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LP5907 For Digital Circuits?

Expert 1961 points
Other Parts Discussed in Thread: LP5907, SN6501

Greetings,

The datasheet for the LP5907 says "LINEAR REGULATOR FOR RF AND ANALOG CIRCUITS".  I am wondering if this regulator will work well for powering a microcontroller.  I understand that it has very low noise, which is needed for analog circuits.  But will digital transients affect its performance more than other regulators not designed for RF and analog?  The main purpose of my circuit is to measure an analog signal using the microcontroller and transmit the filtered results via digital isolators to another circuit.

Thanks,

Greg

  • Greg,

    very glad to know you are interested in LP5907 part.

    would you give us more information about your application? Where does the "digital transients" happens and how it will be?

    If this is a load transient at LP5907 output stage, from the datasheet, we can see LP5907 has a very good load transient, +/-40mV@IOUT = 1mA to 250 mA in 10 μs.

    If this is a voltage transient happened at LP5907 input stage, LP5907's high PSRR will eliminate the input ripple and keep a stable output to your micro controller. 

    Hope this will help you.

  • Hi Jonathan,


    My application is very straight forward.  It is simply a microcontroller circuit that will use about 50 mA and will have an operating frequency of about 120 MHz.  The LP5907 looked like a really nice part, but since I don't deal much with analog or RF I didn't know if there was a tradeoff between low noise and responding to digital loads that have very high edge rates.  Thank you for pointing out the load transient specs from the data sheet.  I should have thought about comparing those specs to other regulators.  I can see now that the LP5907 performs exceptionally well.  I figured there had to be a catch since the LP5907 only costs 0.14 in 1k quantities.  I suppose the bypass capacitors in the circuit are responsible for handling the highest frequency load transients.

    The high PSRR is one feature of the LP5907 that attracted me to it.  Why do the plots of PSRR stop at 100 kHz when some of the curves appear to be sloping in a favorable direction at that point?  I am planning on using the SN6501 for the power supply of this regulator, and the switching frequency of the SN6501 with a 5V Vin is about 430 kHz.

    Thank you and regards,

    Greg

  • HI Greg,

       Thank you for sharing so much information with us.

       LP5907 PSRR chart to 10MHz can be found in the LP5907-Q1 datasheet.

       You may also find some useful information from below topic.

        http://e2e.ti.com/support/power_management/linear_regulators/f/321/t/383568.aspx

     Hope this will help you.

  • Hi Jonathan,

    Thank you very much for answering my questions.  This regulator is going to work very well in my application!

    Regards,

    Greg

  • You are welcome!