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TVS0500: Protection from external harsh environment - required

Part Number: TVS0500
Other Parts Discussed in Thread: TVS1400,

Hi,

I am designing a product has the controller and communication modules. Controller module will be installed in a pit under the ground. Communication module will be installed over the ground. Both these modules are exposed to external harsh environment conditions. The distance between controller and communication module will be 10metre (max), and connected through a cable. The max data rate between these two module is 1Mbps. The noise through the ground is mainly due to external environmental factors (like lightning, thunderstorms, etc). Sometimes, the noise can be due to interference from external factors like ESD, emissions from external EMI sources, etc. I want to ensure that the communication between the modules is reliable, and also the have suitable protections within the modules, in this harsh environment.

I am pursuing single-ended as well as differential signalling along with power lines between these two modules, due to various reasons. The voltage levels present on these signals are as below.

a) Single-ended signal with 3V level

b) Differential signal with +/-12V level

c) Power lines (both VCC and GND) with 3V level

Can you suggest suitable IC(s) with sufficient channels that can protect my below combination of signals, from various possible noises in this harsh environment? Kindly consider that the protection requirement must be preferably Bi-directional (protecting either positive or negative noise).

1) 1 single-ended signal along with VCC & GND

2) 1 differential signal along with VCC & GND

Regards,

Vikas Chandra Rao.

  • Vikas-


    Thanks for reaching out. For lightning protection, you want to reference the IEC61000-4-5 specification in a datasheet which is the harshest common EMC standard, used to simulate lightning surges. as you noted, our TVSxx00 family of devices is designed to protect in these applications. For an explanation about our topology and device advantages, please reference our newly released white paper. As a note, all of our devices will protect against both positive and negative noise - the unidirectional vs bidirectional specification refers to the available working voltage for your system. In this case, I think the TVS0500 and TVS1400 are potentially good options for your design.

    It looks like you are looking for multi-channel solutions. Unfortunately, for devices that offer lightning protection commonly the options are all signal channel due to the size of the devices, however there are of course exceptions. All of our devices currently are single channel however.

    a) Our TVS0500 should be a fit for this application. We provide 43A of lightning protection and our capacitance/transient triggering should enable your 1Mbps (500khz) per second at that low voltage swing.

    b) This option could be trickier because it is bipolar signaling. Depending on the speed, you might be able to use two TVS1400's in a back to back configuration (similar to what is described in the TVS3300 bidirectional characterization app note, but if it is running 0-14V at 1Mbps, we will run into issues with our transient triggering. If this differential signaling is <200kbps, then it should be fine. If it is >200kbps, unfortunate I'm not sure we have a solution at this point though some of our upcoming devices could help. It is also a more awkward fit because you would ideally want a 2 channel device, which we don't have currently.

    c) The TVS0500 is perfect for this as well, offering good protection for the power line.

    Hopefully that will help you get a better understanding of what we can offer! Our Flat-Clamp family should be able to help by offering a robust protection stage with a very small size and low leakage. Feel free to follow up with any questions or reach out directly at alec.forbes@ti.com if you have questions.

    Thanks,

    Alec

  • Hi Alec,

    Thanks for your detailed clarification.

    Is 9.2V clamping for TVS0050 good enough for the signal/power that is running at 3V level? Or do I need to really have lower clamping voltage for better protection? Kindly suggest.

    I forgot to mention that our product is a Battery operated device. So, there is no real Ground/Earth provision (connectivity to real Earth) in our system. Can TVS0500/TVS1400 protect our system as well? If not, do I need to provision something in my system, to overcome this limitation? Kindly clarify.

    Since your devices are single channel, I need to provide 3 to 4 such ICs in the product. Instead, I am also thinking whether I should provide cable shielding and provide one IC between Shield and GND pins alone. Providing shielding might be beneficial from EMI point of view also. Kindly let me know your comments on this approach.

    Regards,

    Vikas Chandra Rao.

  • Vikas-

    To determine if the clamping voltage is low enough, look at your IC abs maximum. As a general rule you should keep surge protection clamping voltages below this to ensure reliability, however because it is a transient it is usually ok to violate slightly. I'd check to see if your IC can sustain that 9.2V.

    As for the lack of a true ground, that doesn't cause a problem. The purpose of the TVS diodes is to clamp the voltage at the input, so connecting them between the input and a virtual ground will work equally well, as long as it provides a shunt current path for any fault current.

    Shielded cables will help indeed with protection against externally coupled surges like lightning, but will not provide perfect protection because it won't be able to clamp any surges internally (IE power switching, hot plugs). It also tends to be relatively expensive for the cables. It certainly is an option, but I would generally recommend best practices as having TVS diodes on each line that can be exposed to a fault. From an EMI perspective, the TVS will also protection against ESD/EFT pulses and will help protect the system.

    Thanks,
    Alec
  • Hi Alec,

    I am pursuing the ICs that are meant for lower power consumption, as my product is battery powered. So, the ICs do not have higher supply voltage range and hence their absolute max rating range of -0.3V to +6V. Do you think I can still pursue TVS0500 for these ICs? Or should I consider some other IC? Kindly suggest if there is any better alternative.

    I understand that TVS diodes provide fault current path to the Ground, and thus protecting the IC's pin (line/signal) that it is connected to. However this current/energy has to be dissipated somehow in the system, or it should be bypassed to the real Earth. Since our product is battery powered (with very less circuitry), and there is no path to the real Earth, the energy is contained within the product itself and it can likely damage some part within the product (through Ground). Kindly correct if my understanding is wrong. Kindly suggest how to avoid this.

    Our product is a very low powered consumption one and the currents are hardly few tens of mA in a very rare times (<1% time only). Also we don't do any hot-plugging once the product is installed. So, I can say that there will not be any internal power surges/transients anywhere generated within the product. Considering this, kindly suggest which option is better - (i) shielded cable with one TVS diode on shield line, or (ii) 3-4 TVS diodes in total for signal/power lines.

    Since I am expecting my product's lifetime to be at least 10yrs, I am much concerned about the product quality and reliability. Kindly suggest the above accordingly.

    Regards,

    Vikas Chandra Rao.

  • Vikas,

    What IC are you trying to protect?

    I do not necessarily agree with your contention that the energy would be contained in your reference ground plane as the energy should be dissipated as heat through the plane that you call ground. Now if that ground plane is not large enough or thermally dissipative (not a real word but still) then your devices could break but that would be due to thermal failure.

    Could you send a schematic for what you are proposing? I am confused on the setup to use 1 TVS or 3-4. My email is c-phillips@ti.com

    As far a reliability goes, we have ran our TVS0500 through 5,000 surge pulses as mentioned in the datasheet with no variation in clamping performance.

    Regards,

    Cameron

  • Hi Cameron,

    I am trying to protect the micro-controller, and it has absolute max range of -0.3V to +6V. It's supply voltage range is 2.0V to 3.6V, and I am supplying 3.0V to it in my product. Kindly suggest how to protect its pins from surges.

    Yes, the energy would try to dissipate within the Ground plane. But my product is just a 2-layer board, and I don't have any dedicated Ground plane. However I am providing Ground pour wherever space is left. I have decided having just 2-layers because, the switching frequency is very low (1MHz max especially for switching regulator),  analog circuitry criticality is lower, and few other non-critical aspects. However cost is an important factor for considering 2-layers over 4-layer PCB. Considering this, I am concerned that parts may get affected through Ground pour/trace. If you have any thoughts on this, kindly let me know.

    I have a cable connecting two different modules of my product. This cable is exposed to external harsh environment, and it's length could be 3metres. This cable has 5 wires : 1 single-ended signal, 3 different VCC lines and 1 GND line. If I have to protect, I need to use 4 TVS diodes. However I can consider the same cable with shielding, where-in 1 diode on the shield line is good enough for protecting the 5 wires within it. So, I want to weigh both these options, and pursue a better option. Hope you have understood these two options. Kindly suggest which approach is better.

    Thanks for confirming that TVS0500 is very reliable.

    Regards,

    Vikas Chandra Rao.

  • Vikas-

    The energy will dissipate as power burnt through the TVS diode, so it should be fine I believe. Without actual testing it's difficult to give exact specifics, but given that your system is expected to run at low power and with little chance of an internal power surge your only risk will be due to external energy coupled from things like lightning. Given this, I think you should be fine with a shielded cable as that will protect the internal cabling and provide a low impedance path to the chassis of your equipment.

    Thanks,
    Alec
  • Hi Cameron/Alec,

    I am trying to protect the micro-controller and an other IC from surges, and they have absolute max range of -0.3V to +6V and -0.3V to (VCC+0.6)V respectively. Their supply voltage range is 2.0V to 3.6V, and I am supplying 3.0V to them in my product. TVS0500 has 9.2V clamp voltage, and I do not think it can protect these ICs. Kindly suggest how to protect their pins from surges.

    Thanks & Regards,

    Vikas Chandra Rao.

  • Vikas,
    As Alec said before it is best to make sure the clamping voltage is below the abs max but there is a possibility if could be violated for a short period of time. The only way to see is to actually test your system with the protection. What is the micro-controller that you are using? If you would like you can send a schematic to me on email: c-phillips@ti.com and I can see that parts you are using.
    Otherwise we do not have a solution that can clamp to 6V currently. However we are aware of this gap and have plans for a lower clamping device in the future.

    Regards,
    Cameron
  • Hi Cameron,

    Thanks for clarifying. Apart from the clamp voltage, there is Vrwm (Reverse Standoff voltage) and Vbr (Breakdown voltage). I am thinking about these two voltages as well apart from Vc (Clamp voltage). I understand that Vc must be lesser than Vabs (Abs max voltage on pin). For my system, what would be the ideal Vrwm and Vbr voltages? As you are aware, I am using 3.0V supply voltage in my system and 6V is the absolute max rating of the pins.

    Do you have any indication, as to when you will be ready with 6V clamp voltage solution?

    Regards,

    Vikas Chandra Rao.

  • Vikas-

    I can't comment publicly on ongiong development, unfortunately. In your situation you need a device with a Vbr of ~3.3V and a Vclamp below 6V, as you have noticed. There are very few devices that are capable of doing this. This is why we are saying that it might be best to slightly violate the Vabs max even though it is not the ideal situation - because there is not an IC that provides the ideal solution unfortunately.

    Thanks,
    Alec