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Old 14th January 2007, 12:49 PM   #1
phn is offline phn  Sweden
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Default TDA1541 and TDA1543 questions

I have read the datasheets, and I'm sure it's in there. But I cannot for my life figure out the output voltages of them. I figure they are current devices. That still doesn't help me.

So how do I go about calculating the outputs?
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Old 14th January 2007, 01:48 PM   #2
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phn

The DAC chips output current and require an external I/V stage. The output voltage depends on the design of I/V stage not the DAC chips themselves.
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Old 14th January 2007, 01:55 PM   #3
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Default Re: TDA1541 and TDA1543 questions

Quote:
Originally posted by phn
I have read the datasheets, and I'm sure it's in there. But I cannot for my life figure out the output voltages of them. I figure they are current devices. That still doesn't help me.

So how do I go about calculating the outputs?
Ohm's Law:
V= I * RIV
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Old 14th January 2007, 02:05 PM   #4
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Oh, and "I" is in the datasheet.
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Old 14th January 2007, 02:38 PM   #5
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Thanks guys.

Yes, the I is in the datasheets. And the TDA1543 datasheet even shows an I/V using a 1.2k resistor, which should mean 2.3mA * 1.2k.

But the TDA1541 has a "typical" output of 4mA. As I understand it, the TDA1541 can not be used with a passive I/V like the TDA1543.

The TDA1545 has an output of just 1mA and the datasheet shows an I/V with 3.9k resistor. That makes perfect sense to me. But then the TDA1541 screwed things up for me.

I'm not completely clueless here. But there evidently are things I don't quite understand.
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Old 14th January 2007, 06:35 PM   #6
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Some more.

The 2.3mA of the TDA1543 and a passive I/V of 2.4kOhms result in about 2Vrms. Ran it in LTSpice.

I'm getting there. But I still have some questions.

I read this about the TDA1543:

"The DAC outputs an analog current proportional to the digitally encoded input signal, and the current is drawn through the output resistors, one for each channel, to produce the output voltage."

Continues...

"The TDA1543 is run at 9 V instead of the normal 5 V. This is done to give the chip enough headroom to output a standard 2 Vrms output signal. The result will be a dangerously warm chip unless heatsinking is used."

What does "headroom" mean here?

Second. Some of the popularity of the TDA1543 is related to the fact that you can use it with a passive I/V. From that I conclude that the TDA1541 cannot be used without a passive I/V. Am I correct? How about the 4mA? If you cannot simply use a 1.5k resistor with the TDA1541, why?
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Old 15th January 2007, 07:56 AM   #7
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The differences should be around Vref pin. TDA1543 and TDA1545 have a Vref pin and the TDA1541 doesn't.
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Old 15th January 2007, 02:59 PM   #8
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Quote:
Originally posted by quantran
The differences should be around Vref pin. TDA1543 and TDA1545 have a Vref pin and the TDA1541 doesn't.
I noticed the Vref pin. But not that it is not on the TDA1541. I think I know what "Vref" stands for. But what does it do? I checked some TDA1543 schematics. Didn't get any wiser.

I also noticed that the DDDAC gets an output of 1.6Vrms from 8.4V. The 47 Labs claims the Progression DAC has an output of 2.1V. I guess the latter must be 2.1Vp.
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Old 15th January 2007, 03:55 PM   #9
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Default Re: TDA1541 and TDA1543 questions

Quote:
Originally posted by phn
I have read the datasheets, and I'm sure it's in there. But I cannot for my life figure out the output voltages of them. I figure they are current devices. That still doesn't help me.

So how do I go about calculating the outputs?
As you have yet read in datasheet and as other have yet told you, TDA 1541 and TDA1543 are output current DAC which require an external *active* I/V converter (i.e. a properly connected op amp or other circuit able to guarantee its input behaviour as a "virtual ground" in order to obtain the maximum current constance - and linearity). So calle "voltage output" DAC, especially if they are of multibit type, simple use an *internal* I/V active converter (i.e. an op amp integrated on the same chip): DAC of this class are inherently current sources, not voltage sources. The real difference with the two "flavour" of DAC is that I/V section is internal or external to the DAC IC, nothing more!

About "Vref". TDA 1541 and TDA 1543 have either Vref connection but, with TDA 1541 (which require dual supply), "vref" is just the ground connection. Besides, the Vref pin of TDA 1543 is to be used as a bias reference for external I/V converter and not for arranging a "passive" I/V converter with resistors. Overriding the question of supplyng TDA 1543 with near the double of voltage for what it's designed for, with IC must be kept in mind that all mode no written down in datasheet may easily turn in a written out of IC itself... be careful with experiment, especially when no internal schematic is provided in datasheet (as is in this case).

Curiosity: why you need to change TDA 1541 (or 1543) in "native voltage out" when they are not thought for?

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Old 15th January 2007, 04:31 PM   #10
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Default Re: Re: TDA1541 and TDA1543 questions

Quote:
Originally posted by Piercarlo


As you have yet read in datasheet and as other have yet told you, TDA 1541 and TDA1543 are output current DAC which require an external *active* I/V converter (i.e. a properly connected op amp or other circuit able to guarantee its input behaviour as a "virtual ground" in order to obtain the maximum current constance - and linearity).
But I have read the datasheets, more than once. I think I have made that more than clear here.

The datasheets may say they require active I/Vs. But we know there are lots of TDA1543 DACs with passive I/Vs.

My problems are not related to the datasheets per se, but my limited knowledge about electronics. For example, I knew what passive and active I/Vs are. But I did not knew you could set the voltage (if that's the right word for it) with a passive I/V. That I learned yesterday. Hence I wrote: "The 2.3mA of the TDA1543 and a passive I/V of 2.4kOhms result in about 2Vrms. Ran it in LTSpice." That was a revelation to me.

Quote:
Originally posted by Piercarlo

Curiosity: why you need to change TDA 1541 (or 1543) in "native voltage out" when they are not thought for?

I don't. The I/V does that. I just didn't know how a passive I/V works. Now I do.

I will try to figure out the rest of your post.
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