SA58670_1

© NXP B.V. 2008. All rights reserved.

Product data sheet

Rev. 01 — 4 January 2008

18 of 25

NXP Semiconductors

SA58670

2.1 W/channel stereo class-D audio amplifier

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”, the power derating

(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 SA58670 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.

11.6 Additional thermal information

The SA58670 HVQFN20 package incorporates an exposed DAP that is designed to

solder the mount directly to the PCB heat spreader. By the use of thermal vias, the DAP

may be soldered directly to a ground plane or special heat sinking layer designed into the

PCB. The thickness and area of the heat spreader may be maximized to optimize heat

transfer and achieve lowest package thermal resistance.

R

th j-a

()

1

derating factor

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

1

0.0416

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

24 K /W

==

=

T

amb max

()

T

j max

()

R

th j-a

()

P

max

×

()

–

150

24

1.5

×

()

–

114

°C

==

=