SA58672 Datasheet, PDF (16/27 Pages) NXP Semiconductors – 3.0 W mono class-D audio amplifier

NXP Semiconductors
SA58672
3.0 W mono class-D audio amplifier
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 may be necessary to use
an LC output filter.
11.7 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 10 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 4:
R_{th( j-a)} = _d----_e---_r---_a---_t--_i--_n---^1g-------_f--_a---_c---_t--_o---_r- = ₀----_.1-₀---₁- = 100 K /W
(4)
For a maximum allowable junction temperature, T_j = 150 °C and R_th(j-a) = 100 K/W and a
maximum device dissipation of 0.84 W (420 mW per channel) and for 1.7 W per channel
output power, 4 Ω load, 5 V supply, the maximum ambient temperature is calculated using
Equation 5:
T _amb(max) = T _j(max) – (R_{th( j-a)} × P_max) = 150 – (100 × 0.84) = 66 °C
(5)
The maximum ambient temperature is 66 °C at maximum power dissipation for 5 V supply
and 4 Ω load. If the junction temperature of the SA58672 rises above 150 °C, the thermal
protection circuitry turns the device off; this prevents damage to the IC. Using speakers
greater than 4 Ω further enhances thermal performance and battery lifetime by reducing
the output load current and increasing amplifier efficiency.
11.8 Additional thermal information
The SA58672 9 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 lower package
thermal resistance.
The SA58672 HVSON10 package has an exposed Die Attach Paddle (DAP), which is
soldered directly to the PCB heat spreader to provide enhanced heat transfer and achieve
lowest package thermal resistance.
SA58672_4
Product data sheet
Rev. 04 — 8 June 2009
© NXP B.V. 2009. All rights reserved.
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