RT9503 datasheet(10/15 Pages) RICHTEK

10 / 15 page

RT9503

DS9503-03 April 2011

www.richtek.com

Application Information

The RT9503 is a fully integrated low cost single-cell Li-

Ion battery charger for portable applications. The RT9503

can be adopted for two input power source, AC USB Input.

It will automatically select the input source and operate

in different mode as below.

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

than the UVP voltage level (4.3V), the RT9503 will enter

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

and USB P-MOSFET is turned off. When ACIN voltage is

between the UVP and OVP threshold levels, the switch

Q1 will be turned on and Q2 will be turned off. So, the

system oad is powered directly from the adapter through

the transistor Q1, and the battery is charged by the

RT9503. Once the ACIN voltage is higher than the OVP or

is lower than the UVP threshold, the RT9503 stops

charging, and then Q1 will be turned off and Q2 will be

turned on to supply the system by battery.

USB Mode : When AC input voltage (ACIN) is lower than

UVP voltage level and USB input voltage is higher than

UVP voltage level (3.9V), the RT9503 will operate in the

USB Mode. In the USB Mode, ACIN P-MOSFET and Q1

are turned off and USB P-MOSFET and Q2 are turned on.

The system load is powered directly from the USB/Battery

through the switch Q2. Note that in this mode, the battery

will be discharged once the system current is higher than

the battery charge current.

Sleep Mode : The RT9503 will enter Sleep Mode when

both AC 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 Mode

USB Mode

VACIN < UVP

VUSB > UVP

Sleep Mode

VACIN < UVP

VUSB < UVP

VACIN > UVP

Power-Path Management

The RT9503 powers the system and independently

charging the battery while the input is AC. This features

reduces the charge time, allows for proper charge

termination, and allows the system to run with an absent

or defective battery pack.

Case 1 : Input is AC

In this case, the system load is powered directly from the

AC adapter through the transistor Q1. For RT9503, Q1

and Q2 act as a switch as long as the RT9503 is ready.

Once the AC voltage is ready (>UVP and <OVP), the

battery charge by RT9503 internal MOSFET and Q1 starts

regulating the output voltage supply system (Q2 is turn

off). Once the AC voltage over operation voltage (<UVP or

>OVP), the RT9503 stop charge battery, Q1 turns off and

Q2 starts supply power for system.

Figure 2. ACIN Input

RT9503

BATT

SYS

ACIN

USB

Battery

AC_ON

BAT_ON

USB

System

VIN

ICharger

ISYS

Case 2 : Input is USB

In this case, the system load is powered directly from the

battery through the switch Q2 (Q1 is turn off). Note in this

case, the system current over battery charge current will

lead to battery discharge.

Figure 3. USB Input

RT9503

BATT

SYS

ACIN

USB

Battery

AC_ON

BAT_ON

USB

System

VIN

ICharger

ISYS

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