RT2702 datasheet(4/20 Pages) RICHTEK

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RT2702

www.richtek.com

DS2702-00 October 2016

is a registered trademark of Richtek Technology Corporation.

Operation

The RT2702 includes a constant on-time synchronous

step-down controller and a linear regulator.

Buck Controller

In normal operation, the high-side N-MOSFET of DrMOS

is turned on when the VFB is lower than VREF, and is turned

off after the internal one-shot timer expires. While the

high-side N-MOSFET of DrMOS is turned off, the low-side

N-MOSFET of that is turned on to conduct the inductor

current until next cycle begins.

Soft-Start

For internal soft-start function, an internal current source

charges an internal capacitor to build the soft-start ramp

voltage. The output voltage will track the internal ramp

voltage during soft-start interval. For external soft-start

function, an additional capacitor, connected between SS

pin and GND, will be charged by a current source and

determines the soft-start time. The RT2702 will track the

slower one soft-start ramp during soft-start process.

POK

The power ok is the output of open-drain buffer. When the

soft-start process is finished, this pin becomes high

impedance.

Current Limit

The current limit circuit employs a unique “valley” current

sensing algorithm. If VCSP is higher than VCSN, the PWM

is not allowed to initiate a new cycle. Thus, the current to

the load exceeds the average output inductor current,

eventually, output drops lower than the under-voltage

protection threshold, inducing IC shutdown.

Over-Voltage Protection (OVP) & Under-Voltage

Protection (UVP)

The output voltage is continuously monitored for over-

voltage and under-voltage conditions. When the voltage

of FB pin exceeds over-voltage threshold (112.5% of VREF),

the PWM signal goes low. When it is less than 87.5% of

VREF, under-voltage protection is triggered and then the

DISB signal will be pulled low to disable DrMOS. The

controller begins hiccup procedure and restart up after

20ms.

VDRV

Internal LDO turns on When the VIN and ENvoltage exceed

the POR rising threshold, respectively. Provide 5V supply

voltage at VDRV pin.

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