RT8088AWSC datasheet(3/16 Pages) RICHTEK

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DS8088A-01 August 2017

www.richtek.com

RT8088A

is a registered trademark of Richtek Technology Corporation.

Operation

The RT8088A is a low voltage synchronous step-down

converter that can support the input voltage range from

2.5V to 5.5V and the output current can be up to 3A. The

RT8088A uses a constant on-time, current mode

architecture. In steady-state operation, the high-side P-

MOSFET is turned on when the current feedback reaches

COMP level which is the amplified difference between the

reference voltage and the feedback voltage. The on-time

of high-side P-MOSFET is determined by on-time

generator which is a function of input and output voltage.

After on-time expires, high-side MOSFET is turned off

and low-side MOSFET is turned on. Until the low-side

current sensing signal reaches the COMP, the high-side

MOSFET is turned on again. In this manner, the converter

regulates the output voltage and keeps the frequency

constant.

The RT8088A reduces the external component count by

integrating the boot recharge MOSFET.

The error amplifier EA adjusts COMP voltage by comparing

the output voltage with the internal I2C set reference voltage.

When the load increases, it causes a drop in the output

relative to the reference, then the COMP voltage rises to

allow higher inductor current to match the load current.

PWM Frequency and Adaptive On-Time Control

The on-time can be roughly estimated by the equation :

where fSW is nominal 3MHz

Auto-Zero Current Detector

The auto-zero current detector circuit senses the LX

waveform to adjust the zero current threshold voltage.

When the current of low-side MOSFET decreases to the

zero current threshold, the low-side MOSFET turns off to

prevent negative inductor current. In this way, the zero

current threshold can adjust for different condition to get

better efficiency.

Under-Voltage Lockout (UVLO)

The UVLO continuously monitors the VCC voltage to make

sure the device works properly. When the VCC is high

enough to reach the UVLO high threshold voltage, the

step-down converter softly starts or pre-bias to its regulated

output voltage. When the VCC decreases to its UVLO

low threshold voltage, the device will shut down.

Power Good

When the output voltage is higher than PGOOD rising

threshold, the PGOOD flag is high.

Output Under-Voltage Protection (UVP)

When the output voltage is lower than 0.4V after soft-

start, the UVP is triggered. The system will be latched

and the output voltage will no longer be regulated during

UVP latched state. Re-start input voltage or EN pin can

unlatch the protection state. Using I2C to shutdown the

system and then re-enable it will also unlatch UVP function.

Over-Current Protection (OCP)

The RT8088A senses the current signal when the low-

side MOSFET turns on. As a result, The OCP is cycle-

by-cycle limit. If the OCP occurs, the converter holds off

the next on pulse until inductor current drops below the

OCP limit.

Soft-Start

An internal current source charges an internal capacitor

to build the soft-start ramp voltage. The typical soft start

time is 150

μs.

Over-Temperature Protection (OTP)

The RT8088A has an over-temperature protection. When

the device triggers the OTP, the system will be latched

and the output voltage will no longer be regulated during

OTP latched state. Re-start input voltage or EN pin can

unlatch the protection state. Using I2C to shutdown the

system and then re-enable it will also unlatch UVP function.

OUT



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