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APA2176OI-TRG

270mW Stereo Cap-Free Headphone Driver

Anpec Electronics 

APA2176/2176A

Application Information

Charge Pump Flying Capacitor (CCPF)

The flying capacitor (C ) affects the load transient of the

CPF

charge pump. If the capacitor’s value is too small, and

then this increases charge pump’s output resistance and

degrades the performance of headphone amplifier.

Increasing the flying capacitor’s value improves the load

transient of charge pump. It is recommended to use the

low ESR ceramic capacitors (X7R type is recommended)

above 2.2µF.

Charge Pump Output Capacitor (C )

CPO

The charge pump needs an output capacitor(C ) to fil-

CPO

ter the negative output current pulse flowing into CVSS

pin as well as reduces the output voltage ripple (CVSS).

The capacitor also sucks in surge current flowing from

the VSS pin, the negative power input pin for the amplifiers.

The output ripple is determined by the capacitance, ESR,

and current ripple of the output capacitor. Increasing the

value of output capacitor and decreasing the ESR can

reduce the voltage ripple. Using a low-ESR ceramic ca-

pacitor greater than 2.2µF is recommended. For reduc-

ing the parasitic inductance and improving the noise

decoupling, place the capacitor near the CVSS and the

PGND pins as close as possible.

Charge Pump Bypass Capacitor (CCPB)

The bypass capacitor(CCPB) connected with PVDD pin sup-

plies the charge pump with surge current as well as re-

duces the voltage ripple on PVDD pin. Using a low-ESR

ceramic capacitor 10µF(typical) is recommended. For

reducing the parasitic inductance and improving the noise

decoupling, place the capacitor near the PV and the

DD

PGND pins as close as possible.

Input Capacitor (Ci)

In the typical application, an input capacitor (C ) is required

i

to allow the amplifier to bias the input signal to the proper

DC level for optimum operation. In this case, Ci and the

input impedance Ri from a high-pass filter with the cutoff

frequency are determined in the following equation:

fC(highpass)

=

1

2πRiCi

(1)

The value of Ci is important to consider carefully because

it directly affects the low frequency performance of the

circuit. Consider the example where Ri is 14kΩ and the

specification that calls for a flat bass response down to

10Hz. The equation is reconfigured as below:

Ci

=

1

2πRifC

(2)

When the input resistance variation is considered, the Ci

is 1µF. Therefore, a value in the range of 1µF to 2.2µF

would be chosen. A further consideration for this capaci-

tor is the leakage path from the input source through the

input network (R + R , C ) to the load.

i

fi

This leakage current creates a DC offset voltage at the

input to the amplifier that reduces useful headroom, es-

pecially in high gain applications. For this reason, a low-

leakage tantalum or ceramic capacitor is the best choice.

When polarized capacitors are used, the negative side of

the capacitor should face the amplifiers’inputs in most

applications because the DC level of the amplifiers’in-

puts are held at 0V. Please note that it is important to

confirm the capacitor polarity in the application.

Power Supply Decoupling (C )

s

The APA2176/2176A is a high-performance CMOS audio

amplifier that requires adequate power supply decoupling

to ensure the output total harmonic distortion (THD+N)

as low as possible. Power supply decoupling also pre-

vents the oscillations caused by long lead length between

the amplifier and the speaker.

The optimum decoupling is achieved by using two differ-

ent types of capacitor that targets on different types of

noise on the power supply leads. For higher frequency

transients, spikes, or digital hash on the line, a good low

equivalent-series- resistance (ESR) ceramic capacitor,

typically 0.1µF, is placed as close as possible to the de-

vice VDD lead for the best performance. For filtering lower

frequency noise signals, a large aluminum electrolytic

capacitor of 10µF or greater placed near the audio power

amplifier is recommended.

Thermal Consideration

Linear power amplifiers dissipate a significant amount

of heat in the package in normal operating condition. The

Copyright © ANPEC Electronics Corp.

19

Rev. A.7 - Jan., 2013

www.anpec.com.tw

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