RT4805AWSC datasheet(4/22 Pages) RICHTEK

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RT4805A

is a registered trademark of Richtek Technology Corporation.

www.richtek.com

DS4805A-02

April

2017

Operation

The RT4805A combined built-in power transistors,

synchronous rectification, and low supply current, it

provides a compact solution for system using advanced

Li-Ion battery chemistries.

In boost mode, output voltage regulation is guaranteed

to a maximum load current of 2A. Quiescent current in

Shutdown mode is less than 1

A, which maximizes

battery life.

Mode

Depiction

Condition

LIN

LIN 1

Linear startup 1

VIN > VOUT

LIN 2

Linear startup 2

VIN > VOUT

Soft-Start

Boost soft-start

VOUT < VOUT(MIN)

Boost

Boost mode

VOUT = VOUT(MIN)

Bypass

Bypass mode

VIN > VOUT(MIN)

LIN State

When VIN is rising, it enters the LIN State. There are

two parts for the LIN state. It provides maximum current

for 1A to charge the COUT in LIN1, and the other one is

for 2A in LIN2. By the way, the EN is pulled high and

VIN > UVLO.

As the figure shown, if the timeout is over the

specification, it will enter the Fault mode.

EN = 1,

Vin > UVLO

LIN 1

Soft-Start

LIN 2

Fault

State

Boost

mode

Timeout < 512

μs

Timeout > 512

μs

Timeout > 1024

μs

Timeout

< 1024

μs

Timeout > 2ms

Timeout < 2ms

Figure 1. RT4805A State Chart

Startup and Shutdown State

When VIN is rising and through the LIN state, it will

enter the Startup state. If EN is pulled low, any function

is turned-off in shutdown mode.

Soft-Start State

It starts to switch in Soft-start state. After the LIN state,

output voltage is rising with the internal reference

voltage.

There is a point, it will go to fault condition, if the large

output capacitor is used and the timeout is over 2ms

after the soft-start state.

Fault State

As the Figure 1 shown, it will enter to the Fault state as

below,



The timeout of LIN2 is over the 1024

s.



It is over the 2ms when the state changed from

Soft-start state to Boost mode.

It will be the high impedance between the input and

output when the fault is triggered. A restart will be start

after 1ms.

Boost Mode

There are two normal operation modes, one is the

Boost mode, and the other one is Bypass mode. In the

Boost mode, it provides the power to load by internal

synchronous switches after the soft-start state.

Bypass Mode

In Bypass mode, output voltage will increase with VIN

when input voltage is rising after the soft-start state.

Bypass Mode Operation

In automatic mode, it transits from Boost mode to

Bypass mode. As the Figure 2 shown, there are three

MOSFET (Q1 to Q3). The Q1 & Q2 is for Boost mode, it

is used by Q3 for Bypass mode. VOUT will be followed

the VIN when VIN is higher than the target output

voltage. As the Figure 3 shown, it is transited by bypass

MOSFET (Q3). VOUT followed the VIN.

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