-48V Hot-Swap Controllers

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11

In the event of a short circuit at the output, the input

supply may dip below the UV threshold, resetting the

circuit breaker. The MAX5948 cycles ON and OFF until

the short is removed, which can be minimized by creat-

ing a deglitching delay at the UV pin with a capacitor

before the UV pin resets the circuit breaker.

Figure 10 shows a circuit that automatically resets the

circuit breaker after a current fault. Transistors Q2 and

Q3 along with C4, D1, R7, and R8 form a programma-

ble one-shot circuit. In normal operation, the GATE pin

is pulled high and Q3 is turned on, pulling node 2 to

GATE pin is pulled low and Q3 turns off. Node 2 starts

to charge C4 and Q2 turns on, pulling the UV pin low

and resetting the circuit breaker. The instant C4 is fully

charged, R8 turns off Q2, UV goes high and the GATE

starts to ramp up. Q3 turns back on and pulls node 2

Q1 from overheating.

Undervoltage and Overvoltage Protection

The UV and OV pins can be used to detect undervolt-

age and overvoltage conditions. The UV and OV pins

are internally connected to analog comparators with

20mV of hysteresis. When the UV voltage falls below its

threshold or the OV voltage rises above its threshold,

the GATE pin is immediately pulled low. The GATE pin

is held low until UV goes high and OV is low indicating

that the input supply voltage is within specification.

The UV pin is also used to reset the circuit breaker after

a fault condition has occurred. The UV pin can be

SENSE

GATE

DRAIN

OV

UV

PWRGD

MAX5948A

-48V RTN

-48V RTN

(SHORT PIN)

*

-48V

*DIODES INC. SMAT70A.

R4

562k

Ω

1%

R8

510k

Ω

5%

R5

19.1k

Ω

1%

R6

562k

Ω

1%

R7

1M

Ω

5%

R9

10k

Ω

1%

R1

0.02

Ω

5%

R3

18k

Ω

5%

R2

10

Ω

5%

C1

150nF

25V

C4

1

µF

100V

Q1

IRF530

D1

1N4148

Q2

2N2222

Q3

ZVN3310

C2

3.3nF

100V

C3

100

µF

100V

GATE

2V/div

NODE2

50V/div

1s/div

NODE 2

Figure 10. Automatic Restart After Current Fault