BMM350 - Selection criteria for the CRST capacitor

[ashareef]

Hi,

I would like to clarify a few things regarding the selection of capacitor for the CRST pin. As pointed out in this post the recommended capacitor is already EOL and one of the suggested alternative is already NRND.

Can you elaborate on the process of choosing the capacitor? Are your recommendations in the datasheet based on testing or do you have something specific that you are looking for in the capacitor? The requirements such as 'low resitance', 'low inductance' given in the BMM350 datasheet are pretty standard, however, 'non-magnetic' is not. If you look at the datasheet of the part that is already EOL, it does not specifically highlight that the capacitor is non-magnetic. If so, why was that part chosen? Similarly, even for the altenatives recommended in the earlier post, I don't see the parts specifically being highlighted as 'non-magnetic' in their respective datasheets. If I search for non-magnetic ceramic capacitors, I do see parts from Knowles and Vishay available, but they are not cheap.

We prefer using capacitors from our internal database whenever possible, unless there is a specific need for a new part. If I could get the criteria used for picking the parts, then I could pick the capactors from our database. If you are unable to provide such a criteria, then please consider providing a couple of subsititutes that are active (in production) and that have the same footprint.

[ashareef]

@BSTRobin Hi, can you please help to clarify the above enquiry?

[BSTRobin]

Hi ashareef,

Thank for your inquiry.
The recommended capacitor in the data sheet has already reached EOL. You can choose other capacitors. Here are some explanations about the factors to consider when choosing a capacitor:
Capacitance value: greater than or equal to 2.2uF
Capacitor size: The capacitor size is small, and the DC bias decays quickly. It is recommended to choose capacitors with a size of 0805. If a small-sized capacitor is chosen, the capacitance value needs to be increased.
DC bias: For example, when powered by 3.3V, if the vertical axis capacitance deviation rate reaches 10%, the capacitance value decreases, affecting the charging and discharging of the capacitor, and thus affecting the voltage required by the sensor. When selecting a capacitor, it is necessary to check whether the new DC bias is better than the DC bias of the reference capacitor. If the DC bias is similar or better, it can be used.
Inductance and ESR parameters: Select capacitors with parameters similar to those in the data sheet.