DRV8823_16 Datasheet, PDF (13/32 Pages) Texas Instruments – 4-Bridge Serial Interface Motor Driver

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7.4 Device Functional Modes
DRV8823
SLVS913E – JANUARY 2009 – REVISED JANUARY 2016
To Logic
Hysteresis
Internal
Pulldown
ESD
Figure 11. Logic Inputs
7.4.1 Bridge Control
The xENBL bits in the serial interface registers enable current flow in each H-bridge when set to 1.
The xPHASE bits in the serial interface registers control the direction of current flow through each H-bridge.
Table 1 shows the logic.
xPHASE
1
0
Table 1. Bridge Control Logic
xOUT1
H
L
xOUT2
L
H
7.4.2 Current Regulation
The motor driver employs fixed-frequency PWM current regulation (also called current chopping). When a
winding is activated, the current through it rises until it reaches a threshold, then the current is switched off until
the next PWM period.
The PWM frequency is fixed at 50 kHz, but may also be set to 100 kHz by factory option.
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 VREF pin.
The full-scale (100%) chopping current is calculated as follows:
5
(1)
Example:
If a 0.5-Ω sense resistor is used and the VREFx pin is 2.5 V, the full-scale (100%) chopping current is
2.5 V / (5 × 0.5 Ω) = 1 A.
Three serial interface register bits per H-bridge (xI2, 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. Table 2 shows the
function of the bits.
Table 2. Bit Functions
xI2
xI1
xI0
Relative Current
(% Full-Scale Chopping Current)
0
0
0
20
0
0
1
38
0
1
0
56
0
1
1
71
1
0
0
83
1
0
1
92
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