LT1172MJ8 Linear Technology, LT1172MJ8 Datasheet - Page 11

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

TYPICAL APPLICATIO S
10V TO
20V
(for Off-Line Applications, See AN25)
***
**
*
+
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.
OPTIONAL
IN
Driving High Voltage FET
AND BATTERY MAY BE TIED TOGETHER. MAXIMUM VALUE FOR V
OUT
LT1170
GND
V
= 0.7 . INDUCTOR SERIES RESISTANCE SHOULD BE LESS THAN 0.4 FOR HIGH EFFICIENCY.
IN
VN2222
V
E2
E1
SW
U
GND
P-P
LT1172
V
5V*
(Note that maximum output currents are divided by 2 for LT1171, by 4 for LT1172.)
IN
TO 400mV
D1
G
1170/1/2 TA05
V
C
V
SW
P-P
FB
C4
0.047 F
D
Q1
WITH C2 = 2 F TANTALUM. IF LOWER RIPPLE IS DESIRED, INCREASE C2, OR ADD
LCD Contrast Supply
R3
15k
100k
R2
50 H
L1**
BAT
IS EQUAL TO THE NEGATIVE OUTPUT + 1V. WITH HIGHER
V
3V TO 20V
200k
BAT
R1
*
OUT
= 25mA.
500
IN
R2
R1
D1
1N914
C3
0.0047 F
PIN FROM 5V. SHUTTING OFF THE 5V SUPPLY
V
X
2V
D1
+
External Current Limit
LT1 170/LT1 171/LT1172
D3
GND
C1
1 F
TANTALUM
BAT
D2
/(R1 + R2 + R3).
LT1170
+
1170/1/2 TA06
C2***
2 F
TANTALUM
V
–10V TO –26V
V
OUT
C
1170/1/2 TA04
11
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