RT9727A datasheet(7/9 Pages) RICHTEK

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RT9727A

DS9727A-01 April 2011

www.richtek.com

Applications Information

The RT9727A is a load switch with wide input voltage range

from 6V to 25V. It provides two paths for discharging the

residual voltage when system shutdown. Besides, the

external MOSFET switch On/Off can be controlled by an

internal current source from the CT pin to the gate of the

MOSFET switch. A novel control is implemented for nearly

constant power to discharge the system residual voltages.

Enable & POR

Power-On reset (POR) occurs when the input voltage rises

above to approximately 4.5V, the RT9727A will be turned

on once the EN pin voltage is higher than 2.4V. After the

RT9727A is turned on, there is 10

μA (typ.) current flows

from CT pin to the gate of the external MOSFET, while

both DCx pin discharge MOSFET are off.

Discharge Operation

When EN is low, the RT9727A will discharge the system

residual voltage using internal MOSFET connected

between the DCx and GND, while CT pin is pulled low.

The discharge current depends on the voltage at the DCx

pin. While both of the voltages at the DC1 and DC2 pins

are lower than 0.5V, the RT9727A will fully turn the internal

MOSFET on to pull the DCx pins low.

Thermal Protection

The RT9727A provides thermal shutdown detection to

protect the device from over-heating in discharge mode.

Once the junction temperature reaches 160

°C, the

RT9727A will stop discharging until the junction

temperature is recovered.

Thermal Considerations

For continuous operation, do not exceed absolute

maximum operation junction temperature. The maximum

power dissipation depends on the thermal resistance of

IC package, PCB layout, the rate of surroundings airflow

and temperature difference between junction to ambient.

The maximum power dissipation can be calculated by

following formula :

PD(MAX) = (TJ(MAX)

− TA) / θJA

Where TJ(MAX) is the maximum operation junction

temperature, TA is the ambient temperature and the

θJA is

the junction to ambient thermal resistance.

For recommended operating condition specification of

RT9727A, the maximum junction temperature is 125

°C

and TA is the maximum ambient temperature. The junction

to ambient thermal resistance

θJA is layout dependent.

For SC-70-6 packages, the thermal resistance

θJA is

333

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

test board. The maximum power dissipation at TA= 25

°C

can be calculated by following formula :

PD(MAX) = (125

°C − 25°C) / (333°C /W) = 0.3W for

SC-70-6 package

The maximum power dissipation depends on operating

ambient temperature for fixed TJ(MAX) and thermal

resistance

θJA . For RT9727A package, the Figure 1 of

derating curves allows the designer to see the effect of

rising ambient temperature on the maximum power

dissipation allowed.

Figure 1. Derating Curves for RT9727A Package

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

100

125

Ambient Temperature (°C)

Single Layer PCB

SC-70-6

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