lpc1756 vbat UL Certification

[quyentran]

We have connected a CR2032 to VBAT of the LPC1756 and it seems like there are questions regarding the protection of the battery against charging currents from the UL certification. Has anyone been in the same situation? Is it useful to know the implemented circuit of VBAT pin of LPC1756?

[udellso]

We are using the LPC1768 with VBAT connected to CR2032 and I just had the same questions coming from CSA.

Can someone from NXP provide us with some more information about the power selector block as shown in the UM10360 user manual Figure 131? I've copied the block diagram below for reference.

Are there internal blocking diodes and current limit resistors to prevent current from VDD(REG)(3v3) to VBAT and vice versa? If there is 3.3V present on VDD(REG)(3v3), will there be reverse charge current flowing out of VBAT?

Is the circuit below implemented internally in the Power selector block, or does that need to be implemented externally?

If there is another equivalent circuit internally, what is the circuit? (to satisfy safety certification questions).