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LM2676-5.0 and capacitance load

Vladimir Naumenkov
Expert 2970 points
Other Parts Discussed in Thread: LM2576, LM2596, LM2676

Dear Sir, please answer

I need 5 V supply, 2.5A current. Input voltage 25V. Temperature: minus 40 - plus 50 C, so I will use 150 µF output tantalum cap. I suppose to use LM2676-5.0 (260 kHz).

Point is that, I need to connect modules (from 1 to 10 pcs.) to my supply. Each module has 47 µF input cap (aluminum electrolytic), then total load cap may be 470  µF. This cap may cause unstable operation of LM2676-5.0?  Probably yes.

What can I do? May be LM2596 (150 kHz) less sensitive to capacitive load? Earlier I used LM2576  (50 kHz) and I know, that it can withstand any cap load – I used 2200 µF and supply worked, but it has high spikes at the out and I could not get rid of them! Please, advise me anything

TIA

Sincerely

Vladimir Naumenkov

www.agat.by

  • 0
    TI__Mastermind 23815 points

    Hi,

    In our EVM of LM2676 i use a 180uF capacitor and on our LM2576 EVM i can use a higher capacitor value at the output because of lower frequency of operation.

    You can try using a 470uF aluminum on the LM2676 and see if it's ok. What kind of spikes do you see on the LM2576? Do you have a scope capture?

    Thanks

    -Arief 

  • 0 in reply to Arief Hernadi
    Expert 2970 points
    Dear Arief, thank you. Point is that I have now concerned not so much in LM2576 - a thing of the past. I'd like to find out with LM2676 - I can use it at 2.5 A witout heathink, then LM2576 requires heathink at 2.5A. QUESTION: If to install choke 150-200 microH before this 470 cap? Can it help for LM2676?
    TIA
  • 0 in reply to Vladimir Naumenkov
    TI__Mastermind 23815 points
    Yes you can add the LC filter because the feedback signal for VOUT is taken before the choke filter. So the downstream capacitor is separated by a choke.
    Be careful about dampening this filter on the input of the circuit down the line. But if you say you have 470 uF aluminum capacitor, then the ESR should be good for dampening.