LPC1112 start up issue

[BYLLLLLLL]

Hi,

We're developing a system based on LPC1112FHN33/102, but we have encountered an occasional MCU startup abnormality issue, and even attempting to pull down the RST signal for reset cannot restore it to normal. The occurrence probability of this issue is approximately between 1/200 and 1/500. We have noted that the chip manual and the errata specify that the voltage of the MCU at the start of its power supply voltage ramp-up must be lower than 200mV. However, our actual measurements show that the voltage before the ramp-up begins is approximately 500mV. We would like to ask whether this abnormal phenomenon of the MCU is caused by the voltage at the start of the ramp-up, or if there are other causes.

[Pablo_Ramos]

Hi @BYLLLLLLL,

Could you please help verify the revision of your devices?

You can find the revision information in Chapter 1: Product Identification of the Errata Sheet for LPC1111/12/13/14/15.

If your devices are marked with revision 'A', 'B', or 'C', they are affected by the errata you mentioned. According to the errata, if the minimum voltage of the power supply ramp is not 200 mV or lower, and the ramp-up time is not 500 ms or faster, the device may not always start up reliably.

Best Regards,
Pablo

[BYLLLLLLL]

Hi Pablo,

I confirm that the device revision is 'C'.

When this issue occurs, the device appears to be completely unresponsive, even unable to reset via the RST signal. I would like to confirm whether the power ramp issue could cause this phenomenon.

Best Regards,
BYLLLLLLL

[Pablo_Ramos · Accepted solution]

Hi @BYLLLLLLL,

Since your ramp-up begins at approximately 500 mV, it does not fulfill the requirements specified in Table 22 of the datasheet (Power-up characteristics), nor does it meet the conditions outlined in the errata. Therefore, we cannot guarantee the correct functionality of the MCU.

I recommend modifying the power supply to comply with the requirements specified in the errata.

Best Regards,
Pablo