Praticing Safe Circuitry: Use a Transorb
Praticing Safe Circuitry: Use a Transorb
(OP)
I've got a circuit I'm trying to design and have a few questions. I'm interfacing a microcontroller to a device with an open collector output. I'm trying to design transient voltage suppression circuitry. I'm looking into using transorbs but I couldn't find any that clamp at a voltage level that is safe for the micro (less that 4.1V) What is the lowest clamping voltage for a SMT transorb? If there isn't a transorb that clamps at ~ 3.6 V , what kind of additional circuitry could I implement to protect the micro. I am controlling my pull up resistor with one of the GPIOs to conserve battery life when I am not reading the input. I was thinking of some transistor buffered circuit, but wasn't quite sure how to implement that.
Thanks for any help!
Thanks for any help!





RE: Praticing Safe Circuitry: Use a Transorb
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Praticing Safe Circuitry: Use a Transorb
RE: Praticing Safe Circuitry: Use a Transorb
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Praticing Safe Circuitry: Use a Transorb
RE: Praticing Safe Circuitry: Use a Transorb
What I'm try to get at is it depends on what you are going to hook to the O.C. on what protection you need! If you are going to hook an LED to it you need NO protection.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Praticing Safe Circuitry: Use a Transorb
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I am trying to read data from an open collector output. That's why I have the pull up.
The transorb is clamping at 5.6V This is higher than the 4.1V max voltage on a pin. Also, the pullup line data-bias is connected directly to the micro, leaving no isolation from a transient voltage. I am wondering if I need a diode on the pullup line or maybe a buffered transistor.
RE: Praticing Safe Circuitry: Use a Transorb
1.5V / 68K = ~22uA
Even on the pullup side, you are still talk a pretty small current.
1.5 / 10K = 150uA
If you are still concerned, do as macgyvers2000 suggested.
RE: Praticing Safe Circuitry: Use a Transorb
I generally try to have a fair sized series resistor with the micro pin, fairly close to the micro. Closer to where the I/O arrives on the board, I use a ESD protection diode and/or small capacitor to ground(a 10 to 47 pF as I do a lot of RF), and/or a high value resistor to ground. Basically several methods to shunt ESD energy to ground, then long trace length (distributed inductance/capacitance), then a resistor to make sure current is limited to any internal protection clamping diode.
But, if you have only a very few I/O to protect, try a zener diode(s) to limit the voltage on the I/O line along with maybe one or more of the other techniques.