Need we protect nPM1100 for situations when VOUTB is still present when VBUS and VBAT becomes disconnected?

[Bob]

According to the nPM1100 (PMIC) datasheet, the absolute maximum rating of VOUTB = VINT +0.3V.

VOUTB is the output of the internal DC/DC buck converter.

VINT is supplied by either VBUS or VBAT and is the input of the internal DC/DC buck converter. When both VBUS and VBAT becomes disconnected, VINT is not powered anymore.

When system operates from VBUS or VBAT, VOUTB is either 3V, 2.7V, 2.1 or 1.8V. On VOUTB we have output capacitance. When system is shut down by removing the battery and USB power, VINT is not powered anymore and VOUTB can be still 3V by the output capacitance before they are drained. This drain time can be quite long, due to very low drain current if system is in sleep.

Question. In this case, are we over the absolute maximum rating of VOUTB = VINT +0.3V and will the nPM1100 be damaged? Or is VINT somehow powered in this case by the remaining voltage on VOUTB?

In other words, can VOUTB be 3V0, without VBUS and VBAT?

If answer is no, how can we protect the nPM1100 against this situation?

[ketiljo]

When the voltage on VOUTB is higher than VINT+0.3 V, the ESD protection diode between the two pins will start to conduct. When VINT is turned off, the diode will quickly discharge the capacitors. Unless you have _very_ large caps on the VOUTB pin, it won't be a problem