LT3464

10

3464f

APPLICATIO S I FOR ATIO

Output Disconnect Considerations

The LT3464 is equipped with an output disconnect that

isolates the load from the input during shutdown. See the

Operation section for a functional diagram. The output

disconnect uses a pass PNP coupled with circuitry that

varies the base current such that the transistor is consis-

tently at the edge of saturation, thus yielding the best

To remain stable, this circuit requires a bypass capacitor

connected between the OUT pin and the CAP pin or

between the OUT pin and ground. A ceramic capacitor with

a value of at least 0.1

µF is a good choice.

when using the CAP pin as the feedback node by setting

the output voltage according to the following formula:

RR

VV

V

OUT

DROP

REF

21

1

=

+









–

In addition, the disconnect circuit has a built in current

limit of 25mA (minimum) to protect the chip during short-

circuit. This feature allows the LT3464 to tolerate an

Figure 4. Feedback Connection Using the CAP Pin and the OUT Pin

CTRL

SHDN

SW

GND

OUT

CAP

FB

LT3464

R2

R1

1

8

7

6

3

5

2

4

CTRL

SHDN

SW

GND

OUT

CAP

FB

LT3464

R2

R1

1

8

7

6

3

5

2

4

3464 F01

indefinite short, but care must be taken to avoid exceeding

the maximum junction temperature.

Inrush Current

while the output capacitor is discharged, an inrush current

will flow through the inductor and integrated Schottky

diode into the output capacitor. Conditions that increase

inrush current include a larger more abrupt voltage step at

inductor with a low saturation current.

While the internal diode is designed to handle such events,

the inrush current should not be allowed to exceed 1 amp.

For circuits that use output capacitor values within the

recommended range and have input voltages of less than

5V, inrush current remains low, posing no hazard to

(more than 5V) and/or a large capacitor is used at the CAP

pin, inrush current should be measured to ensure safe

operation.

COLLECTOR CURRENT (mA)

0

300

250

200

150

100

50

0

510

15

20

3464 F02

30

25