APA0710XAI datasheet(20/29 Pages) ANPEC

20 / 29 page

Rev. A.5 - Oct., 2005

APA0710/0711

www.anpec.com.tw

Application Descriptions

BTL Operation

Vbias

Vo +

Vo -

OP1

OP2

Figure1:

APA0710/1 power amplifier internal configuration

The power amplifier OP1 gain is setting by external

gain setting, while the second amplifier OP2 is

internally fixed in a unity-gain, inverting configuration.

Figure 1 shows that the output of OP1 is connected

to the input to OP2, which results in the output

signals of with both amplifiers with identical in

magnitude, but out of phase 180°. Consequently, the

differential gain for each channel is 2X (Gain of SE

mode).

By driving the load differentially through outputs Vo+

and Vo-, an amplifier configuration commonly referred

to as bridged mode is established. BTL mode operation

is different from the classical single-ended SE amplifier

configuration where one side of its load is connected

to ground.

A BTL amplifier design has a few distinct advantages

over the SE configuration, as it provides differential

drive to the load, thus doubling the output swing for a

specified supply voltage.

Four times the output power is possible as compared

to a SE amplifier under the same conditions. A BTL

configuration, such as the one used in APA0710, also

creates a second advantage over SE amplifiers. Since

the differential outputs, Vo+, Vo- are biased at half-

(1)

)

80k

Cbypass

≤

supply, no need DC voltage exists across the load.

This eliminates the need for an output coupling

capacitor which is required in a single supply, SE

configuration.

Single-Ended Operation

Consider the single-supply SE configuration shown

Application Circuit. A coupling capacitor is required to

block the DC offset voltage from reaching the load.

These capacitors can be quite large (approximately

µF to 1000µF) so they tend to be expensive, occupy

valuable PCB area, and have the additional drawback

of limiting low-frequency performance of the system

(refer to the Output Coupling Capacitor).

The rules described still hold with the addition of the

following relationship :

Output SE/BTL Operation (for APA0710 only)

The ability of the APA0710 to easily switch between

BTL and SE modes is one of its most important costs

saving features. This feature eliminates the requirement

for an additional headphone amplifier in applications

where internal speakers are driven in BTL mode but

external headphoneor speakers must beaccommodated.

Internal to the APA0710, two separate amplifiers drive

Vo+ and Vo- (see Figure 2). The SE/BTL input controls

the operation of the follower amplifier that drives Vo-.

• When SE/BTL is held low, the OP2 is turn on and

the APA0710 is in the BTL mode.

• When SE/BTL is held high, the OP2 is in a high

output impedance state, which configures the

APA0710 as SE driver from Vo+. I

DD is reduced by

approximately one-half in SE mode.

Control of the SE/BTL input can be a logic-level TTL

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