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TPD4S012: Question about the Clamping Voltage of TPD4S012

Wayne Wang20
Expert 4360 points
Part Number: TPD4S012

Hi team,

 My customer needs a TVS diode. The normal signal level is 15V and the protection level needs to be 18V.

In my opinion, the Breakdown Voltage of the TVS needs to be higher than 15V so it won't affect the normal signal. I checked TPD4S012 and it seems a proper one. But the clamping voltage of TPD4S012 is only 8V which confuses me a lot. Normally the Vc is higher than Vbr but Why TPD4S012 has such a spec. Is it a proper device for my customer?

 By the way, I also want to check with you that how I should select the Clamping voltage range if the protection level needs to be 18V. Does the Vc have to be lower than 18V or it can also be higher than 18V?

Best regards,

Wayne

  • 0
    TI__Prodigy 595 points

    Hi Wayne,

    Thanks for reaching out. To answer this question, we'll need to define "clamping voltage", "breakdown voltage" and "working voltage".

    Working voltage will refer to the maximum recommended operating voltage range of your signal. In your application, that number will be 15V so you want to select a diode with a working voltage of 15V or slightly higher. 

    The breakdown voltage of a diode refers to when the diode starts conducting. This value is usually a few volts higher than the working voltage. 

    The clamping voltage measures the voltage across the diode when it is conducting. In an ideal world, the clamping voltage should remain a constant value regardless of what amount of current passes through the diode. However, in the real world, there will be some dynamic resistance across the diode that will cause the clamping voltage to be linearly dependent on the current passing through the diode. 

    The TPD4S012 is a 4 channel device that has a breakdown voltage of 6V (min) on 3 pins (D+, D-, ID) and a 20V breakdown voltage (min) on 1 pin (Vbus). You can think of it as 3 identical diodes + 1 special high voltage diode. Unfortunately, this was one of the older devices in our portfolio so we do not have a working voltage spec'd on the datasheet. However, if you are looking to use this device to protect a 15V interface, you would have to connect this interface to the Vbus pin since that one has a 20V breakdown voltage. 

    However, I'll need a little more information to understand if this device is the proper solution for your application. This diode snaps back to have a clamping voltage around 14V for 0.2A of current during conduction so there may be some risk of data latchup. What 15V interface is this diode going to be protecting? Is it for USB VBus or some sort of signal line?