SA58670_1

© NXP B.V. 2007. All rights reserved.

Objective data sheet

Rev. 01 — 22 June 2007

10 of 18

NXP Semiconductors

SA58670

2.1 W/channel stereo Class D audio amplifier

11.3 PCB layout considerations

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

components very close to the device. Placing decoupling capacitors directly at the power

supply pins increases efficiency because the resistance and inductance in the trace

between the device power supply 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 terminals (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 and INLP/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 greater than 1 MHz. A ferrite bead low-pass

filter functions well for amplifiers that must pass FCC unintentional radiation requirements

at 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 frequency

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

output filter.

11.5 Efficiency and thermal considerations

The maximum ambient operating temperature depends on the heat transferring ability of

the heat spreader on the PCB layout. In Table 3 “Limiting values”, power dissipation, the

power derating factor is given as 41.6 mW/

°C. The device thermal resistance, R

following equation:

(3)

maximum device dissipation of 1.5 W (750 mW per channel) and for 2.1 W per channel

output power, 4

Ω load, 5 V supply, the maximum ambient temperature is calculated using

Equation 4:

(4)

The maximum ambient temperature is 114

°C at maximum power dissipation for 5 V

supply and 4

Ω load. If the junction temperature of the SA58670 rises above 150 °C, the

thermal protection circuitry turns the device off; this prevents damage to IC. Using

speakers greater than 4

Ω further enhances thermal performance and battery lifetime by

reducing the output load current and increasing amplifier efficiency.

R

th j-a

()

1

derating factor

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

1

0.0413

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

24

°C/W

==

=

T

amb max

()

T

jmax

()

R

th j-a

()

P

Dmax

()

×

()

–

150

24

1.5

×

()

–

114

°C

==

=