DAC908: What is the minimum clock frequency for the DAC908?

Fabian Romo

Prodigy 60 points

Part Number: DAC908

Hi.

How are you?

We're interested in the DAC908 device to generate periodic signals. Something similar to a function generator.

My question is: What is the minimum clock frequency at the CLK pin (pin 28)?

Our idea is to create a periodic signal from about 1 kHz to 1 MHz.

The data sheets do not indicate a minimum value of for this frequency.

Regards.

over 2 years ago

0 Chase W over 2 years ago

TI__Mastermind 23760 points

Hi Fabian,

One of our experts will be in touch shortly. Thank you for waiting.

Regards, Chase

0 Camilo Garcia Trujillo over 2 years ago in reply to Chase W

TI__Expert 5035 points

Hi Fabian,

I was able to operate the DAC908 with the default EVM conditions with a clock input down to 1MHz. Keep in mind I am only testing this at room temperature and at nominal voltage. The 1MHz minimum can vary across process, voltage and temperature. There is no way to guarantee this across all parts over both temperature and voltage ranges.

If 1MHz is not low enough, could you please tell me why you want to run a lower clock frequency? And at what rate?

Best,

Camilo G

0 Fabian Romo over 2 years ago in reply to Camilo Garcia Trujillo

Prodigy 60 points

Hi Camilo

Thanks for answering.

We thought of generating a signal with the DAC from 1 MHz, but there is another project in mind where we want to generate a signal from 20 Hz.

Do you think it's possible for it to work at extremely low frequency?

Regards.

0 Camilo Garcia Trujillo over 2 years ago in reply to Fabian Romo

TI__Expert 5035 points

Hi Fabian,

For clarification, are you trying to generate a 20Hz output signal minimum? Or you want the sampling frequency of the DAC to be 20Hz? It is important to know the sampling frequency you want to use because it will define the range of frequencies you can output in the 1^st Nyquist zone.

If you are mostly interested in low frequency signals we do have a precision converter group that is in change of converters under 10MHz.

Here is the link to that forum just in case: https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum

Best,

Camilo G

0 Fabian Romo over 2 years ago in reply to Camilo Garcia Trujillo

Prodigy 60 points

HI.

Ok.

I understand that the DAC sample rate must be higher than the rate you want to generate.

This would imply that the DAC could always be maintained at 165MSPS, while in the digital port data, a signal is generated at a rate of about 20 Hz.

But the idea we have in mind is that the DAC reads an array stored in RAM-type memory. This array has the information of the analog signal to be generated.

So to get different frequencies, I would have to change the sample number of the DAC. For example, for 20 Hz, it could work at 2 kSPS, for a frequency of 2 Hz, the sampling frequency could be equal to 200 SPS.

Is it possible to use small sample rates like the ones I describe?

Regards

0 Chase W over 2 years ago in reply to Fabian Romo

TI__Mastermind 23760 points

Fabian, see my comments below.

Fabian Romo said:
This would imply that the DAC could always be maintained at 165MSPS, while in the digital port data, a signal is generated at a rate of about 20 Hz.

Correct, this is do-able but I think we are a bit confused here as whether or not there are two separate applications which you are asking about? Otherwise, why plan to use a 165MSPS DAC but have a 20Hz output? This is an excessive amount of data as the DAC will repeat the same code 8.25 million times before switching to a new code ?(in order to achieve the 20Hz output). I think you will be better off with one of our precision DACs instead for a low frequency application. https://www.ti.com/data-converters/dac-circuit/precision/products.html

Regards, Chase

0 Fabian Romo over 2 years ago in reply to Chase W

Prodigy 60 points

What we want is to have a calibratable frequency output signal from a minimum (in Hz) to a maximum of 1 MHz

Regards

0 Camilo Garcia Trujillo over 2 years ago in reply to Fabian Romo

TI__Expert 5035 points

Hi Fabian,

The DAC908 is a high-speed converter. And while this part can generate low frequency signals, TI has parts that are designed to operate at these frequencies with better performance since you are not looking into generating high frequency outputs (>10MHz).

We are reassigning this post to the Precision DAC team who have parts that will fulfil your needs more appropriately.

Regards,

Camilo

0 Paul_Frost over 2 years ago in reply to Camilo Garcia Trujillo

TI__Guru 53773 points

Hi Fabian,

Why not consider a precision DAC? Our MDACs are designed for a lower sample rate, but achieve better dynamic performance (THD, SNR) than higher speed converters when operating at a lower speed.

Take a look at the TLC7524 or DAC8806

Thanks,

Paul

0 Fabian Romo over 2 years ago in reply to Paul_Frost

Prodigy 60 points

Okay. I will review this information and any news, I will open a new thread. Thanks

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DAC908: What is the minimum clock frequency for the DAC908?