1

LT4250L/LT4250H

4250lhf

DRAIN

20V/DIV

5A/DIV

500

µs/DIV

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

Negative 48V

Hot Swap Controller

s

Allows Safe Board Insertion and Removal

from a Live – 48V Backplane

s

Circuit Breaker Immunity to Voltage Steps and

Current Spikes

s

Programmable Inrush and

Short-Circuit Current Limits

s

Pin Compatible with LT1640L/LT1640H

s

Operates from –20V to – 80V

s

Programmable Overvoltage Protection

s

Programmable Undervoltage Lockout

s

Power Good Control Output

s

Bell-Core Compatible ON/OFF Threshold

The LT

controllers that allow a board to be safely inserted and

removed from a live backplane. Inrush current is limited to

a programmable value by controlling the gate voltage of an

external N-channel pass transistor. The pass transistor is

turned off if the input voltage is less than the program-

mable undervoltage threshold or greater than the over-

voltage threshold. A programmable current limit protects

the system against shorts. After a 500

µs timeout the

current limit activates the electronic circuit breaker. The

PWRGD (LT4250L) or PWRGD (LT4250H) signal can be

used to directly enable a power module. The LT4250L is

designed for modules with a low enable input and the

LT4250H for modules with a high enable input.

The LT4250L/LT4250H are available in 8-pin PDIP and SO

packages.

s

Central Office Switching

s

– 48V Distributed Power Systems

s

Negative Power Supply Control

Hot Swap is a trademark of Linear Technology Corporation.

, LTC and LT are registered trademarks of Linear Technology Corporation.

Voltage Step On Input Supply

LT4250L

SENSE

C1

†

470nF

25V

C2

†

15nF

100V

C3

0.1

µF

100V

C4

100

µF

100V

Q1

IRF530

R2

10

Ω

5%

R3

†

1k, 5%

R4

†

549k

1%

R6

†

10k

1%

R1

†

0.02

Ω

5%

4

OV

–48V RTN

–48V RTN

(SHORT PIN)

3

2

OV =

71V

*

* DIODES INC. SMAT70A

SPECIFIC AND MUST BE SELECTED BASED

UPON OPERATING CONDITIONS AND DESIRED

PERFORMANCE. SEE APPLICATIONS

INFORMATION.

UV =

38.5V

UV

56

8

7

1

GATE

DRAIN

PWRGD

4250 TA01

+

TRIM

–

–

ON/OFF

LUCENT

JW050A1-E

+

2

9

5V

8

7

6

5

1

4

+

C5

100

µF

16V

+

–48V

INPUT 1

–48V

INPUT 2

UV

RELEASE

AT 43V

R5

†

6.49k

1%

0.1

µF

10V