The D28V0H1U2P5Q is a unidirectional TVS that is intended specifically for the harsh automotive environment.

It’s convenient when we can assume that the voltage on a particular pin will always be more or less what we expect. This is often the case in the low-voltage and digital circuits that are so common these days. Sure, there are always imperfections—a little overvoltage here, a small noise spike there. But often we can simply ignore these things; no protection circuitry is required.

 

All images courtesy of Diodes Incorporated (PDF)

 

But not all electronic environments are so benign. In some cases, a low-voltage signal can be subject to relatively large transients that will (at best) interfere with normal functionality or (at worst) destroy your device. Actually, device destruction is not the worst-case scenario if you consider the possibility of a component catching on fire and eventually reducing the entire system to ashes and charred metal.

This is where transient-suppression products come into play. A common term here is TVS (transient voltage suppressor), though I’ve also heard the rather creative portmanteau “transzorb” (which is apparently a registered trademark of Vishay). These parts are essentially diodes that are placed in parallel with the circuitry that needs to be protected.

 

Breakdown

Actually, in the case of a unidirectional TVS, it would be more correct to say that it is in antiparallel, because the cathode of the TVS is connected to the positive voltage. As with a Zener diode, the relevant voltage rating here is the reverse breakdown voltage (VBR), not the forward voltage.

 

 

The purpose of the TVS is simply to start conducting when the voltage exceeds a certain threshold—and to hopefully not burn up before the voltage returns to normal levels.

This illustrates one of the difficulties in using a TVS. When the voltage goes above VBR, reverse breakdown occurs and the TVS conducts. This clamps the voltage at VBR and diverts the transient current to ground. The circuit is safe now, but what about the TVS? If there is little or no series resistance for limiting the current, the TVS has to fend for itself with whatever (potentially high) currents result from the transient.

This is where manufacturers try to make their components stand out from the crowd. Diodes are not exactly new; I think that most semiconductor companies have the diode thing more or less figured out. The innovation comes into play when these diodes are made capable of surviving large currents and dissipating large amounts of heat.

 

Peak Power and the 10/1000

The D28V0H1U2P5Q TVS from Diodes Inc. has a “peak pulse power dissipation” of 1800 W; if you look in the datasheet, you’ll see that this spec has “10/1000 µs” in the “Conditions” column. You might also notice that this cryptic 10/1000 (aka 10 × 1000) thing appears frequently in discussions of TVS components.

It turns out that 10/1000 µs refers to a standardized transient waveform:

 

 

With a little bit of deductive reasoning, you can conclude from this diagram that the “10” in 10/1000 refers to the length of time from the beginning of the transient to the peak, and that the “1000” refers to the length of time from the beginning of the transient to the “half value.”

TVS manufacturers can’t just say that a particular product can safely handle 1800 W of power dissipation because that implies 1800 joules per second—indefinitely. That’s a lot of power for a little IC; you can boil a pot of water pretty quickly on a 1300 W electric burner. So the 1800 W spec actually tells you that the D28V0H1U2P5Q can safely dissipate peak power of 1800 W in the context of the 10/1000 µs transient waveform.

The marketing information that I saw indicates that this 1800 W spec is 20% higher than the peak power dissipation offered by “comparable solutions.” That’s a bit vague, but if you really need that extra 20%, the D28V0H1U2P5Q is worth a look.

 

Remember to derate! The peak power dissipation spec is only applicable at room temperature and below.

 

Automotive Qualification

Another major selling point for the D28V0H1U2P5Q is its status as an “automotive” part. It is compatible with Automotive Electronics Council reliability requirements  (i.e., AEC-Q101), and Diodes Inc. describes it as an appropriate part for suppressing transients in automotive applications—more specifically, transients associated with inductive loads. However, I’m sure that the D28V0H1U2P5Q could do quite well in industrial environments, and perhaps in military and aerospace systems as well.

 


 

Have you worked with any new TVS components? Feel free to share your experiences in the comments.

 

Comments

1 Comment


  • haythamhakla 2017-04-13

    Hi Robert,
    Thank you for the article.
    After reading a lot about TVS diodes, I’m still not sure I get the whole picture when it comes to choosing the correct TVS for a certain application.
    Here’s the simple task :
    1- I have a microcontroller and I need to protect its inputs from ESD. (the microcontroller inputs are already protected internally by the manufacturer, but I need a more rigourous protection of +-30KV, that I would need to implement externally at each input/output) . I need to select a Uniderctional TVS diode since all my signals are supposed to be above ground.
    2- the microcontroller input pins that I want to protect are 5V, and can tolerate a max of +5.5V and a min of -0.5V.
    All I need is a TVS diode that does that. It should be simple.
    After reading several articles, including yours, I understand that the first step is to select a TVS diode that has a Vrwm slightly above the microcontroller’s input voltage. In my case, it looks like a Vrwm of 5.3V is reasonable since it it above 5V and still less than the max 5.5V of my microcontroller. After reading a couple of application notes from Infineon and littlefuse, they propose TVS with similar Vrwm (5.3V , sometimes 5.5V ) for applications like USB and Keypad, which to the best of my knowledge are also 5V.
    3- The confusion comes with the values of the breakdown voltage and Clamping voltage. The TVS diodes proposed for 5V applications always have a high breakdown voltage ( 6V and up), and a higher clamping voltage at the peak pulse current ( around 9V and higher). Doesn’t that still put the protected device at risk? if the diode start conducting at the breakdown voltage, doesn’t that mean the protected device is already seeing the breakdown voltage which is higher than the max 5.5V?
    Once engineer told me to chose Vrwm as previously mentionned, and not to worry about the high Breakdown and clamping voltage since these are transient event that happen too quickly.
    I am not quite convinced with this logic.
    Also, another question about uniderctional TVS diodes, in the case of a negative transient pulse, will the voltage seen by the protected device be -(TVS forward voltage)?

    I really appreciate your feedback on this.
    (if i sounded too complicated, here’s another way of looking at it: you want to protect your microcontroller input to +-30KV using a uniderctional TVS. The input can tolerate voltage from -0.5V to +5.5V . Which TVS diode would you choose from Digikey or mouser and why?).
    Thanks a lot!