APA0710XAI datasheet(21/29 Pages) ANPEC

21 / 29 page

Rev. A.5 - Oct., 2005

APA0710/0711

www.anpec.com.tw

In Figure 2, input SE/BTL operates as follows :

When the phonejack plug is inserted, the 1k

Ω resistor

is disconnected and the SE/BTL input is pulled high

and enables the SE mode.

When this input goes high level, the Vo- amplifier is

shutdown causing the speaker to mute. The Vo+

amplifier then drives through the output capacitor (C

into the headphone jack.

When there is no headphone plugged into the system,

the contact pin of the headphone jack is connected

from the signal pin, the voltage divider set up by

resistors 100k

Ω and 1kΩ. Resistor 1kΩ then pulls

low the SE/BTL pin, enabling the BTL function.

Input Capacitor, Ci

In the typical application an input capacitor, Ci, is

required to allow the amplifier to bias the input signal

to the proper DC level for optimum operation. In this

case, Ci and the minimum input impedance Ri form a

high-pass filter with the corner frequency determined

in the follow equation :

Application Descriptions (Cont.)

Control

Ω

VDD

100k

Ω

SE/BTL

Headphone

Jack

100k

Ω

vo+

Figure 2: SE/BTL input selection by phonejack plug

FC(highpass)=

πRiCi

(2)

The value of Ci is important to consider as it directly

affects the low frequency performance of the circuit.

Consider the example where Ri is 100k

Ω and the

specification calls for a flat bass response down to

40Hz. Equation is reconfigured as follow :

Ci=

πRifC

(3)

source or a resistor divider network or the mono head-

phone jack with switch pin as shown in Application

Circuit.

Output SE/BTL Operation (for APA0710 only)

Consider to input resistance variation, the Ci is 0.04

µF

so one would likely choose a value in the range of

0.1

µF to 1.0µF.

A further consideration for this capacitor 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 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 capacitors are used, the

positive side of the capacitor should face the amplifier

input in most applications as the DC level there is held

at V

DD/2, which is likely higher that the source DC

level. Please note that it is important to confirm the

capacitor polarity in the application.

Effective Bypass Capacitor, Cbypass

As other power amplifiers, proper supply bypassing is

critical for low noise performance and high power

supply rejection.

The capacitors located on the bypass and power

supply pins should be as close to the dev ice as

possible. The effect of a larger half supply bypass

capacitor will improve PSRR due to increased half-

supply stability. Typical application employ a 5V

regulator with 1.0

µF and a 0.1µF bypass as supply

filtering. This does not eliminate the need for bypassing

the supply nodes of the APA0710/1. The selection of

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