Anyone have gerber files for Vicor DCDC demo board?...We have a noise problem - Page 1
Forum section: electronics / general

author: ocset
author_rank: Super Contributor
timestamp: March 25, 2020, 12:11:55 pm
content: Hi,We know that the Brilliant Vicor DCM3623T50M53C2T00 DCDC modules are in used in millions of PSU’s so assumed that people must have the gerbers for the Demo Board on page 7 of the following document? If so please could you send them here?Vicor Eval Board:-http://www.vicorpower.com/documents/user_guides/vichip/ug_ChiP_DCM_EvalBoard.pdf………………*……………………*………………*……………………*………………*……………………*We are suspecting that since we are using it non isolated on our own test PCB, and just have a single common ground plane under the DCM module, this may be causing our noise issue. We suspect noise from the module is coupling into the ground pour directly under the module and getting back into the DCM3623 and interfering with it. Do you think this is possible? If we could see the gerbers of the Eval Board, then this would go some way to confirming this.I suspect that the Vicor demo board has only chassis ground copper pour directly under the module, but would just like to confirm this with the gerbers?We noticed that the demo board schem on page 7 has a chassis ground connection, and that this is isolated from the circuit primary and secondary grounds. We also noticed that Y capacitors have been place from chassis ground to all the four power rails. However, we noticed that no common mode choke is used. Please could you advise if there is a reason that no common mode choke was used, since, as you know, it is usually needed to form the LC common mode filter with the Y caps?

author: fcb
author_rank: Super Contributor
timestamp: March 25, 2020, 02:11:31 pm
content: Put some figures on it - how much noise, whats the shape of the noise?Are VICOR not helping? You'd kinda assume they'd be forthcoming???

author: ocset
author_rank: Super Contributor
timestamp: March 25, 2020, 04:05:17 pm
content: The noise is in the output current, as in the attached scope.Current is from VIOUT of ACS722 Hall sensor and is {(Volts – 0.33) / 0.264} AmpsThe yellow trace is the vout.The circuit is as in the attached.

author: fcb
author_rank: Super Contributor
timestamp: March 26, 2020, 02:47:21 pm
content: 1. That noise is very low frequency. is the converter in some sort of discontinuous mode? Does this change when you sweep the load.2. Noise is in the output current trace? - this would indicate it's your load creating it.3. What happens when you remove R11? - this links your 0V domains?4. Can you use R26 to isolate the ACS722 psu from the other domains - make sure you aren't picking up a ghost.

author: ocset
author_rank: Super Contributor
timestamp: March 26, 2020, 03:23:40 pm
content: Thanks,Its not a ghost.....i also see it when i cut the power plane through and insert a sense resistor in the module positive output. i just now found out its due to the large 1820uF of output capacitance.When i only have 220uF of output capacitance, the noise goes.The Eval board for this module (DCM3623T50M53C2TOO) only uses 220uF of output capacitanceEval board on page 7:http://www.vicorpower.com/documents/user_guides/vichip/ug_ChiP_DCM_EvalBoard.pdf