xOUT1

xOUT2

3

1

2

3

Drive current

Slow decay (brake)

Fast decay (reverse)

VM

1

2

0.6

CC

FD

DECAY

V

t

R

C

In

V

æ

ö

·

=

·

·

ç

÷

è

ø

DRV8818

www.ti.com

SLVSAX9A

– SEPTEMBER 2011 – REVISED FEBRUARY 2012

Figure 2. Decay Mode

The DRV8818 also supports a mixed decay mode. Mixed decay mode begins as fast decay, but after a period of

time switches to slow decay mode for the remainder of the fixed off time.

Fast and mixed decay modes are only active if the current through the winding is decreasing; if the current is

increasing, then slow decay is always used.

when the current through the winding is decreasing. If the voltage is between these levels, mixed decay mode is

enabled.

In mixed decay mode, the voltage on the DECAY pin sets the point in the cycle that the change to slow decay

mode occurs. This time can be approximated by:

(4)

Mixed decay mode is only used while the current though the winding is decreasing; slow decay is used while the

current is increasing.

Operation of the blanking, fixed off time, and mixed decay mode is illustrated in Figure 3.

Copyright

© 2011–2012, Texas Instruments Incorporated

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