LTC3900
Synchronous Rectifier Driver
for Forward Converters
Fea T Descrip T
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N-Channel Synchronous Rectifier MOSFET Driver The LTC 3900 is a secondary-side synchronous recti-
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Programmable Timeout Protection fier driver designed to be used in isolated forward con-
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Reverse Inductor Current Protection verter power supplies. The chip drives N-channel rectifier
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Pulse Transformer Synchronization MOSFETs and accepts pulse sychronization from the
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Wide V Supply Range: 4.5V to 11V primary-side controller via a pulse transformer.
CC
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15ns Rise/Fall Times at V = 5V, C = 4700pF
CC L
The LTC3900 incorporates a full range of protection for the
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Undervoltage Lockout
external MOSFETs. A programmable timeout function is
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Small SO-8 Package
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
a T
resistance of the catch MOSFET, shutting off the MOSFET
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48V Input Isolated DC/DC Converters
if the inductor current reverses. The LTC3900 also shuts
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Isolated Telecom Power Supplies
off the drivers if the supply voltage is too low.
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High Voltage Distributed Power
L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks
Step-Down Converters
of Linear Technology Corporation. All other trademarks are the property of their respective
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Industrial Control System Power Supplies owners.
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Automotive and Heavy Equipment
Typical a T
ISOLATION
BARRIER
L0
V
OUT
V
IN
3.3V
36V TO 72V
+
D3
40A
C
OUT
Efficiency
T1
C R
Z Z 95
GATE
V = 3.3V
OUT
Q
REG
R
Q1 CS2
R
B 90
R
D
CS1 V = 36V
Z IN
OUT Q3
+
CS
V = 72V
IN
OC
85
CG
Q4
470 V = 48V
IN
V
I CC
SENSE
CS
80
R
TMR
R LTC3900
CS3
10m
LT1952
C
TIMER
VCC
FG 75
C
SG
C
TMR
S SYNC
OUT GND
70
GND COMP
SG T2 R
SYNC
270
65
0 5 10 15 20 25 30 35 40
LOAD CURRENT (A)
R1
OPTO
V
IN
3900 F10b
LT4430
COMP
GND
OCI
OC
FB
R2
3900 F01
Figure 1. Simplified Isolated Synchronous Forward Converter
3900fb
1
EFFICIENCY (%)
ion pplica
ions pplica
ion uresLTC3900
a Te Maxi Mu M r a T p in c F T
(Note 1)
Supply Voltage
TOP VIEW
V ........................................................................12V
CC
+
CS 1 8 SYNC
Input Voltage
CS 2 7 TIMER
CS , TIMER .............................. 0.3V to (V +0.3V)
CC
CG 3 6 GND
SYNC ...................................................... 12V to 12V
V 4 5 FG
CC
Input Current
+ S8 PACKAGE
CS ....................................................................15mA
8-LEAD PLASTIC SO
T = 150C, = 130C/W
JMAX JA
Operating Junction Temperature Range (Note 2)
LTC3900E ........................................... 40C to 125C
LTC3900I............................................ 40C to 125C
LTC3900H .......................................... 40C to 150C
LTC3900MP ....................................... 55C to 150C
Storage Temperature Range ................... 65C to 150C
Lead Temperature (Soldering, 10 sec) .................. 300C
Der in F Ma T
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC3900ES8#PBF LTC3900ES8#TRPBF 3900 8-Lead Plastic Small Outline 40C to 125C
LTC3900IS8#PBF LTC3900IS8#TRPBF 3900 8-Lead Plastic Small Outline 40C to 125C
LTC3900HS8#PBF LTC3900HS8#TRPBF 3900 8-Lead Plastic Small Outline 40C to 150C
LTC3900MPS8#PBF LTC3900MPS8#TRPBF 3900 8-Lead Plastic Small Outline 55C to 150C
LEAD BASED FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC3900ES8 LTC3900ES8#TR 3900 8-Lead Plastic Small Outline 40C to 125C
LTC3900IS8 LTC3900IS8#TR 3900 8-Lead Plastic Small Outline 40C to 125C
LTC3900HS8 LTC3900HS8#TR 3900 8-Lead Plastic Small Outline 40C to 150C
LTC3900MPS8 LTC3900MPS8#TR 3900 8-Lead Plastic Small Outline 55C to 150C
Consult LTC Marketing for parts speciefi d with wider operating temperature ranges. *The temperature grade is identiefi d by a label on the shipping container.
For more information on lead free part marking, go to: