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PT2308P V1.0

- 6 -

November, 2005

2-Channel 300mW Class AB Power Amplifier

PT2308P

4. Output Coupling Capacitor Co

Single power single-ended (SE) configuration generates a DC bias at the output of the amplifier; a

coupling capacitor must be placed at the output to block the DC bias from being sent to the load and

connect a RL at the signal output terminal. The low cut-off frequency may be needs to adjust to

correspond to different load (speaker or earphone) specifications. Similar to the input coupling

the low cut-off frequency is determined by the equation:

The diagram below shows the frequency response when: Co=1000µF/470µF/220µF/100µF.

5. Discharging Resistor (R3)

When the PT2308 is powered ON, the output coupling capacitor Co will start charging. When there is

no load connected at Vout, there will be a DC voltage present. At this time, if a load is suddenly

connected (usually earphone or speaker for general applications), the charged Co will then

discharge through Vout to the load, causing a very loud popping sound, thus, it is recommended to

connect a R3 to regulate the discharge of Co.

The time it takes to discharge is T=CoR3.

The recommended resistance value for R3 is between 1K

Ω ~ 10KΩ, to prevent loading effect from the

amplifier. If the load (ex. Speaker) is permanently connected then R3 can be neglected.