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Old 5th December 2002, 07:31 PM   #11
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Has anyone tried an LC network to separate the signal power instead of RC? It seems to me that this would be better at damping strange transients while not adversely affecting current flow, assuming one picks the right parts. Plus, you won't be blocking DC to the supply pins if you're not using a capacitor in series with them.

And, since it's pretty obvious that a capacitor in series with the signal-power pins causes the magic smoke to be released, what about L in series, and C bypassing to GND? (IOW, build what is essentially a passive 2nd-order lowpass filter in series with the signal supply pins.)

oO
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Old 5th December 2002, 07:43 PM   #12
halojoy is offline halojoy  Sweden
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Default Must be a way to solve this.

Possible causes of the blow up.

IC does not like one stage powered up before the other.
What stage would be first I do not know,
I should guess the driver first then output stage.

Mute and standby is activated, deactivated in wrong order.
In the datasheet there is some diagram
that tries to show how this should be done.
with diode and RC-delay.

A combination of both this things.

Remember that big capacitors in power supply can act as time delaying components.
What is the reference for the mute and standby - at what time is that reference and voltage present?
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Old 5th December 2002, 08:02 PM   #13
vuki is offline vuki  Croatia
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Oddone:
The resistors were in series and caps to ground. I hoped that was obvious from my post.
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Old 7th April 2003, 03:37 AM   #14
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Default Successful slave?

I was about to buy a quantity of TDA7293s, to drive some harder loads.

Did anyone ever get this chip, or any other, working successfully in slave mode?


Regards

Richard
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Old 24th April 2003, 04:10 PM   #15
moamps is offline moamps  Croatia
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Hi, Richard

In past two weeks I made some experiments with three TDA7293 (master + 2 slaves). In one p2p wiring and small heat sink, I have not any problems with PS to +- 45V. But, I find some difference in application notes for this chip according slave wiring.

From:
http://www.ub-elektronik.de/baugr-texte/amp.htm

1. Modular Application (more Devices in Parallel) -

The master chip connections are the same as the normal single ones.
The outputs can be connected together without the need of any ballast resistance.
The slave SGND pin must be tied to the negative supply.
The slave ST-BY pin must be connected to ST-BY pin.
The bootstrap lines must be connected together and the bootstrap capacitor must be increased:
for N devices the bootstrap capacitor must be 22mF times N.
The slave Mute and IN-pins must be grounded.

And from:
http://eu.st.com/stonline/books/pdf/docs/6744.pdf

2. Modular Application (more Devices in Parallel)

The master chip connections are the same as the normal single ones.
The outputs can be connected together without the need of any ballast resistance.
The slave SGND pin must be tied to the negative supply.
The slave ST-BY and MUTE pins must be connected to the master ST-BY and MUTE pins.
The bootstrap lines must be connected together and the bootstrap capacitor must be increased:
for N devices the bootstrap capacitor must be 22mF times N.
The slave IN-pin must be connected to the negative supply.


Different is connection of MUTE pin.

I made wiring according first manual, friend of my was trying second apps, and this don't work.

This chip is very sensitive; I made some experiments with using only output FET-s in slave mode for something like "unity gain gain clone" but without success until now (one fried chip).

Maybe my evidence can help you.

Regards
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Old 29th April 2003, 06:32 PM   #16
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I'm a newbie. (Sorry for my poor english)
I expect doing Amps (mono) with TDA7293 in modular applications.
So my kestion is:
Wich Impedance must be placed (for the speaker) when using 1,2,3 or n chip in slave?
Is there a relationship between that? (I presume that Power dissipation is a fact that cannot be understimate).
Thank you.


moamps, thanks for the Mute advice
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Old 30th April 2003, 09:19 AM   #17
moamps is offline moamps  Croatia
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Hi,

I think that configuration with master and 2 slaves is maximum. With this configuration you have about 3x6A=18 amps peak current, on 2E speaker this is huge power.
You can connect any impedance down to 2E, but must think about power dissipation on chips when choose PS voltage.

My plan is building some active 2way speaker with Seas drivers and one 7293 for high, 2 parallel for bass-midle with overall power about 30-40W, no more.

Regards
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Old 19th March 2006, 12:37 PM   #18
ilimzn is offline ilimzn  Croatia
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Well, I am about 3 years too late here, but anyway:

TDA 7293/94 have relatively poor PSRR, which is why a separate well filtered power supply on the signal section can improve things quite a lot.
Why does it blow up if you connect the signal power via a RC filter to the output power? Well, the reason is rather simple if one knows a bit about IC design:
Looking at the pinout, it becomes obvious that the -Vs signal power pin is connected to the heatsink tab. More importantly, this is the substrate of the IC, which needs to always be the MOST NEGATIVE point in the IC otherwise various structures in it become conductive or even behave as latched-up thyristors, rendering the whole IC a big short circuit. Result: the IC literally explodes.
With a simple RC filter, this will happen on initial power application because the -Vs pin will be more positive than the -Vp pin. A simple cure is to put a (preferably schottky) diode from -Vs to -Vp alowing the filter cap off -Vp to charge 'immediately' with the main power supply.
This is quite easy to see on the 'high efficiency' application diagram, although, they used fast diodes instead of schottky. Many get confused because that is a class G amp, the diodes are there for power supply commutation - however, they also insure that -Vs is never less that 1 diode drop WRT -Vp, ditto for +Vs and +Vp. It is obvious from that schematic that the TDA7293/4 indeed can work with separate Vs and Vp voltages.
It is highly probable, though, that there is amaximum difference in Vs and Vp. Given the power supply voltage difference in the high efficiency application (20V) it is safe to assume that the DMOS process used to manufacture the chips produces similar maximum gate to source voltage limitas as for regular power MOSFETs, about 20V. If separate power supplies are used, care should be taken that Vs never becomes over 20V more than Vp.
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Old 21st March 2006, 12:30 AM   #19
ilimzn is offline ilimzn  Croatia
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I forgot to mention: keeping +Vs a minimum of 7V higher than +Vp also dispenses with the bootstrap capacitor...
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Old 9th April 2006, 01:39 PM   #20
ArtiomR is offline ArtiomR  Lithuania
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ilimzn , thanks for your explanation of the principles of working of this IC
I am going to try to make my TDA7294 working from separate supplies for signal and power parts. My intention is to power the signal part from separate transformers with some 10V higher voltage, than power part (+-27V now). Also, to make sure, the substrate is always the most negative part of the circuit, I will put quite a lot of bypass capacitance in signal supply, a little oversized traffos(around 40-50VA per channel, for fast initial charging of capacitors), and higher value bleeding resistors (than on power part), so that when powered off, the Vp would become zero faster, than signal part.

What do you think about such arrangement? Will it work?

And finally, could you explain please the following:
Quote:
keeping +Vs a minimum of 7V higher than +Vp also dispenses with the bootstrap capacitor...
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