TPS54521: Output Capacitors

Ramgopal Divakar

Part Number: TPS54521

Hello,

I would like to use this circuit to power my DSP C6654 with power draw of 3A worst case. I want to use the circuit on the first page or the 5A circuit. Do I need 4 x 470 uF at the output?

http://www.ti.com/lit/df/tidr731/tidr731.pdf

I have this part in stock - EEFGX0E471R

over 6 years ago

0 Neal Zhang over 6 years ago

TI__Expert 4720 points

Hi Ramgopal,

1. Yes you can use that part and follow the schematic of your attached schematic.

2. The output cap determines the output ripple. If small capacitance is used, the output ripple will be bigger. If you don't need the small output ripple as the test result shows, you can decrease the output capacitance. http://www.ti.com/lit/ug/tidu393/tidu393.pdf

0 Ramgopal Divakar over 6 years ago in reply to Neal Zhang

Expert 1300 points

Hey Neal,
just making sure L1 in the schematic shows 4 uH while the part in the BOM shows 1.5 uH MSS1048-152. So I go by the BOM? Also, I have a 3 mOHM 470 uF cap EEFGX0E471R I thought I can use.

My output is not more than 3A. In the same family there is a 4. 7 uH MSS1048-472NL_ so if I use that can I go lower on the CAP and use 3 instead of 4?

Thanks,
Divakar

0 Neal Zhang over 6 years ago in reply to Ramgopal Divakar

TI__Expert 4720 points

Hi Divakar,
I double checked the bom and find it's still 4uH, see the bellow link:
www.ti.com/.../getliterature.tsp
Yes you can use 4. 7 uH MSS1048-472NL and 3 output cap, but I suggest C6=0.1nF from my calculation

0 Ramgopal Divakar over 6 years ago in reply to Neal Zhang

Expert 1300 points

Neal,

I believe I looked at the same BOM. I do see 4 uH on row 42 in the excel but look at the part number of Coilcraft - MSS1048-152. This is a 1.5 uH part. So which is correct. Is it 1.5 or 4.7 in the actual test hardware? The 4.7 uF you agree above is in the same family of parts. I can use that and the 0.1 uF for C6.

Thanks,

Divakar

0 Neal Zhang over 6 years ago in reply to Ramgopal Divakar

TI__Expert 4720 points

Hi Divakar,
Yes you are right. Sorry I didn't check it carefully. For the actual test, I don't know which is used because it's drawn nine years ago and I couldn't find the engineer who draw it. However, I did a calculation and 1.5uH is more reasonable in this spec. So 1.5uH is suggested in your spec, and you can use 4.7uH if the 1.5uH inductor is not available.

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TPS54521: Output Capacitors