Other Parts Discussed in Thread: ATL431
Tool/software:
I am a San Jose State University Student from the Spartan Racing FSAE team. I just want to ask a few question regarding the UCC256402 controller chip for a DC-DC that is suitable to step 300-400V down to 24.5V.
- My team is designing a very compact converter unit, which has a small transformer and wish to discard the bias windings. So we decide to use an isolated DC-DC converter to supply VCC from the secondary output. How much current should this converter supply to the UCC256402? Also, Page 18 of the brief sheet has a table describes that ratio of 0.6 can be achieved by making the BW pin see 4.5k resistance (option 6) or short to ground (option 8). But the option 8 is not shown in the datasheet. In our case, would you recommend shorting the BW to ground?
- How does the BMT threshold affect the system stability?( Currently BMT_H is 0.6V) In short words, how do I determine the threshold I need knowing that my BMTL/BMTH ratio is currently set at 0.6?
- The the feedback chain I am using the ATL431 in comparator mode. I am still not sure how the FBreplica voltage is being used for control effect as the change of voltage happen rapidly when the output voltage is close to 24.5V. So is this Feedback chain only used to trigger burst mode in my case? I also need to read more about compensator for the feedback circuit.
- In the beginning of the datasheet, the UCC256402 variant is described as having no soft-on/soft-off function. For the capacitor, can I choose any value between 4.7 to 470nF? How is the resistor divider configured to limit max switching frequency to 350kHz?
Much Appreciate you help,
Wenjin Wu