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SN65HVD33: Test issue for SN65HVD33

Zhang Liang
Genius 3145 points
Part Number: SN65HVD33

Hi,

We use the SN65HVD33 for the RS232 interface, and end customer feedback to us there are more than 10pcs are damaged that the A/ B/ Z/ Y short circuit with GND,

we want to know that how to test the below highlight V(TRANS) that we can choose the TVS, and is there any promote testing equipment or institution, thanks?

  • 0
    Guru 286620 points

    You need TVS diodes that can handle the energy of your transients, and that clamp the voltage to some value below the limit.

    Do you know the source of the transients? If it is not connected through 100 Ω (and the current is not limited by another mechanism), then you have to use the lower limit of −9/14 V.

  • 0 in reply to Clemens Ladisch
    Genius 3145 points

    Hi Clemens,

    Thanks for you support,

    BTW, the reference design is CDSOT23-SM712 but the "Maximum Clamping Voltage @ IPP = 17 A" is 26V, the Voltage at any bus terminal (A, B, Y, Z) of SN65HVD33 is -9V to 14V,so please advise why choose CDSOT23-SM712 for the Surge protection, thanks.

  • 0 in reply to Zhang Liang
    TI__Guru 72242 points

    Zhang,

    An expert from TI has been assigned to this thread and will respond by end of business 03/19/2024 CST.

    Thanks for the help Clemens, and thanks for your patience Zhang.

    Regards,

    Eric Hackett 

  • 0 in reply to Zhang Liang
    Guru 286620 points

    Sorry, I overlooked that the 14 V limit is for DC voltages. I suspect that the limit for any transient is higher, and that the 100 Ω test condition actually models the characteristics of a real transient.

  • 0 in reply to Clemens Ladisch
    Genius 3145 points

    Hi Clemens,

    So please advise how to measure the max. Surge voltage for the SN65HVD33, thanks.

  • 0 in reply to Zhang Liang
    TI__Guru 60580 points

    Zhang,

    The datasheet shows the test is done by driving +/-50V into the 100 ohm resistor into the A/B/Y/Z pin for 15uS with 100ns rise and fall time (figure 8-13).

    For clamping, you should try to clamp the pins to below the absolute max rating we spec in the datasheet (14V max for the A, B, Y, Z). This guarantees the device won't break if below that value. 

    You probably need to check with your customer though, do they know how exactly they damaged the device? Did they short the device to a high voltage source or did do they suspect the damage came from ESD? If the answer is ESD, they may require an an ESD diode. If they shorted it to a 50V rail, it might make more sense to go with an RS485 device that can withstand 70V faults instead. 

    -Bobby