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OPA454: How to supply a +/- 50V for OPA454

Andrea Fontana1
Prodigy 210 points
Part Number: OPA454


Hello TI support team,

My application is to drive a tunable optical filter ....  This filter select an optical wavelenght in function of a driving voltage applied to one of its pins ...

The voltage control span from -40V to +40V, but it not consume a lot  (max 500uW).

I was thinking to drive it with an OPA454, drived by a DAC in a way like explained in Figure 73 of the datasheet.

Now the questions:

1) do you agree on this way to proceed ?

2) how can i do to supply, let's say -50V/+50V easily (small footprint) the OPA454 ?

3) this application can be sensible to ripple generated by the supply and by temperature drift, what can be the improvement to do ?

Thanks in advance for your answers

Andrea

  • 0
    TI__Guru* 77541 points

    Hi Andrea, 

    1) do you agree on this way to proceed ?

    Yes. OPA454 is certainly able to drive from -40V to +40V, with <500uW Do you mean that the power dissipation is <500uW to drive the selected pin?

    2) how can i do to supply, let's say -50V/+50V easily (small footprint) the OPA454 ?

    You will need to have dual power supply rail for supply OPA454. say V+ = +50V and V- = -50V with power supply current rating approx. +/- 10mA.  OPA454 is able to supply current more than 50mA. If this particular filter selected pin only draw <500uW, we may be able to find other high voltage precision op amp to drive it. What do you mean by small footprint? Do you want to have +/-50V power supply that has a small footprint or OPA454 or equivalent  op amp with small footprint?

    3) this application can be sensible to ripple generated by the supply and by temperature drift, what can be the improvement to do ?


    If this are requirements, you will need stable +/-50V regulators with low ripple voltage and low temperature drift (linear LDOs perhaps. What is voltage accuracy (XV +/-mV?) you need to control the tunable laser diode application?

    We will recommend something once I am understanding your requirements. 

    Best,

    Raymond

  • 0 in reply to Raymond Zhang1
    Prodigy 210 points

    Hi Raymond,

    1)  Yes, the optical filter doesn't have supply pins, only control pin to polarize the MEMs inside it ...  500uW is the maximum power that the OPA454 should deliver to the load.

    2) Sorry Raymond, i've forgot to mention it in my previous post... No, i don't have +/- 50V on the board ... I have just +12V ... I need to built the +/-50V from SEPIC or other converters .... I would just that the power supply section will not be "enormous" on the board, especially if the current employed is so small ...

    Some suggestions ?

    3) i guess that it is related to the choise done on point (2)

    Thanks

    Andrea

  • 0 in reply to Andrea Fontana1
    TI__Guru* 77541 points

    Hi Andrea,

    The circuit shown in Figure 73  of OPA454 datasheet will definitely work. For 0.5mW  power dissipation, it may seem to be overkill. Do you have to go to up to +/-40V in reference voltage to control the unable laser? 

    Regarding the power supply, you may use Boost, Buck-Boost or SEPIC converter to build +/-50Vdc. Or you may use AC/DC adapters to build your voltage rail. Per the OPA454's datasheet, your op amp voltage rail can be anywhere above less than -43V for negative rail, >43V for positive rail. In other words, the supply voltage rails +/-45Vdc will do, but you may need less voltage ripple type. Please keep in mind that you have very light load the output of the switcher, you need to make sure that the switcher's output is table.

    I recommend that you use a small AC/DC linear voltage regular to create +/-45Vdc for the application, since the current draw is so small. It will be stabler than switching mode power supply under such light load conditions. Please use low ESR capacitors when your connect the +/-45 Vdc output at op amp's voltage rails. 

    Best,

    Raymond