The WiFi S6B Vcc spec is very tight at 3.14-3.46V and the earlier trace showed that when the WiFi comes out of sleep, the current demand on the Vcc could be pulling it out of specification. In order to check if the Vcc is causing the Xbee S6B WiFi modem a problem, I’ve put together a separate regulator based on the TCR3DF335,LM which regulates to 3.35V and can pulse to 400mA, with a normal spec of 300mA.
SMT is so nice when you have the right parts. The TCR3D fits on a SC74 prototyping board with 1uF decoupling, and can fit between the LiIon bat at 4.2V and the LTE Adapter board that carries the X6B and plugs into the Mayfly.
Looking at the trace the Vcc power is much smoother and now well within specification. The Salaea Vcc probe on S6B Vcc, measures close to 3.35 (3.26V), then when S6B turns on drops to 3.31V. When the S6B has a power draws, it drops to 3.28V for up 1.5mS. All within good headroom from the lower 3.14V.
Trace of when the S6B initialization sequence below.
So now just need to let it run for a few days to see if it makes a difference.