RT9758 datasheet(54/61 Pages) RICHTEK

54 / 61 page

RT9758

is a registered trademark of Richtek Technology Corporation.

www.richtek.com

DS9758-03

May 2023

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 WL-CSP-36B 2.74x2.84 (BSC) package, the

thermal resistance,

JA, is 34.7°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) / (34.7°C/W) = 2.88W for a

WL-CSP-36B 2.74x2.84 (BSC) package.

The maximum power dissipation depends on the

operating ambient temperature for the fixed TJ(MAX) and

the thermal resistance,

JA. The derating curves in

Figure 15 allows the designer to see the effect of rising

ambient

temperature

the

maximum

power

dissipation.

Figure 15. Derating Curve of Maximum Power

Dissipation

Layout Considerations

The RT9758 layout guidelines are recommended as

below :



Place low ESR bypass capacitor to GND for

WRX_IN/VBUS/VOUT pin. The bypass capacitor

needs to be placed as close as possible to RT9758.



The capacitor of BST/CFH should be placed as close

as possible to RT9758.



Place flying caps with the RT9758 on same layer.

The flying caps should be placed as close as

possible to the RT9758. The path of flying caps

should be as small as possible.



The WRX_IN, VBUS and VOUT traces should be as

wide as possible to accommodate high charge

current.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

100

125

Ambient Temperature (°C)

Four-Layer PCB

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