RT9730 datasheet(7/9 Pages) RICHTEK

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RT9730

DS9730-01 April 2011

www.richtek.com

Application information

Operation State

The operation state is shown in the following Figure 1. At

power-off state, the RT9730 will check whether VIN is >

UVLO threshold. If VIN is higher than the UVLO threshold,

the RT9730 will check whether the junction temperature

is over the OTP threshold. If the junction temperature is

higher than the OTP threshold, the internal P-MOSFET

will be turned off. If the junction temperature is lower than

the OTP threshold, the RT9730 will check whether VIN is

higher than the OVP threshold or not, if VIN is higher than

the OVP threshold, the RT9730 will turn off the internal P-

MOSFET immediately within 1

μs.

If all of the checks including VIN > UVLO, TJ < OTP and

VIN < OVP are ok, the IC will operate normally.

Figure 1. Operation State Diagram for OVP Function

Input Over Voltage Protection (OVP)

The RT9730 monitors the input voltage to prevent

abnormally high input voltage from causing output system

failures. When the input voltage exceeds the threshold,

the RT9730 will turn off the power MOSFET within 1

μs to

prevent damage to the electronics in the handheld system.

The hysteresis for the input OVP threshold is 100mV.

When the input voltage returns to normal operation voltage

range, the RT9730 re-enables the MOSFET. The RT9730

can with stand an input voltage up to 30V without suffering

damage.

Battery Voltage Monitor

The RT9730 monitors the battery voltage by the OUT pin.

When the battery voltage exceeds the voltage level of (VIN

− 0.2V), the RT9730 will turn off the MOSFET and the

battery will not be charged. The RT9730 will recharge the

battery when the battery voltage is lower than the voltage

level of (VIN

− 0.2V).

Internal Over Temperature Protection (OTP)

The RT9730 monitors its own internal temperature to

prevent thermal failures. When the internal temperature

reaches 140

°C with a built-in hysteresis of 20°C, the IC

turns off the power MOSFET. The IC does not resume

operation until the internal temperature drops below 120

°C.

Input Under Voltage Protection (UVLO)

The RT9730 monitors input voltage to prevent abnormally

low input voltage from causing output system failures.

The RT9730 input under voltage protection threshold is

set to 2.7V. When the input voltage is under the threshold,

the RT9730 will turn off the power MOSFET within 1

μs.

When the input voltage returns to normal operation voltage

range, the RT9730 re-enables the MOSFET.

System Operation Description

Figure 2 shows the connection of RT9730 in a system

diagram. The OUT pin of the SOC will sense the voltage

of the 0.2

Ω sense resistor and the voltage of the VBAT

pin. Then, the GATDRV pin of the SOC can control the

MOSFET of the RT9730 accordingly to determine the level

of the charge current. The power of the SOC is provided

by the CHRIN pin of the RT9730. The RT9730 also provides

OVP function to the SOC. Once the input voltage at the

ACIN pin is higher than the OVP level, the RT9730 will

shutdown to prevent the SOC from damage. If the voltage

of the battery connected to the VBAT pin is full, the RT9730

stops charging by turning off the OUT pin. Input and output

capacitors of 1

μF are recommended to be placed as close

to the IC as possible.

Start

VIN > UVLO

TJ > OTP

VIN > OVP

Power-Off

Status

OTP Status

PFET=OFF

OVP Status

P-MOSFET = Off(Fast)

Normal Status

P-MOSFET = ON

and Control by

GATDRV

Figure 2. Application Diagram of RT9730 with SOC

RT9730

ACIN

GND

CHRIN

OUT

GATDRV

VIN

CIN

COUT

1µF

0.2

SOC

CHRIN

GATEDRV

OUT

VBAT

1µF

Battery

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