Standalone Linear Lithium Battery Charger

Page 7 of 11

3H20N Rev. P001

EC49017

Operation

The EC49017 is a single cell lithium-ion battery charger using a constant-current/constant-voltage algorithm. It can

deliver up to 800mA of charge current (using a good thermal PCB layout) with a final float voltage accuracy of ±1%.

The EC49017 includes an internal P-channel power MOSFET and thermal regulation circuitry. No blocking diode or

external current sense resistor is required; thus, the basic charger circuit requires only two external components.

Furthermore, the EC49017 is capable of operating from a USB power source.

Normal Charge Cycle

A charge cycle begins when the voltage at the VCC pin rises above the UVLO threshold level and a 1% program

resistor is connected from the PROG pin to ground or when a battery is connected to the charger output. If the BAT pin

is less than 2.8V, the charger enters trickle charge mode. In this mode, the EC49017 supplies approximately 1/10 the

programmed charge current to bring the battery voltage up to a safe level for full current charging.

When the BAT pin voltage rises above 2.8V, the charger enters constant-current mode, where the programmed charge

current is supplied to the battery. When the BAT pin approaches the final float voltage (4.22V), the EC49017 enters

constant-voltage mode and the charge current begins to decrease. When the charge current drops to 1/10 of the

programmed value, the charge cycle ends.

Programming Charge Current

The charge current is programmed using a single resistor from the PROG pin to ground. The battery charge current is

1060 times the current out of the PROG pin. The program resistor and the charge current are calculated using the

following equations:

PROG

CHG

CHG

PROG

R

V

I

I

V

R

1060

,

1060





,

The charge current out of the BAT pin can be determined at any time by monitoring the PROG pin voltage using the

following equation:

1060





PROG

PROG

BAT

R

V

I

This actual current will vary from IC to IC. The typical variation is within +/-20%.

Charge Termination

A charge cycle is terminated when the charge current falls to 1/10th the programmed value after the final float voltage

is reached. This condition is detected by using an internal, filtered comparator to monitor the PROG pin. When the

latched off and the EC49017 enters standby mode, where the input supply current drops to 200mA. (Note: C/10

termination is disabled in trickle charging and thermal limiting modes).When charging, transient loads on the BAT pin

can cause the PROG pin to fall below 100mV for short periods of time before the DC charge current has dropped to

this nature do not result in premature charge cycle termination. Once the average charge current drops below 1/10th

the programmed value, the EC49017 terminates the charge cycle and ceases to provide any current through the BAT

pin. In this state, all loads on the BAT pin must be supplied by the battery. The EC49017 constantly monitors the BAT