The MAX77751 has a boost function which enables us to generate a 5.1V rail using its internal DC-DC converter.
However, when boost is enabled I discovered that INOKB was going low, indicating that the charger input is valid. Further investigation showed that the boost 5V rail appears on the input to CHGIN. This means that it is not possible for me to detect the presence of the charger connection when boost is enabled. I dug into the device datasheet and discovered the explanation: the BYP pin is electrically connected to the CHGIN pin:
Now, given that we would obviously not try to charge the battery from a boost rail which is itself powered by the battery, I don't understand why the boost output would be connected back to CHGIN. Especially as this prevents detection of the actual charger connection.
Please can this be explained? Is it because the boost is used in practice to aid charging if the voltage input is <5V, and the fact that it is supplied as an output for us to use is just an aside?
Edit Notes
Added extra notes to the question[edited by: bh4017 at 3:37 PM (GMT -4) on 21 Mar 2023]
