I am wondering what Schottky Diodes I should use on a project I am working on. I must protect a 5VDC signal wire from ESD (both voltage and current). I would like to use the same setup as you have listed on your technical paper (Protecting Inputs in Digital Electronics):
External clipping diodes
To eliminate the use of the microcontroller’s internal diodes, external Schottky clipping diodes can be used. This is shown in Figure 11. Schottky diodes are implemented because they conduct before the internal diodes of the microcontroller (Schottky diodes forward bias at about 0.2 V as opposed to the 0.7 V of the internal diodes). Note that a small series resistor is used to protect the Schottky diodes from overcurrent. As these diodes are only on for a short time, a small resistor works well; something on the order of 10 Ω usually works fine. Alternatively, the 10 Ω resistor can be omitted if the Schottky diodes are beefy enough to handle short-duration, high current pulses.
Figure 11: External clipping diode circuit.
Figure 12 shows the results of this circuit with the input switch circuit. The yellow trace is the positive side of the capacitor, while the green trace is where the resistor meets the Schottky diodes. Note the negative spike is -0.650 V, which is below the forward bias voltage of the microcontroller. A voltage of this level on a well-designed PCB should not cause any problems.
Is there a particular model diode you recommend for this application? Also, what are the parameters I need to know beforehand (voltage & current of input)?
Thank you for using our TechForum. I found some options of Schottky diodes rated for 5VDC reverse voltage. You can see the filters of the specifications that would be needed to find what you are looking for. Click here to view a link to those options.
While discrete rectifier diodes can potentially be used for this purpose, it is perhaps not the best solution. (Note also that devices with a rated reverse voltage significantly greater than 5v would be called for in this case.)
There are devices such as the DRTR5V0U1SO-7 which are specifically designed for this application. So-called “steering” type TVS diodes are used to route the current flow from an ESD event into a board’s power network and away from a sensitive input pin. Since most boards’ power networks contain a significant amount of capacitance, the charge injected by modest ESD events can often be absorbed without creating a voltage high enough to cause damage. The mentioned part also contains a zener-type clamping diode suitable for a 5V supply; in the case that the charge injected by an ESD event exceeds the power network’s ability to absorb it safely, this clamping diode will enter its reverse conduction mode and dissipate the excess, thereby offering protection not only for the I/O pin, but also the supply network.
Devices that are purpose-built for ESD protection are designed and characterized for that use, and generally are recommended over similar devices intended for other purposes.