UB2017

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

6 of 13

www.unisonic.com.tw

QW-R502-868.a

OPERATION

The UTC UB2017 is a single cell lithium-ion battery charger using a constant-current/constant-voltage algorithm. It

can deliver up to 500mA of charge current (using a good thermal PCB layout) with a final float voltage accuracy of

±1.2%. The UTC UB2017 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 UTC UB2017 is capable of operating from a USB power source.

1. Normal Charge Cycle

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 2.9V, the charger enters trickle charge mode. In this mode, the UTC UB2017 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 2.9V, 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 UTC UB2017 enters

constant-voltage mode and the charge current begins to decrease. The charge cycle ends when the charge current

drops to 1/10 of the programmed value.

2. 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:

CHG

PROG

I

V

R

1000

=

,

PROG

CHG

R

V

I

1000

=

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

the following equation:

1000

×

=

PROG

PROG

BAT

R

V

I

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

3. 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.

charge current is latched off and the UTC UB2017 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

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 UTC UB2017

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 UTC UB2017 constantly monitors the BAT pin voltage in standby

once again supplied to the battery. To manually restart a charge cycle in standby mode, the input voltage must be

removed and reapplied, or the charger must be shut down and restarted using the PROG pin.

4. Charge Status Indicator (CHRG)

The charge status output has three different states: strong pull-down (~10mA), weak pull-down (~20μA) and high

impedance. The strong pull-down state indicates that the UTC UB2017 is in a charge cycle. Once the charge cycle

meets the UVLO conditions and the UTC UB2017 is ready to charge. High impedance indicates that the UTC

UB2017