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F28M35H22C: Negative voltage spike on ADCIN pin during power up

Part Number: F28M35H22C

Hi Team,

In my customer's system, they observed a negative -200-300mV voltage spike on the ADCIN pin (122 and 138). The spike is caused by external power supply rather than MCU. And the spike occurs before the 3.3V power of MCU is established.

Since the ADC input range of C2000 is 0-3.3V, they are worried about whether this negative spike will damage the MCU. I believe this is a universal question of all the other pins on C2000 mcus. Will these negative voltage spikes during power up harm our MCU?

Thanks.

  • Weiqi,

    It is not clear which pins are shown in the scope picture.  Is there a single ground reference such that the negative voltage is relative to VSSA?

    Please see the Absolute Maximum Ratings table in the datasheet for conditions which may cause permanent damage to the device:

    -Tommy

  • Hi Tommy,

    Channel 2&4 in the scope are 2 ADCIN pins 122 and 138. And the voltage is relative to VSSA.

    Does the VIN(-0.3V-4.6) covers the input voltage on ADCIN pins? In other word, the negative 200mV spike on this two pins should be all right?

    On the other hand, in the datasheet table 5-38 shows the analog input range is 0-3.3V. So this is just the valid input range that the ADC could work, rather than the absolute value than may damage the device. Is that correct?

    Thanks

  • Weiqi Wang said:
    Does the VIN(-0.3V-4.6) covers the input voltage on ADCIN pins? In other word, the negative 200mV spike on this two pins should be all right?

    Yes, the "Analog voltage" parameter includes the ADCIN pins.

    Weiqi Wang said:
    On the other hand, in the datasheet table 5-38 shows the analog input range is 0-3.3V. So this is just the valid input range that the ADC could work, rather than the absolute value than may damage the device. Is that correct?

    Correct. The Recommended Operating Conditions should be observed while the system is running its application.  The Absolute Maximum Ratings should be observed to avoid permanent damage when the system is not running.