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
10
TYPICAL APPLICATIO S
100 F
C4*
20V TO 30V
+
V
IN
GND
***
**
*REQUIRED IF INPUT LEADS 2"
*
SHUTDOWN
D2, D3 = ER82.004 600mA SCHOTTKY. OTHER FAST SWITCHING TYPES MAY BE USED.
V
BATTERY VOLTAGES, HIGHEST EFFICIENCY IS OBTAINED BY RUNNING THE LT1172 V
WILL AUTOMATICALLY TURN OFF THE LT1172. EFFICIENCY IS ABOUT 80% AT I
R1, R2, R3 ARE MADE LARGE TO MINIMIZE BATTERY DRAIN IN SHUTDOWN, WHICH IS APPROXIMATELY V
FOR HIGH EFFICIENCY, L1 SHOULD BE MADE ON A FERRITE OR MOLYPERMALLOY CORE. PEAK INDUCTOR CURRENTS ARE ABOUT
600mA AT P
OUTPUT RIPPLE IS ABOUT 200mV
A 10 , 1 F TANTALUM OUTPUT FILTER.
LT1170
OPTIONAL
IN
V
IN
AND BATTERY MAY BE TIED TOGETHER. MAXIMUM VALUE FOR V
V
C
OUT
V
R3
1.5k
SW
FB
C2
0.15 F
= 0.7 . INDUCTOR SERIES RESISTANCE SHOULD BE LESS THAN 0.4 FOR HIGH EFFICIENCY.
VN2222
E2
E1
D2
MUR110
U
D3
25V
1W
GND
P-P
LT1172
N* = 1/3
V
5V*
IN
TO 400mV
1
N*
V
C
V
SW
P-P
FB
C4
0.047 F
D1
WITH C2 = 2 F TANTALUM. IF LOWER RIPPLE IS DESIRED, INCREASE C2, OR ADD
LCD Contrast Supply
+
100 F
Flyback Converter
5 H
L2
C4
C1
2000 F
R3
15k
100k
OPTIONAL
R2
50 H
L1**
FILTER
BAT
R1
3.74k
R2
1.24k
IS EQUAL TO THE NEGATIVE OUTPUT + 1V. WITH HIGHER
V
5V
6A
V
3V TO 20V
200k
OUT
BAT
R1
*
OUT
V
= 25mA.
0V
0V
IN
0
0
0
0
IN
D1
1N914
C3
0.0047 F
PIN FROM 5V. SHUTTING OFF THE 5V SUPPLY
V
I
a
PRI
SNUB
c
I
t =
+
d
(I
b
PRI
V
SNUB
V
)(L
I
I
OUT
PRI
PRI
D3
C1
1 F
TANTALUM
L
BAT
)
CLAMP TURN-ON
+ V
I
N • V
D2
PRI
/(R1 + R2 + R3).
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
+
C2***
2 F
TANTALUM
V
–10V TO –26V
OUT
1170/1/2 TA04
1170/1/2 TA03
V
OUT
N
+ V f