LM5085 EVB

dtluigi

Other Parts Discussed in Thread: LM5085

Why the AN1878 (LM5085 Evaluation Board) states (pag.8) that the input capacitance C1 for the DC/DC is a ceramic capacitor "United Chemicon 2220 6.8 μF, 100 VKTS101B685M55N0T00" while the picture of the top side of the EVB (pag.1) clearly shows an electrolytic capacitor?

It's safe for me to mount a ceramic capacitor instead of an electrolytic one on my board?

Best Regards

Luigi

over 8 years ago

0 Vijay86929 over 8 years ago

TI__Genius 11490 points

Hi Luigi,
I just opened a new EVM box. C1 is a ceramic capacitor. Although the footprint (shown in the EVM image) shows electrolytic type. I guess they created the footprint to try out different types.
Thanks and regards,Vijay

0 dtluigi over 8 years ago in reply to Vijay86929

Intellectual 595 points

New question: in the same conditions of the EVB (Vin=12V) I made the design calculation for Rt and found that it should be 96.9kOhm instead of 90,9kOhm to have a 300kHz switching frequency.

Could you verify the design value for that resistor please?

0 Vijay86929 over 8 years ago in reply to dtluigi

TI__Genius 11490 points

90.9k and 96.9k are not that different. The frequency in constant-on-time is dependent on RT and VOUT mainly. Its dependence on VIN is 2nd order. The final tuning of Rt resistor usually happens in the lab.

regards,

0 Vijay86929 over 8 years ago in reply to Vijay86929

TI__Genius 11490 points

Please use the quick-start tool on the LM5085 webpage to do the calculations. I think the small difference could be because of the PFET on/off time difference that is included in the quick-start. It depends on the FET selected.

0 dtluigi over 8 years ago in reply to Vijay86929

Intellectual 595 points

Thank you, but I made a custom one yet! ;)

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LM5085 EVB