Source/Sink Questions....

MyYz400

(Mind you, I'm a beginner with some understanding of Micro Controllers).

I have a question. I have read that the SX can "Source/Sink 30mA". Now to me that means it can either provide voltage, or ground up-to 30mA (each I/O? or cumulatively for all I/Os?). If so, what is the voltage it supplies? Whatever the IC's power pin voltage is? What is the resistance of a given I/O? I assume milli-Ohm range.

But is that the only choices? Is it possible to have a pin go open? Just float? I know this would be bad practice, but could be useful for one of my applications.


Also, do the I/Os have a MTBF? I might want to do PWM, but thousands of switches per second, for possibly years seems like an I/O could go bad and fail?


Thank-you for putting up with my seemingly pointless questions.

MyYz400

Mike Green

1) The 30mA figure is for a single I/O pin. There are additional limits on the total current for a group of 8 I/O pins and the total current for the entire device. See the datasheet for the SX for these limits.

2) The voltage supplied is normally Vdd or Vss (+ supply or ground) less one saturated MOSFET's voltage drop, typically 0.6V. Again, see the datasheet for the specifics.

3) I/O pins have 3 states: input, output low, and output high. The input state is high impedance and is effectively open. You do have to limit the applied voltage since all I/O pins have protective diodes that conduct to Vdd and Vss if the applied voltage goes more than one diode drop above Vdd or below Vss.

4) There's no MTBF for I/O transitions. The failure modes all have to do with applying excessive voltage or drawing excessive current (beyond the chip's "Absolute Maximum" ratings). The SX I/O pins are intended for possible applications involving millions of I/O voltage transitions per second.