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TLV2241: supply bypassing

STEPHEN Julstrom
Prodigy 10 points
Part Number: TLV2241
Other Parts Discussed in Thread: TLV2401

The very low current TLV2241, along with several other TI op amps include in the application information the boilerplate statement, "Use a 6.8 uF tantalum capacitor in parallel with a 0.1 uF ceramic
capacitor on each supply terminal." We were planning on using only the typical 0.1 uf capacitor close to a TLV2241 operating on 5.8 volts in a unity gain follower configuration with a 100 kOhm load, along with another 0.2 uF supply bypass within inches. We're having a difficult time understanding why another 6.8 uF tantalum (or even ceramic) capacitor would be needed, as this would not normally be considered necessary. Is there something special of different about the TLV2241, the TLV2401, and other TI op amps incorporating similar warnings that make that additional capacitance necessary?

  • 0
    TI__Mastermind 23395 points

    Stephen

    While having a good reservoir of charge for circuits that have fast transients is a good idea, it is not required for low power devices such as the TLV2241.  Since the TLV2241 has modest slew rate capability at its output, your plan to limit the capacitance to 0.1uF is valid.  Even if the TLV2241 was a faster device, the bulk capacitor does not need to be placed in close proximity to the amplifier.  The high speed charge response will come from the lower value capacitor value such as the 0.1uF.  The bulk capacitor helps replenish the lost charge on the smaller value capacitors and thus stabilize the voltage seen by the amplifier.  Having the bulk capacitance located somewhere on the board would be sufficient in that case.  You just want to avoid having the bulk capacitance on a different PC board in your system where the charge would need to be replenished over a long cable.

    Thanks for bringing this to our attention and we will be more precise in our bypass capacitance recommendations in the future.

    Chuck