9
LT1431
TYPICAL APPLICATIO S
U
V
IN
0
0
V
OUT
1
2
3
4
6
1
234
LT1431 • TA14
56
5
5V Power Supply Monitor with ±500mV
Window and 50mV Hysteresis
Transfer Function
High Efficiency Buck Converter E = 85% to 89%
65
C2
4.7µF 35V
TANTALUM
V
SW
V
IN
V
C
GND
FB
LT1170
C3
0.1µF
D2
BAT85
D1
BAT85
C1
220µF
35V
R4
100Ω
R2
1k
R6*
23.7k
R7*
24.9k
Q1
VN2222LL
C5
0.047µF
5
4
2
13
C4
0.033µF
D4
BAT85
D3
MBR330
L1
50µH 3A
C6
470µF
16V
1
3
4
8
7
R8*
24.9k
V
IN
OFF
RTN
1
2
R3
10k
NOTES: UNLESS OTHERWISE SPECIFIED
1. ALL RESISTANCES ARE IN Ω, 0.25W, 5%
2. ALL CAPACITANCES ARE IN µF, 50V, 10%
3. SHUTDOWN LOGIC STATE MUST BE DEFINED BY A LOGIC GATE OR BY TYING TO GND
5V
2.5A
R1
470k
R5
680Ω
Q3
2N3904
+
0.12mΩ
ESR
RUN = 0
SHUTDOWN > 3V
1
BOLD LINE INDICATES HIGH CURRENT PATHS
* = 1% FILM RESISTORS
C1 = NICHICON-UPL1V221MPH
C6 = NICHICON-UPL1C471MPH6
D1, D2 = PHILIPS-BAT85
D3 = MOTORALA-MBR330
L1 = COILTRONICS CTX50-3-MP
C3, C4, C5 = WIMA-MKS-2
2
Q2
2N3904
R
TOP
V
+
COLL
REF
R
MID
COMP
VR2
LT1431CN8
+
GND-FGND-S
+
LT1431 • TA15
COLL
REF
GND-F
V
+
GND-S
10Ω**
“HIGH” FOR
OVER VOLTAGE OR
UNDER VOLTAGE
5k
1N4148
COLL
REF
GND-F
V
+
GND-S
10Ω**
5k
4k*1k6k*1k
*DETERMINES WINDOW SIZE
V = (R – 5)(0.5mA)
**SETS HYSTERESIS
LT1431 • TA13
LT1431 LT1431
