RT1735

Copyright © 2023 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS1735-00

December 2023

www.richtek.com

15

15.7

Device Functional Modes

The RT1735 all functional modes.

MODE

VDD

RPD_Gx

TJ

FLAGB

CC

Switches

SBU

Switches

Normal

Operating

Conditions

Powered Off

No Dead Battery Support

<UVLO

Grounded

High-Z

OFF

OFF

Powered Off

Dead Battery Support

<UVLO

Shorted to

CON_CCx

High-Z

OFF

OFF

Powered On

>UVLO

Forced OFF

< OT

High-Z

ON

ON

Fault

Conditions

Thermal Shutdown

>UVLO

Forced OFF

> OT

Low

OFF

OFF

CC Overvoltage Condition

>UVLO

Forced OFF

< OT

Low

OFF

OFF

SBU Overvoltage Condition

>UVLO

Forced OFF

< OT

Low

OFF

OFF

15.8

Thermal Considerations

The junction temperature should never exceed the absolute maximum junction temperature TJ(MAX), listed under

Absolute Maximum Ratings, to avoid permanent damage to the device. The maximum allowable power dissipation

depends on the thermal resistance of the IC package, the PCB layout, the rate of surrounding airflow, and the

difference between the junction and ambient temperatures. The maximum power dissipation can be calculated using

the following formula:

PD(MAX) = (TJ(MAX) - TA) /

JA

where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and

JA is the junction-to-

ambient thermal resistance.

For continuous operation, the maximum operating junction temperature indicated under Recommended Operating

Conditions is 125°C. The junction-to-ambient thermal resistance,

JA, is highly package dependent. For a WQFN-

20L 3x3 package, the thermal resistance,

JA, is 30°C/W on a standard JEDEC 51-7 high effective-thermal-

conductivity four-layer test board. The maximum power dissipation at TA = 25°C can be calculated as below:

PD(MAX) = (125°C - 25°C) / (30°C/W) = 3.33W for a WQFN-20L 3x3 package.

The maximum power dissipation depends on the operating ambient temperature for the fixed TJ(MAX) and the thermal

resistance,

JA. The derating curve in Figure 1 allows the designer to see the effect of rising ambient temperature on

the maximum power dissipation.