins per H-bridge (xI1 and xI0) are used to scale the current in each bridge as a percentage of the full-
scale current set by the VREF input pin and sense resistance. The xI0 and xI1 pins have internal pulldown
resistors of approximately 100 kΩ. The function of the pins is shown in Table 2.
Table 2. H-Bridge Pin Functions
xI1
xI0
RELATIVE CURRENT
(% FULL-SCALE CHOPPING CURRENT)
1
1
0% (Bridge disabled)
1
0
38%
0
1
71%
0
0
100%
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