Original question:
Tool/software:
Data sheet states capacitance on REGN to be between 2.2 and 3.3uF but it has no info on derating.
I am reviewing my design and noticed the derated capacitance is ~1uF (2.2uF nominal capacitance).
I just looked at the EVM schematics and BOM and the capacitor (C30) derated capacitance is ~1uF, very similar to the part I am using.
I just want to make sure keeping the same part will have not unintended consequences.
Tiger, thanks for your comment.
I'm affraid it is not as simple as picking a capacitor with high nominal voltage, it is the physical size of the component (including thickness) and material that counts.
Take for example the part number used in the EVM, Murata's GRM188R6YA225KA12D (2.2UF 35V X5R 0603). This is the derating curve per Murata's Simsurfing tool:
Notice how fast Capacitance drops and at ~6V capacitance is ~0.95uF. If you pick a different P/N rated 25V (see below), capacitance at 6.0V is ~1uF. Notice capacitance drops as fast as the 35V part as DC Voltage increases.
It gets better if you pick a different material (X7S):
In this case, capacitance is 1.5uF at 6.0V.
A bigger (0805) package and X7S gives 1.9uF at 6.0V:
The problem is this is a design revision (other part of the circuit is being changed), layout is done, it is working OK and using a bigger component is not viable.
Data sheet does not provide any information beyond "2.2 to 3.3uF", so I need to know I do not have a risk of failures in the future due to derating not have being taken into account in my design.
Could you check with your design team how critical is this capacitance design wise?
