when i use stm32f429 and SDRAM(IS42S16400J-7TLI),the CKE pin turn to low level after running 20 hours, cause the machine power off,i check the SW initialization is OK, in hardware ,bettween the SDRAM and MCU,there is 33 Ω resistor

[Cchen.6]

this problem can be reproduced every day,but can not find the rootcause,very thanks if someone can help this.