Hello, First Post here.
I have been testing 20 prototype STM32WLE5 boards and have been getting a respectable +20dBm output power at 908 MHz Lora Modulation 125KHz BW drawing 105mA. VR_PA = 2.5V. This is great!
However, on two of the boards the RFO_HP transmitter has failed. No detectable output power at all. I'm thinking the STM part has failed. We have an antenna switch between the TX and RX path. The schematic is basically a copy of the MB1720-HighBand_HighPower-A01_Schematic_Internal.pdf reference design.
On the failed parts the regulated PA voltage has jumped up to the VDD of 3.3V and the board current has dropped to 13mA from the 105mA when the transmitter was working.
The 33nH RF inductor that supplies the VR_PA voltage to the RFO_HP output looks good in that it "ohms" out correctly at 0.6 ohms so that's not blown. It has a max I=260mA, it should be good.
Has anyone else seen this problem? have any clues.
I am worried about reliability.
We've been selling 10's of 1000's of Semtech SX1272 and SX1262 Lora transceivers for ~ 10 years now, they have the same RF blocks as the STMWL32 parts, and I have never seen one of those RFICs have a blown PA output.
