LTC3900_1 Datasheet, PDF (17/20 Pages) Linear Technology – Synchronous Rectifier Driver for Forward Converters

typical applications
Synchronous Forward Converter With Pulse Skip Mode
LTC3900
V_IN
36V TO 72V
2.2µF
PZTA42
V_U1
82k
1.5mH
1_• 7
PDZ10B
BAS516
6
10
V_IN
2 _{• FG}
Si7430
1.5nF
5
T1
PA0369
PA1671
HA2165
CG
10nF
B0540W
2.2R
10k
100µF
* R_DCM
V_OUT
3.3V
30A
470µF
V_AUX
V_FB
22k
33k
BC857
115k
0.1µF
0.47µF
13.3k
LT1952-1
1 _COMP
2 _{FB = 1.23V}
3 _ROSC
4 _SYNC
S_OUT ¹⁶
V_IN ¹⁵
OUT ¹⁴
PGND ¹³
5 _MAXDC
DELAY ¹²
6 _{VR = 2.5V}
7 _SD
8 _GND
OC ¹¹
I_SENSE ¹⁰
BLANK ⁹
22.1k
158k
442k
S_OUT
133k
910Ω
82k
V_IN
0.015R
V_U1
1µF
V_FB
1.2k
B0540W
0.22µF
1k
BCX55
PDZ7.5B
PS2801-1
270R
BAS516
0.02µF
10k
10k
CG
3.3M
1 _CS+
2 _CS–
3
CG
4
V_CC
8
SYNC
7
TIMER
6
GND
5
FG
LTC3900
1µF
38.3k
470pF
FG 560R
220pF
S_OUT
•
PE-68386
LT4430
1
6
V_CC
2
OPTO
5 ^1.96k
GND COMP
3
OC
4
FB
1µF
18.2k
15nF
82.5k
47pF
V_OUT
3900 TA06a
*CONVERTERS THAT USE THE LTC3900 CAN BE FORCED TO OPERATE IN DISCONTINUOUS CURRENT MODE
AT LIGHT LOADS BY OFFSETTING THE CURRENT SENSE INPUT WITH R_DCM RESISTOR.
The Discontinuous Current Mode (DCM) Operation of Circuit is About 10% More Efficient
with 1A-2A Loads. The No Load Input Current is 15mA in DCM Versus 90mA in CCM.
95
85
75
65
V_IN = 48V
55
V_OUT = 3.3V
CONTINUOUS
45
CURRENT MODE
DISCONTINUOUS
CURRENT MODE
35
0
5 10 15 20 25 30
I_OUT (A)
3900 TA06b
3900fb
17