LT1763 Series
U
W U U
APPLICATIONS INFORMATION
The ADJ pin of the adjustable device can be pulled above
or below ground by as much as 7V without damaging the
device. Iftheinputisleftopencircuitorgrounded, theADJ
pin will act like an open circuit when pulled below ground
and like a large resistor (typically 100k) in series with a
diode when pulled above ground.
When the IN pin of the LT1763-X is forced below the OUT
pin or the OUT pin is pulled above the IN pin, input current
will typically drop to less than 2µA. This can happen if the
input of the device is connected to a discharged (low
voltage) battery and the output is held up by either a
backup battery or a second regulator circuit. The state of
the SHDN pin will have no effect on the reverse output
current when the output is pulled above the input.
In situations where the ADJ pin is connected to a resistor
divider that would pull the ADJ pin above its 7V clamp
voltage if the output is pulled high, the ADJ pin input
current must be limited to less than 5mA. For example, a
resistor divider is used to provide a regulated 1.5V output
fromthe1.22Vreferencewhentheoutputisforcedto20V.
The top resistor of the resistor divider must be chosen to
limitthecurrentintotheADJpintolessthan5mAwhenthe
ADJ pin is at 7V. The 13V difference between output and
ADJpindividedbythe5mAmaximumcurrentintotheADJ
pin yields a minimum top resistor value of 2.6k.
100
T = 25°C
IN
J
V
LT1763-1.5
= 0V
90
80
70
60
50
40
30
20
10
0
CURRENT FLOWS
INTO OUTPUT PIN
V
OUT
= V
ADJ
(LT1763)
LT1763
LT1763-1.8
LT1763-2.5
LT1763-3
LT1763-5
LT1763-3.3
In circuits where a backup battery is required, several
different input/output conditions can occur. The output
voltage may be held up while the input is either pulled to
ground, pulledtosomeintermediatevoltageorisleftopen
circuit. Current flow back into the output will follow the
curve shown in Figure 7.
4
0
1
2
3
5
6
7
8
9
10
OUTPUT VOLTAGE (V)
1763 F07
Figure 7. Reverse Output Current
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TYPICAL APPLICATION
S8 Package
8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
.189 – .197
(4.801 – 5.004)
NOTE 3
.045 ±.005
.160 ±.005
.050 BSC
7
5
8
6
.053 – .069
(1.346 – 1.752)
.004 – .010
(0.101 – 0.254)
.245
MIN
.150 – .157
(3.810 – 3.988)
NOTE 3
.228 – .244
(5.791 – 6.197)
.050
(1.270)
BSC
.014 – .019
(0.355 – 0.483)
TYP
.010 – .020
(0.254 – 0.508)
.030 ±.005
TYP
× 45°
1
2
3
4
RECOMMENDED SOLDER PAD LAYOUT
.008 – .010
(0.203 – 0.254)
0°– 8° TYP
NOTE:
INCHES
(MILLIMETERS)
1. DIMENSIONS IN
3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
.016 – .050
2. DRAWING NOT TO SCALE
(0.406 – 1.270)
SO8 0303
1763fa
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-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
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