Detailed Description

The MAX4987AE/MAX4987BE are overvoltage protec-

tion devices with integrated ESD protection for USB

FET and protect low-voltage systems against voltage

faults up to +28V. If the input voltage exceeds the over-

voltage threshold, the internal nFET switch is turned off

to prevent damage to the protected components. The

30ms debounce time prevents false turn-on of the inter-

nal nFET switch during startup. An open-drain active-

low logic output is available to signal that a successful

power-up has occurred.

Device Operation

The MAX4987AE/MAX4987BE have an internal oscilla-

tor and charge pump that control the turn-on of the

internal nFET switch. The internal oscillator controls the

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

charge-pump startup, after a 30ms internal delay, turns

on the internal nFET switch and asserts ACOK (see

pump is disabled.

Internal nFET Switch

The MAX4987AE/MAX4987BE incorporate an internal

nFET switch with a 100m

Ω (typ) on-resistance. The

nFET switch is internally driven by a charge pump that

generates a voltage above the input voltage. The

MAX4987AE/MAX4987BE is equipped with a 1.5A (min)

current-limit protection that turns off the nFET switch

within 5µs (typ) during an overcurrent fault condition.

Autoretry

The MAX4987AE/MAX4987BE have an overcurrent

autoretry function that turns on the nFET switch again

after a 30ms (typ) retry time (see Figure 2). 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 30ms retry time result in a very low duty

cycle in order to keep power consumption low. If the

faulty load condition is not present, the switch remains on.

Undervoltage Lockout (UVLO)

The MAX4987AE has a 2.55V undervoltage-lockout

threshold (UVLO), while the MAX4987BE has a 4.15V

high impedance.

Overvoltage-Protection Controller

with USB ESD Protection

6

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UVLO

OVLO

IN

OUT

ACOK

Figure 1. MAX4987AE/MAX4987BE Timing Diagram