LAUNCHXL-F28379D: LAUNCHXL-F28379D

6th Sep is a holiday in US and hence please expect a delay in response.

Thanks. I was thinking no one has seen my question. Alright, I will wait. Thank you again.

Hi Faisal,

Can you give some further details on what you're trying to implement? You want to use 6 DAC signals to represent the current/voltage measurements the F2837x measures to another device? This isn't clear to me.

The F28379D LaunchPad brings out two DAC signals (A and B) and it also has four PWM DACs. see https://www.ti.com/lit/spraa88 for usage.

Faisal said:

My question is that is there any DAC extension board so that I can get more DAC signals from the computer (host)? Let's say, instead of 4, I can get 6 or 8 DACs.

I'm not aware of such a board within TI, but it may exist. Third parties probably may have some solution for this.

Best,

Kevin

Hi Kevin,

Please check the below picture. I want to take 6 DAC signals from F28379D and use it as the input of F28377S. This is a kind of loop.

I was checking the F28379D brochure and I am a bit confused. Does it come with 3 DAC or 2 DAC? In MATLAB, I could see DAC0, DAC1, and DAC2 as the three DAC signals that could come out of the F28379D board.

Thank you.

Hi Faisal,

DACOUTC of the F28379D device is not brought out to a header on the F28379d LaunchPad, only A and B are. I'm not familiar with the configuration in Matlab, it's likely board agnostic and not just for the LaunchPad however.

Best,

Kevin

Hi Kevin.

So, do you have any idea about the figure that I attached in my previous comment?

Hi Faisal,

On the LaunchPad you can use DACOUTA, DACOUTB, and then the four PWM DACs I mentioned earlier for your use case.

Best,

Kevin

Hi Kevin,

Thanks. Do you know how to quality of DAC output by using PWM pins is? How much does it deviate from the actual DAC signal? Can I get roughly 99% the same as the signal that is being transmitted by the DAC pin?

Thanks

Hi Faisal,

The app note I linked gives further details on the usage (link below as well).

https://www.ti.com/lit/spraa88

What's on the LaunchPad design uses a 1st order LPF, so performance will likely be less than this.

Best,

Kevin

Hi Kevin,

It is written Launchpad-F28379D has 3 DACs but you said, it has two. I am totally confused.

Faisal,

That's the F28379D device. The LaunchPad PCB only brings out two of the three DACs to a connector pin. Pins 10 of the below:

Best,

Kevin

The 4 DACs you refer to are actually PWM signals with 1st order low-pass filters, as shown by Kevin Allen18. So they are not enough to represent signals with fast dynamic behavior. The 28379D chip has 3 native DACs with high bandwidth ( shown in the datasheet of the chip), however, the launchpad only wired 2 of them into the board. The DAC C for god knows what reason, was not wired by texas into the board. One question that I would like to be answered by the TI engineers. 

If you wanna send out more signals, what you can do is to design high-order low-pass filters (very sharp filters) with high cutoff frequency, and modulated your signals using the PWM pins at very high frequency (400khz or higher). Is the same solution the board uses with these 4 DACs, but improving the filter topology. If you design your filters nicely and use enough high switching frequency, you can easily output high-frequency signals. I use LPF with 4th order and 30khz cutoff frequency, with PWM switching at 400khz or 500khz. This gives me between 8 to 9 bit resolution output. And you can use all 12 channel of PWM as DAC outputs   

Hi Renan,

Thanks. I have searched yesterday and found the below URLs.

https://www.ti.com/tool/DAC80504EVM

https://www.ti.com/tool/DAC81416EVM

https://www.ti.com/tool/DAC128S085EVM

For example, the last one gives me 8 DAC signals but I don't know how to connect this with the microcontroller and MATLAB Simulink. Do you have any idea about that?

Thank you.

Hi Renan,

Thanks for the added comments and details, you're exactly right. As for the reason why DAC_C was not wired out to a board header, I'm not certain since the board was designed before I joined TI. However, I'll note that the LaunchPad designs for our devices always have some constraints and limitations when defining a pin-out for compatibility across different Boosterpacks / EVMs. We often have to make some trade-off decisions like this, especially for the higher pin-count devices (like the 337-BGA used here).

Best,

Kevin

Hi Faisal,

For those EVMs you found you should check how they interface with an MCU. Maybe through a communications port like SPI or I2C. MATLAB may have modules for configuring the comms peripherals like that. You would then need to reference the EVM manuals / device datasheets for the proper protocol to communicate with them.

Best,

Kevin

Hi Kevin,

Sure, I will but the fact is that the prices of those three EVMs are different and I want to buy something that may solve my problem. If I have to pay for that EVM board and it is not going to work, that would be a waste of money. But, yes, you're right.

Thanks

Hi Kevin,

I am searching on how to use DAC128S085 in MATLAB and if there was no relevant information, I will follow your instructions.

Thanks a lot.