DRV8840_15 Datasheet, PDF (10/28 Pages) Texas Instruments – DC Motor Driver IC

DRV8840
SLVSAB7D – MAY 2010 – REVISED DECEMBER 2015
Feature Description (continued)
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ENBL
PHASE
DECAY
I[4:0]
VREF
VCP, VGD
OCP
Pre-
drive
PWM
DAC
5
OCP
-
+
A =5
VM
VM
OUT1
OUT2
DCM
ISEN
Figure 5. Motor Control Circuitry
There are multiple VM, ISEN, OUT, and VREF pins. All like-named pins must be connected together on the PCB.
7.3.2 Bridge Control
The PHASE input pin controls the direction of current flow through the H-bridge, and hence the direction of
rotation of a DC motor. The ENBL input pin enables the H-bridge outputs when active high, and can also be
used for PWM speed control of the motor. Note that the state of the DECAY pin selects the behavior of the
bridge when ENBL = 0, allowing the selection of slow decay (brake) or fast decay (coast). Table 1 shows the
logic.
DECAY
0
1
X
X
Table 1. H-Bridge Logic
ENBL
0
0
1
1
PHASE
X
X
1
0
OUT1
L
Z
H
L
OUT2
L
Z
L
H
The control inputs have internal pulldown resistors of approximately 100 kΩ.
7.3.3 Current Regulation
The maximum current through the motor winding is regulated by a fixed-frequency PWM current regulation, or
current chopping. When the 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 DC motors, current regulation is used to limit the start-up and stall current of the motor. Speed control is
typically performed by providing an external PWM signal to the ENBLx input pins.
If the current regulation feature is not needed, it can be disabled by connecting the ISENSE pins directly to
ground and the VREF pins to V3P3.
The PWM chopping current is set by a comparator which compares the voltage across a current sense resistor
connected to the ISEN pin, multiplied by a factor of 5, with a reference voltage. The reference voltage is input
from the VREF pin, and is scaled by a 5-bit DAC that allows current settings of zero to 100% in an approximately
sinusoidal sequence.
10
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