Unable to get proper output from Gyroscope

Thank you, hgavcar 

Even on the working device, 38V sounds really high. I am wondering if we should look at the voltage rating on the capacitors in their circuit.  For example, we have found that X7R capacitance can be heavily dependent on the ration of the applied voltage to the rated voltage.  

Hi NevadaMark and hgavcar ,

I will provide the schematics and other assembly/solder details shortly. PFB other details below:

C_p is 1 uF 0805 50V X7R 10%

Board 1
CP = 38.4V, Vreg = 1.878V, Vdd = 3.324V

Board 2
CP = 25V, Vreg = 1.88V, Vdd = 3.33V

Board 3
CP = 38.4V, Vreg = 1.882V, Vdd = 3.31V

Thank you! Just for your information, our team is supporting a weeklong event, so our next round of responses might be delayed. 

Hi hgavcar and NevadaMark ,

I went through the assembly report and found that Baking temperature used was +125°C for 9hrs. Could that be the reason for the above mentioned behaviour?

Absolute Maximum Rating section of datasheet mentions +105°C as storage temperature.

Also, FYI, we have made few boards earlier with the same schematics and BOM, however, from a different vendor and those boards are working fine, Cp voltage on that board is 31.9V.

Hi usr 

Thanks for the additional information.

VDD and VREG look nominal on all boards, so the digital and low-voltage domains appear to be operating correctly. The main concern is the CP voltage: under normal operation it should be around 31 V, but the measured values vary significantly (25 V to 38 V), indicating inconsistent charge-pump behavior.

Since the same schematic and BOM worked correctly on earlier boards from a different vendor (CP ≈ 31.9 V), this points more toward a manufacturing process (soldering/baking) or assembly-related effect rather than a design issue.

The Cp capacitor itself seems to be rated up to 125 °C, so it is unlikely to be the limiting factor. However, the ADXRS290 storage temperature is specified up to +105 °C, and extended exposure above this limit could potentially affect analog performance (note that short excursions above 125 °C can occur during soldering as recommended in datasheet). I will re-check the sensor qualification documentation to better understand how the storage temperature limits are defined and what margin exists beyond the datasheet specification.

Could you please confirm how long the sensor was exposed to 125 °C during the bake process?

Hi hgavcar ,

Baking temperature used was +125°C for 9hrs.

Hi usr ,

First of all, wishing you Happy New Year!

I’ve reviewed the ADXRS290 qualification documentation and prior test results, and the +125 °C / 9-hour baking condition does not appear to be an issue based on those findings.

You mentioned that the same schematic and BOM worked correctly on earlier boards from a different vendor, so this seems more likely related to a manufacturing or assembly process difference rather than a design issue. Do you know of any differences in the soldering, baking, or assembly processes used by the previous vendor compared to the current one? 

As another potential aspect to look into, under normal operation the CP voltage is expected to be around 31 V, and a capacitor-related effect could influence this. As NevadaMark  previously noted, X7R capacitance can be strongly dependent on the ratio of applied voltage to the rated voltage. Since C_P is currently 1 µF, 0805, 50 V, X7R (10%), would it be possible to try an alternative capacitor option (e.g., higher voltage rating or different dielectric) and see whether the CP voltage behavior changes?

Hi hgavcar ,

Happy New Year to you too!!!

We replaced the gyros and asked the vendor to keep the baking temperature under the absolute maximum rating and follow the soldering guide mentioned in the datasheet. Data from gyro seems to be correct. Thank you very much for all the help.

We are yet to check the Cp, on the previous working boards it was approximately 31.9V. What is the expected tolerance value for Cp?

Hi hgavcar ,

Happy New Year to you too!!!

We replaced the gyros and asked the vendor to keep the baking temperature under the absolute maximum rating and follow the soldering guide mentioned in the datasheet. Data from gyro seems to be correct. Thank you very much for all the help.

We are yet to check the Cp, on the previous working boards it was approximately 31.9V. What is the expected tolerance value for Cp?

Hi usr 

I’m glad to hear that the issue has been resolved and the new gyros are behaving as expected.

For ADXRS290, the typical charge pump (CP) voltage is around 31 V. We don’t specify a strict min/max tolerance range in the datasheet, but in practice, values within roughly ±1 V of the typical level are generally considered acceptable. That said, if the CP voltage deviates significantly from its nominal value, it means the internal DC bias required for proper gyro operation is also shifting. This can impact the device’s operating dynamics and may lead to changes in sensor performance. So keeping CP close to the typical value is important for stable and optimal operation.

Hi hgavcar NevadaMark ,

We have new boards with assembly as defined in the datasheet, data appears to be correct, however, appears to have more noise. The voltage across CP is consitently around 35V in all the new boards. I am planning to change the capacitor and use 100V rated capacitor (CC0805KKX7R0BB105), i will report back the result.

Hi usr 

Thanks for the update. 35 V on the CP node is a bit higher than the typical value ( apprx. 31 V), but it might vary depending on the capacitor characteristics and board parasitics. Trying a higher voltage-rated capacitor is a good step.

Please let us know the results after the change.

Hi hgavcar ,

I am awaiting for the capacitor with higher rated voltage, meanwhile, I have one other query, reference schematics from ADXRS290 datsheet has 1 bypass capacitor of 1uF for pin 14 & Pin 18 and evaluation user guide has two 1uF capacitor across those pins. Which configuration is recommended?

Datasheet: www.analog.com/.../ADXRS290.pdf

Evaluation kit: www.analog.com/.../EVAL-ADXRS290Z_UG-780.pdf

The datasheet shows the minimum configuration with a single 1 µF capacitor on VS, while the evaluation board uses two capacitors in parallel for additional decoupling margin. Given your case, using either is acceptable, but adding a second capacitor can help improve supply stability and noise performance.

Hi hgavcar 

We used CC0805KKX7R0BB105, which is 1 uF 100V. Voltage across Cp is still 35.8V. For your reference, Vddio is 3.318V, Vreg is 1.84 and Vs is 3.3246.

Also, the voltage across the Cp capacitor seems consistent with the board we got manufactured from another vendor last year with the same schematics. Voltage across that board was also around 35V.

Is there something else we can check?

Hi hgavcar , NevadaMar 

Is there something else we can check?

Hi usr 

I’m also checking this internally and will get back to you soon.

Just to make sure I understand correctly: on the new boards CP is around 35V, and the sensor output looks generally correct but slightly noisier — is that right?

Is this behavior consistent across all newly produced boards, or only some of them?

Also, could you share a screenshot or a short data capture of the sensor output? It would help us better understand what “noisier” looks like in your case.

Hi hgavcar 

PFA the output of the gyro. HPF and LPF are in default mode. 

XLSX

Hi usr 

Thanks for sharing the data.

From a first look, the gyro output itself looks reasonably normal — I don’t see a clear indication of abnormal behavior in terms of bias or general signal behavior. The offset looks reasonable, and while the noise appears slightly higher on a quick look. This could be influenced by the measurement setup and the data collection rate.

Regarding the 35V level: although I previously mentioned 31V as a typical value, internally we confirmed that for this device family the charge pump voltage can vary from part to part due to production trimming. So seeing 35V can still be within normal variation, especially if the rest of the signals look consistent.

Also, while the datasheet refers to a higher internal update rate (4250 Hz), your data seems to be collected at 375 Hz. Depending on filtering, bandwidth, and logging method, this can influence the observed noise level.

Compared to the earlier data shared in the thread, where some voltages looked clearly abnormal, the current measurements appear more consistent and do not show the same level of deviation.

If possible, it would be helpful to understand:

• whether this behavior is consistent across multiple newly produced units
• whether all units show similar 35V levels and comparable offset/noise behavior
• and if the sensitivity looks consistent

This would help confirm whether what you are seeing is normal unit-to-unit variation for this batch.

Thanks