RTC with LSE blocking controller operation, boot issue

[NitishGhadage]

I am using STM32L431RCT6 controller, configured RTC with external LSE (32.768 KHz), for which my controller is not working, not booting up for normal process, everything is stopped. But when i switch from LSE to LSI, everything works fine. Why does this happen? Also changed the LSE low drive capability to high, still having the same issue. 

[waclawek.jan]

Most probably your LSE oscillator does not oscillate.

Read AN2867.

It may be better to use a 32.768kHz oscillator (as a part) rather than a crystal (and then use LSY BYPASS).

JW

[AScha.3]

Typical symptom for not running LSE clock.

Have VBAT connected to a 3v cell. (otherwise it cannot run)

Set drive level high and verify LSE clock running ,

• with high impedance (!) probe and scope, on lse out pin (if crystal is used )
• or using MCO , set mux to LSE , check with scope on MCO 32kHz signal

If no signal...try another crystal, maybe its broken. (happens sometimes)