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PT2309 V1.2

- 4 -

August, 2006

Headphone Driver IC

PT2309

FUNCTION DESCRIPTION

POWER SUPPLY

The operating voltage of PT2309 is from 3V to 5V, In general operation 5V is recommended.

It should connect a modest bias capacitor nearby the power source terminal. It can improve IC stability

and decrease the noise output. Suggestion value of capacitor is from 0.1µF to 10µF.

POP AND CLICK SUPPRESS

For normal operation, the Input/Output port of a power amplifier powered by a single supply voltage

must have a stable DC bias. Each time turn on the Vcc the input/output pins will present 1/2 Vcc DC

bias voltage. For blocking the DC bias flowing to another circuit, each input/output port should have a

DC blocking capacitor, it will charge/discharge when power on or off, the capacitance is relative with

the pop noise. In general condition to prevent the pop noise, the time constant of bypass cap (CB) on

the bypass pin will be set to maximum. Higher CB value will extend the stable time, and also can

suppress the noise heard when power-on. In supply voltage=5V and CB=10µF, stable time is approx

1s. The value of CB also relative with the value of the DC blocking capacitor connected in input

terminal. In general condition the time constant of DC blocking capacitor should be less than CB stable

time. Recommend parts values please refer to application circuit.

INPUT CAPACITOR

Input capacitor decide the bandwidth and charge time constant, due to there is a 50KΩ impedance, so

input terminal charge period constant is:

Tin= (2π × 50KΩ × Cin)

If Cin=1µF, Tin=0.3s, Low frequency lower limit is 3Hz. This capacitor can use a non-polarity SMD

capacitor。

OUTPUT CAPACITOR

The headphone driver is designed to drive 32Ω headphone load, it needs a larger capacitance to

extending the lower frequency cut off point. If driving a small headphone a 100µF capacitor is a good

choice and the low frequency limit is around 50Hz; for better low frequency performance a 220µF

capacitor is recommended and it’s low frequency can extend to 22Hz. Due to charge/discharge time

constant is shorter than CB stable time, so it will not have pop and click noise.