DAC8775: Simplification for 0-20 mA positive output only

Jason Harrington

Part Number: DAC8775

Tool/software:

TI,

I am currently testing the 8775EVM board, and everything appears to be working as intended. I plan to use three of the four channels strictly for 0–20 mA output. I would like to utilize the full input voltage range of the DAC (12–36 V). If I do not use the negative power supply on any of the channels, plan to use the buck-boost feature with full tracking, and do not intend to use the fourth channel, what simplifications can I make to the reference design? Am I able to eliminate some of the external components? With the exception of the inductor, can I eliminate all of the components in the red rectangle and tie LP_A and VNEG_IN_A to ground? I would assume that there aren't any components that I can remove on the output side?

Thanks,

Jason

1 month ago

0 Joseph Wu 1 month ago

TI__Guru* 96135 points

Jason,

If you're not planning on using the negative supply, you can eliminate a lot of the components from the negative buck boost.

In your figure, you put a dotted line around those components, but you would also connect the VNEG_IN_x to GND. This connection is described in the datasheet in the Power Supply Recommendations section on page 67. In particular, look at Figure 136.

Joseph Wu

0 Jason Harrington 1 month ago in reply to Joseph Wu

Prodigy 50 points

Thanks Joseph, it was silly for me to not catch that.

0 Joseph Wu 1 month ago in reply to Jason Harrington

TI__Guru* 96135 points

Jason,

No problem. I would note that if you have the EVM, you could test this with a little bit of modification to the board. Taking Channel A, you could remove the jumper at JP2, and then unsolder the diode at D3, I think you would get the schematic that you would use.

At that point, you would have the test point for VNEG_A, and you can attach an external supply there.

Joseph Wu

0 Jason Harrington 1 month ago in reply to Joseph Wu

Prodigy 50 points

I'll give it a try, it seems that for my application I would tie VNEG_IN_A to GND.

0 Joseph Wu 1 month ago in reply to Jason Harrington

TI__Guru* 96135 points

Jason,

I think that if you're tying VNEG_IN_x to GND, then you wouldn't need to remove the diode, and you can just use the jumper. Note that there is a jumper that is connected to AVSS, which would be GND on the board.

Joseph Wu

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DAC8775: Simplification for 0-20 mA positive output only