7811R current on 1 pin when the pin is a Input

[fmeraz]

Hello,

my application is using 32 bit I/O on the PXI-7811R.

the way it should work is simple;

increment a HEX 2 binary level and track-it with the DIO.

as an example;

send a 0XFFFFFFFFF and the 7811R should read a 1's on all 32bits which it does but i see my power supply reading approximate 827mA? whow....... so that means i have 24mA per pin and plus 59ma from a driver i'm using in series....

so the questions is does the 7811R have a loading issue, i measures 49.5ohms in from ANY dio to GROUND and it has a resistance of 49.5 OHMS....

i'm i doing some thing wrong or does the 7811R does really consume 24mA per pin... can some one help....

[MattP]

Hello,

24 mA per pin seems a rather high amount to see drawn by each of the pins.  The thing I'm mainly curious about, however, is what kind of driver are you using in the circuit?  Also, I'm not sure also how you arrived at the amperage breakdown you mentioned.  Are you actually measuring the driver's current draw to be 59 mA and each pin to be 24 mA? Is the board operating normally otherwise?

Many of our devices have a 50-Ohm pull-up resistor at the inputs, so reading 49.5 or so Ohms at the input is not unreasonable.

[fmeraz]

Matt,

thanks for your reply.

to answer the 59mA, this is the current from my testboard plugged and it only consumes 59mA of power i hav around 12 part or so.

as for the 24mA this is striaght from the 7811R driver without plugged in on my test circuit....how did i measure that well, i used a 10K series resistor just to limit the current and stuck it right on the connector and apllied 3.3V this puts me over the 2.4 VIL, so that means a 1 on the 7811R and that holds to be true since the NI-LABVIEW LED indicated that....

i agree 24mA is too much put i can't explain it..?

[MattP]

Hello,

The normal draw of the board should be less than this.  I'm checking with our folks here for an exact figure.  As a simple test to verify that your board is working properly, try setting one of the digital lines as an output and wire it to a digital input line.  The maximum current we can source for each line is just 5 mA, so this should show that the board itself isn't actually drawing 24 mA per channel.  Give this a try and let me know if you can toggle the digital line successfully.

[fmeraz]

Matt, I do see that the DIO 0 to 31 toggle on increments of 1 bit from 0 to 0xFFFFFFFF, I have no problem fliping the bits but i notice the current was increasing when i was getting into the upper MSB from 0x0000FFFF, i was already consuming 375mA.... and this is straight onto the connector without my test interface card.... here is how i determined the 24mA i plugged a DC power supply (3.3V @ 850mA current limit) and DIP switch in series with then 32bit IO's meaning (32 switch togglable) and toggle them thus creating a 1 on the switch when is on. it take approximate 24ma to create this and this current adds up as you increase in bits up to 768mA (approx).

[MattP]

You may want to verify the Digital Enable state of the lines - they should have Digital Enable set to false to put the lines in the high-impedance state that you would expect for an input rather than the low-impedance that you're seeing now.  We have a KnowledgeBase article that sounds very much like what you're seeing - please give it a look and try the suggestions, you may find that they solve the problem.  Please note that the article assumes LabVIEW FPGA version 7.1 or 7.0, if you're using 8.x, you'll need to use the Output Enable FPGA I/O Method Node for each digital line to disable the output circuitry.  Please let me know if this works for you!