LTC3721-2 LINER [Linear Technology], LTC3721-2 Datasheet - Page 12

• Manufacturer Part Number: LTC3721-2
• Description: Synchronous Rectifier Driver for Forward Converters
• Manufacturer: LINER [Linear Technology]

applicaTions inForMaTion
LTC3900
the driver dissipation, the total gate charge Q
This parameter is found on the MOSFET manufacturers
data sheet.
The power dissipated in each LTC3900 MOSFET driver
is:
where f
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the LTC3900 for your layout:
1. Connect the 4.7µF bypass capacitor as close as possible
to the V
Typical applicaTions
12
P
0.22µF
DRIVER
0.1µF
SW
CC
115k
and GND pins.
2.2k
is the switching frequency of the converter.
= Q
59k
13.2k
27k
G
22k
• V
10k
33k
CC
370k
L1: PA0713, PULSE ENGINEERING
ALL CAPACITORS X7R, CERAMIC, TDK
7
3
9
5
6
1
2
• f
SD_V
R
BLANK
SS_MAXDC
V
COMP
FB = 1.23V
R
OSC
SW
= 2.5V
36V TO 72V
SEC
LT1952
+V
IN
36V to 72V, 3.3V at 40A Synchronous Forward Converter
DELAY
I
PGND
SENSE
SOUT
GND
OUT
V
47k
82k
OC
IN
14
15
8
13
12
11
10
16
V
B1
18V
BAT760
G
470
39k
BCX55
is used.
12V
V
B1
1nF
220pF
BAS516
Si7846
0.1µF
2.2µF
0.010R
2. Connect the two MOSFET drain terminals directly to
the transformer. The two MOSFET sources should be as
close together as possible.
3. Keep the timer, SYNC and V
from the high current path of Q3, Q4 and T1.
4. Place the timer capacitor, C
to the LTC3900.
5. Keep the PCB trace from the resistors R
R
Connect the other ends of the resistors directly to the drain
and source of the MOSFET, Q4.
PA0912.002
CS3
•
•
•
to the LTC3900 CS
V
1nF
Q4470-B
33nF
B1
C13
C14
1µF
1µF
• •
8V BIAS
BIAS
8V
Q2
PH3230
2x
5
6
4
8
560R
1
2
3
FG
GND
V
SYNC
V
GND
OC
CC
IN
LTC3900
LT4430
PH3230
R22
270
NEC
PS2701
TIMER
COMP
OPTO
CS
CS
Q3
2x
CG
FB
+
–
+
15k
/CS
3
1
2
7
6
5
4
BIAS
8V
–
1nF
TMR
pins as short as possible.
CC
L1
10k
10k
10k
regulator circuit away
, as close as possible
3.3k
R23
10pF
C16
6.8nF
C15
3900 TA01
C
100µF
3x
OUT
CS1
R24
27.4k
1%
R25
6.04k
1%
, R
V
3.3V, 40A
OUT
CS2
3900fb
and