15

LT1763 Series

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-

tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

Figure 7. Reverse Output Current

OUTPUT VOLTAGE (V)

100

90

80

70

60

50

40

30

20

10

0

1763 F07

0123

4

5

67

8

9

10

CURRENT FLOWS

INTO OUTPUT PIN

LT1763

LT1763-5

LT1763-3.3

LT1763-1.5

LT1763-1.8

LT1763-2.5

LT1763-3

The ADJ pin of the adjustable device can be pulled above

or below ground by as much as 7V without damaging the

device. If the input is left open circuit or grounded, the ADJ

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.

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

from the 1.22V reference when the output is forced to 20V.

The top resistor of the resistor divider must be chosen to

limit the current into the ADJ pin to less than 5mA when the

ADJ pin is at 7V. The 13V difference between output and

ADJ pin divided by the 5mA maximum current into the ADJ

pin yields a minimum top resistor value of 2.6k.

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, pulled to some intermediate voltage or is left open

circuit. Current flow back into the output will follow the

curve shown in Figure 7.

.016 – .050

(0.406 – 1.270)

.010 – .020

(0.254 – 0.508)

× 45°

0

°– 8° TYP

.008 – .010

(0.203 – 0.254)

SO8 0303

.053 – .069

(1.346 – 1.752)

.014 – .019

(0.355 – 0.483)

TYP

.004 – .010

(0.101 – 0.254)

.050

(1.270)

BSC

1

2

3

4

.150 – .157

(3.810 – 3.988)

NOTE 3

8

7

6

5

.189 – .197

(4.801 – 5.004)

NOTE 3

.228 – .244

(5.791 – 6.197)

.245

MIN

.160

±.005

RECOMMENDED SOLDER PAD LAYOUT

.045

±.005

.050 BSC

.030

±.005

TYP

INCHES

(MILLIMETERS)

NOTE:

1. DIMENSIONS IN

2. DRAWING NOT TO SCALE

3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.

MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)

S8 Package

8-Lead Plastic Small Outline (Narrow .150 Inch)

(Reference LTC DWG # 05-08-1610)

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 2

µA. 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.