CS4412 datasheet(21/22 Pages) CIRRUS

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DS749A1

CS4412

8. THERMAL CHARACTERISTICS

8.1

Thermal Flag

This device is designed to have the metal flag on the bottom of the device soldered directly to a metal plane

on the PCB. To enhance the thermal dissipation capabilities of the system, this metal plane should be cou-

pled with vias to a large metal plane on the backside (and inner ground layer, if applicable) of the PCB.

In either case, it is beneficial to use copper fill in any unused regions inside the PCB layout, especially those

immediately surrounding the CS4412. In addition to improving in electrical performance, this practice also

aids in heat dissipation.

The heat dissipation capability required of the metal plane for a given output power can be calculated as

follows:

θCA = [(TJ(MAX) - TA) / PD] - θJC

where,

θCA = Thermal resistance of the metal plane in °C/Watt

TJ(MAX) = Maximum rated operating junction temperature in °C, equal to 150 °C

TA = Ambient temperature in °C

PD = RMS power dissipation of the device, equal to 0.15*PRMS-IN or 0.176*PRMS-OUT (assuming 85% effi-

ciency)

θJC = Junction-to-case thermal resistance of the device in °C/Watt

Parameter

Symbol

Min

Typ

Max

Units

Junction to Case Thermal Impedance

θJC

-1

°C/Watt

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