DRV8812_13 Datasheet, PDF (9/22 Pages) Texas Instruments – DUAL-BRIDGE MOTOR CONTROLLER IC

DRV8812
www.ti.com
SLVS997F – OCTOBER 2009 – REVISED AUGUST 2013
Decay Mode
During PWM current chopping, the H-bridge is enabled to drive current through the motor winding until the PWM
current chopping threshold is reached. This is shown in Figure 2 as case 1. The current flow direction shown
indicates the state when the xENBL pin is high.
Once the chopping current threshold is reached, the H-bridge can operate in two different states, fast decay or
slow decay.
In fast decay mode, once the PWM chopping current level has been reached, the H-bridge reverses state to
allow winding current to flow in a reverse direction. As the winding current approaches zero, the bridge is
disabled to prevent any reverse current flow. Fast decay mode is shown in Figure 2 as case 2.
In slow decay mode, winding current is re-circulated by enabling both of the low-side FETs in the bridge. This is
shown in Figure 2 as case 3.
Figure 2. Decay Mode
The DRV8812 supports fast decay, slow decay and a mixed decay mode. Slow, fast, or mixed decay mode is
selected by the state of the DECAY pin - logic low selects slow decay, open selects mixed decay operation, and
logic high sets fast decay mode. Note that the DECAY pin sets the decay mode for both H-bridges.
Mixed decay mode begins as fast decay, but at a fixed period of time (75% of the PWM cycle) switches to slow
decay mode for the remainder of the fixed PWM period.
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.
nRESET and nSLEEP Operation
The nRESET pin, when driven active low, resets the internal logic. It also disables the H-bridge drivers. All inputs
are ignored while nRESET is active.
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