Datasheet

12
LT1185
1185ff
Time Delayed Start-Up
Low Input Voltage Monitor Tracks Dropout Characteristics
+
–
REF GND
FB
V
OUT
LT1185V
IN
R
LIM
***
D1
D2
R3**
15k
C3*
D3
†
C2
2.2µF
V
IN
R2
R1
2.37k
C1
2.2µF
TANT
+
–
V
OUT
LT1185 • TA06
ALL DIODES 1N4148
*SEE CHART FOR DELAY TIME VERSUS (C3)(R3//R
LIM
) PRODUCT
**FOR LONG DELAY TIMES, REPLACE D2 WITH 2N3906 TRANSISTOR AND USE R3 ONLY FOR
CALCULATING DELAY TIME. R3 CAN INCREASE TO 100k
***I
LIM
IS ≈11k/R
LIM
, INSTEAD OF 15k, BECAUSE OF VOLTAGE DROP IN D1. TEMPERATURE
COEFFICIENT OF I
LIM
WILL BE ≈0.11%/°C, SO ADEQUATE MARGIN MUST BE ALLOWED
FOR COLD OPERATION
†
D3 PROVIDES FAST RESET OF TIMING. INPUT MUST DROP TO A LOW VALUE TO RESET TIMING
Q1**
+
+
Delay Time
INPUT VOLTAGE (V)
0
TIME CONSTANTS (t)*
1.5
2.0
2.5
15
25
LT1185 • TA07
1.0
0.5
0
510 20
3.0
3.5
4.0
30
*t = (R3//R
LIM
)(C3) =
( )
R3 • R
LIM
R3 + R
LIM
(C3)
TYPICAL APPLICATIO S
U
R6**
1k
+
–
4k
R1
2.37k
R2
2.6k
R7
27k
C1
2.2µF
TANT
V
OUT
–
+
OPTIONAL HYSTERESIS
≈2M
LT1006
†
V
–
V
+
3
2
4
7
“LOW” FOR LOW INPUT
OUTPUT SWINGS FROM V
IN
+
TO V
IN
–
R3
360k
R4**
1k
R5*
0.01Ω
C2
2.2µF
TANT
REF GND
FB
V
OUT
LT1185V
IN
+
–
V
IN
*3" #26 WIRE
**R4 DETERMINES TRIP POINT AT I
OUT
= 0
R6 DETERMINES INCREASE OF TRIP POINT AS I
OUT
INCREASES
TRIP POINT FOR V
IN
= V
OUT
()
1 +
R4 • R7
R3 • R6
+ I
OUT
R5 • R7
R6
FOR VALUES SHOWN, TRIP POINT FOR V
IN
IS:
V
OUT
+ 0.37V AT I
OUT
= 0 AND V
OUT
= 1.18V AT I
OUT
= 3A
†
DO NOT SUBSTITUTE. OP AMP MUST HAVE COMMON MODE
RANGE EQUAL TO NEGATIVE SUPPLY
LT1185 • TA05
+
+