stm32L151 not wakeup in a long time in stop mode use rtc

[akang.1]

Hi,

all , please help me . I use stm32L151. when rtc wake up timer is 30 or smaller minuts, the board can wake up, and work . but when rtc timer is 6 or long hours, the board some times not wake up . what happened ? I need a long sleep (many hours) for save power.