I have a few quick questions based on soldering the cat4101 board:
I bought the Aoyue Soldering station that DWZM mentioned, and it is very nice! The only problem is I have never used a soldering iron with a temperature set before. What temp should I use to make sure I don't fry the 4101 IC but still solder fast enough to be safe?
I usually set the iron near 300c. Don't have any justification for that, other than it works great for me.
Also, I thought there was some instructions on how to solder the IC so you get alot of connection to the surface underneath it (for thermal conduction) as well as the tab out there, but I have searched RC for awhile now and not come across anything. Basically, do you try and cover the entire ground plane with solder or just make sure the tab is connected?
Yes, you really do want a thorough connection across the entire pad for best thermal conductivity.
This is what I do:
1) Tin the ground pad on the board with a thin coat of solder (heat it up with the iron for a few seconds, touch solder to it, and move the tip of the iron back and forth as if spreading butter to distribute the solder across the pad)
2) Tin the "back" of the tab on the part using the same method
3) Hold the part in place with tweezers or a pick, and lay the tip of the iron down on the board right along the junction between the exposed edge of the tab on the part and the edge of the pad as it shows under the part. Leave it there until the tinned solder flows together and bonds. If it doesn't look like enough solder, feed some more in while the iron is still there.
Quick question for the group here, would you guys consider using a resistor before the driver to reduce the V of the PSU so that as little heat as possible is generated by the CAT4101s? In the case of the potrans 24V PSU's I'd see a resistor as an extension to the pot they already have.
It's my guess that the pot onboard the potrans PSUs is adjusting a sense resistance some internal chip is using to set the output voltage, NOT just dropping the output voltage directly. The pot just looks WAY too small to dissipate several watts. Can you not get yours down low enough?
I think I need a 0.24 ohm resistor for Rsense, not sure about how you go about figuring the value for Rs. I found a 40V schottky diode that handle up to 2A. I am struggling with the inductor, and haven't looked at the caps yet.
The Rs value is basically set such that the current limit won't kick in under normal operation for the peak current through the chip. So, using your inductor size, figure the peak current, then choose an Rs value for that current. The spreadsheet from OnSemi is really helpful in doing these calcs. You have some freedom on Rs as it doesn't come into play during normal operation, so the calculated value is really a minimum, not a specific requirement.
The caps shouldn't be an issue, most of them are rated way over what you need. The inductor will indeed be a problem; current rating and inductance seem to have an inverse relationship. You may need to "allow" a smaller inductance than you'd like to get the current rating you need.
I may do this instead, but how close to 1A can this driver be run at safely? The IC has a 1A max right?
If you kept the voltage drop as small as possible, I would see no issue running it right at 1A. The thing you want to watch for is hitting the temperature limit, and even dropping two or three volts at 700mA I didn't hit it - so at 1A and .5v drop, you should be totally fine.
). The good news is that I ordered ten boards and this only occurred on one of the twelve that they sent me.
