power amp tda ic running too hot?

[DuncanB]

Please could anybody help this is probably a very elementary question.

I have a chosen a TDA7263M 12wx12w stereo power amplifier and created a pcb
from the application schematic from the manufacturers data sheet. The
temperature of the case of the IC in operation levels out at approx 97c.

From cold the ic draws about 1.3A until this high temp is reached and then
current draw drops to approx .7A and the temp is maintained.

I have used various heat sinks 6c/w and much larger but the ic continues to
draw high current until the whole sink is 97c and then the current drops
back.


I have reduced the gain using the loopback circuits but this has no effect
on the temp. I have replaced the ic from stock twice. Checked the signal
tracks and the electrolytics etc a number of times. I have gone to bed
reading the data sheet.

I am missing something so stupid but I do not really now what else to try.
Unless this is the Temp that the chip runs at, can anybody offer any
suggestions please, I would be very grateful.


duncan

 

[CFoley1064]

Subject: power amp tda ic running too hot?
From: "DuncanB" d-h-b@freenet.co.uk
Date: 9/22/04 6:24 AM Central Daylight Time
Message-id: <1095852275.85636.0@iris.uk.clara.net



Please could anybody help this is probably a very elementary question.

I have a chosen a TDA7263M 12wx12w stereo power amplifier and created a pcb
from the application schematic from the manufacturers data sheet. The
temperature of the case of the IC in operation levels out at approx 97c.

From cold the ic draws about 1.3A until this high temp is reached and then
current draw drops to approx .7A and the temp is maintained.

I have used various heat sinks 6c/w and much larger but the ic continues to
draw high current until the whole sink is 97c and then the current drops
back.


I have reduced the gain using the loopback circuits but this has no effect
on the temp. I have replaced the ic from stock twice. Checked the signal
tracks and the electrolytics etc a number of times. I have gone to bed
reading the data sheet.

I am missing something so stupid but I do not really now what else to try.
Unless this is the Temp that the chip runs at, can anybody offer any
suggestions please, I would be very grateful.


duncan

Hi, Duncan. This is a good stereo amplifier IC, but it does want to be bad. I
assume you're working off the application suggestion on page 5 of the data
sheet:

http://www.st.com/stonline/books/pdf/docs/1476.pdf

A few questions, if you don't mind:

* First, are you getting any sound output at all? What's happening when you
turn it on?
* What are your speakers? 8 ohm, 4 ohm, 2 ohm? It makes a difference. This
IC is a voltage amplifier, and lower load resistance = greater current = much
greater power.
* Have you looked at relevant parts of the circuit with a scope for
oscillations? If so, what did you see?
* What's your supply voltage?
* If you're going to crank power from this IC, you need a really big heat
sink. As Aahnold would say, 6C/W is "girlie-man" stuff. Massive is where you
want to be here, especially if you're crankin'. Use heat sink compound, and
either screw it down to the heat sink or use clips.
* Are you using the PCB layout on p.5, or did you perfboard it? A perfboard
layout doesn't have a good chance of success, unless you're _very_ careful.
I've seen a successful application of this circuit where the design was done
double-sided with a ground plane. The engineer who did the layout said it made
the circuit more stable. He usually knew what he was talking about.
* Are you using the components listed on the applications page, or did you
substitute? If so, what for what?
* Did you just use generic 1000uF caps, or did you get ones which have better
high frequency response/lower ESR?
* What kind of cap did you use for C4 (the 0.1uF cap in parallel with the
1000uF power supply cap)?
* Are you using wirewound resistors for R5 and R6? I believe using 2 ea. 1/2W
10 ohm film resistors in parallel would be a better idea.

Need more data.

Chris