SE9017 Datasheet, PDF(6/11 Page) Seaward Electronics Inc. – Standalone Linear Lithium Battery Charger

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SE9017 Datasheet, PDF (6/11 Pages) Seaward Electronics Inc. – Standalone Linear Lithium Battery Charger

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Operation

The SE9017 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 Â±1%. The SE9017

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 SE9017 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 SE9017 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 (4.2V), the SE9017 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:

RPROG

= 1060V

ICHG

, ICHG

= 1060V

RPROG

The charge current out of the BAT pin can be

determined at any time by monitoring the PROG pin

voltage using the following equation:

I BAT

VPROG

RPROG

â¢ 1060

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 PROG pin voltage falls below

100mV for longer than tTERM (typically 1ms), charging

is terminated. The charge current is latched off and

the SE9017 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 1/10th the programmed value. The 1ms

filter time (tTERM) on the termination comparator

ensures that transient loads of this nature do not

result in premature charge cycle termination. Once

the average charge current drops below 1/10th the

programmed value, the SE9017 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 SE9017 constantly monitors the BAT pin voltage

Revision 4/16/2009

Preliminary and all contents are subject to change without prior notice

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