V2 Board Assembly & Checkout

A project log for Classic HP Calculator LiPo Battery Pack

Safe and convenient power for HP 35/45/55/67 Calculators

tomcircuittomcircuit 12/16/2020 at 21:570 Comments

I received the V2 circuit boards from PCBWay earlier this week. These sport blue soldermask, to differentiate them from the red V1 boards (that are not immune to HP charger). The USPS package with components from DigiKey was delayed a bit (normal for this time of year, particularly for this year) but eventually made its way to my house.

I assembled the boards and did a brief checkout:

During my testing, I found something interesting: With "no load" (just my Fluke DMM) across the contact pads, there was only a very small voltage (less than 150mV) present .  This seems very reasonable - I'm guessing the MAX40203 needs to see some differential voltage across the MOSFET before it decides it must be "on". I bridged JP2 to pull the MAX40203 ENABLE pin high, and the voltage across the contact pads matched the LiPo battery voltage, even with only a DMM load.  So, for now, I'm leaving JP2 bridged. Note that this behavior matches the simulation that I did previously, where the MAX40203 would not conduct when the simulated load was abruptly connected.