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About the spec of ADUM2250

I have a question about input supply current spec.

Does the spec change depending on data rate?

if so what is the data rate for this current spec on data sheet(attached file)?

Best reagards,

Tarzan

ADUM2250_spec.pdf
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  • Hello Tarzan,

    Yes and no.  Below the refresh rate if 1Mbps the current at VDD is an interaction between the data and the refresh circuit, and is complex but changes around a fixed level.  What is going on is that if you were to send data in at .9Mbps it would refresh just before you send the data, so the current is  higher since more pulses are being transmitted.  If you send data at 1.1mbps, then refresh is supressed and the current is lower.  Below the refresh rate, you will get these steps in Idd at the harmonics of the refresh.  This is hard to explain and usually not of much value, so we figure out what the worst case current is, which is at 2Mbps, and just say it is less than that all the way to DC.  If you were to plot Idd as a function of frequency, it would look like an increasing saw tooth on top of the constant 1Mbps current draw of the refresh circuit.  Above the refresh rate, it will be a monotonically increasing slope.  The ADuM2250 is not meant to run above 1Mbps, so we just call it constant and ignore the jaggies.

    So the data rate for the current in the spec sheet is actually 2Mbps, you will actually see less than that, at lower frequencies.

    Best Regards,

    MSCantrell

Reply
  • Hello Tarzan,

    Yes and no.  Below the refresh rate if 1Mbps the current at VDD is an interaction between the data and the refresh circuit, and is complex but changes around a fixed level.  What is going on is that if you were to send data in at .9Mbps it would refresh just before you send the data, so the current is  higher since more pulses are being transmitted.  If you send data at 1.1mbps, then refresh is supressed and the current is lower.  Below the refresh rate, you will get these steps in Idd at the harmonics of the refresh.  This is hard to explain and usually not of much value, so we figure out what the worst case current is, which is at 2Mbps, and just say it is less than that all the way to DC.  If you were to plot Idd as a function of frequency, it would look like an increasing saw tooth on top of the constant 1Mbps current draw of the refresh circuit.  Above the refresh rate, it will be a monotonically increasing slope.  The ADuM2250 is not meant to run above 1Mbps, so we just call it constant and ignore the jaggies.

    So the data rate for the current in the spec sheet is actually 2Mbps, you will actually see less than that, at lower frequencies.

    Best Regards,

    MSCantrell

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