DRV8823_16 Datasheet, PDF (14/32 Pages) Texas Instruments – 4-Bridge Serial Interface Motor Driver

DRV8823
SLVS913E – JANUARY 2009 – REVISED JANUARY 2016
www.ti.com
Table 2. Bit Functions (continued)
xI2
xI1
xI0
Relative Current
(% Full-Scale Chopping Current)
1
1
0
98
1
1
1
100
7.4.3 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 μs. Note that the blanking time also
sets the minimum on-time of the PWM.
7.4.4 Decay Mode
During PWM current chopping, the H-bridge is enabled to drive through the motor winding until the PWM current
chopping threshold is reached (see case 1 in Figure 12). The current flow direction shown indicates positive
current flow in Figure 12.
After the chopping current threshold is reached, the H-bridge can operate in two different states: fast decay or
slow decay.
In fast-decay mode, after the PWM chopping current level is reached, the H-bridge reverses state to allow
winding current to flow in a reverse direction. As the winding current approaches 0, the bridge is disabled to
prevent any reverse current flow. See case 2 in Figure 12 for fast-decay mode.
In slow-decay mode, winding current is recirculated by enabling both of the low-side FETs in the bridge (see
case 3 in Figure 12).
VM
1
xOUT1
3
2
xOUT2
1 Drive current
2 Fast decay (reverse)
3 Slow decay (brake)
Figure 12. Decay Mode
The DRV8823 supports slow decay and also a mixed-decay mode. Mixed-decay mode begins as fast decay, but
at a fixed period of time (75% of the PWM cycle) it switches to slow decay mode for the remainder of the fixed
PWM period.
14
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