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LMR34206-Q1: Design

Part Number: LMR34206-Q1

I am performing a design with the LMR34206-Q1 with the following requirements:

  • Input voltage: 8,6V to 18V. Up to 42V in transient
  • Output voltage: 5V
  • Max. Output current: approx. 250mA

I hope you could clarify some design concepts:

  • K: what exactly this ripple factor referring to?
  • When using the equation to select the inductor, it uses Maximum output current. Do I need to consider as well minimum current? The inductor value coming from the equation would be bigger then...
    • My results are giving me so far.
      • Condition with equation 4: 0.66uH min
      • Condition with equation 3: 3.58uH min with K = 0.4 and Vin max = 18V
    • Are we safe as long as the inductor value >3.58uH? I selected 10uH 
  • For selecting the output capacitance:
    • What means AVout? Is this the maximum variation of the output voltage we target independently of the consumption?
    • What means AIout? Is this the maximum difference in current we can have at the output?
    • K: what exactly this ripple factor referring to?
      • It is referring to inductor ripple. Often we recommend 20-30% (k=0.2 to 0.3)
    • When using the equation to select the inductor, it uses Maximum output current. Do I need to consider as well minimum current? The inductor value coming from the equation would be bigger then...
      • Consider nominal input voltage and max load current for modest inductor selection 
      • My results are giving me so far.
        • Condition with equation 4: 0.66uH min
        • Condition with equation 3: 3.58uH min with K = 0.4 and Vin max = 18V
      • Are we safe as long as the inductor value >3.58uH? I selected 10uH 
    • For selecting the output capacitance:
      • What means AVout? Is this the maximum variation of the output voltage we target independently of the consumption?
        • Yes
      • What means AIout? Is this the maximum difference in current we can have at the output?
        • Yes

    I recommend utilizing BOMS provided in table 3 of the datasheet. They were designed for you exact conditions.