Detailed Description

The MAX4978–MAX4981 family of devices is a combi-

nation of an overvoltage protector, overcurrent limiter,

and lithium-ion battery overcharge protector (MAX4980/

MAX4981). These devices feature a low 85mΩ (typ)

on a portable device. If the input voltage exceeds the

overvoltage threshold (OVLO) or falls below the under-

voltage threshold (UVLO), the FET is turned off to pre-

vent damage to the protected components. The internal

charge pump’s 160ms debounce time prevents false

turn-on of the internal FET during startup.

SDT is an

active-low open-drain output that asserts low during the

debounce time after a valid voltage is applied to the

input (MAX4978/MAX4979).

The MAX4978–MAX4981 feature an overcurrent limiter

as a second layer of protection for a lithium-ion battery

charger that limits current to a 900mA (MAX4978/

MAX4979/MAX4980) or 1950mA (MAX4981) threshold

for a 20ms blanking time. At the end of the blanking time,

if current is still at the threshold, the FET is turned off and

the device restarts the cycle after 160ms. The battery

voltage monitor measures the voltage of a lithium-ion

battery and disables the FET if the battery voltage

exceeds 4.4V (MAX4980/MAX4981).

Autoretry

timer begins counting. The timer resets if the overcur-

fault still exists, the cycle is repeated. If the fault has

been removed, the FET stays on.

Undervoltage Lockout (UVLO)

The MAX4978 has a 4.4V UVLO threshold, while the

MAX4979/MAX4980/MAX4981 have a 2.63V UVLO

threshold. When an undervoltage lockout condition

occurs with high load current, the voltage at the input to

the UVLO comparator may recover due to internal para-

sitic resistance causing the device to restart.

Overvoltage Lockout (OVLO)

The MAX4979 has a 6.8V OVLO threshold, while the

MAX4978/MAX4980/MAX4981 have a 5.7V OVLO

threshold.

Battery Overcharge Protector

(MAX4980/MAX4981)

The MAX4980/MAX4981 feature a battery overcharge

protection input (BAT) that triggers a voltage fault, turn-

Startup Debounce Time Indicator (SDT)

(MAX4978/MAX4979)

SDT is an open-drain output that asserts low during the

startup debounce time and during the autoretry time.

SDT returns to high impedance once the charge pump

turns on. This feature is useful for discharging the AC

adapter capacitance during the startup debounce time

(Figures 1, 2).

Thermal Shutdown Protection

The MAX4978–MAX4981 have a thermal-shutdown fea-

ture to protect the devices from overheating. The

device immediately turns off when the junction temper-

ature exceeds +160°C (typ). These devices exit thermal

shutdown after the junction temperature cools by 10°C

(typ).

EN Input

EN is an active-low enable input. Drive EN low for nor-

mal operation. Drive

EN high to disable the device.

Applications Information

IN Bypass Capacitor

For most applications, bypass IN to GND with a 1µF

ceramic capacitor as close to the device as possible to

enable ±15kV (HBM) ESD protection on IN. If the power

source has significant inductance due to long lead

length, take care to prevent overshoots due to the LC

tank circuit and provide protection if necessary to pre-

vent exceeding the 30V absolute maximum rating on IN.

BAT Bypass Capacitor

For most applications, bypass BAT to GND with a 1µF

ceramic capacitor as close to the device as possible to

enable ±15kV (HBM) ESD protection on BAT. If high

ESD protection is not necessary, no capacitor is

required on BAT.

ESD Test Conditions

ESD performance depends on a number of conditions.

The MAX4978–MAX4981 are specified for ±15kV

(HBM) typical ESD resistance on IN and BAT when IN

and BAT are bypassed to ground with a 1µF low ESR

ceramic capacitor. Contact Maxim for a reliability report

that documents test setup, methodology, and results.

Overvoltage Protector with

Active Current Limit

8

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