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REF3430: Why does RFE3430's Output Current support -10 mA?

Eggsy Pang
Expert 4985 points
Part Number: REF3430
Other Parts Discussed in Thread: REF102

Hi team,

I saw RFE3430's Output Current support -10 mA in the datasheet.

1. Why REF3430 can support Negative current output?

I also saw REF30xx support 25mA Output Current.

2. Can REF30xx support output Negative current? If not, Why?

I also saw REF31xx support ±10 mA current output in the first page of datasheet, like below pic1.

But in the page"7.3 Recommended Operating Conditions", REF31xx just support 25mA rather than 10mA, like below pic2.

3. So which one is corret for REF31xx current output ? And why are there differences in two pages in datasheet?

Hope to get your suggestion for above three questions?

Thanks!

Pic1:

 

Pic2:

  • 0
    TI__Mastermind 19370 points

    Hi Eggsy,

    1. Why REF3430 can support Negative current output? The bandgap of the REF34 goes into a buffer that supports the +/- 10mA. This is shown in figure 9.2.

    I also saw REF30xx support 25mA Output Current. Just like the REF30 the output buffer of the bandgap supports +25mA but in this case it does not support current sinking?

    2. Can REF30xx support output Negative current? If not, Why? The output buffer was not designed to support it. Traditionally, older voltage references only needed to source current and not sink. In more modern references, there is the need for both.

    I also saw REF31xx support ±10 mA current output in the first page of datasheet, like below pic1.

    But in the page"7.3 Recommended Operating Conditions", REF31xx just support 25mA rather than 10mA, like below pic2.

    3. So which one is corret for REF31xx current output ? And why are there differences in two pages in datasheet? I would use the +/-10mA on REF31 because the EC table shows characterization for +/-10mA. I need to investigate +25mA.

    Hope to get your suggestion for above three questions?

    Thanks!

  • 0 in reply to Marcoo Z
    TI__Expert 4985 points

    Hi Marcoo,

    Thanks for your help!

    Why does reference need sink current?

    And what is the purpose of reference with current sinking function?

    Compared with reference without current sinking function, what is the advantage of REF3430 ?

    Thanks!

  • 0 in reply to Eggsy Pang
    TI__Mastermind 19370 points

    Hi Eggsy,

    The purpose of sinking current is if the output of the reference is a higher voltage than expected. Keep in mind that voltage references are very versatile and not just always connected to an ADC or DAC. Sometimes they can be use as pull-up voltages or for as a reference for level shifting. There are situations where the voltage reference powers an ADC + pull-up resistor + level shifting + other circuitry. In these type of applications, during start-up the system might have one voltage rail higher than Vout of the VREF. It is very system specific and it is better to have it and not have it.

    Another function would be to boost the current output. IF you look at the REF102 datasheet at figure 7, some of the circuits require the device to sink current if not in use.

    www.ti.com/.../ref102.pdf

    -Marcoo