SA58670_1

© NXP B.V. 2007. All rights reserved.

Objective data sheet

Rev. 01 — 22 June 2007

9 of 18

NXP Semiconductors

SA58670

2.1 W/channel stereo Class D audio amplifier

11. Application information

11.1 Power supply decoupling considerations

The SA58670 is a stereo Class D audio amplifier that requires proper power supply

decoupling to ensure the rated performance for THD+N and power efficiency. To decouple

high frequency transients, power supply spikes and digital noise on the power bus line, a

low Equivalent Series Resistance (ESR) capacitor, of typically 1

µF is placed as close as

possible to the PVDD terminals of the device. It is important to place the decoupling

capacitor at the power pins of the device because any resistance or inductance in the

PCB trace between the device and the capacitor can cause a loss in efficiency. Additional

decoupling using a larger capacitor, 4.7

µF or greater may be done on the power supply

connection on the PCB to filter low frequency signals. Usually this is not required due to

high PSRR of the device.

11.2 Input capacitor selection

The SA58670 does not require input coupling capacitors when used with a differential

be biased within the common-mode input voltage range. If high pass filtering is required or

if it is driven using a single-ended source, input coupling capacitors are required.

The high pass corner frequency created by the input coupling capacitor and the input

resistors (see Table 6) is calculated by Equation 1:

(1)

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 in the system design. Small speakers in wireless and cellular

phones usually do not respond well to low frequency signals, so the high pass corner

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)

Table 6.

Gain selection

G1

G0

Gain (V/V)

Gain (dB)

Input impedance (k

Ω)

00

2

6

28.1

01

4

12

17.3

10

8

18

9.8

1

1

16

24

5.2

f

C

1

2

π R

i

×

C

i

×

-----------------------------

=

C

i

1

2

π R

i

×

f

C

×

-----------------------------

=