LT1172CQ Linear Technology, LT1172CQ Datasheet - Page 12

IC SWTCHNG REGULATOR HI-EFF 5-DD

LT1172CQ

Manufacturer Part Number
LT1172CQ
Description
IC SWTCHNG REGULATOR HI-EFF 5-DD
Manufacturer
Linear Technology
Type
Step-Down (Buck), Step-Up (Boost), Inverting, Cuk, Flyback, Forward Converterr
Datasheet

Specifications of LT1172CQ

Internal Switch(s)
Yes
Synchronous Rectifier
No
Number Of Outputs
1
Voltage - Output
1.25 ~ 40 V
Current - Output
1.25A
Frequency - Switching
100kHz
Voltage - Input
3 ~ 40 V
Operating Temperature
0°C ~ 100°C
Mounting Type
Surface Mount
Package / Case
D²Pak, TO-263 (5 leads + tab)
Power - Output
100W
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant

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LT1170/LT1171/LT1172
TYPICAL APPLICATIONS
12
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 10Ω, 1μF TANTALUM OUTPUT FILTER.
OPTIONAL
+
IN
Driving High Voltage FET
AND BATTERY MAY BE TIED TOGETHER. MAXIMUM VALUE FOR V
OUT
LT1170
= 0.7Ω. INDUCTOR SERIES RESISTANCE SHOULD BE LESS THAN 0.4Ω FOR HIGH EFFICIENCY.
GND
V
IN
VN2222
E2
E1
V
GND
SW
P-P
LT1172
V
5V*
IN
TO 400mV
(Note that maximum output currents are divided by 2 for LT1171, by 4 for LT1172.)
D1
G
V
1170/1/2 TA05
C
V
SW
P-P
FB
C4
0.047μF
WITH C2 = 2μF TANTALUM. IF LOWER RIPPLE IS DESIRED, INCREASE C2, OR ADD
D
Q1
LCD Contrast Supply
R3
15k
100k
R2
50μH
L1**
BAT
IS EQUAL TO THE | NEGATIVE OUTPUT | + 1V. WITH HIGHER
V
3V TO 20V
200k
BAT
R1
*
OUT
500Ω
= 25mA.
R2
R1
IN
D1
1N914
V
C3
0.0047μF
PIN FROM 5V. SHUTTING OFF THE 5V SUPPLY
X
2V
D1
External Current Limit
+
GND
D3
C1
1μF
TANTALUM
BAT
D2
LT1170
/(R1 + R2 + R3).
+
1170/1/2 TA06
V
C2***
2μF
TANTALUM
C
V
–10V TO –26V
OUT
1170/1/2 TA04
117012fg

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