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LM4128: Output Resistance

Samm Flanagan
Prodigy 20 points
Part Number: LM4128

I am currently using the LM4128-2.5 as a reference for a Differential Amplifier and the specification for the amplifier requires the reference voltage device have an output resistance <100ohm if connected directly to the common mode output pin. I had a look through the datasheet but I cannot find this information, does anyone know what it is?

  • 0
    TI__Mastermind 19550 points

    Hi Samm,

    As you noticed, there is no typical output impedance graph on this datasheet. But there is a way to calculate the output impedance at DC
    Zout = (Vopen - Vload) / (Iopen - Iload). Using figure 2 from the data sheet and that equation, you can select 2 points and calculate a rough estimate backwards. When I did this I calculated 0.5 Ohms, which is typical of an series VRef. This value is only at DC and will stay constant but eventually increase at high frequencies (10k Hz and above). It is common for a capacitor at the load to be added to cut off the high frequency output impedance. The LM4128 can drive your amplifier.

    -MZ