RT4805AWSC datasheet(14/22 Pages) RICHTEK

14 / 22 page

RT4805A

is a registered trademark of Richtek Technology Corporation.

www.richtek.com

DS4805A-02

April

2017

The maximum VRIPPLE occurs when VIN is at

minimum and ILOAD is at maximum.

Output Discharge Function

With the EN pin set to low, the VOUT pin is internally

connected

GND

internal

discharge

N-MOSFET switch.

This feature prevents residual charge voltages on

capacitor connected to VOUT pins, which may impact

proper power up of the system.

Current Limit

The RT4805A employs a valley-current limit detection

scheme to sense inductor current during the off-time.

When the loading current is increased such that the

loading is above the valley current limit threshold, the

off-time is increased until the current is decreased to

valley-current threshold. Next on-time begins after

current is decreased to valley-current threshold.

On-time is decided by (VOUT VIN) / VOUT ratio. The

output voltage decreases when further loading

current increase. As the following figure shown, the

current limit function is implemented by the scheme.

Valley Current Limit

IIN (DC)

DIL

Inductor Current

I =

D

IIN (DC)

Figure 4. Inductor Currents In Current Limit Operation

Protection

The RT4805A features some protections, such as

OCP, OVP, UVP and OTP. As the table shown, it is

described the protection actions.

Protection Type

Threshold Refer to

Electrical Spec.

Protection Method

Shut Down

Delay Time

Reset Method

OCP

IL > 4A

Turn on UG until IL < 4A

2ms

After FAULT 1ms

OVP

VIN > 6V

Turn off UG, LG,

BYP_MOS

No delay

VIN < 5.7V

UVP

VIN <1.6V

Turn off UG, LG,

BYP_MOS

No delay

VIN>1.7V

OTP

TEMP > 160oC

Turn off UG, LG,

BYP_MOS

No delay

OTP Hysteresis = 20oC

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