APA2069 datasheet(21/26 Pages) ANPEC

21 / 26 page

Rev. A.1 - Aug., 2005

APA2069

www.anpec.com.tw

Application Descriptions (Cont.)

Power Supply Decoupling, Cs

The APA2069 is a high-performance CMOS audio

am plifier that requires adequate power supply

decoupling to ensure the output total harmonic

distortion (THD) is as low as possible. Power supply

decoupling also prevents the oscillations causing by

long lead length between the amplifier and the speaker.

The optimum decoupling is achieved by using two

different type capacitors that target on different type 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 placed as

close as possible to the device V

DD lead works best.

For filtering lower-frequency noise signals, a large

aluminum electrolytic capacitor of 10

µF or greater

placed near the audio power amplifier is recommended.

Optimizing Depop Circuitry

Circuitry has been included in the APA2069 to minimize

the amount of popping noise at power-up and when

coming out of shutdown mode. Popping occurs

whenever a voltage step is applied to the speaker. In

order to eliminate clicks and pops, all capacitors must

be fully discharged before turn-on. Rapid on/off

switching of the device or the shutdown function will

cause the click and pop circuitry.

The value of Ci will also affect turn-on pops (Refer to

Effective Bypass Capacitance). 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 Cbypass, turn-on pop

can be 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. In a SE

configuration, the output coupling capacitor, C

C, is of

particular concern.

This capacitor discharges through the internal 10k

Ω

resistors. Depending on the size of C

C, t he t ime

constant can be relatively large. To reduce transients

in SE mode, an external 1k

Ω resistor can be placed in

parallel with the internal 10k

Ω resistor. The tradeoff

for using this resistor is an increase in quiescent current.

In the most cases, choosing a small value of Ci in the

range of 0.33

µF to 1µF, Cb being equal to 4.7µF and

an external 1k

Ω resistor should be placed in parallel

with the internal 10k

Ω resistor should produce a

virtually clickless and popless turn-on.

A high gain amplifier intensifies the problem as the

small delta in voltage is multiplied by the gain. So it

is advantageous to use low-gain configurations.

Shutdown Function

In order to reduce power consumption while not in use,

the APA2069 contains a shutdown pin to externally

turn off the amplifier bias circuitry. This shutdown

feature turns the amplifier off when a logic low is placed

on the SHUTDOWN pin. The trigger point between a

logic high and logic low level is typically 2.0V. It is

best to switch between ground and the supply V

DD to

provide maximum device performance.

By switching the SHUTDOWN pin to low, the amplifier

enters a low-current state, I

DD<1µA. APA2069 is in

shutdown mode. On normal operating, SHUTDOWN

pin pull to high level to keeping the IC out of the

shutdown mode. The SHUTDOWN pin should be tied

to a definite v oltage to av oid unwanted state

changes.

BTL Amplifier Efficiency

An easy-to-use equation to calculate efficiency starts

out as being equal to the ratio of power from the power

APA2069 Datasheet(PDF) 21 Page - Anpec Electronics Coropration

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