LT1952EGN-1#PBF Linear Technology, LT1952EGN-1#PBF Datasheet - Page 21

• Manufacturer Part Number: LT1952EGN-1#PBF
• Description: IC CTLR PWM SGL SWITCH 16-SSOP
• Manufacturer: Linear Technology

Specifications of LT1952EGN-1#PBF

• Pwm Type: Current Mode
• Number Of Outputs: 1
• Frequency - Max: 560kHz
• Duty Cycle: 90%
• Voltage - Supply: 6.82 V ~ 25 V
• Buck: No
• Boost: No
• Flyback: Yes
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: Yes
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 16-SSOP
• Frequency-max: 560kHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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 fi xed 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.
Effi ciency for the LT1952 based bus converter in Figure 16
0.47μF
0.1μF
115k
59k
13.2k
27k
10k
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
OSC
REF
36V TO 72V
SEC
LT1952
V
IN
DELAY
I
PGND
SENSE
SOUT
GND
OUT
V
47k
82k
OC
IN
14
15
8
13
12
11
10
16
V
U1
18V
BAT760
470Ω
39k
BCX55
12V
V
U1
2.2μF, 100V
1μF
PH21NQ15
220pF
BAS516
0.1μF
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.
9mΩ
2x
2x
PA0815.002
Figure 15. LT1952-Based Synchronous ‘Bus Converter’
Effi ciency vs Load Current (For Circuit in Figure 16)
•
•
T1
•
1nF
Q4470-B
1μF
96.0
95.5
95.0
94.5
94.0
93.5
93.0
• •
T2
BIAS
4
8V
Si7370
2x
6
560W
5
6
4
8
FG
GND
V
SYNC
8
CC
LT1952/LT1952-1
LOAD CURRENT (A)
LTC3900
10
PH4840
L1: PA1494.242 PULSE ENGINEERING
T1: PULSE ENGINEERING
T2: COILCRAFT
TIMER
CS
CS
12
2x
CG
+
–
15k
R
3
1
2
7
T
14
BIAS
8V
16
V
V
1nF
C
IN
OUT
2.4μH
T
= 48V
10k
18
= 12V
10k
10k
1952 F15
20
C
33μF, 16V
X5R, TDK
3x
1952 F16
V
12V, 20A
OUT
OUT
21
19521fd