LT1172MJ8 Linear Technology, LT1172MJ8 Datasheet - Page 10

• Manufacturer Part Number: LT1172MJ8
• Description: SP-SWREG/Monolithic, 100kHz 5A 2.5A And 1.25A High Efficiency Switching Regulato
• Manufacturer: Linear Technology

LT1 170/LT1 171/LT1172
OPERATIO
With t
voltage shift is 3.8mV. This is not particularly bother-
some, but note that high offsets could result if R3 were
reduced to a much lower value. Also, the synchronizing
10
TYPICAL APPLICATIO S
100 F
C4*
20V TO 30V
+
S
GND
= 0.2 s, f
V
IN
V
IN
LT1170
Synchronizing with Bipolar Transistor
GND
*REQUIRED IF INPUT LEADS 2"
S
LT1170
V
U
= 150kHz, V
C
V
IN
R3
C1
V
C
2N2369
V
R3
1.5k
SW
FB
C2
0.15 F
C
= 1.5V, and R3 = 2k, offset
U
D2
MUR110
D3
25V
1W
R2
2.2k
39pF
C2
N* = 1/3
R1
3k
1
N*
FROM 5V
1170/1/2 OP01
LOGIC
D1
Flyback Converter
+
100 F
5 H
L2
C4
C1
2000 F
OPTIONAL
FILTER
transistor must sink higher currents with low values of R3,
so larger drives may have to be used. The transistor must
be capable of pulling the V
to ensure synchronizing.
R1
3.74k
R2
1.24k
V
5V
6A
OUT
GND
V
IN
LT1170
V
0V
0V
IN
0
0
0
0
Synchronizing with MOS Transistor
V
V
I
C
a
PRI
SNUB
c
R3
I
C1
t =
d
(I
b
PRI
V
* SILICONIX OR EQUIVALENT
VN2222*
SNUB
V
)(L
I
I
OUT
PRI
PRI
L
)
CLAMP TURN-ON
C
+ V
I
N • V
PRI
pin to within 200mV of ground
f
/N
SPIKE
IN
PRIMARY FLYBACK VOLTAGE =
LT1170 SWITCH VOLTAGE
AREA “a” = AREA “b” TO MAINTAIN
ZERO DC VOLTS ACROSS PRIMARY
SECONDARY VOLTAGE
AREA “c” = AREA “d” TO MAINTAIN
ZERO DC VOLTS ACROSS SECONDARY
PRIMARY CURRENT
SECONDARY CURRENT
LT1170 SWITCH CURRENT
SNUBBER DIODE CURRENT
R2
2.2k
1N4158
D1
D2
1N4158
100pF
C2
1170/1/2 TA03
FROM 5V
1170/1/2 OP02
LOGIC
V
OUT
117012ff
N
+ V f