RT4823WSC datasheet(4/20 Pages) RICHTEK

4 / 20 page

RT4823

is a registered trademark of Richtek Technology Corporation.

www.richtek.com

DS4823-01

September 2022

Free-Running Mode

If both voltages of VIN and VOUT are lower than 2.2V,

the Boost converter will into free-running mode. In this

mode, switching frequency operation is 1.5MHz and

duty cycle of Boost converter is 25%. It is translation of

power-on stage, and there is implemented current limit

function for converter soft-start. The current limit level

should be lower than 900mA.

EN and BP

As Table 1 shows, there are three device states in the

RT4823. When EN and BP pull low, it is shutdown

mode, and the quiescent current is less than 1

A. If EN

pulls high (BP do not care), the RT4823 is in boost

mode and it is with low quiescent operation. If BP pulls

high and EN pulls low, the RT4823 is in bypass mode.

There should be a delay time (< 250

s) from EN

pull-high to power ready, to guarantee normal operation.

Table 1. Pin Configuration for Converter

EN Input

BP Input

Mode Define

Device State

Shutdown Mode

The device is shut down. The device shutdown current is

approximately 1

A (max).

Do not care

Boost Mode

The device is active in Boost PFM low quiescent mode.

The supply current is approximately 4

A (typ.).

Bypass Mode

The device is in forced bypass mode.

Enable

The boost can be enabled or disabled by the EN pin.

When the EN pin is higher than the threshold of

logic-high, the device starts operating as shown in

Figure 1 operation diagram. In shutdown mode, the

converter stops switching, and the internal control

circuit is turned off. The output voltage is discharged by

component consumption (such as Cap ESR) since

there is no discharge function in this state.

Soft-Start State

During

soft-start

state,

VOUT

reaches

99%

VOUT_Target, the RT4823 will enter boost operation.

When system powers on with heavy loading (higher

than pre-charge current), the RT4823 is in pre-charge

state until loading release.

Boost/Auto Bypass Mode

There are two normal operation modes, the boost

mode, and the auto bypass mode. In the boost mode

(VIN – 0.3V < VOUT_Target), the converter boosts output

voltage to VOUT_Target, and delivers power to loading by

internal synchronous switches after the soft-start state.

In the auto bypass mode (VIN – 0.3V ≥ VOUT_Target),

input voltage will deliver to the output terminal loading

directly. That can provide maximum current capacity

with the RT4823. Detailed information is shown in the

Boost Mode section.

Boost Mode (Auto PFM/PWM Control Method)

In order to save power and improve efficiency at low

loads, the Boost converter operates in PFM (Pulse

Frequency Modulation) as the inductor drops into DCM

(Discontinuous

Current

Mode).

The

switching

frequency is proportional to loading to reach output

voltage

regulation.

When

increases

and

inductor current is in continuous current mode, the

Boost automatically enters PWM mode.

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