Document
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 VCC rating allows the part to be driven from the output voltage 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
VIN 36V TO
72V
10µF 15.4k
412k EN/UVLO
VIN
LT3748
RFB RREF
5.33:1
60Ω • 100pF •
147k
6.04k
10Ω 1µF 2.2k
30.9k 0.1µF
TC GATE
SS SENSE VC GND INTVCC
12.1k 15nF
4.7µF
12mΩ
400µF LT8309 VCC
DRAIN GATE INTVCC
GND 4.7µF
VOUT + 5V, 8A
6.2V
VOUT–
8309 TA01a
EFFICIENCY (%)
Efficiency vs Load Current
100
95 90 VIN = 48V WITH LT8309
85 80 VIN = 48V WITH PDS760 DIODE
75
70
65 012345678
LOAD CURRENT (A)
8309 TA01b
For more information www.linear.com/LT8309
8309fa
1
LT8309
Absolute Maximum Ratings
(Note 1)
VCC.............................................................................40V INTVCC GATE.............................................................10V DRAIN...................................................................... 150V Maximum Junction Temperature........................... 125°C Operating Temperature Range (Note 2)
LT8309E............................................. –40°C to 125°C LT8309I.............................................. –40°C to 125°C LT8309H............................................. –40°C to 150°C Storage Temperature Range................... –65°C to 150°C
Pin Configuration
TOP VIEW
GATE 1 GND 2 INTVCC 3
5 DRAIN 4 VCC
S5 PACKAGE 5-LEAD PLASTIC TSOT-23
θJA = 215°C/W
Order Information
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT8309ES5#PBF
LT8309ES5#TRPBF
LTGFZ
5-Lead Plastic TSOT-23
–40°C to 125°C
LT8309IS5#PBF
LT8309IS5#TRPBF
LTGFZ
5-Lead Plastic TSOT-23
–40°C to 125°C
LT8309HS5#PBF
LT8309HS5#TRPBF
LTGFZ
5-Lead Plastic TSOT-23
–40°C to 150°C
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: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
8309fa
2 For more information www.linear.com/LT8309
LT8309
E lectrical Characteristics The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
PARAMETER
CONDITIONS
MIN TYP MAX
Input Voltage Range
l 4.5
40
VCC Quiescent Current Comparator
Not Switching, INTVCC = 8V
300 345
Turn-On Threshold Turn-Off Threshold
RS = 0Ω RS = 0Ω
l –69 –57 –45
17 21 25
l 16
28
Drain Voltage Latch Reset Minimum Off-Time
RS = 0Ω
1.21 75 95 115
Minimum On-Time
310 360 410
Drain Current
Out of Pin
l 9.5
10 10.5
INTVCC Linear Regulator INTVCC Quiescent Current INTVCC Voltage Range INTVCC Regulation Voltage INTVCC UVLO Dropout (VCC to INTVCC) Current Limit
Not Switching, INTVCC = 8V IINTVCC = –10mA, VIN = 7V
4.5 l 6.8
1 l 30
100 117 10
7 7.2 4.03
1.3 1.6 42 55
Gate Driver
Turn-On Propagation Delay (tD(ON)) Turn-Off Propagation Delay (tD(OFF)) tr GATE Driver Output Rise Time tf GATE Driver Output Fall Time Pull-Up Resistance
RS = 0Ω, –100mVOD, VDS to VGATE RS = 0Ω, –100mVOD, VDS to VGATE CL = 3300pF CL = 3300pF
31 40 26 36 21 11 2.7
Pull-Down Resistance
0.8
UNITS V µA
mV mV mV
V ns ns µA
µA V V V V mA
ns ns ns ns Ω Ω
Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LT8309E is guaranteed to meet performance s.