RT9501APF datasheet(8/9 Pages) RICHTEK

8 / 9 page

RT9501A/B

Preliminary

DS9501A/B-07 March 2007

www.richtek.com

Condition

STAT Pin

In battery charging cycle

High

Charge cycle completed

Low

Temperature fault or charge

function disable or sleep mode

High Impedance

Selecting an External PNP Pass-Transistor or

P-Channel MOSFET:

The RT9501 drives an external PNP transistor or

P-

Channel MOSFET to control the charging current. The

specifications must be concerned are the voltage and

current rating and package power dissipation. The external

switch is performed as a linear regulator. The maximum

power loss occurs when the constant current regulation

starts at the beginning, and it can be calculated

approximately from following equation:

I(SNS) is the constant regulation current.

The minimum voltage drop between the sense-resistor

is 100mV, and the minimum precharge threshold voltage

is 2.8V.

The external pass device with PCB heatsinking must be

rated for the maximum power dissipation.

D(MAX)

(SNS)

= I

- 0.1V - 2.8V)

Charge status indication

The RT9501 indicates the status of the charger on the 3-

state STAT pin. The following table shows the statuses of

this pin.

Selecting Input/Output Capacitor

In analog circuit applications, to place a high-frequency

decoupling capacitor nearby the controller IC between

input power source and ground is very important. A 0.1uF

ceramic is recommended. If a high ripple and noise input

power is chosen, it should have enough capacitance to

reduce the disturbance.

A 0.1uF to 1uF output capacitor is recommended to control

the output voltage and keep the output voltage ripple small

when the battery is disconnected.

FB1

O(REG)

FB2

V= 2.1 (1+

) V

Figure 8. For FB pin Function

BATT

STAT

VDD

GND

Battery

FB1

FB2

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