Part Number: CC2340R2
Hi team,
I was chatting with my customer and they had some questions about the internal LFOSC on the CC2340R2... one of the primary questions was on its accuracy and where it was specified. It is my understanding that this is not a parameter we normally test for as the variation is quite large and non-linear depending on various factors like voltage level, device state, fab.
The related E2E thread mentioned 600ppm/degC which is a temperature coefficient, so it represents drift strictly due to temperature. It sounds like this info was derived from antoher device where the RC osc design was similar as I have not been able to find this characterized anywhere else.
Does the internal oscillator have a nominal accuracy at 25C (or whatever temperature), like crystals do? Is the nominal accuracy expected to vary quite a bit from IC to IC (independent of temperature and voltage)? Or is the variation due only to external factors like temperature and voltage?
In addition, my understanding is the customer will need to be careful with using the internal oscillator (based on the errata):
CLK_01:
Bluetooth Low Energy link not being maintained when using LFOSC only
Revisions Affected See Table 1-1
Description:
A small percentage of devices do not maintain a Bluetooth Low Energy link if LFOSC is used as a sleep clock due to random timing error above 500PPM.
Workaround:
A software workaround are available in the SimpleLink F3 SDK >= 8.10.xx to allow devices to operate in the broadcaster, observer and peripheral roles when using LFOSC only. When the software workaround is used, the device can see short periods of operation with reduced throughput and increased power consumption when the timing error occurs. This software workaround does not support the central role. To completely avoid the consequences of increased power consumption and connection throughput or support the Central role, TI recommends using an external 32.768kHz crystal.
The value that they set to allow for the RX window widening is the Peripheral Extra LFOSC PPM value. It is set to 1500, which is the default. Is this the correct parameter? And is this value correct?
Is 1500 even better than a setting for 500 or 600 PPM? Or is it the opposite of what you would first think?
Best,
Luke