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MAX4943ELAT

Overvoltage-Protection Controllers with Internal FET

Maxim Integrated 

Overvoltage-Protection Controllers with

Internal FET

IN

OUT

ACOK

tOFF

tON

80% VIN

tINDBC

10% VIN

tACOK

tINDBC

tACOK

OVLO

UVLO

tOFF

tINDBC

Figure 2. Timing Diagram

Device Operation

The MAX4943–MAX4946/MAX4949 have an internal

oscillator and charge pump that control the turn-on

of the internal switch. The internal oscillator controls

the timers that enable the turn-on of the charge pump

and controls the state of the open-drain ACOK

output. If VIN < VUVLO or if VIN >VOVLO, the internal

oscillator remains off, thus disabling the charge pump.

If VUVLO < VIN < VOVLO, the internal charge pump is

enabled. The charge-pump startup, after a 15ms (typ)

internal delay, turns on the internal switch (see Figure 2).

ACOK is held high during startup until the ACOK 30ms

(typ) blanking period expires. At this point, the device is

in its on state.

At any time, if VIN drops below VUVLO or rises above

VOVLO, ACOK is pulled high and the charge pump

is disabled.

Internal Switch

The MAX4943–MAX4946/MAX4949 incorporate an

internal nFET with a 80mΩ (typ) RON. The switch is

internally driven by a charge pump that generates a 5V

voltage above the input voltage. The internal switch is

equipped with 1.2A (min) current-limit protection that

turns off the switch within 10µs (typ) during an overcur-

rent fault condition.

Autoretry

The MAX4943–MAX4946 have an overcurrent autoretry

function that turns on the switch again after a 15ms (typ)

retry time (see Figure 3). If the faulty load condition is still

present after the blanking time, the switch turns off again

and the cycle is repeated. The fast turn-off time and

15ms retry time result in a very low duty cycle to keep

power consumption low. If the faulty load condition is not

present, the switch remains on.

Latch

The MAX4944B/MAX4945B/MAX4949 do not have the

autoretry function, and the switch latches off after an

overcurrent fault. The switch remains off until the over-

current fault has been removed. The switch turns back

on when the adapter voltage goes below VUVLO and

then returns to the valid operating range.

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