SA58670 Просмотр технического описания (PDF) - NXP Semiconductors.
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SA58670 Datasheet PDF : 25 Pages
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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
factor is 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) by Equation 3:
Rth( j-a) = d----e---r---a---t--i--n---1g-------f--a---c---t--o---r- = 0---.--0--1-4---1---6- = 24 K /W
(3)
For a maximum allowable junction temperature Tj = 150 °C and Rth(j-a) = 24 K/W and a
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:
T amb(max) = T j(max) – (Rth( j-a) × Pmax) = 150 – (24 × 1.5) = 114 °C
(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.
SA58670_3
Product data sheet
Rev. 03 — 11 June 2009
© NXP B.V. 2009. All rights reserved.
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