We are using DA14580 on PAN1740 module.
The module is used on a coin battery powered products.
On the product a microcontroller communicates with DA14580 over UART.
We are experiencing with some modules connection problems.
We have noticed that it happens when battery voltage is higher like 3.1V - 3.3V.
This is new topic as I have further findings and question in previous one is 'completed'. I have received new units from production showing this problem.
Our production software is running without any problems as long supply voltage is below 3.25V.
With higher voltages it is running for a few seconds. I can see the product popping up in Windows Bluetooth pairing. If I am fast enough I can get PIN prompt. However I cannot complete pairing.
We have implemented basic support for RF Master (start/stop) for tests. It is possible to communicate with it over whole supply range (up to 3.6V).
To eliminate any possible mistake introduced by us, we used example application from SDK:
It has been compiled without any modifications.
I can see Bluetooth device as DIALOG-PRXR when I start the Bluetooth module on our device.
Everything is fine up to 3.25V - I can see the unit and I can pair it in Windows (no PIN).
As soon as I increase voltage to 3.3V it is running again for few seconds only - right after power on the device is popping up, but I cannot complete pairing.
The module is booting over UART without any problems up to (at least) 3.6V.
The Panasonic module (PAN1740) we are using has very little external components (inductor, two crystals and few capacitors).
Voltages mentioned are supplies of our product. The module is supplied through IO pin of a microcontroller, so actual voltage on the module is lower (around 50mV less).
The problem is showing with some units only. Others work without any fuss (pairing and communication) up to 3.6V (and higher :-) ).
What could cause such behavior? Where should I search further?