SA58671 Datasheet, PDF (18/24 Pages) NXP Semiconductors – 1.2 W/channel stereo class-D audio amplifier

NXP Semiconductors
SA58671
1.2 W/channel stereo class-D audio amplifier
11.5 Efficiency and thermal considerations
The maximum ambient 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 9.12 mW/K. The device thermal resistance, R_th(j-a) is the
reciprocal of the power derating factor. Convert the power derating factor to R_th(j-a) by
Equation 3:
R_{th( j-a)} = _d----_e---_r---_a---_t--_i--_n---^1g-------_f--_a---_c---_t--_o---_r- = ₀----_.-₀---₀-¹--₉---₁---₂- = 110 K /W
(3)
For a maximum allowable junction temperature, T_j = 150 °C and R_th(j-a) = 110 K/W and a
maximum device dissipation of 0.6 W (300 mW per channel) and for 1.2 W per channel
output power, 4 Ω load, 5 V supply, the maximum ambient temperature is calculated using
Equation 4:
T _amb(max) = T _j(max) – (R_{th( j-a)} × P_max) = 150 – (110 × 0.60) = 84 °C
(4)
The maximum ambient temperature is 84 °C at maximum power dissipation for 5 V supply
and 4 Ω load. If the junction temperature of the SA58671 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.
11.6 Additional thermal information
The SA58671 16 bump WLCSP package ground bumps are soldered directly to the PCB
heat spreader. By the use of thermal vias, the bumps 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.
12. Test information
AP585
AUDIO
ANALYZER
Fig 16. Test circuit
INxP
OUTxP
DUT
INxN
OUTxN
15 µH
15 µH
AUX0025
RL
30 kHz
LOW-PASS FILTER
+−
POWER
SUPPLY
AP585
MEASUREMENT
INPUTS
002aad417
SA58671_2
Product data sheet
Rev. 02 — 24 October 2008
© NXP B.V. 2008. All rights reserved.
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