XTR300: XTR300 output

Regarding this diagram, could I connect J6 and connect the load between OUT+ and OUT-, then measure the load voltage to determine the current? This is my current approach.

Hi Junzhe, 

Are you using the onboard Vref or externally supplying a Vref? And if you are not using an external Vref, is J7 shorted or open? 

What outputs are you targeting? Are you using in bidirectional current mode or single ended output mode? 

And yes, you can connect a load between OUT+ and OUT- and measure the load voltage to determine the current. 

Regards,
Ashley 

Hi Ashley,

I use external Vref, the value of it is 3V. I removed J7. I want bidirectional current mode. I expected a current output of ±10mA. I've used the XTR300 before, and I think the results before is followed to the transfer function. I'm confused why this time there is an offset.

Best,

Sam

Hi Sam, 

Are you using +/-15 V for the supply voltage? And did you verify that the Ros and Rset is 1k? What is the exact resistance of these resistors? 

I will also verify this setup in the lab to see what output current I get on my side. 

Thank you!
Regards,
Ashley

Hi Ashley,

My supply is ±20V, I checked the value of Ros and Rset, I used precise resistor, their value are 1K for both. 

I redo the test, the input is 2.011V and 1.004V, the output is (variation between 3.052 to 3.027) and  ((variation between -3.080 to -3.052) for 300ohm load.

Best,

Sam

Hi Sam, 

Noted thanks for the information. Did you notice any of the error flag LEDs at the top light up during your testing? 

Regards,
Ashley

Hi Ashley,

No, all LEDs are off.

Best,

Junzhe

Hello Junzhe,

Your transfer function here will be Iout = 10*(Vin/Rset + (Vin-Vref)/Ros). 

In your first case where Vin is 2.011V, Vref is 3V, Rset and Ros are 1k, your ideal current output will be 10*(2.011mA + -0.989mA), or 10.022mA. This through a 300Ohm resistor should give you 3.066V. Your low current should be 10*(1.004mA + -1.996mA), or -9.92mA, which would give a resulting output voltage of 2.976V 

Junzhe Zhang said:

I redo the test, the input is 2.011V and 1.004V, the output is (variation between 3.052 to 3.027) and  ((variation between -3.080 to -3.052) for 300ohm load.

Per your results above, this seems to align with the transfer function of the XTR300, is my understanding correct, and this is resolved?

Best,
Gerasimos

Hi Gerasimos,

Thank you for your reply. I understand that the XTR300's transfer function accepts your calculation results. However, my results seem to have a relatively large error compared to the ideal results. Furthermore, my output is not stable and varies within a certain range. I would like to know the reasons for these two problems.

Best,

Junzhe

Junzhe,

Are you able to precisely measure the resistance of your resistors, or provide the precision level of the resistors (0.1%, 1%, etc) This would be for Rset, Ros, and the 300 ohm resistor you are passing the current through.

Additionally, what equipment are you using to measure the voltages? Is this a handheld DMM, or a benchtop DMM?

What accuracy target are you expecting?

Best,
Gerasimos