RT4805A

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is a registered trademark of Richtek Technology Corporation.

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DS4805A-02

April

2017

14

Output Discharge Function

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

connected

to

GND

by

an

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.

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

Inductor Current

V

D

IN

I =

L

Lf

D

f

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

Turn off UG, LG,

BYP_MOS

No delay