RT9505 datasheet(9/11 Pages) RICHTEK

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RT9505

DS9505-02 April 2011

www.richtek.com

Charge State

CHG_S

PGOOD

ACIN

Charge

Charge done

OFF

The parameter KSET = 300 ; VSET = 2.5V. RSETA is the

resistor connected between the ISETA and GND.

Figure 3. ACIN Mode Charge Current Setting

Pre- Charge Current Setting

During a charge cycle if the battery voltage is below the

VPRECH threshold, the RT9505 applies a pre-charge mode

to the battery. This feature revives deeply discharged cells

and protects battery life. The RT9505 internal determines

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

Battery Voltage Regulation

The RT9505 monitors the battery voltage through the BATT

pin. Once the battery voltage level closes to the VREG

threshold, the RT9505 voltage enters constant phase and

the charging current begins to taper down. When battery

voltage is over the VREG threshold, the RT9505 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 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.

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

RSETA (k)

RSETA (k

Ω)

Temperature Regulation and Thermal Protection

In order to maximize the charge rate, the RT9505 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

RT9505 throttles back on the charge current in order to

maintain a junction temperature around the thermal

regulation threshold (125

°C). The RT9505 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 chip from damage.

Selecting the Input and Output Capacitors

In most applications, the most important is the high-

frequency decoupling capacitor on the input of the RT9505.

A 1uF ceramic capacitor, placed in close proximity to input

pin and GND pin is recommended. In some applications

depending on the power supply characteristics and cable

length, it may be necessary to add an additional 10uF

ceramic capacitor to the input. The RT9505 requires a

small output capacitor for loop stability. A 1uF ceramic

capacitor placed between the BATT pin and GND is typically

sufficient.

Layout Consideration

The RT9505 is a fully integrated low cost single-cell Li-

Ion battery charger ideal for portable applications. Careful

PCB layout is necessary. For best performance, place all

peripheral components as close to the IC as possible. A

short connection is highly recommended. The following

guidelines should be strictly followed when designing a

PCB layout for the RT9505.

Input capacitor should be placed close to IC and

connected to ground plane. The trace of input in the

PCB should be placed far away the sensitive devices or

shielded by the ground.

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