Datasheet > RT4805A

RT4805A

更新时间： 2024-02-04 04:41:54

品牌	Logo	应用领域
立锜 - RICHTEK		/
页数	文件大小	规格书
22页	1412K
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RT4805A 技术参数

Status：	Active	Vin (min) (V)：	1.8
Vin (max) (V)：	5	Vout (min) (V)：	2.85
Vout (max) (V)：	4.4	Output Adj. Method：	Digital
Iq (typ) (mA)：	0.055	SW Current Limit (typ) (A)：	4
Freq (typ) (kHz)：	2500	Freq (min) (kHz)：	2000
Freq (max) (kHz)：	3000	Ron (typ) (Ohm)：	0.04;0.06
Features：	Adjustable Current Limit;Current Mode Control;Cycle-by-Cycle Current Limit;Enable Input;Internal Compensation;OCP;OVP;Power Good;UVP	Package Type：	WL-CSP1.67x1.67-16(BSC)

RT4805A 数据手册

RT4805A

Operation

Startup and Shutdown State

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.

When V_INis 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.

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.

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.

Mode

Depiction

Condition

LIN 1

LIN 2

Linear startup 1

Linear startup 2

Boost soft-start

Boost mode

V_IN> V_OUT

LIN

V_IN> V_OUT

Fault State

Soft-Start

Boost

V_OUT< V_OUT(MIN)

V_OUT= V_OUT(MIN)

V_IN> V_OUT(MIN)

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

below,

Bypass

Bypass mode

 The timeout of LIN2 is over the 1024s.

LIN State

 It is over the 2ms when the state changed from

Soft-start state to Boost mode.

When V_INis rising, it enters the LIN State. There are

two parts for the LIN state. It provides maximum current

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

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

V_IN> UVLO.

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

As the figure shown, if the timeout is over the

specification, it will enter the Fault 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.

EN = 1,

Vin > UVLO

LIN 1

Bypass Mode

Timeout < 512μs

Timeout > 512μs

In Bypass mode, output voltage will increase with VIN

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

Soft-Start

Timeout

LIN 2

Timeout > 1024μs

Bypass Mode Operation

< 1024μs

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. V_OUTwill be followed

the V_INwhen V_INis higher than the target output

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

MOSFET (Q3). V_OUTfollowed the V_IN.

Timeout > 2ms

Timeout < 2ms

Fault

State

Boost

mode

Figure 1. RT4805A State Chart

is a registered trademark of Richtek Technology Corporation.

www.richtek.com

DS4805A-02 April 2017

1 2 345 6 7...22

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