DRV8828_15 Datasheet, PDF (10/21 Pages) Texas Instruments – H-BRIDGE MOTOR CONTROLLER IC

DRV8828
SLVSA11F – OCTOBER 2009 – REVISED DECEMBER 2013
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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 DRV8828 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. The DECAY pin has both an internal pullup resistor of approximately 130 kΩ
and an internal pulldown resistor of approximately 80 kΩ. This sets the mixed decay mode if the pin is left open
or undriven.
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 the H-bridge, the voltage on the ISEN 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.
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