How much is the input impedance of Micorchip dsPIC33 chip ??

[yzou_ua]

I'm interfacing the encoder output w. QEI pins. I wonder how much is the input impendance of these pins on chip... Could someone let me know?
Thx alot!

 

[horace1]

if you look at the data sheet of the dsPIC33 you are using it will have a section on electrical characteristics

e.g. for the dsPIC33FJ128MC802 download the data sheet from
dsPIC33FJ128MC802

and look at section 31.0 ELECTRICAL CHARACTERISTICS

 

[yzou_ua]

Thx but I have tried this way and nothing is found...
What I need is the input impedance of QEI pins but what given is for "A/D" or "D/A" pins... Faint...

 

[horace1]

with QEI the pins are digitial (make sure you set the pins to be digital) - does TABLE 31-9: DC CHARACTERISTICS: I/O PIN INPUT SPECIFICATIONS which gives the leakage current help?
are you having problems connecting your device?

 

[luben111]

usually the pin loading is between 5 and 10 pF. If the pin has more features then the capacitance could be higher

 

[yzou_ua]

Let me put it specifically: My encoder signal is 0 - 5VDC pulses, as u know, and I just use a voltage divider (400Ohm & 600Ohm) to shift it down to 0 -3VDC. I havn't tried this yet, but I'm concerning about the impedance issue. That is, is my impedance of "encoder + voltage divider" much smaller than that of DSP QEI pins?

with QEI the pins are digitial (make sure you set the pins to be digital) - does TABLE 31-9: DC CHARACTERISTICS: I/O PIN INPUT SPECIFICATIONS which gives the leakage current help?
are you having problems connecting your device?

 

[bigdogguru]

Typically, an I/O pin on the dsPIC33F series where VSS ≤ VPIN ≤ VDD, has an impedance in the 2MΩ to 3MΩ range.

So if you design your voltage divider to ensure VSS ≤ VPIN ≤ VDD you shouldn't have a problem.

Does that answer your question?

 

[btbass]

You should not have a problem with those sort of values.
In automotive it is common practice to put a 33K series resistor, mounted close to the pin, on digital input pins that go to the outside world.
This is for ESD protection, as during transient testing, the connections are zapped with up to 8Kv positive and negative spikes.

 

[yzou_ua]

Thanks alot, guru and btbass! I gonna go ahead top try...