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MSP430F5438A: UART_ESD_protection

Ganesh V
Prodigy 120 points
Part Number: MSP430F5438A
Other Parts Discussed in Thread: TPD2E001, ESD351

Tool/software:

Hi,

We are using MSP430F5438AIPZ controller for our module. one of this UART connecting with external connector to send and receive the data, I would like add ESD diode for protection purpose.

I'm concerned about the 'TPD2E001-SOT553' ESD diode used on the TX and RX lines in our legacy design. The breakdown voltage is 11V, which means it starts conducting at 11V and clamps the voltage to VCC+25V as per datasheet.

 During voltage spikes, this could result in a clamped voltage of ~28.3V, which is then applied to the TX and RX lines of the MSP MCU. However, the MSP MCU has a maximum rated voltage of 3.6V, so I'm unsure how the ESD diode protects the MCU in this scenario

It seems I may have misunderstood the ESD protection mechanism. Could you please clarify how the 'TPD2E001-SOT553' ESD diode protects the MSP MCU from voltage spikes

Provide me suitable ESD diode part number for my case.

Thanks

Ganesh V 

  • 0
    Guru 42085 points

    The dose makes the poison. As long as the spikes are in very short duration, the internal ESD diodes on the chip can handle them.

  • 0 in reply to Keith Barkley
    Prodigy 120 points

    Hi,

    Thanks for your reply..

    For clear understanding.

    Does the MSP430 have internal ESD protection? If so, does that mean external ESD protection for UART and other I/O lines is unnecessary? In that case, would the 'TPD2E2001' (or 'TPD2E001') external ESD protection diode not provide any additional benefits?

  • 0 in reply to Ganesh V
    Guru 42085 points

    Yes, and No.

    There are internal diodes on the MSP430, but they are not that robust, it is always a good idea to provide external protection for connections to the outside world.

  • 0 in reply to Keith Barkley
    Prodigy 120 points

    Will "TPD2E2001" diode is advisable for UART signals?

    My concern is its clamping voltage is 25V+VCC how this will protect from voltage spike ? 25V+VCC will damage my MCU right.

    This case TI have any suggested ESD diode for UART? 

  • 0 in reply to Ganesh V
    Guru 42085 points

    From the datasheet:

  • 0 in reply to Ganesh V
    Guru 24335 points

    ESD protection is a complicated subject about which books have been written.

    Your diode limits, hopefully, the peak voltage. Putting a resistor between that and the MCU will limit the fault currents in its internal diodes.

    When I say hopefully, I mean that. You have to be concerned about where the ESD energy goes. It will not magically vanish.

    Looking at the TPDE001 data sheet, it can be used in two different ways.

    In the first there is no connection to Vcc. Voltage on the I/O pins then needs to rise high enough so that the breakdown voltage of the central diode is reached. That will be greater than 11V.

    Or you can connect to Vcc and the diodes clamp the I/O pins to Vcc plus a forward drop. Very much like the diodes in the MCU but with hopefully better ability to withstand ESD transients.

  • +1
    TI__Genius 14382 points

    Hi Ganesh,
    Both advices from Keith and David are good to follow.

    Best Regards,

    Diego Abad

  • 0 in reply to Diego Abad Sajamin
    Prodigy 120 points

    .Hi Diego,

    One more question.

    Below Image is our case just assume, 

    MSP34 abs Max ratting 3.6V

    ESD diode Clamping is 6.5V as per datasheet.

    During normal operation this ESD diode operate like open circuit.

    During my transient spike this will start biasing this case ESD diode clamp voltage is 6.5V, the same 6.5V enter to MSP340 and this is higher than 3.6V 

    this case how this will protect the MCU?

    or Across the ESD diode clamp voltage is 6.5V but sue the MSP340 internal protection diode will take a role protecting this voltage VCC+Vf (diode Frwd drop) ? 

    Please provide your suggestions on this.

    Thanks

    Ganesh V

  • 0 in reply to Ganesh V
    Guru 24335 points

    You should read slaa530, MSP430 System-Level ESD Considerations.

  • 0 in reply to Ganesh V
    TI__Genius 14382 points

    Hi Ganesh,
    Let me consult with my team on this. I would recommend to read the guide that David recommended (specifically the TVS Diodes section) in the meantime. 

    Best Regards,

    Diego Abad

  • 0 in reply to Ganesh V
    TI__Genius 14382 points

    Hi Ganesh,
    If you can change the Diode to an ESD351, it will guarantee a good range of protection for the MSP430 line. Alternatively, you can add a current-limiting resistor before the ESD diode input to improve performance.
    Best Regards,
    Diego Abad

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