APA0714 Просмотр технического описания (PDF) - Anpec Electronics

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APA0714

3W Mono Fully Differential Audio Power Amplifier

Anpec Electronics 

APA0714

Application Information

Input Resistance (Ri)

The gain for the APA0714 is set by the external input re-

sistors (Ri) and internal feedback resistors (Rf).

AV = Rf

(1)

Ri

The internal feedback resistors are 40kΩ typical. For the

performance of a fully differential amplifier, it’s better to

select matching input resistors Ri1 and Ri2. Therefore,

1% tolerance resistors are recommended. If the input

resistors are not matched, the CMRR and PSRR perfor-

mance are worse than using matching devices.

Input Capacitor (C )

i

When the APA0714 is driven by a differential input source,

the input capacitor may not be required.

In the single-ended input application, an input capacitor,

Ci, is required to allow the amplifier to bias the input sig-

nal to the proper DC level for optimum operation. In this

case, C and the input resistance R form a high-pass filter

i

i

with the corner frequency determined in the following

equation:

FC(highpass)

=

1

2πRiCi

(2)

The value of C must be considered carefully because it

i

directly affects the low frequency performance of the circuit.

Consider the example where Ri is 10kΩ and the specifi-

cation that calls for a flat bass response down to 100Hz.

The equation is reconfigured below:

Ci

=

1

2πRiFc

(3)

When the input resistance variation is considered, the Ci

is 0.16µF. So a value in the range of 0.22µF to 0.47µF

would be chosen. A further consideration for this capaci-

tor is the leakage path from the input source through the

input network (Ri + Rf, Ci) to the load.

This leakage current creates a DC offset voltage at the

input of the amplifier. The offset reduces useful

headroom, especially in high gain applications. For this

reason, a low-leakage tantalum or ceramic capacitor is

the best choice. When polarized capacitors are used, the

positive side of the capacitor should face the amplifier

input in most applications because the DC level of the

amplifiers’inputs are held at V /2. Please note that it is

DD

important to confirm the capacitor polarity in the application.

Effective Bypass Capacitor (CBYPASS)

The BYPASS pin sets the VDD/2 for internal reference by

voltage divider. Adding capacitors at this pin to filter the

noise and regulator the mid-supply rail will increase the

PSRR and noise performance.

The capacitors should be as close to the device as

possible. The effect of a larger bypass capacitor will im-

prove PSRR due to increased supply stability.

The bypass capacitance also affects to the start time. The

large capacitors will increase the start time when device

in shutdown.

Optimizing Depop Circuitry

Circuitry has been included in the APA0714 to minimize

the amount of popping noise at power-up and when com-

ing out of shutdown mode. Popping occurs whenever a

voltage step is applied to the speaker. In order to elimi-

nate clicks and pops, all capacitors must be fully dis-

charged before turn-on. Rapid on/off switching of the de-

vice or the shutdown function will cause the click and pop

circuitry.

The value of Ci will also affect turn-on pops. The bypass

voltage ramp up should be slower than input bias voltage.

Although the BYPASS pin current source cannot be

modified, the size of CBYPASS can be changed to alter the

device turn-on time and the amount of clicks and pops.

By increasing the value of C , turn-on pop can be

BYPASS

reduced. However, the tradeoff for using a larger bypass

capacitor is to increase the turn-on time for this device.

There is a linear relationship between the size of CBYPASS

and the turn-on time.

A high gain amplifier intensifies the problem as the small

delta in voltage is multiplied by the gain. Hence, it is ad-

vantageous to use low-gain configurations.

Power Supply Decoupling Capacitor (Cs)

The APA0714 is a high-performance CMOS audio ampli-

fier that requires adequate power supply decoupling to

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

as low as possible. Power supply decoupling also pre-

Copyright © ANPEC Electronics Corp.

16

Rev. A.2 - Apr., 2010

www.anpec.com.tw

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