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TPD4E1U06DBVEVM: When Clamping Voltage Exceeds Maximum Input Voltage Of Input

Matt Lang
Intellectual 540 points

Part Number: TPD4E1U06DBVEVM

I have been reading about protection methods against a static discharge using TVS diodes, and I have a few specific questions still.

  1. Using the TPD4E1U06DBVR as an example, the Clamping voltage is 15V typical. The graph for a static event is below.

    This device is said to be designed for USB 2.0 applications. But most MCUs D+, D- and VUSB power pins can not exceed more than 5V. Or other parts for that matter. It looks like the part will see 15V during the active clamping after the transient. More than 220nS in the graph above. Would that not still damage the part? 15V is quite a bit higher. I would just like some clarification as to why this does not damage parts every time static hits like this. I have read that for protection, you need to choose a clamping voltage that does not exceed the max of the part, but I have a hard time finding a TVS diode that has 5V standoff voltage and has a maximum clamping voltage anywhere near 5 to 6V. Usually much higher like 10-24V.
  2. During the static event, say if it's on an MCU I/O pin. Wouldn't the intrinsic clamping diodes start conducting at some point and cause damage? I assume the TVS protects the input in this case because by the time the body diodes forward bias and start conducting any current high enough to do damage, the TVS would have already absorbed the static event? Is that right?
  3. The block diagram kind of looks like the data lines have standard diode clamping, maybe shottkey diodes, instead of TVS. Since the spec says all pins have a clamping of 15V typ, I am assuming they are all TVS, but the different symbols mean something else? Are the data lines TVS and still have a 15V typ clamping voltage like the graph above?
  • +1
    TI__Genius 14390 points

    Hi Matt,

    1.

    The 5 V Abs max rating of the IC you're protecting is likely a DC rating, ESD/Surge events are transient events so they are not the same. If the device does have transient ratings I would stay below those ratings. You will have some margin since the ESD voltage is being clamped in the nS range, the clamping voltage does not need to be 5 or 6 V.

    As you've found there won't be many devices that have working voltage of 5.5 V and a clamping voltage close to 5 V, there will usually be a few volts difference between the working voltage and the breakdown voltage. It's best to conduct bench testing to verify if the clamping voltage is low enough to protect the IC. 

    2.

    The TVS diode will protect the input by shunting the current to ground once the voltage on the line goes above the breakdown voltage, after that the only current that would flow into the IC pin is the leakage current from the diode. The voltage is clamped within a few nS so there should be no issue with the input clamp diodes of the MCU, protecting MCU I/Os is a very common application for our devices. 

    3. 

    The inputs are all standard TVS diode inputs. They will all have the same typical clamping voltage spec. 

    Regards,

    Sebastian