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LT1529CT-3.3

3A Low Dropout Regulators with Micropower Quiescent Current and Shutdown

Linear Technology 

LT1529

LT 1529-3.3/LT 1529-5

APPLICATI S I FOR ATIO

In some applications it may be necessary to leave the input

to the LT1529 unconnected when the output is held high.

This can happen when the LT1529 is powered from a

rectified AC source. If the AC source is removed, then the

input of the LT1529 is effectively left floating. The reverse

output current also follows the curve in Figure 3 if the VIN

pin is left open. The state of the SHDN pin will have no

effect on the reverse output current when the VIN pin is

floating.

When the input of the LT1529 is forced to a voltage below

its nominal output voltage and its output is held high, the

output current will follow the curve shown in Figure 3 . This

can happen if the input of the LT1529 is connected to a

discharged (low voltage) battery and the output is held up

by either a backup battery or by a second regulator circuit.

When the VIN pin is forced below the OUTPUT pin or the

OUTPUT pin is pulled above the VIN pin, the input current

will typically drop to less than 2µA (see Figure 4). The state

of the SHDN pin will have no effect on the reverse output

current when the output is pulled above the input.

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VOUT = 3.3V (LT1529-3.3)

VOUT = 5V (LT1529-5)

4

LT1529-3.3

3

LT1529-5

2

1

0

0

1

2

3

4

5

INPUT VOLTAGE (V)

LT1529 • F04

Figure 4. Input Current

U

PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted.

0.256

(6.502)

0.060

(1.524)

0.060

(1.524)

0.183

(4.648)

0.075

(1.905)

0.300

(7.620)

BOTTOM VIEW OF DD PAK

HATCHED AREA IS SOLDER PLATED

COPPER HEAT SINK

Q Package

5-Lead Plastic DD Pak

(LTC DWG # 05-08-1461)

0.060

(1.524)

TYP

0.330 – 0.370

(8.382 – 9.398)

0.143

+0.012

–0.020

( ) 3.632

+0.305

–0.508

0.390 – 0.415

(9.906 – 10.541)

15° TYP

0.165 – 0.180

(4.191 – 4.572)

0.059

(1.499)

TYP

0.057 – 0.077

(1.447 – 1.955)

0.028 – 0.038

(0.711 – 0.965)

0.013 – 0.023

(0.330 – 0.584)

0.045 – 0.055

(1.143 – 1.397)

0.004

+0.008

–0.004

( ) 0.102

+0.203

–0.102

0.095 – 0.115

(2.413 – 2.921)

0.050 ± 0.012

(1.270 ± 0.305)

Q(DD5) 0396

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 circuits as described herein will not infringe on existing patent rights.

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