Preliminary

TMPA2155DM

Rev.1.0

December 24, 2007

Copyright ©2005, Tai-1 Microelectronics Corp.

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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 85%.

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.

Internal circuit for shutdown is shown below.

Pop-less

The shutdown pin is designed to give pop-less start up. The RC delay provided by external

R(=100k ohms) and external C(=1uF) introduces enough delay for the internal circuitry to be

stable before the signal is fed to the speaker. This delay is good for shutdown ON-OFF and

power UP-DOWN operations.

Voltage gain

The voltage gain is defined in the table on page 3. For lower voltage gain one can add external

input resistors to input pins. If external resistors are used they should be well matched. Well

matched input resistors are also required even for single ended input configuration for low

noise.