UCC28630: When using the UCC28630 in a 24VDC supply, increasing the output load shuts the output down.

Tim

If you did not, we recommend you use our excel design calculator http://www.ti.com/lit/zip/sluc537 to verify that this design can support the entire desired operating range.

Table 3. (page 42) of the UCC28630 datasheet has a list of all fault conditions that UCC28630 measures for.  If any of them are triggered, UCC28630 will stop operation.  Depending on the fault, it will either be a latch fault response (where VDD needs to be removed, which is done by removing the AC input) or auto restart (where once VDD discharges to VDD(reset) (5V typ) before attempting to start up again.

When you start up into a 10Ω load, one of these faults may be triggering.  I recommend that you measure the key pins during this undesired startup operation to see which one is triggering the fault.  Once you identify which fault is being triggered, you can adjust the components that connect to the pin to prevent it from triggering fault shutdown.

Best Regards,

Eric

We have changed components from the original design : 

R24= .10 ohm

C3/C4= 220 uf (one cap)

22K DRV pull down

R18= 28K

R30= 32.4K

R29= 2.2M

Here is the original design schematic:

I then did plots of the DC Output, VDD, and CS pins at 150 ohm and 10 ohm load.

See the plots below:

Then removed R21:

Tim

How did you determine these new component values?  If you did not, we recommend you use our excel design calculator http://www.ti.com/lit/zip/sluc537 to calculate what the component values should be.

If you have any concerns about using the excel design calculator, we recommend that you use our webench calculator (on the right side of this page http://www.ti.com/product/UCC28630) to determine what the recommended external component values are.  We recommend that you verify all the components you use match the recommendation.

Best Regards,

Eric

These values are from the Web Bench simulator, 24VDC @ 6A entered in.

I noticed there was a BOM along with the web design schematic, attached.

A couple differences I saw between the 801-3 design (top line) and the web design (bottom line)- below, were:

C12= 1) 220uf

Cout= 9) 220uf [2000uf]

D14= BAV70 Fast Switching

D6= Schottky 70V- 15ma

D15= MURS120 Superfast Recovery 200V- 1A

D3= Schottky 200V- 2A

D10/D11= CGRM4007 General Purpose 100V-1A

D4/D5= Ultrafast 800V-1A

C21/C22= 1uf/47uf

Cdd= 22uf

D3/D6= SMCJ100A 100v + 100v= 200v

Dz1= 150v

Whaich of those differences look significant to you?

Tim

I don't understand what your question is.  Our recommendation is to follow the design values that you generated from the webench design.  I do not understand where the design that you are comparing it has come from, so I cannot comment about any of those component values.  If you see a discrepancy between that design and the webench model, we recommend you modify the design to match the webench model value.

Best Regards,

Eric

We are following the webench basic model, only with some additional low value current limiting resistors. Do you have any plots of what the different pins on the UCC28630 should look like? We are getting pulses like below:

However we found this on the web, which doesn't match: