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OutPut Capacitor for LMZ14203HTZ

Varunesh Kumar
Intellectual 820 points
Other Parts Discussed in Thread: LMZ14203H

Is there any limit on the O/P Capacitor for LMZ14203HTZ ?

My Specs are Vin = 24 V , Vout = 15V , from 0.2 Amp to 2 Amps .

I intend to use 10 Nos of 22uF /  25 V Ceramic MLCC ,1206 Size ; Ceff = 220 uF 

Thanks and regards

  • 0
    TI__Mastermind 18940 points
    Hello Varunesh,

    Using the capacitor combination you mentioned should be OK. The effective capacitance you are going to get is probably in the 100uF range. (considering the DC bias effects on the ceramic caps and the 15V bias on 25V rated caps). Be sure to include feedforward capacitor (in parallel with the top feedback resistor). It can be used to adjust/optimize the load transient response later on when you evaluate your design.

    Cheers,
    Denislav
  • 0 in reply to Denislav Petkov
    Intellectual 820 points

    Hello Denislav 

    Thanks for your prompt reply .

    Yes, we are using 22 nF as Feed Forward Capacitor .

    One more Q pl : Is there any lower limit on the ESR of the O/P Capacitor ?

    Second , does the LMZ14203HT require a minimum value of O/P Ripple for Control stability ?

    Thanks and Rgds 

  • 0 in reply to Varunesh Kumar
    TI__Mastermind 18940 points

    Hello Varunesh, 

    Good question. The COT architecture needs some ESR ripple from the output capacitor for stability.

    However the LMZ14203H uses a control scheme which derives most of the necessary ripple from the low side power FET Rdson. This allows you to use low ESR capacitors (i.e. ceramics) on the output. On the other end, too much ESR (along with the feed forward capacitor passing through all the ripple to FB) can trip the OVP protection. Section 8.2 of the datasheet has a schematic with component values (Figure 46). There is a suggested ESR range for the output capacitor (assuming Cff is 0.022uF).

    Cheers, 
    Denislav