SA58670_1

© NXP B.V. 2008. All rights reserved.

Product data sheet

Rev. 01 — 4 January 2008

17 of 25

NXP Semiconductors

SA58670

2.1 W/channel stereo class-D audio amplifier

Since the value of the input decoupling capacitor and the input resistance determined by

the gain setting affects the low frequency performance of the audio amplifier, it is

important to consider this during the system design. Small speakers in wireless and

cellular phones usually do not respond well to low frequency signals, so the 3 dB cut-off

frequency may be increased to block the low frequency signals to the speakers. Not using

input coupling capacitors may increase the output offset voltage.

(2)

11.3 PCB layout considerations

Component location is very important for performance of the SA58670. Place all external

components very close to the SA58670. Placing decoupling capacitors directly at the

power supply voltage pins increases efficiency because the resistance and inductance in

the trace between the SA58670 power supply voltage pins and the decoupling capacitor

causes a loss in power efficiency.

The trace width and routing are also very important for power output and noise

considerations.

For high current pins (PVDD, PGND and audio output), the trace widths should be

maximized to ensure proper performance and output power. Use at least 500

µm wide

traces.

For the input pins (INRP, INRN, INLP and INLN), the traces must be symmetrical and run

side-by-side to maximize common-mode cancellation.

11.4 Filter-free operation and ferrite bead filters

A ferrite bead low-pass filter can be used to reduce radio frequency emissions in

applications that have circuits sensitive to frequencies greater than 1 MHz. A ferrite bead

low-pass filter functions well for amplifiers that must pass FCC unintentional radiation

requirements for frequencies greater than 30 MHz. Choose a bead with high-impedance

at high frequencies and very low-impedance at low frequencies. In order to prevent

distortion of the output signal, select a ferrite bead with adequate current rating.

For applications in which there are circuits that are EMI sensitive to low frequencies

(< 1 MHz) and there are long leads from amplifier to speaker, it is necessary to use an LC

output filter.

Table 6.

Gain selection

G1

G0

Gain (V/V)

Gain (dB)

Input impedance (k

Ω)

LOW

LOW

2

6

28.1

LOW

HIGH

4

12

17.3

HIGH

LOW

8

18

9.8

HIGH

HIGH

16

24

5.2

C

i

1

2

π R

i

×

f

3dB

–

×

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