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I'm designing a series of 1-Wire components for my SmartHome Bus and use the DS2480B as Busmaster. Because the cable I run around the house has 3 wires (24V, 1-Wire, GND), I'd like to protect the DS2480B from overvoltage caused by accidentally short-circuiting the 24V and DQ lines. If possible, the design should also protect the Busmaster from ESD.

Note that I don't use 12V EEPROM programming, so the Voltage on the 1W line should never exceed 5V during normal operation. The DS2480B has an absolute max rating of 14V on the 1W line.

This is the original circuit proposed by Maxim to RC-Filter the 1W line and to protect the DS2480B from ESD:

DS2480B original circuit

I think I cannot use the DS9503 because it requires that both GND and 1W go through the package. Because I have additional components further down the bus that draw several 100mA of current (from 24V) and the DS9503 has a max current through package of 80mA rating, I can't loop GND through the DS9503.

So I came up with the following designs:

  1. Use a Polyfuse in Series with the Resistor (reduce the resistor so that resistor + R_Fuse =~ 62) and add a Zener-Diode between the DS2480B and the Resistor. Protect with Zener and Fuse If 24V is connected to the 1W line, the Zener will short-circuit the excess voltage to GND and letting the fuse trip. Problems/Questions:

    • Is this feasible?
    • What kind of Zener and Fuse would I need to use so the Zener survives the hit, and the Fuse adds a reliable, low resistante during normal operation?
  2. Same as 1., but add a P-Type Mosfet between the Fuse and the Resistor. Protect with Zener, Fuse and Mosfet Now, the Mosfet would short-circuit the 24V to GND, causing the fuse to trip faster and taking off load from the resistor and the Zener. However, the Mosfet has to take the hit this time. However, even the smallest Mosfets can take 0.8A continuous and 5A pulsed max currents, so they should be okay.

  3. Use a Polyzen-Fuse such as TE ZEN056V075A48LS. Protect with PolyZen-Fuse Problems/Questions:

    • During normal operation, the current would flow from V_OUT to V_IN through the package. Is this an issue?

Which design would you recommend, or what kind of dimensions for the components would you use? Additionally: How do I protect all the components from ESD? Can I still use the DS9503 and just connect one of the GND pins (and if so, which)? or both?

Of course, if you have better ideas, I'm all ears.

Thanks a lot in advance!

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  • \$\begingroup\$ Why are you feeding 24V and not (say) 5V? \$\endgroup\$ – Andy aka May 27 '15 at 10:56
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    \$\begingroup\$ several reasons: 24V is a common voltage in smart homes, so there are plenty of components working off it (such as switches with displays, presence detectors, smoke detectors etc). I already have 24V PSUs in my fuse box. Also, I'm running a lot of relays off the 24V rail - sometimes the current adds up to 300mA. Since the bus is quite long (up to 100 meters), and providing 24V*300mA = 7.2W off a 100m 5V rail would require a ridiculous wire diameter. \$\endgroup\$ – final May 27 '15 at 11:40
  • \$\begingroup\$ Is 1-wire comms suitable for upto 100m? \$\endgroup\$ – Andy aka May 27 '15 at 11:42
  • \$\begingroup\$ maximintegrated.com/en/app-notes/index.mvp/id/5026 this may be suitable with modification \$\endgroup\$ – Andy aka May 27 '15 at 11:49
  • \$\begingroup\$ it depends a bit on the structure of the network, but yes, 1-wire can do up to 200m of network weight with the DS2480B as driver - with custom drivers you can go even significantly higher than that. The problem with the depl-mode mosfet is that it has a forward voltage drop of up to 2V, and I already use this to protect all my slaves - can't have two of them in series. Unless you have a good proposal of how to modify the circuit. \$\endgroup\$ – final May 27 '15 at 11:54
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Something vital to remember when powering current-hungry devices on the bus cable, is that ground lift quickly becomes a problem, i.e. the DQ-GND voltage diff decreases since GND is lifted by the 24V loads.

If using a CAT5 cable, this can be mitigated by using multiple wires for GND. But with several 100's of mA in the return wire, I'm not sure that will be enough.

A local example: lighting up a 20mA LED with a DS2408 at the far end of my ~80m home network was enough to render the whole net unusable, power cycling it was the only way to get it back. When using three GND leads instead of one (in the CAT5), it works like a charm. Not sure about the rest of the load on the net, but it's some 20+ DS18B20 and a few DS2406's, nothing fancy.

(Sorry, don't have enough reputation to comment, so using Answer even if it is not an Answer...)

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  • \$\begingroup\$ that's a fair comment, I haven't thought about this yet - thanks for the input. I'm using KNX-Bus wire which has a 0.5mm^2 wire cross section (on all leads), so that's about the equivalent of 2.5 CAT5 leads. So far everything ran smoothly with currents of about 150mA. But my slaves are scattered, so the max distance from source is probably only 30 meters, while I easily have 100m of network weight (i.e. total amount of wire connected to 1W) \$\endgroup\$ – final Jun 4 '15 at 6:32
  • \$\begingroup\$ Interesting to hear on another setup! At 30m the voltage drop probably doesn't get as big, as with my ~80m.In a previous case, I had a relay in the middle of the bus (~40m?) which when triggered, brought down the bus as well. Never tried with multiple grounds at that time though. \$\endgroup\$ – Johan Ström Jun 5 '15 at 17:12
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I now use a Depletion Mode Mosfet for Overvoltage protection with a low on resistance (Maxim uses a DN3135 in some examples which has about 35Ω, but I found that Infineon's BSS159N has even typically 3Ω at V(gs)=0V). I connect the Gate to the chip's VCC line which is always 5V.

The mosfet shuts off at about V(gs)=-3V (max), so the maximum voltage the chip should be exposed to is 8V. Because the Mosfet has a standoff voltage of 60V, my 24V polarity protection is no problem. For ESD-Protection, I use a TVS Diode with 24V standoff and low capcitance (<10pF), as capacitance is the enemy of long 1-wire buses.

Hope this helps someone in the future

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  • \$\begingroup\$ Can you share the designs of your solution for overvoltage protection? \$\endgroup\$ – user104542 Mar 23 '16 at 18:25

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