APA2011 datasheet(19/27 Pages) ANPEC

19 / 27 page

Rev. A.4 - Aug., 2013

www.anpec.com.tw

APA2011/2011A

Application Information

Square Wave Into The Speaker

Apply the square wave into the speaker may cause the

voice coil of speaker jump out the air gap and deface the

voice coil. However, this depends on the amplitude of

square wave is high enough and the bandwidth of speaker

is higher than the square wave’s frequency. For 500kHz

switching frequency, this is not issued for the speaker

because the frequency is beyond the audio band and

can’t significantly move the voice coil, as cone movement

is proportional to 1/f2 for frequency out of audio band.

Input Resistor, R

The APA2011/2011A’s input resistor is fixed and the value

is 25k

Ω. The input resistance has wide variation (+/-5%)

is caused by manufacture. The gain also can be set by

the external resistors (Riexr).

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 form a high-pass filter with the corner

frequency determined in the following equation:

(4)

)

C(highpass

The value of C

i must be considered carefully because it

directly affects the low frequency performance of the circuit.

Where R

i is 25kΩ (minimum) and the specification calls

for a flat bass response down to 100Hz. Equation is

reconfigured as below:

(5)

When the input resistance variation is considered, the C

is 0.064

µF, so a value in the range of 0.1µF to 0.22µF

would be chosen. A further consideration for this capaci-

tor is the leakage path from the input source through the

input network (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, especially in high gain

applications. For this reason, a low-leakage tantalum or

ceramic capacitor is the best choice. When polarized ca-

pacitors are used, the positive side of the capacitor should

face the amplifier input in most applications because the

DC level of the amplifier input is held at V

DD/2. Please note

that it is important to confirm the capacitor polarity in the

application.

Ferrite Bead Selection

If the traces form APA2011/2011A to speaker is short, the

ferrite bead filters can reduce the high frequency radiated

to meet the FCC & CE required.

A ferrite that has very low impedance at low frequencies

and high impedance at high frequencies (above 1 MHz)

is recommended.

Output Low-Pass Filter

If the traces form APA2011/2011A to speaker are short, it

don’t require output filter for FCC & CE standard.

A ferrite bead may be needed if it’s failing the test for FCC

or CE tested without the LC filter. The figure 5 is the sample

for added ferrite bead; the ferrite show choosing high

impedance in high frequency.

Figure 5. Ferrite Bead Output Filter

Figure 6 and 7 and are examples for added the LC filter

(Butterworth), it’s recommended for the situation that the

trace form amplifier to speaker is too long, and needs to

eliminate the radiated emission or EMI.

Ω

1nF

Ferrite

Bead

Ferrite

Bead

(3)

)

(

Riexr

100

iexr

Ω

For fully differential operating, the R

iexr (Ri1& Ri2) match is

very important for CMRR, PSRR, and harmonic distortion

performance. It’s recommended to use 1% tolerance re-

sistor or better. Keep the input trace as short as possible

to limit the noise injection. The gain is recommended to

set 5.6V/V or lower for optimal the APA2011/2011A’s

performance.

APA2011 Datasheet(PDF) 19 Page - Anpec Electronics Coropration

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