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TPS3823: TPS3823 MR PIN

Martin Ma
Prodigy 80 points
Part Number: TPS3823
Other Parts Discussed in Thread: TPS35

Hello TI,

I would like to inquire about the usage of the MR pin on TPS3823. I have connected the MR pin to a GPIO on my MCU, and I am wondering if there is a required delay for the MR pin to trigger. After triggering the MR pin using the GPIO, I noticed that the GPIO may be pulled high immediately. Currently, the RESET function is not working properly. Are there any requirements for the usage of the MR pin to ensure proper operation of the RESET function?

Thank you.

  • 0
    Prodigy 80 points

    I have attached my schematic diagram. The MCU used is CY7C6813A, which outputs a signal through a GPIO pin to the MR pin of TPS3823. Then, TPS3823 performs a RESET procedure on the CY7C68013A MCU. However, the entire RESET action is not functioning properly and often fails to RESET the MCU successfully. To resolve this issue, I need to add a small capacitor between the MR pin of TPS3823 and ground to enable the MCU to RESET properly.

    Please assist me in addressing any usage issues with this configuration. Thank you.

  • 0 in reply to Martin Ma
    TI__Mastermind 19070 points

    Hi Martin,

    Are you using the WD functionality of the device?

    Jesse 

  • 0
    TI__Mastermind 24135 points

    Hi Martin,

    Thank you for your question and your schematic. We are currently looking into your schematic and the issue at hand. In the meantime, can you please provide the signal that is being output to the MR pin of TPS3823 so that we may better assist you.

    Thank you,

    Joshua Austria

  • 0 in reply to Joshua Austria
    Prodigy 80 points

    Hi, Joshua

    The signal is output from the MCU's GPIO to the MR pin of the TPS3823, and it is a 3.3V TTL signal. Typically, this signal remains in a high state, but when a reset is required, the MCU sets the signal to a low state, causing the MR pin of the TPS3823 to go low, triggering the MCU's reset pin and entering the reset state.

    During reset, the MCU's GPIO pin may be in a high state or a high impedance state, meaning that the MR pin of the TPS3823 may quickly return to a high state or a floating state.

    Currently, my solution is to add a capacitor to the MR pin, and I suspect that the use of the TPS3823_MR pin may require an active low state for a period of time to avoid abnormal output of the TPS3823's reset pin and prevent abnormal reset of the MCU.

  • 0 in reply to Joshua Austria
    Prodigy 80 points

    Hi, Joshua


    When the MR pin is triggered, the TPS3823 begins the RESET output.
    At this point, does the TPS3823's RESET output still be affected by the MR pin's input state changes, or are they independent of each other?

  • 0 in reply to Joshua Austria
    Prodigy 80 points

    Hi, Joshua

    another question about WDI

    If the state of RESET output pin of TPS3823 is during the low level and now I let the input of WDI pin is set to high impedance, will the state of RESET output pin immediately become high level?

    thanks

  • 0
    TI__Mastermind 24135 points

    Hi Martin, 

    Thank you for your patience in these questions.TPS3823 requires a continuous low signal into the MR pin for TPS3823 to output a continuous reset signal to your MCU. In the absence of that signal, the MR pin will be left floating/high and TPS3823 will cease outputting the proper reset signal to your MCU as you noted. In order to ensure your MCU has ample time to conclude its reset procedure, the MR pin must be held low for that entire period of time. The capacitor that you added should add enough of a "delay" for the reset procedure on your MCU to conclude, as you have stated. 

    Additionally, in regards to your last question, the TPS3823 does not have an active disable pin for the WDI to trigger a reset during operation. The TPS35 and associated families do have an active disable pin for watchdog if you would like to work through this functionality. 

    Please let me know if you have any more questions,

    Joshua Austria

  • 0 in reply to Joshua Austria
    Prodigy 80 points

    Hi, I just want to confirm about WDI.

    Are you saying that when TPS3823 is executing RESET output (low state), during the low state, if WDI is set to high-impedance state, will TPS3823 immediately output the RESET signal to high, and end the RESET output process?
    Or does TPS3823 still output a fixed RESET signal width and it is not affected by WDI?

  • 0 in reply to Martin Ma
    TI__Mastermind 24135 points

    Hi Martin,

    If TPS3823 is executing a low state RESET output, if WDI is set to high impedance, TPS3823 will still execute a low state RESET as long as either the VDD is still below the threshold voltage of the device or MR is held low. TPS3823 will still output a low RESET in these cases. 

    However, if VDD is above the threshold voltage of the device and MR is left floating/held high, and WDI is what is keeping RESET low, setting WDI to a high-impedance state will cause the TPS3823 to go high. Essentially, if MR is held low, VDD is below the threshold voltage of the device, or WDI would cause the device to output a low RESET, TPS3823 will output a low RESET. 

    Hope this helps,

    Joshua Austria