Nxp Semiconductors SA58670A User Manual

SA58670A_2

© NXP B.V. 2008. All rights reserved.

The maximum ambient operating temperature depends on the heat transferring ability of
the heat spreader on the PCB layout. In

, the power derating

factor is given as 41.6 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

(3)

For a maximum allowable junction temperature T

j

= 150

°

C and R

th(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

(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 SA58670A rises above 150

°

C, the

thermal protection circuitry turns the SA58670A 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.

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
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.

th j-a

(

)

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

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

24 K /W

=

=

=

(

)

(

)

th j-a

(

)

×

(

)

–

×

(

)

–

°

=

=

=

002aad417

POWER

SUPPLY

+

−

INxP

INxN

OUTxP

OUTxN

15 

µ

H

15 

µ

H

DUT

RL

AUX0025

30 kHz

LOW-PASS FILTER

AP585

MEASUREMENT

INPUTS

AP585

AUDIO

ANALYZER