LT1952IGN Linear Technology, LT1952IGN Datasheet - Page 21

• Manufacturer Part Number: LT1952IGN
• Description: IC,SMPS CONTROLLER,CURRENT-MODE,SOP,16PIN,PLASTIC
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
48V to Isolated 12V, 20A (No Opto-Coupler)
‘Bus Converter’
The wide programmable range and accuracy of the LT1952
Volt-Second clamp makes the LT1952 an ideal choice for
‘Bus Converter’ applications where the Volt-Second clamp
provides line regulation for the converter output. The 48V
to 12V 20A ‘Bus Converter’ application in Figure16 shows
a semi-regulated isolated output without the need for an
optocoupler, optocoupler driver, reference or feedback
network. Some ‘Bus Converter’ solutions run with a fixed
50% duty cycle resulting in an output variation of 2-to-1
for applications with a 72V to 36V input range. The LT1952
uses an accurate wide programmable range Volt-Second
clamp to initially program and then control power supply
output voltage to typically ±10% for the same 36V to 72V
input range. Efficiency for the LT1952-based bus con-
verter in Figure 16 achieves a high 94% at 20A (Figure 15).
0.47µF
0.1µF
115k
59k
13.2k
27k
10k
U
370k
Figure 16. 36V to 72V Input to 12V at 20A No ‘Optocoupler’ Synchronous ‘Bus Converter’
7
3
9
5
6
1
2
SD_V
R
BLANK
SS_MAXDC
V
COMP
FB
REF
OSC
U
36V TO 72V
SEC
LT1952
V
IN
W
DELAY
I
PGND
SENSE
SOUT
GND
OUT
V
47k
82k
OC
IN
14
15
8
13
12
11
10
16
V
U1
18V
U
BAT760
470Ω
39k
BCX55
12V
V
U1
2.2µF, 100V
1µF
PH21NQ15
220pF
BAS516
0.1µF
The solution is only slightly larger than 1/4 “brick” size and
uses only ceramic capacitors for high reliability.
Figure 15. LT1952-Based Synchronous ‘Bus Converter’ Efficiency
9mΩ
2x
2x
PA0815.002
•
•
T1
•
96.0
95.5
95.0
94.5
94.0
93.5
93.0
vs Load Current (For Circuit in Figure 16)
1nF
Q4470-B
1µF
• •
4
T2
BIAS
12V Bus Converter Efficiency
8V
6
Si7370
2x
8
5
6
4
8
560Ω
LOAD CURRENT (A)
FG
GND
V
SYNC
10
CC
LTC3900
PH4840
L1: PA1494.242 PULSE ENGINEERING
T1: PULSE ENGINEERING
T2: COILCRAFT
12
TIMER
CS
CS
2x
CG
14
+
–
15k
R
3
1
2
7
T
BIAS
8V
16
V
V
IN
OUT
= 48V
1nF
18
C
= 12V
2.4µH
T
1952 F15
10k
10k
10k
20
LT1952
C
33µF, 16V
X5R, TDK
3x
1952 F16
V
12V, 20A
OUT
21
OUT
1952f