RT6208

Copyright © 2015 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS6208-00

May

2015

www.richtek.com

3

Function Block Diagram

FB

Comparator

Internal

Regulator

Shutdown

Comparator

VIN

GND

SW

FB

EN

6V

5k

HS Switch

Current

Comparator

0.8V

Logic &

Deadtime

Control

1.21

LS Switch

Current

Comparator

UVLO

Current

Sense

Current

Sense

1ms Ramp

2

μA

2V

ISET

PGOOD

Generator

PGOOD

1

μA

+

-

+

+

-

AGND

Operation

The RT6208 is a step-down DC/DC converter with

internal power switches that uses Hysteresis Mode

control, combining low quiescent current, which results

in high efficiency across a wide range of load currents.

Hysteresis

Mode

operation

functions

by

using

Boundary Conduction Mode (BCM) to ramp the

inductor current through the internal power switches,

followed by a sleep cycle where the power switches are

off and the load current is supplied by the output

capacitor. During the sleep cycle, the RT6208 draws

only 25

A of supply current. At light loads, the BCM

cycles are a small percentage of the total cycle time

which minimizes the average supply current, greatly

improving efficiency.

Scheme of Hysteresis Mode

The feedback comparator monitors the voltage on the

reference, as shown in Figure 1. If this voltage is

greater than the reference, the comparator activates a

sleep mode in which the power switches and current

comparators are disabled, reducing the VIN pin supply

current to only 25

A. As the load current discharges

decreases. When this voltage falls 5mV below the

800mV reference, the feedback comparator trips and

enables BCM. At the beginning of the BCM, the internal

high-side power switch (P-channel MOSFET) is turned

on and the inductor current begins to ramp up. The

inductor current increases until either the current

exceeds the peak current comparator threshold, or the

ON time of the high-side MOSFET exceeds 5

μs during

high-side power switch is turned off, and the Low-side

power switch is turned on. The inductor current ramps

down until the reverse current is close to zero. If the

reference, the high-side power switch is turned on

again and another cycle commences which keep the

inductor current operated in a boundary conduction

mode. The average current during the BCM will

normally be greater than the average load current. For

this architecture, the maximum average output current