APA2174 datasheet(13/21 Pages) ANPEC

13 / 21 page

Rev. A.6 - Dec., 2011

www.anpec.com.tw

APA2174

Application Information (Cont.)

Input Resistor, R

i (Cont.)

(6)

)

Gain(A

The external gain setting is recommended using from

-1V/V to -10V/V, and the R

i is in the range from 1kΩ to

47k

Ω. It’s recommended to use 1% tolerance resistor or

better. Keep the input trace as short as possible to limit

the noise injection. The gain is recommended to set

-1V/V, and R

i is 10kΩ, and Rf is 10kΩ.

Feedback Resistor, R

Refer the figure 3, the external gain is setting by R

i and Rf;

and the gain setting is recommended using from -1V/V to

-10V/V. The R

f is in the range from 4.7kΩ to 100kΩ. It’s

recommended to use 1% tolerance resistor or better.

Power Supply Decoupling, C

The APA2174 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 and PVDD lead for the best performance. For

filtering lower frequency noise signals, a large alumi-

num electrolytic capacitor of 10

µF or greater placed near

the audio power amplifier is recommended.

Charge Pump Bypass Capacitor, C

CPB

The bypass capacitor (CCPB) relates with the charge

pump switching transient. The capacitor’s value is same

as flying capacitor (2.2

µF). Place it close to the PVDD and

PGND.

Charge Pump Flying Capacitor, C

CPF

The flying capacitor affects the load transient of the charge

pump. If the capacitor’s value is too small, then that will

degrade the charge pump’s current driver capability and

the performance of line drive amplifier.

Increasing the flying capacitor’s value will improve the

load transient of charge pump. It is recommended using

t h e l o w E S R c e r am i c c ap ac i t o r s ( X 7 R t y p e i s

recommended) above 2.2

µF.

Charge Pump Output Capacitor, C

CPO

The output capacitor’s value affects the power ripple di-

rectly at CV

SS (VSS). Increasing the value of output capaci-

tor reduces the power ripple. The ESR of output capacitor

affects the load transient of CV

SS (VSS). Lower ESR and

greater than 2.2

µF ceramic capacitor is a recommendation.

Layout Consideration

Figure 2: TQFN4x4-20B Land Pattern Recommendation

1. All components should be placed close to the APA2174.

For example, the input capacitor (C

i) should be close to

APA2174’s input pins to avoid causing noise coupling

to APA2174’s high impedance inputs; the decoupling

capacitor (C

S) should be placed by the APA2174’

s power

pin to decouple the power rail noise.

2. The output traces should be short and wide (>20mil),

3. The input trace should be short and symmetric.

4. The power trace width should be greater than 20mil.

5. The TQFN Thermal PAD should be soldered on PCB,

and the ground plane needs soldered mask (to avoid

short circuit) except the Thermal PAD area.

2.2mm

0.5mm

0.35mm

Ground

Plane for

ThermalPAD

ThermalVia

Diameter

0.3mm X 5

0.9mm

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