RT9526GE 데이터 시트보기 (PDF) - Richtek Technology

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RT9526GE

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

Richtek Technology 

RT9526

Power Good

This open-drain output pin is used to indicate the input

voltage status. The PGB output asserts low when

1. VIN > VPOR

2. VIN − VBATT > VOS

3. VIN < VOVP

It can be used to drive an LED or communicate to the

host processor. Note that ON indicates the open-drain

transistor is turned on and LED is bright.

CHG_SB Indication

The CHG_SB pin is an open-drain output capable to at

least 10mA current when the charger starts to charge and

turns off when the EOC current is reached. The CHG_SB

signal is interfaced either with a micro processor GPIO or

an LED for indication.

End-Of-Charge Current (EOC)

Connect a resistor between the IMIN pin and GND to set

the EOC current. The EOC current level, IIMIN, is

programmable via the external resistor, RIMIN, as shown

in the following equation :

IIMIN

=

4148

RIMIN

(mA)

Upon reaching the End-Of-Charge (EOC) current, the

charger indicates charge completion via the CHG_SB pin,

but the charger continues to output 4.2V voltage. Figure

1 shows the typical charge profile and the EOC/reset

event. The CHG_SB signal asserts low when the trickle

charge starts and changes to high at EOC. After EOC is

reached, the charge current has to rise above 75% of

ICHG_FAST before the CHG_SB signal is allowed to turn on

again. A current surge after EOC may occur due to a load

connected to the battery.

Temperature Regulation and Thermal Protection

In order to maximize charge rate, the RT9526 features a

junction temperature regulation loop. If the power

dissipation of the IC results in junction temperature greater

than the thermal regulation threshold (115°C), the RT9526

will cut back on the charge current and disconnect the

battery in order to maintain thermal regulation at around

115°C. This operation continues until the junction

temperature falls below thermal regulation threshold

(115°C) by the hysteresis level. This feature prevents the

maximum power dissipation from exceeding typical design

conditions.

Selecting the Input and Output Capacitors

In most applications, a 1μF high frequency decoupling

capacitor placed in close proximity to the input is sufficient.

However, depending on the power supply characteristics

and cable length, it may be necessary to add an additional

10μF ceramic capacitor to the input. For the RT9526, a

small output capacitor is required for loop stability. A 1μF

ceramic capacitor placed between the BATT pin and GND

is typically sufficient.

Thermal Considerations

For recommended operating condition specifications of

the RT9526, the maximum junction temperature is 125°C

and TA is the ambient temperature. The junction to ambient

thermal resistance, θJA, is layout dependent. For

SOT-23-6 packages, the thermal resistance, θJA, is

250°C/W on a standard JEDEC 51-3 single-layer thermal

test board. For WDFN-8L 2x2 packages, the thermal

resistance, θJA, is 165°C/W on a standard JEDEC 51-3

single-layer thermal test board. For WDFN-8L 2x3

packages, the thermal resistance, θJA, is 120°C/W on a

standard JEDEC 51-3 single-layer thermal test board. The

maximum power dissipation at TA = 25°C can be calculated

by the following formula :

PD(MAX) = (125°C − 25°C) / (250°C/W) = 0.400W for

SOT-23-6 package

PD(MAX) = (125°C − 25°C) / (165°C/W) = 0.606W for

WDFN-8L 2x2 package

PD(MAX) = (125°C − 25°C) / (120°C/W) = 0.833W for

WDFN-8L 2x3 package

The maximum power dissipation depends on the operating

ambient temperature for fixed TJ (MAX) and thermal

resistance, θJA. For the RT9526 packages, the derating

curves in Figure 2 allow the designer to see the effect of

rising ambient temperature on the maximum power

dissipation.

www.richtek.com

10

DS9526-01 April 2011

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