LTC3722-2 Linear Technology, LTC3722-2 Datasheet - Page 25

• Manufacturer Part Number: LTC3722-2
• Description: Synchronous Dual Mode Phase Modulated Full Bridge Controllers
• Manufacturer: Linear Technology

OPERATIO
Current Doubler
The current doubler secondary employs two output induc-
tors that equally share the output load current. The trans-
former secondary is not center-tapped. This configuration
provides 2x higher output current capability compared to
similarly sized single output inductor modules, hence the
name. Each output inductor is twice the inductance value
as the equivalent single inductor configuration and the
transformer turns ratio is 1/2 that of a single inductor
secondary. The drive to the inductors is 180 degrees out
of phase which provides partial ripple current cancellation
in the output capacitor(s). Reduced capacitor ripple cur-
rent lowers output voltage ripple and enhances the
U
Figure 15. Ripple Current Cancellation vs Duty Cycle
OUTPUT RIPPLE
NORMALIZED
ATTENUATION
CURRENT
1
0
0
NOTE: INDUCTOR(S) DUTY CYCLE
IS LIMITED TO 50% WITH CURRENT
DOUBLER PHASE SHIFT CONTROL.
DUTY CYCLE
capacitors’s reliability. The amount of ripple cancellation
is related to duty cycle (see Figure 15). Although the
current doubler requires an additional inductor, the induc-
tor core volume is proportional to LI
is small. The transformer construction is simplified with-
out a center-tap winding and the turns ratio is reduced by
1/2 compared to a conventional full wave rectifier configu-
ration.
Synchronous rectification of the current doubler second-
ary requires two ground referenced N-channel MOSFETs.
The timing of the LTC3722-1/LTC3722-2 drive signals is
shown in the Timing Diagram.
0.25
LTC3722-1/LTC3722-2
0.5
1922 • F13
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2
, thus the size penalty
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372212i