RT9907

18

DS9907-11 May 2014

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Copyright 2014 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

Protection

Current limit (CH2, CH3)

The current of high-side P-MOSFET is sensed cycle by

cycle to prevent over current. If the current is higher than

1.5A (typical), then the high-side P-MOSFET is off and

the low-side N-MOSFET is on. This state is latched and

then reset automatically at next clock cycle.

Under Voltage (CH2, CH3)

The status of under voltage is decided by comparing FB2

(or FB3) voltage with 0.4V. This function is enabled after

soft start finishes. If the FB2 (or FB3) voltage is less than

0.4V, then the high/low-side Power MOS are turned off

immediately. And this state is latched. After a dummy

count period, the CH2 (or CH3) begins a soft-start

procedure.

However, if the status of under voltage remains after 3

successive times of soft-start, then CH2 (or CH3) is

latched.

UV remain after 3

successive soft-start

How to reset?

CH2 CH2 is latched, and whole

IC is shut down

Toggle ENM

CH3 CH3 is latched

Toggle EN3 or ENM

Over Voltage Protection (CH2)

Over voltage protection (OVP) is used to protect the

external parts connected to the output of CH2. If the FB2

and low-side N-MOSFET is on. This status is latched and

could be reset by toggling ENM.

Reference

The chip has an internal 0.8V reference voltage, which is

the inputs of the error amplifiers of the CH1, CH2, and

CH3 to compare the difference of feedback voltage. The

reference voltage can be set up stably when the supplied

power (VDDM) is above 1.5V, and EN1 (or EN2, EN3)

goes high.

Thermal Protection

Thermal protection function is integrated in the chip. When

the chip temperature is higher than 180

°C, the controllers

of CH1, CH2, and CH3 are shutdown. 10 degree C is the

hysteresis range of temperature to prevent unstable

operation when the thermal protection happens. When

the thermal protection is relieved, the chip operates well

again.