LM2577 calculator?

Karl lautman

Other Parts Discussed in Thread: LM2577, LM2587

I've worked through the component calculations from the LM2577 datasheet, in a spreadsheet, but I'm questioning some of the results, so it occurred to me there may be an official TI calculator for this stuff somewhere. Is there (there should be)? If not, does it make sense that the Iripple(RMS) should be 1.71A for the following inputs:

Vout: 20V
Vf: .5V
Vin(min.): 4.75V
iload(max.): .45A

Not a lot of capacitors meet the Iripple spec (2.6A) based on that iripple(RMS); certainly no SMD parts I can find.

Thanks.

over 8 years ago

0 Frank De Stasi over 8 years ago

TI__Guru 73515 points

The LM2577 does not have a calculator. However, the LM2587 is enabled on Webench. The RMS currents should be the same for the same design.

I have attached a Webench design for your conditions for the LM2587; the RMS current seem smaller than you calcs.

webench_design_433359_238_863480011.pdf

0 Karl lautman over 8 years ago in reply to Frank De Stasi

Prodigy 220 points

Thanks. I'll try my design based on the LM2587.

0 Karl lautman over 8 years ago in reply to Frank De Stasi

Prodigy 220 points

Actually, I ran my own Web Bench on the LM2587 and, while I got the same results as you, the diode appears to be installed backwards on the PCB (see below). According to the datasheet (and logic), the cathode is supposed to be towards Vout, not the inductor.

LM2587 PCB.pdf