RT9709 datasheet(8/12 Pages) RICHTEK

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RT9709

DS9709-02 April 2011

www.richtek.com

Applications Information

Power Up

The RT9709 has an input under voltage lockout (UVLO)

threshold of 2.6V with a built-in hysteresis of 100mV.

Before the input voltage reaches the UVLO threshold, the

RT9709 is off. When the input voltage is over the UVLO

threshold; the RT9709 will delay for 10ms and after the

10ms delay, the soft-start will be activated. The 10ms delay

allows any transients at the input during a hot insertion of

the power supply to settle down before the IC starts to

operate.

During the soft-start transition, the RT9709 slowly turns

on the internal MOSFET to reduce the inrush current.

Enable Control

The RT9709 offers an enable (EN) input. When the EN pin

is pulled to logic high (>1.5V), the RT9709 will be shut

down. When the EN pin is pulled to logic low (<0.4V), the

RT9709 will be powered on.The EN pin has an internal

pull-down resistor so that leaving the EN pin floating can

enable the IC.

Warning Indication Output

The WRN pin is an open-drain output that indicates a LOW

signal when any protection event occurs (Input OVP, Output

OCP, OTP and Battery OVP). When the protection events

are released and then the WRN pin indicates a HIGH signal.

The 4-bit binary counters for the battery OVP and the OCP

are reset to zero when the IC is re-enabled.

Over Temperature Protection (OTP)

The RT9709 monitors its own internal temperature to prevent

thermal failures. The chip turns off the MOSFET when the

internal temperature reaches 140

°C with a built-in

hysteresis of 50

°C. The IC will resume to normal operation

until the internal temperature falls to 90

°C.

Input Over Voltage Protection

The RT9709 monitors the input voltage to prevent the input

over voltage leading to output system failures. The input

OVP threshold is set to 6.8V for the RT9709. When the

input voltage exceeds the threshold, the RT9709 outputs

a logic signal to turn off the internal MOSFET within 1us

to prevent the device in the handheld system from

damaging. The hysteresis of the input OVP threshold is

100mV. When the input voltage is reduced to the normal

operation voltage range, the RT9709 will re-enable the

MOSFET.

Battery Over Voltage Protection

The RT9709 monitors the battery voltage by the VB pin.

When the battery voltage exceeds the 4.35V battery OVP

threshold, the RT9709 has a built-in 180us blanking time

to prevent any transient voltage from triggering the battery

OVP. If the OVP situation still exists after 180us, the

internal MOSFET will be turned off and the WRN pin

indicates a LOW signal. The battery OVP threshold has a

30mV built-in hysteresis. The control logic contains a 4-

bit binary counter. If the battery over voltage event occurs

for consecutive 16 times, the MOSFET will be turned off

permanently. The OVP latch status can be reset by the

EN pin.

Selecting RVB

The RT9709 monitors the battery voltage by the VB pin.

The RT9709 will be turned off when the battery voltage

exceeds the 4.4V battery OVP threshold. The VB pin is

connected to the battery pack positive terminal via an

isolation resistor (RVB) and the resistor is an important

component. The RVB determines some parameters such

as battery OVP threshold error and VB pin leakage current.

Generally, it is necessary to decrease the RVB for reducing

the battery OVP threshold error. However, this will increase

the VB pin leakage current. So, it is an important issue to

get a trade-off between the battery OVP threshold error

and the VB pin leakage current, the allowable resistance

of the RVB is 200k

Ω to 1MΩ.

Over Current Protection (OCP)

The RT9709 monitors the output current to prevent the

output short or the charging of the battery with an excessive

current. The OCP (Over Current Protection) threshold can

be set by the ILIM pin. The RT9709 has a built-in 170us

delay time to prevent any transient noise triggering from

the OCP. If the OCP situation still exists for 170us, the

internal MOSFET will be turned off and the WRN pin

indicates a LOW signal. When the OCP happens for

consecutive 16 times, the internal MOSFET will be turned

off permanently unless the input power is recycled or the

enable pin is toggled.

RT9709 Datasheet(PDF) 8 Page - Richtek Technology Corporation

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