LTC3900_1 Datasheet, PDF (1/20 Pages) Linear Technology – Synchronous Rectifier Driver for Forward Converters

LTC3900
Synchronous Rectifier Driver
for Forward Converters
Features
n _{N-Channel Synchronous Rectifier MOSFET Driver}
n _{Programmable Timeout Protection}
n _{Reverse Inductor Current Protection}
n _{Pulse Transformer Synchronization}
n _{Wide VCC Supply Range: 4.5V to 11V}
n _{15ns Rise/Fall Times at VCC = 5V, CL = 4700pF}
n _{Undervoltage Lockout}
n _{Small SO-8 Package}
Applications
n _{48V Input Isolated DC/DC Converters}
n _{Isolated Telecom Power Supplies}
n _{High Voltage Distributed Power}
Step-Down Converters
n _{Industrial Control System Power Supplies}
n _{Automotive and Heavy Equipment}
Description
The LTC^®3900 is a secondary-side synchronous recti-
fier driver designed to be used in isolated forward con-
verter power supplies. The chip drives N-channel rectifier
MOSFETs and accepts pulse sychronization from the
primary-side controller via a pulse transformer.
The LTC3900 incorporates a full range of protection for the
external MOSFETs. A programmable timeout function is
included that disables both drivers when the synchroniza-
tion signal is missing or incorrect. Additionally, the chip
senses the output inductor current through the drain-source
resistance of the catch MOSFET, shutting off the MOSFET
if the inductor current reverses. The LTC3900 also shuts
off the drivers if the supply voltage is too low.
L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
Typical Application
V_IN
36V TO 72V
ISOLATION
BARRIER
T1
GATE
Q1
OUT
Q3
OC
470Ω
I_SENSE
LT1952
10mΩ
C_SG
S_OUT
GND COMP _SG
T2
L0
D3
+
C_OUT
C_Z
R_CS2
R_CS1
CS⁺
Q4
R_CS3
CG
CS^–
V_CC
LTC3900
TIMER
FG
SYNC _GND
R_SYNC
270Ω
R_Z
R_B
D_Z
R_TMR
C_VCC
C_TMR
Q_REG
V_IN
OPTO
GND ^LT4430 COMP
OCI
OC
FB
Figure 1. Simplified Isolated Synchronous Forward Converter
V_OUT
3.3V
40A
R1
R2
3900 F01
Efficiency
95 _{VOUT = 3.3V}
90
V_IN = 36V
85
80
V_IN = 72V
V_IN = 48V
75
70
65
0 5 10 15 20 25 30 35 40
LOAD CURRENT (A)
3900 F10b
3900fb
1