MAX5963UTL+T【PDF 14/20 页】IC HOT SWAP DIO ORING CTL 40TQFN

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Sheet目录43

10页 11页 12页 13页 [14页]15页 16页 17页 18页

Dual, 7.5V to 76V, Hot-Swap and

Diode ORing Controller

14 ______________________________________________________________________________________

An external resistor connected to TCL and an internal

1/128 integrating counter determines the current-limit

timeout. If the current-limit threshold is exceeded for

more than roughly 100ns (comparator and logic

delays), the timer counts up. Note that multiple consec-

utive overcurrent occurrences may cause the current-

limit timer to trip (Figure 2).

During an output short-circuit event or a gross over-

load, the load current overshoots and causes V

SENSE_

to exceed the fast pulldown current-limit threshold volt-

age (V

THF

). The MAX5963 responds with much

stronger GATE_ pulldown currents (I

GDP_

and/or I

GDF_

)

to quickly bring the load current back down to the pro-

grammed current limit.

In extreme cases where V

SENSE_

is less than V

more than 700mV (typ), the MAX5963 immediately pulls

GATE1_ and GATE2_ low with a 1A (typ) peak pulldown

current to disconnect the load from the power supply.

Following an overcurrent event, the gates of the exter-

nal MOSFETs are held low (latched) if the device is in

latchoff mode. Toggle ON_ to restart the device under

these conditions. If RETRY is pulled high or connected

to BP or PS, the device pulls the gates high again fol-

lowing the automatic restart delay t

OFFCL

Current-Limit Threshold

The MAX5963 features adjustable current limits for

channel A and channel B. Set the current-limit threshold

voltage (V

CL_TH

) for both channels by connecting a

resistor, R

, from CL to PS. Calculate V

CL_TH

using

the following equation:

CL_TH

= I

CLSET

x R

where I

CLSET

is the 100礎 (typ) current-limit set current

shown in the Electrical Characteristics table.

Connect a sense resistor (R

SENSE_

) between PS and

SENSE_ to set the individual current limits for channel A

and channel B. Calculate the required sense resistor for

each channel using the following equation:

where I

CL_LIMIT

is the maximum channel current limit.

Current-Limit Timeout

The MAX5963 autoretry feature attempts to restart the

device following the adjustable current-limit timeout,

limiting the duty cycle of the MOSFETs under continu-

ous fault conditions. The autoretry timeout is equal to

128 times the current-limit timeout:

OFFCL

(ms) = 128 x t

(ms)

Set the current-limit timeout from 1ms to 30ms by con-

necting a resistor between TCL and ground. See Figure 3

for resistor values and associated timeouts. Connect TCL

to BP to select the 1ms (typ) default current-limit timeout.

Circuit Breaker

The MAX5963 features internal circuit-breaker circuitry

that functions as a current monitor. Once the output

current exceeds the circuit-breaker limit (I

CB_LIMIT

), the

circuit-breaker timer begins. When the circuit-breaker

timeout (t

) is reached, GATE_ is pulled low and a

fault condition is asserted (Figure 1).

An external resistor connected to TCB and an internal

1/1 integrating counter determines the circuit-breaker

timeout. If the circuit-breaker threshold is exceeded for

more than roughly 100ns (comparator and logic

delays), the timer counts up. Note that multiple consec-

utive circuit-breaker overcurrent occurrences may

cause the circuit-breaker timer to trip (Figure 4).

Following a circuit-breaker event, the gates of the exter-

nal MOSFETs are held low (latched) if the device is in

latchoff mode. If RETRY is pulled high or connected to

BP, the device pulls the gates high again following the

automatic restart delay t

OFFCB

SENSE_

CL_TH

CL_LIMIT

CURRENT-LIMIT

TRIPS

OUT_

SLOPE = -1/128

SLOPE = 1

TIMER

Figure 2: Current-Limit Timeout Following Consecutive

Overcurrent Events

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