DAC161S997: Can't current

Yannick Burkhalter

Part Number: DAC161S997

Hello everybody

For a project in my company I am using the DAC161S997 to simulate a 4 to 20 mA interface. The Problem is that i can't measure a current at the output. I can write and read to the DAC. I have written 0x015E to the Error_Config register to configure the errors. The Status Register returns me the value 0xE3. I have used the circuit from the DS for the typical application.

My problem is as I mentioned, that I can't measure a current at the output and the suggested Transistor PZT3904 gets a little bit hot. A short circuit should not be the problem.

over 7 years ago

0 Kevin Duke over 7 years ago

TI__Mastermind 46290 points

Yannick,

It sounds like you have built your own PCB for the design. Could you provide your schematic for first-order inspection / debugging?

When you power-up the PCB without any register writes, do you observe any output? For a loop-powered system there should be some default current on the loop or the system is not starting up.

From the schematic level, can you describe how you have configured the measurement?

0 Yannick Burkhalter over 7 years ago in reply to Kevin Duke

Prodigy 100 points

I used the scheme for the typical application but you can see my scheme on the left side.

To measure the current i have connected a multimeter to close the loop and mesure the current. I have also tried to use a 100 Ohm resistor in series to the mutlimeter.

0 Kevin Duke over 7 years ago in reply to Yannick Burkhalter

TI__Mastermind 46290 points

Yannick,

How are the 3.3V and 12V supplies being provided to this board? How are those supplies connected to one another (ground connections). Meanwhile the DMM is connected directly across pins 1 and 2 of J16?

0 Kevin Duke over 7 years ago in reply to Kevin Duke

TI__Mastermind 46290 points

...sorry for the second post, but when you connect everything and make the measurement you are observing 0mA in the DMM?

0 Yannick Burkhalter over 7 years ago in reply to Kevin Duke

Prodigy 100 points

The supplies are generated from to DC/DC converters. One 24 to 3.3V converter and one 24 to 12V converter. The ground is connected to both supplies over a ground plane on the PCB.

And yes i have connected the fluke 179 directly to J16.

0 Kevin Duke over 7 years ago in reply to Yannick Burkhalter

TI__Mastermind 46290 points

Yannick,

The problem I see here is that there are several current loops in this setup. In a typical configuration for 2-wire transmitters the transmitter itself, the supply, and the measurement source (ADC / DMM / etc.) are all in series. In this setup it sounds like you have the elements in parallel. Current is going to return to the supplies through GND, and the DMM is not in series with GND, so no current should be flowing through J16.

0 Yannick Burkhalter over 7 years ago in reply to Kevin Duke

Prodigy 100 points

Okey i think I can see what you mean. Basically J16-2 should be connected to the powersupply and not to GND if I can see that correct.

0 Kevin Duke over 7 years ago in reply to Yannick Burkhalter

TI__Mastermind 46290 points

Yannick,

Essentially the DMM on the J16 connector needs to be in series with the current return path in order for the system to function correctly.

0 Yannick Burkhalter over 7 years ago in reply to Kevin Duke

Prodigy 100 points

Good Morning

Now I have changed the scheme. It should be correct now i think. I can still write to the DAC and i receive no errors but the out current is always at 11.7 mA and it is dependent on the resistor which is in series at J16. I can't measure any voltage at the out pin and at the resistor R10. Maybe I have missunderstood your instructions. But I actually do't know where i made the mistake that it still doesn't work.

0 Paul_Frost over 7 years ago in reply to Yannick Burkhalter

TI__Guru 53773 points

Yannick,

Let's continue this in the new thread:
e2e.ti.com/.../639295

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DAC161S997: Can't current