Tool/software:
Hi,
We are using DRV425 on a new design and we sometimes get strange offset steps (shifts around 200nT) in the measurement results of certain IC’s.
Here is my measurement setup:
- 9 x DRV425s placed in a zero Gauss chamber
- Rshunt = 22 Ohm , VDD =5C, Vref = 2.5V external ( tried Vref internal, the same issue appears), RSEL 0 and 1 = 0, BSEL =1 => fc_DRV425 = 47kHz
- At the DRV425 output we have an RC low-pass filter at 37kHz (430 Ohm + 10nF)
- We acquire the signal with an 16bits ADC and, in this case, we software average a block of 100 acquisitions (at fs = 2kHz => 50ms block) and repeat this block average every 100ms.
- Temperature room 22°C
With this setup we have the following results (see measurements on graph):
- Some DRV425 fluxgate have low noise: around 120nTpp (it's perfect).
- Other DRV425 are noisier: around 400nTpp (I haven’t figured out why yet as we have the same PCB and environnment. Any clues?)
- And sometimes in certain IC’s (easy to see on DRV425s with less noise), you get steps from 150nT to 250nT. I did a lot of tests to understand where this was coming from, but I couldn’t find it. I was able to isolate our circuit (ADC + AOP +Vref) at the output of the DRV425 by removing the DRV425 and having only Vref (2.5V) instead of Vout to confirm that the problem was not coming from my circuit. I can swap the DRV425 from one circuit to another (ADC + AOP + Vref), when I do that, the issue follows the DRV425.
Have you ever seen this kind of behavior? Are these DRV425 damaged? Does this be due to the solder reflow process?
Thank you very much for your help.
Sebastien
