LT8309
Secondary-Side
Synchronous Rectifier Driver
Fea T Descrip T
n
Works with DCM and BCM/CrCM Conduction Mode The LT 8309 is a secondary-side synchronous rectifier
Flyback Topologies driver that replaces the output rectifier diode in a flyback
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V : 4.5V to 40V topology. By replacing the diode with a N-channel MOSFET,
CC
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Supports Up to 150V MOSFETs applications are no longer restricted by the heat constraints
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26ns Turn-Off Propagation Delay of the output diode. The IC replicates the behavior of a
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Accurate Minimum On and Off Timers for Reliable diode by sensing the drain-to-source voltage to determine
Operation when the current becomes negative. The LT8309's low
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Adjustable and Accurate Trip Point: +5mV to 30mV minimum on- and off-times help improve noise immunity.
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1 Gate Driver Pull-Down
The fast propagation delay of 26ns allows applications to
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SOT-23 5-Lead Package
operate in discontinuous conduction mode (DCM) and
critical conduction mode (CrCM). The gate driver features
a T
a 0.8 pull-down device for fast turn-offs. The 40V V
CC
rating allows the part to be driven from the output volt-
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High Output Current Flybacks
age or the rectified drain voltage of the MOSFET. A low
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High Efficiency Flybacks
quiescent current of 400A maximizes efficiency at low
output currents.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of
Linear Technology Corporation. All other trademarks are the property of their respective owners.
Typical a T
40W, 5V Isolated Telecom Supply Efficiency vs Load Current
5.33:1
100
+
V
IN V
OUT
36V TO
5V, 8A
10F 412k
60 400F
72V 95
V
EN/UVLO IN
V = 48V WITH LT8309
10 LT8309 IN
100pF
90
15.4k
V
CC
LT3748
147k
1F
R
FB
85
R
REF
6.2V
V = 48V WITH PDS760 DIODE
2.2k
IN
6.04k
80
DRAIN
INTV
CC
TC GATE GATE
75
GND
SS SENSE
70
30.9k V GND INTV
C CC
4.7F
12m
V
OUT
12.1k 65
0.1F
4.7F
0 1 2 3 4 5 6 7 8
8309 TA01a
15nF
LOAD CURRENT (A)
8309 TA01b
8309fa
1
For more information www.linear.com/LT8309
EFFICIENCY (%)
ion pplica
ions pplica
ion uresLT8309
a Te Maxi Mu M r a T p c F T
(Note 1)
V ............................................................................40V
TOP VIEW
CC
INTV GATE ............................................................10V
CC
GATE 1 5 DRAIN
DRAIN .....................................................................150V
GND 2
Maximum Junction Temperature .......................... 125C INTV 3 4 V
CC CC
Operating Temperature Range (Note 2)
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
LT8309E ............................................ 40C to 125C
= 215C/W
JA
LT8309I ............................................. 40C to 125C
LT8309H ............................................ 40C to 150C
Storage Temperature Range .................. 65C to 150C
o r D i n F Ma T
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LT8309ES5#PBF LT8309ES5#TRPBF LTGFZ 5-Lead Plastic TSOT-23 40C to 125C
LT8309IS5#PBF LT8309IS5#TRPBF LTGFZ 5-Lead Plastic TSOT-23 40C to 125C
LT8309HS5#PBF LT8309HS5#TRPBF LTGFZ 5-Lead Plastic TSOT-23 40C to 150C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to: