LTC1698 Datasheet, PDF (1/24 Pages) Linear Technology – Isolated Secondary Synchronous Rectifier Controller

LTC1698
Isolated Secondary
Synchronous Rectifier Controller
FEATURES
s _{High Efficiency Over Wide Load Current Range}
s _{±0.8% Output Voltage Accuracy}
s _{Dual N-Channel MOSFET Synchronous Drivers}
s _{Pulse Transformer Synchronization}
s _{Optocoupler Feedback Driver}
s _{Programmable Current Limit Protection}
s _{±5% Margin Output Voltage Adjustment}
s _{Adjustable Overvoltage Fault Protection}
s _{Power Good Flag}
s _{Auxiliary 3.3V Logic Supply}
s _{Available in 16-Lead SSOP and SO Packages}
U
APPLICATIO S
s _{48V Input Isolated DC/DC Converters}
s _{Isolated Telecommunication Power Systems}
s _{Distributed Power Step-Down Converters}
s _{Industrial Control Systems}
s _{Automotive and Heavy Equipment}
DESCRIPTIO
The LTC^®1698 is a precision secondary-side forward
converter controller that synchronously drives external
N-channel MOSFETs. It is designed for use with the
LT^®3781 primary-side synchronous forward converter
controller to create a completely isolated power supply.
The LT3781 synchronizes the LTC1698 through a small
pulse transformer and the LTC1698 drives a feedback
optocoupler to close the feedback loop. Output accuracy
of ±0.8% and high efficiency over a wide range of load
currents are obtained.
The LTC1698 provides accurate secondary-side current
limit using an external current sense resistor. The input
voltage at the MARGIN pin provides ±5% output voltage
adjustment. A power good flag and overvoltage input are
provided to ensure proper power supply conditions. An
auxiliary 3.3V logic supply is included that supplies up to
10mA of output current.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
V_IN
36V to 72V
Q1
L1
V_DD BIAS ₊
+
C_OUT
R2
R1
V_OUT
D1
T1
Q2
D2
R_PRISEN
TG BG
C_SG
SG
T2
1
10
Q4
Q3
2
V_DD PWRGD ₈
R_C
R5
CG
V_FB
16
C_C
FG LTC1698
C_FB
12
I_SNS
6
V_COMP
R_SECSEN
C_SYNC
11
I_SNSGND
15
SYNC
13 ^RCILM
I_COMP
9
OVPIN
C_CILM
R_SYNC
R4
7
MARGIN
V_MARGIN
LT3781
REF
V_FB
V_C
R_F
C_F
R_E
ISOLATION
BOUNDARY
R_K
5
14
V_AUX
OPTODRV
V_AUX
3.3V
C_K
PGND GND
O.1µF ^10mA
3
4
1681 F01
PLEASE REFER TO FIGURE 12 IN THE TYPICAL APPLICATIONS
SECTION FOR THE COMPLETE 3.3V/15A APPLICATION SCHEMATIC
Figure 1. Simplified 2-Transistor Isolated Forward Converter
1698f
1