Background / Observation:
During startup, I observe a phase where the SYS voltage is held steady by the hysteresis strategy (VSYS_CHG with VSYS_CHG_HYS), while the BAT voltage rises slowly from a low level. In this phase, the main boost is charging the BAT pin, and SYS is maintained above the charging threshold.
My Questions:
1.
BATFET Operation Mode: During this startup hysteresis phase (SYS held steady, BAT slowly rising), is the BAT switch (BATFET) operating in fully-on mode (low-resistance pass, ~0.59–0.85 Ω) or in a current-limited mode (behaving like an LDO with active current limiting)?
I believe a current-limited mode would be safer for battery protection, especially when connecting a deeply discharged or small-capacity battery. This understanding directly impacts my battery selection and system safety design.
2.
SYS Stability Under Excess Input Power: If the input power from the harvester is large and exceeds the battery charging current capability during this phase, can the SYS voltage still be maintained stably? Or will SYS rise uncontrollably because the excess energy cannot be absorbed by the battery?
This is critical for my design because I need to ensure SYS does not overshoot and damage the system load during high-input, low-battery conditions.
Best Regards,
Luo Jiang