TDF8590TH NXP Semiconductors, TDF8590TH Datasheet - Page 17

• Manufacturer Part Number: TDF8590TH
• Description: The TDF8590TH is a high-efficiency class-D audio power amplifier with low powerdissipation for application in car audio systems
• Manufacturer: NXP Semiconductors

NXP Semiconductors
TDF8590TH_2
Product data sheet
12.5 Heat sink requirements
12.6 Pumping effects
In some applications it may be necessary to connect an external heat sink to the
TDF8590TH. The thermal foldback activates on T
the relationship between the maximum power dissipation before activation of the thermal
foldback and the total thermal resistance from junction to ambient:
The power dissipation is determined by the efficiency
measured as a function of output power is given in
be derived as function of output power (see
Example of a heatsink calculation for the 8
When the TDF8590TH is used in a SE configuration, a so-called pumping effect can
occur. During one switching interval, energy is taken from one supply (e.g. V
part of that energy is delivered back to the other supply line (e.g. V
When the voltage supply source cannot sink energy, the voltage across the output
capacitors of that voltage supply source will increase: the supply voltage is pumped to
higher levels. The voltage increase caused by the pumping effect depends on:
R
•
•
•
•
•
•
•
•
•
•
•
•
th j a –
An audio signal with a crest factor of 10 (the ratio between peak power and average
power is 10 dB), this means that the average output power is 1/10th of the peak power
The peak RMS output power level is 130 W (0.5 % THD level)
The average power is 0.1
The dissipated power at an output power of 13 W is approximately 5 W
The total R
The total thermal resistance R
R
would then be: 11
Speaker impedance
Supply voltage
Audio signal frequency
Value of decoupling capacitors on supply lines
Source and sink currents of other channels
th(j-c)
=
= 1.1 K/W, R
T
----------------------- -
j
–
P
th(j-a)
T
amb
= (140
th(c-h)
Rev. 02 — 23 April 2007
(1.1 + 1) = 8.9 K/W
2
= 0.5 K/W to 1 K/W (dependent on mounting), so R
85) / 5 = 11 K/W, if the maximum expected T
80 W SE (4 ) or 1
130 W = 13 W
th(j-a)
= R
th(j-c)
Figure
BTL application with 27 V supply:
+ R
j
= 140 C. The expression below shows
Figure
24).
th(c-h)
160 W BTL (8 ) class-D amplifier
of the TDF8590TH. The efficiency
+ R
23. The power dissipation can
th(h-a)
TDF8590TH
SSA1
© NXP B.V. 2007. All rights reserved.
) and visa versa.
amb
DDA1
= 85 C
), while a
th(h-a)
17 of 30