RT9501APF datasheet(6/9 Pages) RICHTEK

6 / 9 page

RT9501A/B

Preliminary

DS9501A/B-07 March 2007

www.richtek.com

Detection

First, the FB/CE pin must connect to VDD or a voltage

divider to enable the charge function. And then if a battery

is already inserted and the input power source is absent,

the RT9501 will enter sleep mode to prevent draining

power from battery. When input power source and battery

are both existed, another detection is the battery

temperature. The TS pin voltage must be in the allowed

range as shown in Figure 6 and the electrical

characteristics, and then the RT9501 will start the charge

cycle according to the battery voltage conditions.

Precharge Mode

When the battery voltage is lower than the precharge

threshold VO(MIN), the RT9501 begins to charge the battery

in precharge mode. In this condition, the precharge current

is set at approximately 10% of the constant regulation

current. The purposes of small precharge current are to

minimize the power dissipation on the external switch

during the precharge period and to revive deeply

discharged battery cells.

I(SNS)

O(REG)

Application Information

Charge Profile

Regulation voltage

Regulation current

Precharge threshold

voltage

Precharge

mode

Precharge current =

Charge termination current

Constant current

regulation mode

Constant voltage regulation

and charge termination mode

Recharge voltage

Recharge

mode

Figure 3. Typical charge profile

Constant Current Regulation Charge Mode

When the battery voltage is between the precharge

threshold VO(MIN) and the regulation voltage VO(REG), the

RT9501 starts the constant current regulation charge

mode. RT9501 monitors charge current with voltage drop

between two terminals of a sense-resistor, RCS, which

connects to pin VDD and CS. The following equation can

calculate the desired charging current.

Figure 4

FB/CE

BATT

STAT

VDD

GND

Battery

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