DRV8823_15 Datasheet, PDF (8/21 Pages) Texas Instruments – 4-BRIDGE SERIAL INTERFACE MOTOR DRIVER

DRV8823
SLVS913D – JANUARY 2009 – REVISED JANUARY 2010
www.ti.com
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. The
following table shows the logic:
xPHASE
1
0
xOUT1
H
L
xOUT2
L
H
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. It may also be set to 100 kHz via 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. The function of the bits is
shown below:
Relative Current
xI2
xI1
xI0
(% 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
1
1
0
98
1
1
1
100
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 ms. Note that the blanking time also
sets the minimum on time of the PWM.
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