RT9503 datasheet(12/15 Pages) RICHTEK

12 / 15 page

RT9503

DS9503-03 April 2011

www.richtek.com

200

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1000

1200

0.5

1.5

2.5

3.5

4.5

5.5

6.5

7.5

8.5

9.5

RSETA (k)

RSETA (k

Ω)

Figure 6. AC 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 RT9503 applies a pre-charge mode

to the battery. This feature revives deeply discharged cells

and protects battery life. The RT9503 internal determines

the pre-charge rate as 10% of the fast-charge current.

Battery Voltage Regulation

The RT9503 monitors the battery voltage through the BATT

pin. Once the battery voltage level closes to the VREG

threshold, the RT9503 voltage enters constant phase and

the charging current begins to taper down. When battery

voltage is over the VREG threshold, the RT9503 will stop

charge and keep to monitor the battery voltage. However,

when the battery voltage decreases 100mV below the

VREG, it will be recharged to keep the battery voltage.

Charge Status Outputs

The open-drain CHG_S and AC_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

bright.

Charge State

CHG_S

AC_PGOOD

Charge

ACIN

Charge Done

OFF

Charge

OFF

USB

Charge Done

OFF

Temperature Regulation and Thermal Protection

In order to maximize charge rate, the RT9503 features a

junction temperature regulation loop. If the power

dissipation of the IC results in a junction temperature

greater than the thermal regulation threshold (125

°C), the

RT9503 throttles back on the charge current in order to

maintain a junction temperature around the thermal

regulation threshold (125

°C). The RT9503 monitors the

junction temperature, TJ, of the die and disconnects the

battery from the input if TJ exceeds 125

°C. This operation

continues until junction temperature falls below thermal

regulation threshold (125

°C) by the hysteresis level. This

feature prevents the maximum power dissipation not

exceeded typical design conditions.

External Timer

As a safety mechanism the RT9503 has a user-

programmable timer that monitors the pre-charge and fast

charge time. This timer (charge safety timer) is started at

the beginning of the pre-charge and fast charge period.

The safety charge timeout value is set by the value of an

external capacitor connected to the TMR pin (CTMR), if pin

TMR is short to GND, the charge safety timer is disabled.

As CTMR = 0.1uF, TPRECH is ~2460 secs and TFAULT is 8 x

TPRECH. TPRECH = CTMR x 2460/0.1u

As timer fault, re-plug-in power or pull high and re-pull low

EN can release the fault condition.

As a safety mechanism, the RT9503 has a user-

programmable timer that monitors the pre-charge and fast

charge time. This timer(charge safe timer) is started at

the beginning of the pre-charge and fast-charge period.

The safety charge timeout value is set by an external

capacitor (CT) connected between TIMER pin and GND.

The timeout fault condition can be released by resetting

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