LTC3901_15 Datasheet, PDF (11/16 Pages) Linear Technology – Secondary Side Synchronous Driver for Push-Pull and Full-Bridge Converters

APPLICATIO S I FOR ATIO
V_IN
MA
T3
MB
ISOLATION
BARRIER
MC
T4
T1
MD
LTC3901
L1
+
V_OUT
L2
C_OUT
A
B
C
D
LTC3722-1
FULL-BRIDGE CONTROLLER
COMP V_FB
E
F
ME
the
MF
6 _CSE+
3 _ME
5 _CSE–
16
V_CC
8,10
GND
LTC3901
11 _CSF+
14 _MF
1
PV_CC
12 _CSF–
4,13
PGND
9
SYNC
7
TIMER
T2
OUT
FB
OPTOCOUPLER
DRIVER
COMP
3901 F10
Figure 10. Simplified Isolated Full-Bridge Converter
MA
MB
MC
MD
E
F
SYNC
0V
ME
MF
3901 F11
Figure 11. Full-Bridge Converter Switching Waveforms
In the first period, MB turns off, E goes low (followed by
MA turning on), and the LTC3901 forces ME to turn off.
The primary side delivers power to the load through
MOSFET MF, T1 and L1.
In the second period, MA remains on, MD turns off, and
MC turns on. E goes high and the LTC3901 forces both ME
and MF to conduct. This is the free-wheeling period with
the T1 secondary output shorted.
In the third period, MA turns off, F goes low (followed by
MB turning on), and the LTC3901 forces MF to turn off.
The primary side delivers power to the load through
MOSFET ME, T1 and L2.
Like the second period, the last period is a free-wheeling
period. MB remains on, MC turns off, MD turns on, F goes
high, and the LTC3901 forces both ME and MF to conduct.
The timeout and current sense operations are the same as
in the push-pull application.
3901f
11