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Original question:

LM5067: calculation of Rin

LM5067: Rin calculation for Vin close to Vz

MarcoB
Prodigy 235 points
Part Number: LM5067

Hi,

For Vin < 12.35V Rin is not needed, but what happens if Vin is very close to Vz?

What is the internal Vcc range (min-max) admitted for the device to work properly? It's not specified on datasheet.

I need to calculate Rin for Vin ranging from 12V to 18V.

Regards,

Marco

  • 0
    TI__Guru** 105611 points

    Hi Marco,

    The internal Vcc voltage should be >8.7V (defined as POREN in the datasheet) to enable all the functions in the device. So, for your Vin range Rin can be calculated as = (Vinmin- POREN)/ 2mA =  (12V-8.7V)/2mA  = 1.65k Ohm

    At max Vin, the sourcing current is (18V-12.35V)/1.65k = 3.39mA. 

    Please let me know if it is not clear.

    Best Regards, Rakesh