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tlv70033 - Odd Noise Problem

Alex52381
Intellectual 810 points
Other Parts Discussed in Thread: TPS717

Hello All,

I am using a tlv70033 positive supply regulator (fixed to 3.3V). The supply is supposed to be low noise, and able to source 200 mA of current.

My setup:

- lab bench top power supply (switching)

- tlv70033 

- 0.1 uF ceramic input cap

- 10 uF ceramic output cap

When I plug in the regulator to a standard lab power supply's +5V fixed output, I see a very clean DC power level.

The issue becomes when I attach a 51.5 mA load from an analog to digital converter. The power supply suddenly becomes very noisy! See the waveform below:

This was taken from a scope with (AC coupled). Note how noisy the signal is, pushing 140 mV noise spikes! Is there something that I am missing in terms of regulating the supply voltage? Is this expected behavior of the tlv70033 at only a fraction of its current sourcing limit?

Thanks,

Alex

  • 0
    TI__Expert 8890 points

    Hi Alex,

    I hope that you will provide a schematic and more detail on the ADC specs.  Engineers typically use linear regulators to power sensitive circuits but never-the-less they are not  ideal voltage sources.  For a variety of reasons the regulator control loop may or may not respond correctly to noise generated by the load at the output of the regulator.  The output impedance of the regulator changes across the frequency domain of typical operation, the LDO cannot sink current from the load, and the internal reference is not impervious to noise interference. 

    We typically recommend the TPS717, fixed, voltage LDO for these applications due to the fact that it has an extra added pin for capacitively shunting reference noise to ground and because of its wide bandwidth.  (And note, that at least 10nF should be used at the noise reduction pin).

    Bill

     

  • 0 in reply to Bill Stokes
    Intellectual 810 points

    Bill,

    Thanks for the quick reply. I am using the AD9281 (http://www.analog.com/en/analog-to-digital-converters/ad-converters/ad9281/products/product.html) from analog devices along with the TI regulator. I have the setup on a breadboard, see the following partial schematic.

    The capacitors are ceramic.

    Thanks,

    Alex