RT9502

11

DS9502-02 April 2011

www.richtek.com

Figure 3. Temperature Sensing Circuit

T2

T1

NTC

TS

TS

T1

T2

NTC

TS

TS

R(R

+ R

)

V

= I

R

+ R

+ R

Turn off when V

2.5V or V

0.5V

×

≥≤

Battery

A

TS

Temperature

Sense

NTC

0.1uF to 10uF

SET

charge_ac

SET

SETA

V

I

= K

R

Fast-Charge Current Setting

Case 1 : ACIN Mode

The RT9502 offers ISETA pin to determine the ACIN charge

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

calculated as following equation.

resistor connected between the ISETA and GND.

Figure 4. ACIN Mode Charge Current Setting

Case 2 : USB Mode

When charging from a USB port, the ISETU pin can be

used to determine the charge current of 100mA or 500mA.

A low-level signal of ISETU pin sets the charge current at

100mA and a high level signal sets the charge current at

500mA.

Pre- Charge Current Setting

During a charge cycle if the battery voltage is below the

VPRECH threshold, the RT9502 applies a pre-charge

mode to the battery. This feature revives deeply discharged

cells and protects battery life. The RT9502 internal

determines the pre-charge rate as 10% of the fast-charge

current.

Battery Voltage Regulation

The RT9502 monitors the battery voltage through the BATT

pin. Once the battery voltage level closes to the VREG

threshold, the RT9502 voltage enters constant phase and

the charging current begins to taper down. When battery

voltage is over the VREG threshold, the RT9502 will stop

charge and keep to monitor the battery voltage. However,

when the battery voltage decreases 100mV below the

Charge Status Outputs

The open-drain CHG_S and PGOOD outputs indicate

various charger operations as shown in the following table.

These status pins can be used to drive LEDs or

communicate to the host processor. Note that ON

indicates the open-drain transistor is turned on and LED

is bright.

Charge State

CHG_S

PGOOD

Charge

ON

ON

ACIN

Charge done

OFF

ON

Charge

ON

OFF

USB

Charge done

OFF

OFF

0

200

400

600

800

1000

1200

0.5

1.5

2.5

3.5

4.5

5.5

6.5

7.5

8.5

9.5

Ω)