MAX8903NETI+T datasheet(19/30 Pages) MAXIM

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MAX8903A–E/G/H/J/N/Y

2A 1-Cell Li+ DC-DC Chargers

for USB and Adapter Power

Maxim Integrated

When the charger is turned on, the charge current ramps

from 0A to the ISET current value in typically 1.0ms.

Charge current also soft-starts when transitioning to fast-

charge from prequal, when the input power source is

switched between USB and DC, and when changing the

USB charge current from 100mA to 500mA with the IUSB

logic input. There is no di/dt limiting, however, if RISET is

changed suddenly using a switch.

Battery Charger

While a valid input source is present, the battery charg-

er attempts to charge the battery with a fast-charge

current determined by the resistance from ISET to

GND. Calculate the RISET resistance according to the

following equation:

RISET = 1200V/ICHGMAX

Monitoring Charge Current

The voltage from ISET to GND is a representation of the

battery charge current and can be used to monitor the

current charging the battery. A voltage of 1.5V repre-

sents the maximum fast-charge current.

If necessary, the charge current is reduced automati-

cally to prevent the SYS voltage from dropping.

Therefore, a battery never charges at a rate beyond the

capabilities of a 100mA or 500mA USB input, or over-

loads an AC adapter. See Figure 5.

When VBAT is below VBATPQ, the charger enters pre-

qual mode and the battery charges at 10% of the maxi-

mum fast-charge rate until the voltage of the deeply

discharged battery recovers. When the battery voltage

reaches VBATREG and the charge current drops to 10%

of the maximum fast-charge current, the charger enters

the DONE state. The charger restarts a fast-charge

cycle if the battery voltage drops by 100mV.

Charge Termination

When the charge current falls to the termination thresh-

old (ITERM) and the charger is in voltage mode, charg-

ing is complete. Charging continues for a brief 15s

top-off period and then enters the DONE state where

charging stops.

Note that if charge current falls to ITERM as a result of

the input or thermal limiter, the charger does not enter

DONE. For the charger to enter DONE, charge current

must be less than ITERM, the charger must be in volt-

age mode, and the input or thermal limiter must not be

reducing charge current.

Charge Status Outputs

Charge Output (

CHG)

CHG is an open-drain, active-low output that indicates

charger status.

CHG is low when the battery charger is

in its prequalification and fast-charge states.

CHG goes

high impedance if the thermistor causes the charger to

go into temperature suspend mode.

When used in conjunction with a microprocessor (µP),

connect a pullup resistor between

CHG and the logic

I/O voltage to indicate charge status to the µP.

Alternatively,

CHG can sink up to 20mA for an LED

charge indicator.

Fault Output (

FLT)

FLT is an open-drain, active-low output that indicates

charger status.

FLT is low when the battery charger has

entered a fault state when the charge timer expires.

This can occur when the charger remains in its prequal

state for more than 33 minutes or if the charger remains

in fast-charge state for more than 660 minutes (see

Figure 6). To exit this fault state, toggle

CEN or remove

and reconnect the input source.

When used in conjunction with a microprocessor (µP),

connect a pullup resistor between

FLT and the logic I/O

voltage to indicate charge status to the µP.

Alternatively,

FLT can sink up to 20mA for an LED fault

indicator. If the

FLT output is not required, connect FLT

to ground or leave unconnected.

Charge Timer

A fault timer prevents the battery from charging indefi-

nitely. The fault prequal and fast-charge timers are con-

trolled by the capacitance at CT (CCT).

1.5

MONITORING THE BATTERY

CHARGE CURRENT WITH VISET

1200V/RISET

BATTERY CHARGING CURRENT (A)

DISCHARGING

VISET (V)

Figure 5. Monitoring the Battery Charge Current with the

Voltage from ISET to GND

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