MAX3223: MAX3223IDBR

Some ripple is normal for charge pumps.

The datasheet tells you to use a smaller capacitor C1.

I tried a 0.047uf at C1 and it made no difference. The ripples on the positive pulse are at 0.8Vpp. 

The ripple size is determined by the ratio of the flying capacitor (C1 or C2) and the storage capacitor (C3 or C4).

Check if C2 affects V+ instead. You can also try increasing C3.

Hi Thomas,

So Clemens ideas are generally a pretty good place to start - have you had any luck with varying the C2 capacitance as suggested?

If not - one thing that you could do that would probably be helpful based on your results - add a discrete capacitive load (a capacitor to ground) to help filter off some of the higher frequency noise. The longer cable has more capacitance so is acting as a filter. If you can find the capacitance per foot or meter on the 3 foot cable and find the eq. capacitance of 2.5 feet of cable you can size a discrete capacitor - the standard is up to 2500pF but if you don't need that much i wouldn't try to max it out.

Please let me know if either of these solutions work for the problem!

Best,

Parker Dodson

I tried C1 = 0.1uF, C2,C3,C4 = 0.47uf there is still the same noise occurring on the positive pulse.

I tested a 1000pF and 2200pFcapacitor to gnd on the Tx line, result was no improvement. Next I am going to try varying C2, C3, C4 values more. 

Hi Thomas,

Please let me know what you find - in the meantime can you share the 3 foot cable part number if you have it available as well as the shorter cable's part number?

Best,

Parker Dodson

Both cables are the 26 AWG flat telephone cord.

I tried many variation with all the capacitors with no improvement with the ripple on the positive side of the pulse. Is this Tx output signal acceptable with my application of a 6 inch cable connected to another MAX3223 transceiver?