PAM8901 / PAM8908

Document number: DS36456 Rev. 2 - 2

9 of 13

www.diodes.com

October 2016

© Diodes Incorporated

PAM8901 / PAM8908

Application Information

The basic PAM8901 / PAM8908 application circuit is shown in page 2.

Gain Control

The PAM8901 / PAM8908 has four gain settings which are controlled with pins G0 and G1. The following table gives an overview of the gain

function.

G0 Voltage

G1 Voltage

Amplifier Gain

≤0.6V

≤0.6V

-6dB

≥1.4V

≤0.6V

0dB

≤0.6V

≥1.4V

3dB

≥1.4V

≥1.4V

6dB

Input Coupling Capacitors

Input coupling capacitors block any DC bias from the audio source and ensure maximum dynamic range. Input coupling capacitors also minimize

PAM8901 / PAM8908 turn-on pop to an inaudible level. The input capacitors are in series with PAM8901 / PAM8908 internal input resistors,

creating a high-pass filter. The following Equation calculates the highpass filter corner frequency.

C

R

2

1

f

IN

IN

TT

impedance values.

G0 Voltage

G1 Voltage

≤0.6V

≤0.6V

26.4kΩ

≥1.4V

≤0.6V

19.8kΩ

≤0.6V

≥1.4V

16.5kΩ

≥1.4V

≥1.4V

13.2kΩ

For a given high-pass cutoff frequency, the minimum input coupling capacitor is found as:

R

f

2

1

C

IN

C

TT

Equation shows the input coupling capacitors must be at least 0.6µF to achieve a 20Hz highpass corner frequency. Choose a 0.68µF standard

value capacitor for each PAM8901 / PAM8908 input (X5R material or better is required for best performance).

Charge Pump Flying Capacitor, HPVDD Capacitor and HPVSS Capacitor

The PAM8901 / PAM8908 uses a built-in charge pump to generate a positive and negative voltage supply for the headphone amplifiers. The

charge pump flying capacitor connects between CAP+ and CAP-. It transfers charge to generate the positive and negative supply voltage. The

HPVDD capacitor or HPVSS capacitor must be at least equal in or larger than value to the flying capacitor to allow maximum charge transfer. Use

low equivalent-series-resistance (ESR) ceramic capacitors (X5R material or better is required for best performance) to maximize charge pump

efficiency. Typical values are 1µF for the HPVDD, HPVSS and flying capacitors.

Power Supply Decoupling Capacitors

The PAM8901 / PAM8908 TrueCapFree headphone amplifier requires adequate power supply decoupling to ensure that output noise and total

harmonic distortion (THD) remain low. Use good low equivalent-series-resistance (ESR) ceramic capacitors (X5R material or better is required for

best performance). Place a 2.2µF capacitor within 5mm of the PVDD pin. Reducing the distance between the decoupling capacitor and PVDD

minimizes parasitic inductance and resistance, improving PAM8901 / PAM8908 supply rejection performance. Use 0402 or smaller size capacitors

if possible.