Intro

At first look BQ25895 looks like ideal solution for modern electronics (configurable charger 5A with dynamic current adjust + ORing), but in reality it can't be used in some designs.

🔺 Issue Description

Significant voltage drop (dip) on VSYS cause system reboot and not able to start.

❔ Causing

I believe it's related to the design of the IC, it's just can't handle short current spikes without battery.

🔧 Issue Fix

Unfortunately, good solution don't exist, but here is advices how to improve stability:

1. Short D-, D+ if it's not connected to the USB.
2. Higher supply voltage (ideally 12V or 9V)
3. Increasing PMID capacitors by 470uF 16V
4. Set maximum VSYS capacitance (but not exceed because if Input current regulation during start up: 200mA)
5. Disabling charger -> slightly make situation better, but not fully.
6. Soft start for all load on VSYS (e.g. DC-DC with SS pin)
7. Set ILIM to 3A

✔ Fixed

The most significant improvements is boost USB 5V to 9V and capacitor 470uF at PMID give a pretty stable result.

Conclusions