Datasheet

11
LTC1844 Series
1844fa
In circuits where a backup battery is required, several
different input/output conditions can occur. The output
voltage may be held up externally while the input is either
pulled to ground, pulled to some intermediate voltage or
left open circuit. The LTC1844 features reverse current
protection to limit current draw from any supplementary
power source at the output. When V
IN
is pulled to ground
or is left open circuit, I
IN
and I
OUT
are less than 0.1µA for
V
OUT
= 0V to 7V.
When V
IN
is held constant and V
OUT
varied, current flow
will follow the curves shown in Figure 7. With V
OUT
held
below V
OUT(NOM)
, the LTC1844 will be in current limit
trying to pull V
OUT
up. With V
OUT
held between V
OUT(NOM)
and V
IN
, I
IN
will be at the normal quiescent current level
and I
OUT
will be 1µA to 2µA. As V
OUT
is pulled above V
IN
,
I
OUT
temporarily increases to 30µA until the reverse cur-
rent protection circuitry activates and reduces I
OUT
to less
than 10µA.
Alternatively, when V
OUT
is held constant and V
IN
varied,
current flow will follow Figure 8’s curves. I
OUT
will be less
than 10µA at all times except for a brief spike just below
2.7V before the reverse current protection circuitry
activates.
APPLICATIONS INFORMATION
WUU
U
Figure 7. Reverse Current vs Output Voltage
Figure 8. Reverse Current vs Input Voltage
OUTPUT VOLTAGE (V)
0
0
CURRENT (µA)
5
15
20
25
50
35
2
4
5
I
IN
1844 F07
10
40
45
30
1
3
6
7
LTC1844-2.8
T
J
= 25°C
V
IN
= 3.3V
CURRENT FLOWS
INTO PINS
I
OUT
IN CURRENT
LIMIT BELOW
2.8V
INPUT VOLTAGE (V)
0
CURRENT (µA)
0.5
1.0
1.5 2.0
1844 F08
2.5
100
90
80
70
60
50
40
30
20
10
0
3.0
I
OUT
I
IN
LTC1844-2.8
T
J
= 25°C
V
OUT
= 2.7V
CURRENT FLOW
INTO PINS
IN CURRENT
LIMIT ABOVE
2.7V
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.