RT9502

10

DS9502-02 April 2011

www.richtek.com

Application Information

Automatically Power Source Selection

The RT9502 is a battery charger IC which is designed for

Li-ion Battery with 4.2V rated voltage.

The RT9502 can be adopted for two input power source,

ACIN or USB Input. It will automatically select the input

source and operate in different mode as below.

ACIN Mode : When the ACIN input voltage (ACIN) is higher

than the UVP voltage level (4.4V), the RT9502 will enter

ACIN Mode. In the ACIN Mode, ACIN P-MOSFET is turned

on and USB P-MOSFET is turned off.

USB Mode : When ACIN input voltage is lower than UVP

voltage level and USB input voltage is higher than UVP

voltage level (4.4V), the RT9502 will operate in the USB

Mode. In the USB Mode, ACIN P-MOSFET is turned off

and USB P-MOSFET is turned on.

Sleep Mode : The RT9502 will enter Sleep Mode when

both ACIN and USB input voltage are removed. This feature

provides low leakage current from the battery during the

absence of input supply.

Figure 1. Input Power Source Operation Mode.

ACIN Over Voltage Protection

The ACIN input voltage is monitored by an internal OVP

comparator. The comparator has an accurate reference of

2.5V from the band-gap reference. The OVP threshold is

set by the internal resistive. The protection threshold is

set to 6.5V. When the input voltage exceeds the threshold,

the comparator outputs a logic signal to turn off the power

P-MOSFET to prevent the high input voltage from damaging

the electronics in the handheld system. When the input

over oltage condition is removed (ACIN < 6V), the

comparator re-enables the output by running through the

soft-start.

Battery Temperature Monitoring

The RT9502 continuously monitors battery temperature

by measuring the voltage between the TS and GND pins.

The RT9502 has an internal current source to provide the

bias for the most common 10k

Ω negative-temperature

coefficient thermal resistor (NTC) (see Figure 2). The

RT9502 compares the voltage on the TS pin against the

internal VTS_HIGH and VTS_LOW thresholds to determine

if charging is allowed.

When the temperature outside the VTS_HIGH and

VTS_LOW thresholds is detected, the device will

immediately stop the charge. The RT9502 stops charge

and keep monitoring the battery temperature when the

temperature sense input voltage is back to the threshold

between VTS_HIGH and VTS_LOW, the charger will be

resumed. Charge is resumed when the temperature returns

to the normal range. However the user may modify

thresholds by the negative-temperature coefficient thermal

resistor or adding two external resistors. (see Figure 3.)

The capacitor should be placed close to TS(Pin 9) and

connected to the ground plane. The capacitance value

(0.1uF to 10uF) should be selected according to the quality

of PCB layout. It is recommended to use 10uF if the layout

is poor if prevent noise.

TS

TS

NTC

TS

TS

V

= I

R

Turn off when V

2.5V or V

0.5V

×

≥≤

Figure 2. Temperature Sensing Configuration

0.1uF to 10uF

Battery

A

TS

Temperature

Sense

NTC

ACIN Mode

USB Mode

Sleep Mode