DAC161S997: Power supply for DAC161S997 on VA and VD

Fangzhou Zhao

Prodigy 40 points

Part Number: DAC161S997

Hello,

are the power supplies for analog-block VA and for digital-block VD internally connectet?

is it possible to use different power supplies for VA COMA and VD COMD.

over 3 years ago

0 Akhilesh K over 3 years ago

TI__Mastermind 18756 points

Hi,

These two are not internally connected, you can power up the same with different power supplies. Please note these shares common ground internal to the device ( there is no isolation between COMA and COMD)

Since the recommended operating voltages for both VA and VD are same ( 3.3V), why you want to power them with separate power supplies? As such in a typical implementation( loop powered systems), you want to operate them with the loop regulated supplies. Please see the applications section in the datasheet for more information. We have characterized this device with VA = VD = 3.3V

Regards,

0 Fangzhou Zhao over 3 years ago in reply to Akhilesh K

Prodigy 40 points

Hello AK,

thanks for the reply, my purpose is to use one MCU to control two DAC161S997s for two current loops. As you said the COMA and COMD are internally connectet, I might need a isolator between the MCU and one of the DAC161S997.

0 Akhilesh K over 3 years ago in reply to Fangzhou Zhao

TI__Mastermind 18756 points

Hi,

Please post the schematics once you are done with your design. I will be happy to help.

I am closing this thread as of now, you can reopen the same once you have done with your design

Regards,

0 Fangzhou Zhao over 3 years ago in reply to Akhilesh K

Prodigy 40 points

Hello AK,

I have done a simple example for my application, will it work? The IC1 is a digital isolator, it shall pass the data between the mcu and the DAC161S991(U8).

0 Akhilesh K over 3 years ago in reply to Fangzhou Zhao

TI__Mastermind 18756 points

Hi,

I am afraid this scheme will not work here. Your loop power supply is referred to which ground here? looking at the schematics, you want to isolate the two DAC's right and powered up using the same loop supply?

Regards,

0 Fangzhou Zhao over 3 years ago in reply to Akhilesh K

Prodigy 40 points

Hello AK,

yes you are right, sorry for the mistake. there shall be two seperated 24V supplies.

0 Akhilesh K over 3 years ago in reply to Fangzhou Zhao

TI__Mastermind 18756 points

Hi,

Can you redraw the same and resend? Also we have multiple blog posts explaining this in details.

https://e2e.ti.com/blogs_/archives/b/precisionhub/posts/2-wire-4-20ma-sensor-transmitters-background-and-common-issues-part-5

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/945188/faq-designing-with-4-20ma-current-loop-transmitters-xtrs-faq-links?tisearch=e2e-sitesearch&keymatch=4%25252525252525252520to%2525252525252525252020mA#

Regards,

0 Fangzhou Zhao over 3 years ago in reply to Akhilesh K

Prodigy 40 points

Hello AK,

now it looks like this...

+1 Akhilesh K over 3 years ago in reply to Fangzhou Zhao

TI__Mastermind 18756 points

Hi,

This scheme can work, Needs to verify thoroughly.

Did you read the above blogs to understand different tradeoffs in designing multiple isolated 4-20mA transmitters? I am copying one of our Apps engineers who worked on these to comment on the same.

Regards,

0 Fangzhou Zhao over 3 years ago in reply to Akhilesh K

Prodigy 40 points

Hello AK,

yes I have read the blog, these are really helpful, thanks for your support.

0 Akhilesh K over 3 years ago in reply to Fangzhou Zhao

TI__Mastermind 18756 points

Hi,

Thanks, If Katlynne have any comments on the schematics, she will reply back to you on this thread.

Regards,

0 Katlynne Jones over 3 years ago in reply to Fangzhou Zhao

TI__Mastermind 28058 points

Hi Fangzhou,

I notice a few more small errors in this schematic.

I do not see where you are applying a supply to the VA pins on the two DAC161S997s. I suspect you want to apply VCC1 and VCC2 to the respective VA pins.
Connect EERLVL pin to COMD or VD so if there is a timeout error the OUT current will go to an expected level. Or disable this feature using the MASK_SPI_ERR bit of the ERR_CONFIG register.

You are missing a second diode on the loop connected to P2.

Everything else looks ok to me.

Best,

Katlynne Jones

Data converters

Data converters forum

DAC161S997: Power supply for DAC161S997 on VA and VD