APA2012_18 datasheet(11/19 Pages) ANPEC

11 / 19 page

Rev. A.7 - Mar., 2018

www.anpec.com.tw

APA2012

Application Information (Cont.)

Over Current Protection

The APA2012 monitors the output current, and when the

current exceeds the current-limit threshold, the APA2012

turn-off the output stage to prevent the output device from

damages in over-current or short-circuit condition. The IC

will turn-on the output buffer after 100ms, but if the over-

current or short-circuits condition is still remain, it enters

the Over-Current protection again. The situation will cir-

culate until the over-current or short-circuits has be

removed.

Thermal Protection

The over-temperature circuit limits the junction tempera-

ture of the APA2012. When the junction temperature

exceedsT

J=+170

C, a thermal sensor turns off the output

buffer, allowing the devices to cool. The thermal sensor

allows the amplifier to start-up after the junction tempera-

ture down about 150

C. The thermal protection is de-

signed with a 25

C hysterics to lower the average T

J dur-

ing continuous thermal overload conditions, increasing

lifetime of the IC.

Input Resistance, R

The gain of the APA2012 has been set by the external

resistors (R

in ).

(1)

2X150k

Gain(Av)

Ω

For fully differential operating, the R

in match is very impor-

t ant fo r CMRR, PSRR and ha r m oni c di s tort ion

performance. It

’s recommended to use 1% tolerance re-

sistor or better. Keeping the input trace as short as pos-

sible to limit the noise injection.

The gain is recommended to set as 2V/V or lower for

APA2012 optimal performance.

Input Capacitor, C

In the typical application, an input capacitor, C

in, is required

to allow the amplifier to bias the input signal to the proper

DC level for optimum operation. In this case, C

in and the

minimum input impedance R

in from a high-pass filter with

the corner frequency are determined in the following

equation:

(2)

)

C(highpass

The value of C

in must be considered carefully because it

directly affects the low frequency performance of the circuit.

For example, when R

in is 100kΩ and the specification

calls for a flat bass response are down to 40Hz. The

equation is reconfigured as below:

(3)

When input resistance is considered, the C

in is 0.2µF.

Therefoe, a value in the range of 0.22

µF to 0.1.0µF would

be chosen. A further consideration for this capacitor is the

leakage path from the input source through the input net-

work (R

in + Rf, Cin) to the load.

This leakage current creates a DC offset voltage at the

input to the amplifier that reduces useful headroom, es-

pecially 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 appli-

cations because the DC level of the amplifiers

’ inputs are

held at V

DD/2. Please note that it is important to confirm the

capacitor polarity in the application.

Power Supply Decoupling, C

The APA2012 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-

vents the oscillations being caused by long lead length

between the amplifier and the speaker.

The optimum decoupling is achieved by using two differ-

ent types of capacitors that target on different types 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, is placed as close as possible to the de-

vice VDD pin for the best operation. For filtering lower

frequency noise signals, a large aluminum electrolytic

capacitor of 10

µF or greater is placed near the audio power

amplifier is recommended.

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