DRV8833 Datasheet, PDF (9/22 Pages) Texas Instruments – DUAL H-BRIDGE MOTOR DRIVER

DRV8833
www.ti.com
Figure 2 shows the current paths in different drive and decay modes.
VM
SLVSAR1B – JANUARY 2011 – REVISED AUGUST 2011
VM
1
xOUT1
2
3
1 Forward drive
2 Fast decay
1
xOUT2 _{3 Slow decay}
xOUT1
2
3
xOUT2
1 Reverse drive
2 Fast decay
3 Slow decay
FORWARD
Figure 2. Decay Modes
REVERSE
Current Control
The current through the motor windings may be limited, or controlled, by a fixed-frequency PWM current
regulation, or current chopping. For DC motors, current control is used to limit the start-up and stall current of the
motor. For stepper motors, current control is often used at all times.
When an H-bridge is enabled, current rises through the winding at a rate dependent on the DC voltage and
inductance of the winding. If the current reaches the current chopping threshold, the bridge disables the current
until the beginning of the next PWM cycle. Note that immediately after the current is enabled, 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. This blanking time also sets the minimum on time of the PWM when operating in current
chopping mode.
The PWM chopping current is set by a comparator which compares the voltage across a current sense resistor
connected to the xISEN pins with a reference voltage. The reference voltage is fixed at 200 mV.
The chopping current is calculated in Equation 1.
I=
CHOP
200 mV
¾ _R
ISENSE
(1)
Example:
If a 1-Ω sense resistor is used, the chopping current will be 200 mV/1 Ω = 200 mA.
Once the chopping current threshold is reached, the H-bridge switches to slow decay mode. Winding current is
re-circulated by enabling both of the low-side FETs in the bridge. This state is held until the beginning of the next
fixed-frequency PWM cycle.
Note that if current control is not needed, the xISEN pins should be connected directly to ground.
Copyright © 2011, Texas Instruments Incorporated
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