LT1952EGN(RevD) データシートの表示（PDF） - Linear Technology
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LT1952EGN Datasheet PDF : 24 Pages
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LT1952/LT1952-1
APPLICATIONS INFORMATION
48V to Isolated 12V, 20A (No Opto-Coupler)
‘Bus Converter’
The wide programmable range and accuracy of the
LT1952/LT1952-1 Volt-Second clamp makes the LT1952/
LT1952-1 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/LT1952-1 use 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 converter in Figure 16
achieves a high 94% at 20A (Figure 15). The solution is
only slightly larger than 1/4 “brick” size and uses only
ceramic capacitors for high reliability.
96.0
95.5
95.0
94.5
94.0
93.5
VIN = 48V
VOUT = 12V
93.0
4 6 8 10 12 14 16 18 20
LOAD CURRENT (A)
1952 F15
Figure 15. LT1952-Based Synchronous ‘Bus Converter’
Efficiency vs Load Current (For Circuit in Figure 16)
0.47μF
0.1μF
VIN
36V TO 72V
VU1
47k
82k
18V
BCX55
12V
T1
PA0815.002
••
BAS516
0.1μF
Si7370
2x
PH4840
2x
2.4μH
10k
VOUT
12V, 20A
COUT
33μF, 16V
X5R, TDK
3x
370k
13.2k
115k
27k
7
SD_VSEC
3
ROSC
9
BLANK
5
SS_MAXDC
59k 10k
LT1952
6
VREF
1
COMP
2
FB
14
OUT
15
VIN
8
GND
13
PGND
12
DELAY
11
OC
10
ISENSE
16
SOUT
2.2μF, 100V
2x
•
PH21NQ15
2x
LTC3900
5 FG
CG 3
6 GND
CS+ 1
10k
VU1
BAT760
1μF
4 VCC
CS– 2
10k
8V 8 SYNC TIMER 7
1μF
39k
BIAS
RT
15k
CT
1nF
9mΩ
1nF
8V
470Ω
220pF
560W
BIAS
L1: PA1494.242 PULSE ENGINEERING
T1: PULSE ENGINEERING
T2
Q4470-B
T2: COILCRAFT
1952 F16
Figure 16. 36V to 72V Input to 12V at 20A No ‘Optocoupler’ Synchronous ‘Bus Converter’
19521fd
21
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