APA2180 datasheet(14/22 Pages) ANPEC

14 / 22 page

Rev. A.3 - Dec., 2012

APA2180

www.anpec.com.tw

Application Information

Charge Pump Flying Capacitor (C

CPF)

The flying capacitor (C

CPF) affects the load transient of the

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 recommend to use the low

ESR ceramic capacitors (X5R or X7R type is recommended)

above 1

µF.

Charge Pump Output Capacitor (C

CPO)

The charge pump needs an output capacitor(C

CPO) to fil-

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 V

SS 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 1

µF is recommended. For reducing

the parasitic inductance and improving the noise

decoupling, place the capacitor near the CVSS and PGND

pins as close as possible.

Input Capacitor (C

In the typical application, an input capacitor (C

i) is required

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

DC level for optimum operation. In this case, C

i and the

input impedance R

i from a high-pass filter with the cutoff

frequency are determined in the following equation:

The value of C

i must be considered carefully because it

directly affects the low frequency performance of the circuit.

Consider the example where R

i is 14kΩ and the specifi-

cation that calls for a flat bass response down to 10Hz.

The equation is reconfigured as below:

When input resistance variation is considered, the C

i is

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

be chosen. A further consideration for this capacitor is the

leakage path from the input source through the input net-

work (R

i + Rf, Ci) to the load.

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

The APA2180 is a high-performance CMOS audio ampli-

fier that requires adequate power supply decoupling to

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

low as possible. Power supply decoupling also prevents

the oscillations being caused by long lead length be-

tween the amplifier and the speaker.

The optimum decoupling is achieved by using two differ-

ent types of capacitor that target 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 0.1

µF, 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 10

µF or greater placed near the audio power

amplifier is recommended.

Thermal Consideration

(1)

(2)

)

C(highpass

Linear power amplifiers dissipate a significant amount

of heat in the package in normal operating condition. The

first consideration to calculate maximum ambient tem

peratures is the numbers from the Power Dissipation vs.

Output Power graphs are per channel values, so the dis-

sipation of the IC heat needs to be doubled for two-chan-

nel operation. Given

JA, the maximum allowable junc-

tion temperature (T

JMax), the total internal dissipation (PD),

and the maximum ambient temperature can be calcu-

APA2180 Datasheet(PDF) 14 Page - Anpec Electronics Coropration

APA2180 Datasheet(HTML) 14 Page - Anpec Electronics Coropration

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Datasheet Download

Link URL