SA58670 NXP Semiconductors, SA58670 Datasheet - Page 17

• Manufacturer Part Number: SA58670
• Manufacturer: NXP Semiconductors

NXP Semiconductors
SA58670_3
Product data sheet
11.3 PCB layout considerations
11.4 Filter-free operation and ferrite bead filters
Table 6.
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.
Equation 2
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 m 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.
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.
C
G1
LOW
LOW
HIGH
HIGH
i
=
------------------------------------- -
2
Gain selection
R
G0
LOW
HIGH
LOW
HIGH
is solved for C
i
1
f
–
3dB
Gain (V/V)
2
4
8
16
Rev. 03 — 11 June 2009
i
:
Gain (dB)
6
12
18
24
2.1 W/channel stereo class-D audio amplifier
Input impedance (k )
28.1
17.3
9.8
5.2
SA58670
© NXP B.V. 2009. All rights reserved.
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