A4952_16 Datasheet, PDF (6/11 Pages) Allegro MicroSystems – Full-Bridge DMOS PWM Motor Drivers

A4952 and
A4953
Full-Bridge DMOS PWM Motor Drivers
Synchronous Rectification
When a PWM off-cycle is triggered by an internal fixed off-time
cycle, load current will recirculate. The A4952/A4953 synchro-
nous rectification feature turns-on the appropriate DMOSFETs
during the current decay, and effectively shorts out the body
diodes with the low R_DS(on) driver. This significantly lowers
power dissipation. When a zero current level is detected, syn-
chronous rectification is turned off to prevent reversal of the load
current.
Mixed Decay Operation
The bridges operate in Mixed Decay mode. Referring to the
lower panel of the figure below, as the trip point is reached, the
device goes into fast decay mode for 50% of the fixed off-time
period. After this fast decay portion the device switches to slow
decay mode for the remainder of the off-time. During transitions
from fast decay to slow decay, the drivers are forced off for the
Crossover Delay, t_COD . This feature is added to prevent shoot-
through in the bridge. During this “dead time” portion, synchro-
nous rectification is not active, and the device operates in fast
decay and slow decay only.
Mixed Decay Mode Operation
V_PHASE
+
I_{OUT 0}
–
See Enlargement A
Enlargement A
Fixed Off-Time, t_off = 25 µs
0.50 × t_off
0.50 × t_off
I_Trip
I_OUT
t_COD
Fast Decay
t_COD
Slow Decay
t_COD
Allegro MicroSystems, LLC
6
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com