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LMH3401 LMH5401 Power Supply Rejection

Tony Rohlev
Prodigy 230 points
Other Parts Discussed in Thread: LMH5401, LMH3401

Hello,

Both the LMH3401 and LMH5401 list the power supply rejection ratio (PSRR) in the electrical characteristics but they do not show the frequency (of the power supply ripple) at which the data is taken, or even more useful, a graph of PSRR vs Ripple Frequency.


Is this data available?

Thank you,

Tony

  • 0
    TI__Genius 13935 points
    Hi Tony,

    The PSRR listed is the DC value. The amplifier PSRR will roll off with frequency at roughly the same rate as the HD3 performance vs frequency.

    The reason there is no PSRR graph in the datasheet is that we have no way to accurately inject RF energy into the power supply pins, so we cannot measure PSRR directly.

    For frequencies up to 200MHz, the PSRR is close to the DC value and is also aided by the supply bypass capacitors. Above 200 MHz the PSRR performance will begin to drop, but will be aided by the PCB layout. Solid power supply planes will provide much better PSRR than thin supply traces.

    At 1GHz and above it is difficult to predict PSRR behavior because it will be very dependent on the PCB layout. It is best not to rely on the amplifier PSRR at frequencies above 1GHz.

    Regards,
    Loren