LT1170 View Datasheet(PDF) - Linear Technology
Part Name
Description
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LT1170 Datasheet PDF : 20 Pages
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LT1170/LT1171/LT1172
TYPICAL APPLICATIO S
Flyback Converter
VIN
20V TO 30V
+
C4*
100µF
VIN
VSW
LT1170
FB
GND
VC
R3
1.5k
C2
0.15µF
L2 OPTIONAL
5µH FILTER
C4
100µF
VIN
N* = 1/3 D1
VOUT
5V
0V
D3
25V
1 N*
1W
+ C1
6A
0V
D2
MUR110
2000µF
R1
3.74k
0
0
R2
1.24k
0
*REQUIRED IF INPUT LEADS ≥ 2"
0
VSNUB
CLAMP TURN-ON
SPIKE
a
b
VOUT + Vf
PRIMARY
FLYBACK
VOLTAGE
=
VOUT +
N
Vf
LT1170 SWITCH VOLTAGE
AREA “a” = AREA “b” TO MAINTAIN
ZERO DC VOLTS ACROSS PRIMARY
c
d
N • VIN SECONDARY VOLTAGE
AREA “c” = AREA “d” TO MAINTAIN
ZERO DC VOLTS ACROSS SECONDARY
∆I
IPRI
PRIMARY CURRENT
IPRI/N
SECONDARY CURRENT
IPRI
LT1170 SWITCH CURRENT
IPRI
t
=
(IPRI)(LL)
VSNUB
SNUBBER DIODE CURRENT
1170/1/2 TA03
LCD Contrast Supply
OPTIONAL
SHUTDOWN
5V*
VIN
E2
VSW
L1**
50µH
LT1172
R2
100k
E1
FB
GND
VC
VN2222
R3
15k
C4
0.047µF
VBAT*
3V TO 20V
D1
R1
1N914
200k
+ C1
1µF
TANTALUM
C3
0.0047µF
D2
D3
VOUT
–10V TO –26V
C2***
2µF
TANTALUM
D2, D3 = ER82.004 600mA SCHOTTKY. OTHER FAST SWITCHING TYPES MAY BE USED.
* VIN AND BATTERY MAY BE TIED TOGETHER. MAXIMUM VALUE FOR VBAT IS EQUAL TO THE NEGATIVE OUTPUT + 1V. WITH HIGHER
BATTERY VOLTAGES, HIGHEST EFFICIENCY IS OBTAINED BY RUNNING THE LT1172 VIN PIN FROM 5V. SHUTTING OFF THE 5V SUPPLY
WILL AUTOMATICALLY TURN OFF THE LT1172. EFFICIENCY IS ABOUT 80% AT IOUT = 25mA.
R1, R2, R3 ARE MADE LARGE TO MINIMIZE BATTERY DRAIN IN SHUTDOWN, WHICH IS APPROXIMATELY VBAT /(R1 + R2 + R3).
** FOR HIGH EFFICIENCY, L1 SHOULD BE MADE ON A FERRITE OR MOLYPERMALLOY CORE. PEAK INDUCTOR CURRENTS ARE ABOUT
600mA AT POUT = 0.7Ω. INDUCTOR SERIES RESISTANCE SHOULD BE LESS THAN 0.4Ω FOR HIGH EFFICIENCY.
*** OUTPUT RIPPLE IS ABOUT 200mVP-P TO 400mVP-P WITH C2 = 2µF TANTALUM. IF LOWER RIPPLE IS DESIRED, INCREASE C2, OR ADD
A 10Ω , 1µF TANTALUM OUTPUT FILTER.
1170/1/2 TA04
10
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