Tool/software:
In ther inital iteration of using this chip which was designed inhouse and post validation it given to a vendor for design based on the inhouse schematic. A discrepancy was noticed in the immobilizer action max working distance compared to the inhouse designed MK2 FOB where both have the same schematic and component values.
Inhouse FOB max Immo distance: 5CM from transmitter antenna
Vendor FOB max Immo distance: 3CM from transmitter antenna
VDDSW caps in both the design: 1uF/25V + 100nF/25V
Post the CL caps they are connected to both the VDD pin with 100nF/25V caps on each pin as shown below
Both the FOB designs use the same LF 3 axis antenna from sumida CAS13D31B-472
Measurement
The LF burst duration from the transmitter is 150mS. Upon measuring the voltage build up on the VDDSW caps we found the below waveform.
Note: Transmitter antenna and module was exactly the same for both the FOBs during testing.
Image 1: Voltage on VDDSW caps of Inhouse designed FOB at 5CM
Image 2: Voltage on VDDSW caps of Vendor designed FOB at 5CM
In the inhouse designed FOB waveform we can see that the voltage constantly builds up for 150mS and reaches till 2.84V but in the vendor designed FOB waveform we can see that voltage quickly builds up to 1.3V and then gradually rises to peak voltage of 1.48V.
Steps taken to mitigate the issue
- The same firmware was flashed on both the RF432 chips ensure the wake pattern in same.
- Used the capacitors of exact same MPN on both the FOBs.
Conclusion
The discrepancy exist even after making all the above changes.
