SA58670A_2 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 02 — 23 October 2008 18 of 24
NXP Semiconductors SA58670A
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. InTable 3 “Limiting values”, the power derating
factoris given as 41.6 mW/K. The device thermal resistance, Rth(j-a) is the reciprocal of the
power derating factor. Convert the power derating factor to Rth(j-a) byEquation 3:
(3)
For a maximum allowable junction temperature Tj=150 °C and Rth(j-a) = 24 K/W and a
maximum device dissipation of 1.5W (750 mW per channel) and for 2.1 W per channel
outputpower, 4 Ωload, 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 Ωload. If the junction temperature of the SA58670A rises above150 °C, the
thermal protection circuitry turns the SA58670A off; this prevents damage to IC. Using
speakers greater than 4Ω fur ther enhances thermal performance and battery lifetime by
reducing the output load current and increasing amplifier efficiency.

11.6 Additional thermal information

The SA58670A 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
maybe 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.
12. Test information
Rth j-a() 1
derating factor
------------------------------------------1
0.0416
---------------- 24 K/W===
Tamb max()Tj max()Rth j-a()Pmax
×()–150 24 1.5×()–114 °C===
Fig 17. Test circuit
002aad417
POWER
SUPPLY
+−
INxP
INxN
OUTxP
OUTxN
15 µH
15 µH
DUT RLAUX0025
30 kHz
LOW-PASS FILTER
AP585
MEASUREMENT
INPUTS
AP585
AUDIO
ANALYZER