MAX14544ETA+T【PDF 9/10 页】IC ACCY SWITCH OVP PROTECT 8TDFN

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Sheet目录42

5页 6页 7页 8页 [9页]10页

28V-Capable, I

LIM

BUS

Accessory Switch

fault-blanking timeout, FLAG asserts low. FLAG is not

asserted when load-transient fault is less than t

BLANK

The fault blanking time only applies to forward current-

limit faults.

A reverse current-limit fault, thermal fault, or OVP fault

causes FLAG to assert immediately and does not wait

for the blanking time.

Thermal Shutdown

The MAX14544/MAX14545 have a thermal-shutdown

feature to protect the devices from overheating. The

device turns off and FLAG goes low immediately (no

fault blanking) when the junction temperature exceeds

+150NC. The MAX14544/MAX14545 turns back on when

the device temperature drops approximately 15NC.

OVLO and UVLO

The MAX14544/MAX14545 feature an overvoltage pro-

tection. When IN goes above V

OVLO

(6.0V max), the

switch turns off and FLAG goes low immediately with

no fault-blanking time. When IN drops below V

UVLO

(1.8V min), the switch turns off but FLAG stays high. The

MAX14544/MAX14545 turns back on when IN is in the

operating range.

Applications Information

Input Capacitor

To limit the input-voltage drop during momentary output

short-circuit conditions, connect a capacitor from IN to

GND. A 10FF ceramic capacitor is adequate for most

applications; however, higher capacitor values further

reduce the voltage drop at the input and are recom-

mended for lower voltage applications.

Output Capacitor

Connect a 1FF ceramic capacitor from OUT to GND.

This capacitor helps prevent inductive parasitics from

pulling OUT negative during turn-off, thus preventing

the MAX14544/MAX14545 from tripping erroneously. If

the load capacitance is too large, then current may not

have enough time to charge the capacitance and the

device assumes that there is faulty load condition. The

maximum capacitive load value that can be driven from

OUT is obtained by the following formula:

?/DIV>

FWD_MIN BLANK_MIN

MAX

Layout and Thermal Dissipation

To optimize the switch response time to output short-

circuit conditions, it is very important to keep all traces

as short as possible to reduce the effect of undesirable

parasitic inductance. Place input and output capacitors

as close as possible to the device. IN and OUT must be

connected with short traces to the power bus.

During normal operation, the power dissipation is small

and the package temperature change is minimal. If the

output is continuously shorted to ground at the maximum

supply voltage, the operation of the switches with the

autoretry option does not cause problems because the

total power dissipated during the short is scaled by the

duty cycle:

IN_MAX OUT_MAX BLANK

MAX

RETRY

BLANK

51.6mW

?/DIV>

where V

IN_MAX

= 5.5V, I

OUT_MAX

= 600mA, t

BLANK

10.5ms, and t

RETRY

= 661.5ms.

Attention must be given to the MAX14545 where the

latchoff condition can be manually reset by toggling EN

from high to low. If the latchoff time duration is not suf-

ficiently high, it is possible for the device to reach the

thermal-shutdown threshold and never be able to turn

the device on until it cools down.

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