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RT9526AGQW

Linear Single Cell Li-Ion Battery Charger with Input Over Voltage Protection

Richtek Technology 

RT9526A

Application Information

The RT9526A is a fully integrated low cost single cell Li-

ion battery charger operable in Constant Current (CC) mode

or Constant Voltage (CV) mode. The CC mode current is

set with the external resistor, RISET, and the CV mode

voltage is fixed at 4.2V. If the battery voltage is below a

typical 2.55V pre-charge threshold, the RT9526A charges

the battery with a trickle current until the battery voltage

rises above the pre-charge threshold. The RT9526A is

capable of being powered up from AC adapter and USB

(Universal Serial Bus) port inputs.

4.2V

ICHG_FAST

2.8V

16.7 %

ICHG_FAST

CHG_SB

Trickle

CC

CV

Charge

Voltage

Charge

Current

IIMIN

CHG

Indication

Figure 1. Typical Charge Profile

75 %

ICHG_FAST

Time

VIN Over Voltage Protection

The input voltage is monitored by the internal comparator.

The OVP threshold is set at 7V (typ.). When the input

voltage exceeds the threshold, the controller outputs a

logic signal to turn off the power P-MOSFET to prevent

high input voltage from damaging the electronics in the

handheld system. Nevertheless, an AC input voltage over

28V will still damage the RT9526A. When the input over

voltage condition is removed, the controller will enable

the output again by running through soft-start.

Charger Enable Input

ENB is an active-low logic input to enable the charger.

Drive the ENB pin low or leave it floating to enable the

charger. This pin has a 200kΩ internal pull down resistor.

So when left floating, the input is equivalent to logic-low.

Drive this pin high to disable the charger.

Battery Charge Profile

The RT9526A charges a Li-ion battery under Constant

Current (CC) mode or Constant Voltage (CV) mode. The

constant current of ISET is set via the external resistor,

RISET, and the constant voltage is fixed at 4.2V. If the battery

voltage is below a typical 2.55V pre-charge threshold, the

RT9526A charges the battery with a trickle current until

the battery voltage rises above the pre-charge threshold.

When the battery voltage reaches 4.2V, the charger enters

CV mode and regulates the battery voltage at 4.2V to

fully charge the battery without the risk of over charge.

a. Battery Pre-Charge Current

During a charge cycle, if the battery voltage is below the

pre-charge threshold, the RT9526A applies a pre-charge

mode to the battery. This feature revives deeply discharged

cells and protects battery life. The internally determined

pre-charge rate of the RT9526A is 16.7% of the constant

charge current.

b. Battery Fast-Charge Current (CC Mode)

The RT9526A offers ISET pin to determine the fast-charge

current via an external resistor, RISET, connected between

ISET and GND. The fast-charge current can be calculated

by the following equation :

ICHG_FAST

= KISET

x

VISET

RISET

(mA)

KSET = 9959; VSET = 1.22 (typ.)

Battery Charge Current vs. RISET

1400

1200

1000

800

600

400

200

0

10

19

28

37

46

55

RISET (k Ω)

Figure 2

DS9526A-01 April 2011

www.richtek.com

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