DRV8802-Q1_15 Datasheet, PDF (10/26 Pages) Texas Instruments – DRV8802-Q1 Automotive DC Motor-Driver IC

DRV8802-Q1
SLVSCI2A – JUNE 2014 – REVISED JUNE 2014
www.ti.com
Feature Description (continued)
7.3.2 Bridge Control
The xPHASE input pins control the direction of current flow through each H-bridge, and therefore control the
direction of rotation of a DC motor. The xENBL input pins enable the H-bridge outputs when active high, and can
also be used for PWM speed control of the motor. Table 1 lists the H-bridge logic.
Table 1. H-Bridge Logic
xENBL
0
1
1
xPHASE
X
1
0
xOUT1
see ⁽¹⁾
H
L
xOUT2
see ⁽¹⁾
L
H
(1) Depends on state of the DECAY pin. See the Decay Mode and
Braking section.
7.3.3 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. When 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 change the current that is used to
microstep the motor. For DC motors, current regulation is used to limit the start-up and stall current of the motor.
The PWM chopping current is set by a comparator that 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 38%, 71%, and 100% of full-
scale, plus zero.
Use Equation 1 to calculate the full-scale (100%) chopping current.
I_(CHOP)
=
V_{( xVREF )}
5 ´ R_(ISENx)
(1)
For example:
If a 0.5-Ω sense resistor is used and the voltage on the xVREF pin is 3.3 V, the full-scale (100%) chopping
current is 3.3 V / (5 × 0.5 Ω) = 1.32 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 xVREF input pin and sense resistance. Table 2 lists the function of the pins.
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%
Note that when both xI bits are 1, the H-bridge is disabled and no current flows.
For example:
If a 0.5-Ω sense resistor is used and the voltage on the xVREF pin is 3.3 V, the chopping current is 1.32 A at
the 100% setting (xI1, xI0 = 00). At the 71% setting (xI1, xI0 = 01) the current is 1.32 A × 0.71 = 0.937 A. At
the 38% setting (xI1, xI0 = 10) the current is 1.32 A × 0.38 = 0.502 A. If (xI1, xI0 = 11) the bridge is disabled
and no current will flow.
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