Tai-1 Microelectronics

TMPA401DM

www.taimec.com.tw

May 25, 2005

Copyright

©2004,Tai-1 Microelectronics Corp.

6

DETAILED DESCRIPTION

Efficiency

The output transistors of a class D amplifier act as switches. The power loss is mainly due to

the turn on resistance of the output transistors when driving current to the load. As the turn on

resistance is so small that the power loss is small and the power efficiency is high. With 8 ohm

load the power efficiency can be better than 82%.

PCB layout for power dissipation

No heat sink is necessary for power dissipation. However the PCB layout should be well

designed to dissipate heat for high output power. With 80% power efficiency the generated

heat when driving 15 watts to the 8 ohm load is about 3.75 watts. The heat can be carried out

through the thermal pad of the device to the PCB. To ensure proper dissipation of heat the

PCB has to have heat path from the bottom of the device which is soldered to the PCB. The

area of the metal on the PCB for heat dissipation should be big enough. It is suggested that

both sides of the PCB are used for power dissipation.

Shutdown

The shutdown mode reduces power consumption. A LOW at shutdown pin forces the device in

shutdown mode and a HIGH forces the device in normal operating mode. Shutdown mode is

useful for power saving when not in use. This function is useful when other devices like

earphone amplifier on the same PCB are used but class D amplifier is not necessary.

Pop-less

A soft start capacitor can be added to the HFRC pin. This capacitor introduces delay for the

internal circuit to be stable before driving the load. The pop or click noise when power up/down

or switching in between shutdown mode can be thus eliminated. The delay time is proportional

to the value of the capacitance. It is about 300ms for a capacitor of 1uF.

Differential input VS single ended input

Differential input offers better noise immunity over single ended input. A differential input

amplifier suppresses common noise and amplifies the difference voltage at the inputs.

For

single ended applications just tie the negative input end of the balanced input structure to

ground. If external input resistors are used, the negative input has to be grounded with a

series resistor of the same value as the positive input to reduce common noise.

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