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:
- First, I connected a LiPo battery + series current-meter to the board via J2
- Approx 100uA of static current is consumed by the MAX40203 (and perhaps Z1 leakage) with no-load across the PCB battery contact pads (those that mate with the calculator).
- The MAX40203 'ideal diode' allows current to flow from the LiPo battery, through the MAX40203, into a small resistive load (~50mA)
- Voltage drop across the MAX40203 while it is conducting is very low
- Next, I applied a 10V source, current-limited to 50mA, across the PCB contact pads (to simulate what happens when an HP charger is present)
The voltage across the pads clamped at around 5V. This is required to keep the MAX40203 voltage with specification
There is no current flow 'into' the LiPo battery; the MAX40203 is indeed preventing charger current from entering the battery
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.