LT8309_15 Datasheet, PDF (1/14 Pages) Linear Technology – Secondary-Side Synchronous Rectifier Driver

LT8309
Secondary-Side
Synchronous Rectifier Driver
Features
n _{Works with DCM and BCM/CrCM Conduction Mode}
Flyback Topologies
n _{VCC: 4.5V to 40V}
n _{Supports Up to 150V MOSFETs}
n _{26ns Turn-Off Propagation Delay}
n _{Accurate Minimum On and Off Timers for Reliable}
Operation
n _{Adjustable and Accurate Trip Point: +5mV to –30mV}
n _{1Ω Gate Driver Pull-Down}
n _{SOT-23 5-Lead Package}
Applications
n _{High Output Current Flybacks}
n _{High Efficiency Flybacks}
Description
The LT^®8309 is a secondary-side synchronous rectifier
driver that replaces the output rectifier diode in a flyback
topology. By replacing the diode with a N-channel MOSFET,
applications are no longer restricted by the heat constraints
of the output diode. The IC replicates the behavior of a
diode by sensing the drain-to-source voltage to determine
when the current becomes negative. The LT8309's low
minimum on- and off-times help improve noise immunity.
The fast propagation delay of 26ns allows applications to
operate in discontinuous conduction mode (DCM) and
critical conduction mode (CrCM). The gate driver features
a 0.8Ω pull-down device for fast turn-offs. The 40V V_CC
rating allows the part to be driven from the output volt-
age or the rectified drain voltage of the MOSFET. A low
quiescent current of 400µA 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 Application
40W, 5V Isolated Telecom Supply
V_IN
36V TO
72V
10µF
15.4k
412k
EN/UVLO ^VIN
LT3748
R_FB
R_REF
5.33:1
•
60Ω
100pF •
10Ω
147k
1µF
6.04k
2.2k
30.9k
0.1µF
TC
GATE
SS
SENSE
V_C
GND INTV_CC
12.1k
15nF
4.7µF
12mΩ
400µF
LT8309
V_CC
DRAIN
INTV_CC
GATE
GND
4.7µF
V_OUT ⁺
5V, 8A
6.2V
V_OUT–
8309 TA01a
Efficiency vs Load Current
100
95
V_IN = 48V WITH LT8309
90
85
80
V_IN = 48V WITH PDS760 DIODE
75
70
65
012345678
LOAD CURRENT (A)
8309 TA01b
For more information www.linear.com/LT8309
8309fa
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