TDA8920B_2
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
Product data sheet
Rev. 02 — 07 November 2005
17 of 34
Philips Semiconductors
TDA8920B
2
×
100 W class-D power amplifier
If two or more class-D amplifiers are used in the same audio application, it is strongly
recommended that all devices run at the same switching frequency. This can be realized
by connecting all OSC pins together and feed them from an external central oscillator.
Using an external oscillator it is necessary to force pin OSC to a DC-level above SGND for
switching from the internal to an external oscillator. In this case the internal oscillator is
disabled and the PWM modulator will be switched on the external frequency. The
frequency range of the external oscillator must be in the range as specified in the
switching characteristics; see
In an application circuit:
•
Internal oscillator: R
OSC
connected between pin OSC and V
SSA
•
External oscillator: connect the oscillator signal between pins OSC and SGND; R
OSC
and C
OSC
removed
13.5 Heatsink requirements
In some applications it may be necessary to connect an external heatsink to the
TDA8920B. Limiting factor is the 150
°
C maximum junction temperature T
j(max)
which
cannot be exceeded. The expression below shows the relationship between the maximum
allowable power dissipation and the total thermal resistance from junction to ambient:
(5)
P
diss
is determined by the efficiency (
η
) of the TDA8920B. The efficiency measured in the
TDA8920B as a function of output power is given in
. The power dissipation can
be derived as a function of output power (see
The derating curves (given for several values of R
th(j-a)
) are illustrated in
A maximum junction temperature T
j
= 150
°
C is taken into account. From
maximum allowable power dissipation for a given heatsink size can be derived or the
required heatsink size can be determined at a required dissipation level.
R
th j
a
–
(
)
T
j max
(
)
T
amb
–
P
diss
------------------------------------
=
