LTC4255

13

4255f

Power-Up into a Short-Circuit

When a channel powers-up with a shorted load, the

RELAY1 pin will pull low immediately and the GATE1 pin

will start to pull high (point B Figure 11) after a turn-on

will reach a constant value and the programmable current

programmed via bits B4 to B5. When the current limit

timer expires, the GATE1 and FAULT pins will pull low, the

current limit fault status bit (D0) will be set, and the retry

Figure 11. Power-Up Sequence with Shorted Load on Channel 1 with Autoretry Disabled

APPLICATIO S I FOR ATIO

4255 F11

BO

ACK

AO

ACK

STOP BIT

SCL

SDA

SHORT-CIRCUIT STATUS

(D0)

OPEN-CIRCUIT STATUS

(D4)

POWER_OK

(C0)

FAULT

RELAY1

GATE1

OUT1

AB

C

D

E

F

G

H

I

FET

TURNS ON

CL TIMER

EXPIRES CHANNEL

LATCHES OFF

FAULT CLEARED

STOP BIT

FET

CURRENT

If the autoretry enable bit (B1) is not set, the channel will

remain off until the fault is cleared by setting the fault clear

bit (B0) and the channel is turned back on by setting the

switch enable bit (A0) and the relay enable bit (A4)

(point F). If the fault clear bit (B0) is set before the retry

timer expires (point E) the channel turn-on will be delayed

until the timer expires to enforce the maximum retry duty

and sets the maximum ratio of the FET on-time to off-time

under a short-circuit condition.

DC

t

tt

R

CL

CL

R

=

+