Constant offset(26mV) in BL2100 DAC output

Rabbit
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1

Hi,
We are using the Rabbit BL2100 SBC and have found the BL2100 to be very apt to our needs and everything has worked well except one snag - there is an offset of ~30mV on the DAC output that does not disappear.

Using the s/w provided, we have calibrated the DAC output - at desired voltages above 0.030V, we have offset of nearly 0V and gain of nearly 1 (which is perfect).
However, for desired voltages from 0.000V - 0.026V, we have a constant output voltage of 0.026V. Our application is sensitive to voltages above 1mV, thus we would like for the output to be within 1mV of zero at an input of 0.00-0V.

Other details - our voltmeter can measure 0.000V, so the meter is not the issue. It measures 0.000V on DAC00 when the rabbit is off, once the rabbit is switched on, it shows the 26mV reading straight away.
We have tried common chassis ground for the rabbit GND and AGND, and have also tried not having a common ground. In both cases, we have the constant 26mV output at input < 26mV.

Any help/suggestions etc. you might have would be greatly appreciated!
Thanks!

2

That does appear to be a little bit high but based on the TI data sheet for the TLV5618, the 0 offset error is quoted at +/- 12mV. The DAC is followed by a non inverting amplifier with a gain of 4 so you are going to see something in the +/- 48mV range of an offset for 0 output.

1 Like
3

thank you for your reply!
i guess we will need a small circuit externally to null the offset.

4

I think so, it is one of the compromises you run into when the DAC and associated buffers are run of a single positive supply and you want to get close to 0 on the output.