LT8311_15 Datasheet, PDF (1/48 Pages) Linear Technology – Synchronous Rectifier Controller with Opto-Coupler Driver for Forward Converters

LT8311
FEATURES
Synchronous Rectifier
Controller with Opto-Coupler
Driver for Forward Converters
DESCRIPTION
n _{Wide Input Supply Range: 3.7V to 30V}
n _{Preactive Mode:}
n _{No Pulse Transformer Required}
n _{DCM Operation at Light Load}
n _{SYNC Mode:}
n _{FCM or DCM Operation at Light Load}
n _{Achieves Highest Efficiency}
n _{1.5% Feedback Voltage Reference}
n _{10mA Opto-Coupler Driver}
n _{Output Power Good Indicator}
n _{Integrated Soft-Start Function}
APPLICATIONS
n _{Offline and HV Car Battery Isolated Power Supplies}
n _{48V Isolated Power Supplies}
n _{Industrial, Automotive and Military Systems}
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.
The LT^®8311 is used on the secondary side of a forward
converter to provide synchronous MOSFET control and
output voltage feedback through an opto-coupler. The
LT8311’s unique preactive mode allows control of the
secondary-side MOSFETs without requiring a traditional
pulse transformer for primary- to secondary-side com-
munication. In preactive mode, the output inductor current
operates in discontinuous conduction mode (DCM) at
light load. If forced continuous mode (FCM) operation is
desired at light load, the LT8311 can, alternatively, be used
in SYNC mode, where a pulse transformer is required to
send synchronous control signals from the primary-side
IC to the LT8311.
The LT8311 offers a full featured opto-coupler controller,
incorporating a 1.5% reference, a transconductance error
amplifier and a 10mA opto-driver. Power good monitoring
and output soft-start/overshoot control are also included.
The LT8311 is available in a 16-lead FE package with pins
removed for high voltage spacing requirements.
TYPICAL APPLICATION
18V to 72V, 12V/8A Active Clamp Isolated Forward Converter
V_IN
18V to
72V
4.7µF
×3
100k
5.9k
UVLO_VSEC
V_IN
100nF
2.2µF
100V
4:4
••
100nF
6.8µH
2k
FSW
OVLO
AOUT
1.82k
LT3753
10k
2k
1.78k
FG
FB
CSW
LT8311
CSP
71.5k
49.9k
240kHz
IVSEC
RT
31.6k
SYNC
S_OUT
TAO
TAS
TOS
TBLNK
GND SS1
OUT
ISENSEP
OC
ISENSEN
INTV_CC
COMP
SS2 FB
34k
0.47µF
1µF
2k
100k
10pF
100k
6mΩ
4.7µF ^100Ω
1µF
1.78k
1.5k
15nF
2.94k
CG
V_IN
CSN
PGOOD
OPTO
COMP
INTV_CC
SYNC PMODE
SS TIMER GND
124k
1µF
1k
2.2nF
For more information www.linear.com/LT8311
20k
2.2nF
100k
68pF
22µF
×2
V_OUT
+ ^12V
470µF
11.3k
100k
V_OUT
4.7µF
2.2µF
8311 TA01
8311f
1