Hello TI,
we are using the LMR23630A to power a GSM module.
Our layer structure is as follows
Signal+GND pour
GND
VCC
Signal+GND pour
The datasheet mentions that when the vin source is more than 5cm away from the LMR23630A, bulk capacitance maybe required.
The Vin trace is 0.8mm wide and nearly 12cm long. This trace exists is the third plane (VCC) From here I use vias to connect to the top plane where the Vin is a polygon.
The 12cm trace has an inductance around 220nH from a web based calculator.
How do I decide if I really do need the bulk capacitance.
1. The module is supplied by an automotive battery, taking into account capacitance derating and safety, I think we need at least 50V rated capacitor. The biggest question I have is, can I go with aluminium electroytic capacitors or should I rather go for the polymer based ones (OSCON etc)
2. The bulk capacitance is not used for bypassing high frequency ripples. So should the common guideline of keeping the return loop path as short as possible apply for the bulk capacitance too? Or is it ok to position the bulk capacitance as the layout permits? Or should I stick to the EVM layout?