RT9503 datasheet(11/15 Pages) RICHTEK

11 / 15 page

RT9503

DS9503-03 April 2011

www.richtek.com

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, but ACIN input voltage over 18V still leads the

RT9503 to damage. 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 Voltage condition is removed (ACIN

< 6V), the comparator re-enables the output by running

through the soft-start.

Battery Temperature Monitoring

The RT9503 continuously monitors battery temperature

by measuring the voltage between the TS and GND pins.

The RT9503 has an internal current source to provide the

bias for the most common 10k

Ω negative-temperature

coefficient thermal resistor (NTC) (see Figure 4). The

RT9503 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 RT9503 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 5.)

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.

Figure 4. Temperature Sensing Configuration

0.1uF to 10uF

Battery

Temperature

Sense

ITS

VBATT

NTC

= I

Turn off when V

2.5V or V

0.5V

≥≤

Figure 5. Temperature Sensing Circuit

RT2

Battery

Temperature

Sense

ITS

VBATT

NTC

RT1

0.1uF to 10uF

NTC

R(R

+ R

)

= I

+ R

Turn off when V

2.5V or V

0.5V

≥≤

Fast-Charge Current Setting

Case 1: ACIN Mode

The RT9503 offers ISETA pin to determine the ACIN charge

rate from 100mA to 1.2A. The charge current can be

calculated as following equation.

SET

charge_ac

SET

SETA

= K

The parameter KSET = 300 ; VSET = 2.5V. RSETA is the

resistor connected between the ISETA and GND.

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