STM32WB05 not advertising via BuckBoost

[RAdam.1]

I have an STM32WB05 board (approx 30mm x 30mm) with the following major components :

STM32WB05KZV6TR, LTC4095EDC, LTC3531ES6-3.3, LSM6DSV80XTR
I have followed the reference design for running on SMPS.

When running directly from VDD (3.3V) it works great. Advertising, connecting reliably.

When running through the BuckBoost it does not advertise (with either a LiPo feeding or a bench PSU at 4V or via the USB charging circuit) . No errors, no obvious issues.. just cant see or connect to it over BLE.  I checked that TX_SEQUENCE was active and it is. Registers look the same for both modes. 
VDD does have some noise but it is within spec for the LTC3531 in burst mode. 
I purchased a TinySA Ultra+ and have taken traces. I can see the advertising (attached)
Really need to help to diagnose.. is it a lost cause having the BuckBoost on a board this small?

Let me know how to configure the TinySA also for more detailed traces as i am struggling (so is Claude!)

 

[rich.g.williams]

Could it be that the Buck Boost is making too much noise that swamps the BLE?  You could repeat your scope trace with and without the Buck Boost running.

Why do you need boost?  with a LDO linear regulator with about 150mV dropout,  a LiPo will run your PCB fine ?

[RAdam.1]

Hi Rich,

Thanks so much for the quick reply

Well its getting the typical Buck/Boost noise when in burst mode (that sawtooth that is to spec of the LTC). I have a LiPo that goes from 4.2V to maybe 2.8V - are you suggesting i use an LDO to 1.8V? 3.3V wouldnt have the headroom would it?
 

Richard

[rich.g.williams]

What you can do is use a 3.3V version of the LD39200 it has a LDO of 130mV.

Have a look at the attached LD39200 datasheet, it will work at your minimum LiPo voltage. As the LiPo  drops below target of 3.3V, the LD39200 enters its "dropout region" and the internal pass transistor is driven fully on, turning it into a low value resistor.

The minimum operating VDD for the STM32WB05 is 1.7V. If VDD drops below 1.65 V, it will automatically trigger a device reset.

If your current consumption is low, as the LiPo drops to 2.85V you can expect the VDD from the LD39200 to be close to 2.75V so MCU is safe, it will carry on working.