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Original question:

TPS3850-Q1: Design with MCU and startup trouble

TPS3850-Q1: The MCU is getting reset continuously.

CHandana S R Naik
Prodigy 40 points
Part Number: TPS3850-Q1

Tool/software:

Dear Team, 

The connection of Supervisor circuit and MCU is given below. What suggestion could you give us to make it functional? The MCU is STM32L496ZGT3. The pin 25 is connected with the supervisor RESET pin. 

  • 0
    TI__Intellectual 1340 points

    Hi,

    Which variant of TPS3850-Q1 is being used? If you are using the adjustable threshold configuration then the resistor divider is incorrect. Figure 8-3 from the datasheet shows the proper configuration:

    More information of the adjustable sense configuration is available in section 8.1.3 of the datasheet.

    -Henry

  • 0 in reply to Henry Naguski
    Prodigy 40 points

    Hi Team,

    We are using TPS3850G09QDRCRQ1 as our supervisor still the mcu is getting reset any solution? In the current schematics what will be the output state high or low? 

    If there is any issue, then how's the switching state of the reset?

  • +1 in reply to CHandana S R Naik
    TI__Intellectual 1340 points

    TPS3850G09QDRCRQ1 is a fixed threshold variant of the device, with a 0.9V nominal voltage, so it will not work in the configuration shown in the schematic.

    The adjustable variants are those with yy(y) = 01, TPS3850H01QDRCRQ1 for example. I would recommend replacing the device with either a 3.3V nominal voltage fixed threshold version (and remove the external resistor divider) or the adjustable threshold version if OV monitoring is not required.

    Please note that we do not recommend placing external resistor dividers on fixed threshold devices, as there are internal resistors to the device that we do not provide detailed specifications for, which will affect the accuracy of an external divider.

    -Henry

  • 0 in reply to Henry Naguski
    Prodigy 40 points

    We tried with removing the divider resistors still facing the same issue MCU is still getting reset Kindly suggest any other way to make supervisor work

  • +1 in reply to CHandana S R Naik
    TI__Intellectual 1340 points

    You are using a device meant to monitor 0.9V nominal voltages with a 4% threshold. So VIT+ = 0.936V, and VIT- = 0.864V. Having 3.3V on the sense input is causing an overvoltage condition which causes the reset.

    You need to replace the device with one meant to monitor 3.3V nominal rails, or one meant for adjustable thresholds. Note that the adjustable threshold variant only has undervoltage monitoring, it will not assert the reset for overvoltage conditions.

    -Henry

  • 0 in reply to Henry Naguski
    Prodigy 40 points

    Thank you so much for your prompt response!