Datasheet

LTC3900
17
3900fb
Typical applicaTions
Synchronous Forward Converter With Pulse Skip Mode
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.
3900 TA06a
16
15
14
13
12
11
10
9
COMP
FB = 1.23V
R
OSC
SYNC
MAXDC
V
R
= 2.5V
SD
GND
S
OUT
V
IN
OUT
PGND
DELAY
OC
I
SENSE
BLANK
1
2
3
4
5
6
7
8
LT1952-1
Si7430
22k
S
OUT
133k
V
OUT
3.3V
30A
HA2165
V
OUT
13.3k
442k
22.1k
V
FB
V
U1
1µF
82k 1.2k
910Ω
158k
0.1µF
0.47µF
V
FB
BC857
33k
115k
V
IN
T1
PA0369
BAS516
100µF
PA1671
470µF
BAS516
270R
FG
PZTA42
PDZ10B
1.5mH
V
U1
1
6
7
10
2.2µF
V
IN
36V TO 72V
V
IN
1.5nF
0.015R
1µF
82k
2
5
•
•
•
CG
1k
PS2801-1 LT4430
1.96k
18.2k
82.5k
47pF
15nF
560R
PE-68386
S
OUT
BCX55
PDZ7.5B
FG
470pF
220pF
CG
0.22µF
B0540W
B0540W
1µF
10k
10nF
10k
38.3k
V
AUX
R_DCM
3.3M
2.2R
0.02µF
10k
LTC3900
CS
+
CS
–
CG
V
CC
SYNC
TIMER
GND
FG
1
2
3
4
8
7
6
5
•
•
V
CC
GND
OC
OPTO
COMP
FB
1
2
3
6
5
4
+
*
*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.
I
OUT
(A)
0
65
75
95
15 25
3900 TA06b
55
45
5 10
20 30
35
85
EFFICIENCY (%)
CONTINUOUS
CURRENT MODE
DISCONTINUOUS
CURRENT MODE
V
IN
= 48V
V
OUT
= 3.3V