lt3710 Linear Technology Corporation, lt3710 Datasheet - Page 11

• Manufacturer Part Number: lt3710
• Description: Secondary Side Synchronous Post Regulator
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
forward converter with synchronous rectification. The
primary side controller uses an LT3781, a current mode
2-transistor forward controller with built-in MOSFET driv-
ers. On the secondary side, an LTC1698 is used to provide
the voltage feedback for the 3.3V output, as well as the gate
drive for the synchronous MOSFETs. The error amplifier
output is fed into the optocoupler and then relayed to
LT3781 on the primary side to complete the 3.3V regula-
tion. The 1.8V output is generated by the LT3710 circuit.
A planar transformer PA0191 built by Pulse Engineering is
employed as the power transformer in this design. This
transformer is constructed on a PQ20 core with a nine turn
primary winding, two turn secondary winding and seven
turn auxiliary winding for the LT3781 bias supply. Because
V
SEC
CCS
1 F
Figure 3b. 36V to 72V DC to 3.3V/10A and 1.8V/10A Dual Output Isolated Power Supply (Part 2 of 2, See Previous Page)
180pF
10k
C37 680pF
0.01 F
10k
10pF
U
13
14
17
5
7
4
6
VA
SYNC
SS
V
CSET
PGND
ILCOMP
PGND
U
CC
OUT
10
0.033 F
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
LT3710
BOOST
330pF
1
3.3k
W
TGATE
BGATE
GBIAS
V
BGS
CL
CL
4.7 F
SW
FB
8
16V
+
–
16
2
3
15
9
11
12
0.01 F
U
CMDSH-3
CMDSH-3
10
0.1 F
16V
the maximum secondary voltage V
MOSFETs are chosen with the consideration that the
secondary voltage overshoot is typically 20% to 30% of
V
its low R
thermally enhanced PowerPak SO-8 package.
The switching frequency of the circuit is about 230kHz.
1500V input to output isolation is provided. Additional
features of this design include primary side on/off control,
overvoltage protection and undervoltage lockout. The
complete design will mount within a standard half brick PC
board with about half inch height.
Si7440DP
5% secondary side trimming on the 3.3V output, input
SP
Si7440DP
. In this particular design, Si7440DP is selected due to
SD(ON)
CEP125-IR8
SUMIDA
B340A
1.8 H
, 30V V
0.006
1%
DSS
rating and its compact and
3.01k
1%
2.32k
1%
3710 F03b
220
+
SP
4700pF
is about 16V, 30V
680 F
4V
POSCAP
LT3710
+
680 F
4V
POSCAP
11
V
1.8V/10A
OUT2
3710f