SA58670 Datasheet, PDF (9/18 Pages) NXP Semiconductors – 2.1 W/channel stereo Class D audio amplifier

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
audio source that is biased from 0.5 V to V_DD − 0.8 V. In other words, the input signal must
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:
f_C
=
--------------¹---------------
2π × R_i × C_i
(1)
Table 6.
G1
0
0
1
1
Gain selection
G0
Gain (V/V)
0
2
1
4
0
8
1
16
Gain (dB)
6
12
18
24
Input impedance (kΩ)
28.1
17.3
9.8
5.2
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.
Equation 1 is solved for C_i:
C_i
=
--------------¹--------------
2π × R_i × f_C
(2)
SA58670_1
Objective data sheet
Rev. 01 — 22 June 2007
© NXP B.V. 2007. All rights reserved.
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