A4953ELJTR-T Allegro Microsystems Inc, A4953ELJTR-T Datasheet - Page 6

• Manufacturer Part Number: A4953ELJTR-T
• Description: IC PWM MOTOR DVR FULL 8-SOIC
• Manufacturer: Allegro Microsystems Inc

Specifications of A4953ELJTR-T

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

A4952 and
A4953
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
power dissipation. When a zero current level is detected, syn-
chronous rectification is turned off to prevent reversal of the load
current.
DS(on)
Mixed Decay Mode Operation
driver. This significantly lowers
V
PHASE
I
OUT
I
Trip
–
+
0
t
COD
0.50 × t
Full-Bridge DMOS PWM Motor Drivers
Fast Decay
Fixed Off-Time, t
off
Enlargement A
I
t
COD
OUT
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
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.
off
= 25 μs
Slow Decay
0.50 × t
See Enlargement A
off
t
COD
COD
. This feature is added to prevent shoot-
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
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