checking the PO pin

I should check that the PO pin is connected correctly. In figure 8 in the application note there is only a pullup shown. I have taken the series resistor out and the result seems a little better.



The other thing to do is to check if it helps to have the pull up closer to the chip. I will check this now.

first removed what I thought was the pullup (R12) the result is shown below which seems very similar to the previous.



to be sure that I have disconnected all the resistors, I have removed a link close to the chip. This time I get the change that I was after.




Now I will try with just a 1.2K pullup directly from PO to 5V.



That is much nicer. Better try now with a load on this. I will try to go back to the original circuit but with a 1k pullup.

I decided it was easier to just add a series resistor (82R). The result looks worse. but remember that it is driving the optocoupler.



I will just remove this an put in a wire as the app note suggests. I will also replace the 1k2 with 1k pullup (minimum app note recommends)




looks okay. Tomorrow I will need to determin how small I can make the pullup to improve the shape.

I just had a thought that the app note recommends the use of 1k to 10k pullups, however that is for interfaceing directly into a microcontroller or dsp. Maybe as I am going into an opto first, I need more current.