Datasheet

xOUT1
xOUT2
3
1
2
3
Drive current
Slow decay (brake)
Fast decay (reverse)
VM
1
2
DRV8823
www.ti.com SLVS913D –JANUARY 2009–REVISED JANUARY 2010
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. This is shown in Figure 3 as case 1. The current flow direction shown indicates
positive current flow in the step table below.
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 3 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 3 as case 3.
Figure 3. 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) switches to slow decay mode for the remainder of the fixed
PWM period.
Slow or mixed decay mode is selected by the state of the xDECAY bits in the serial interface registers. If the
xDECAY bit is 0, slow decay is selected. If the xDECAY bit is 1, mixed decay is selected.
Copyright © 2009–2010, Texas Instruments Incorporated Submit Documentation Feedback 9
Product Folder Link(s): DRV8823