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How can the AD2S1210 typical differential output (EXC to EXC) = 7.2 V p-p with AVDD =5.25?

The datasheet shows power requirement as 5.25 V max.

The typical differential output (EXC to EXC) is shown as  7.2 V p-p.

How is this possible? Am I missing something?

Thanks for your help

  • SAM25,

    The excitation output is measured differentially (EXC-EXCB) and thus each output only need swing between ground (0v) and 3.6V) which is within the supply rails; note that each output is in anti-phase so the output will swing from +3.6 to -3.6V (differential) thus 7.2 Vp-p.


  • Thanks Sean,

    I suppose I have to rephrase the question.

    Here goes:

    If the maximum supply to the chip from "chip ground" to "chip supply" is 5.25 V, how can the chip produce 7.2 V ?

    Does the EXC swing below ground somehow? Does the chip have some kind of boost converter inside

    I'm still missing something here?

    Thanks again Sean

    Figure below

    V positive chip rail________________________________________



                                                                                        Regardless of waveform

                                                                                        peak to peak has to be between

                                                                                          these two rails?




  • Sam,

    Yes both waveforms (EXC, EXCB) swing between the supply rails.  

    The easiest way to visualize this is to consider that EXC and EXCB are defined as follows.

    EXC = A*sin(wt), EXCB = A*sin(wt+180)

    So if A = 3.6Vpp then when I subtract (difference) EXCB from EXC I get

    Asin(wt) - (-Asin(wt) )= 2A sin(wt).   Thus the differential excitation voltage across the output coil is 7.2V pp but the absolute voltage at either end of the coil never goes below ground or above the supply.  


  • Sean,

    I don't see the maximum sourcing/sinking current specified for the EXC pins. typical is shown as a test condition @ 100uA.

    Is there a document that specifies this?


  • SAM25,

    The output drive is very limited and I don't believe it is specified in the datasheet which in retrospect is unfortunate.   The intention is for those pins to drive a succeeding drive stage that would drive the resolver coil.   The intention is for that stage to have a relatively high impedance such that the load current doesn't exceed on the order of 1mA.