LTC3722-1 LINER [Linear Technology], LTC3722-1 Datasheet - Page 26

• Manufacturer Part Number: LTC3722-1
• Description: Synchronous Dual Mode Phase Modulated Full Bridge Controllers
• Manufacturer: LINER [Linear Technology]

LTC3722-1/LTC3722-2
OPERATIO
Full-Bridge Gate Drive
The full-bridge converter requires high current MOSFET
gate driver circuitry for two ground referenced switches
and two high side referred switches. Providing drive to the
ground referenced switches is not too difficult as long as
the traces from the gate driver chip or buffer to the gate and
source leads are short and direct. Drive requirements are
further eased since all of the switches turn on with zero
VDS, eliminating the “Miller” effect. Low turn-off resis-
tance is critical, however, in order to prevent excessive
turn-off losses resulting from the same Miller effects that
were not an issue for turn on. The LTC3722-1/LTC3722-2
26
U
LTC3722
LTC3722
OUTA
OUTC
OUTE
OUTF
OR
0.1 F
Figure 17. High Side Gate Driver Circuitry
TRANSFORMER
Figure 16. Isolated Drive Circuitry
SIGNAL
1:2
0.1 F
2k
REGULATED
BIAS
BAT
54
does not require the propagation delays of the high and
low side drive circuits to be precisely matched as the
DirectSense ZVS circuitry will adapt accordingly. As a
result, LTC3722-1/LTC3722-2 can drive a simple NPN-
PNP buffer or a gate driver chip like the LTC1693-1 to
provide the low side gate drive. Providing drive to the high
side presents additional challenges since the MOSFET
gate must be driven above the input supply. A simple
circuit (Figure 17) using a single LTC1693-1, an inexpen-
sive signal transformer, and a few discrete components
provides both high side gate drives (A and C) reliably.
LTC1693-1
IN
GND
V
1/2
CC
OUT
IN1
GND1
GND2
IN2
LTC1693-1
OUT1
OUT2
2 F
CER
V
IN
POWER
MOSFET
BRIDGE
LEG
3722 F14
3722 F15
372212i