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TCA9517: Icc as a function of switching frequency

Part Number: TCA9517

What is the relationship between switching frequency and current consumption on Vcca and Vccb?  Device will be operated with Vcca = 1.8V and Vccb = 3.3V at 80KHz.  Need to know the maximum ICC on both rails under these conditions.

Also, what is the difference between the TCA9517 and the TCA9517A?  I can't find anything in the datasheets.

  • Hi Ronnie,

    TCA9517A is designed to have a higher low-level input voltage threshold (specified as VILC) in order to better interface to I2C devices with weaker pull-down strength.

    As for the ICC versus operating rate, this is unfortunately something I don't have available. Generally I wouldn't expect a large increase during operation as compared to the static cases defined in the datasheet. We could take a look at this on a unit in our lab if you would like, though, to be sure. If so, could you please tell us how much load capacitance would be expected in the application as well as the equivalent pull-up resistances that would be present on the SDAA, SCLA, SDAB, and SCLB lines?

    Regards,
    Max
  • I expect that the VCCB load (3.3V) will 100 pF of trace capacitance.  The 3.3V pull-up is 3.3K ohms.  The VCCA (1.8V) would likely have a trace capacitance of less than 50 pF and the pull-up resistor is 750 ohms, but this 750 ohm pull-up is pulled up to a different 1.8V source on a different card, and I am only interested in the Vcca (1.8V) current required into the TCA9517.  The switching frequency is 80 KHz and this is an i2c application.  I would be interested in knowing both Ivcca and Ivccb nominal and peak currents.  We are placing 100 nF capacitors at each power pins for decoupling.  Thanks for your help.

  • Ronnie,

    Thanks for the additional data. I ordered some units so that we can take these measurements for you. We should be able to provide an update next week.

    Max
  • Hello Ronnie,
    Do you have a data density condition you anticipate to be using. I am need to know what your data density is, in other words how often do you send commands (also the length of commands) and how long you are idle between commands. It can make a big difference in Icc measurements. I have a test setup here that will give me an estimate. I will only be doing a clock signal for both SDA and SCL. There are a huge amount of data patterns that you could use to test power dissipation, but using a straight clock with 50% duty cycle is the worst case.
    -Francis Houde
  • Hello Ronnie,

    I did some testing at fosc = 80 kHz, 100 kHz, and 400k Hz at 5% and 50% data density.  Here are the results.  Keep in mind that ICCA has the pull up  resistors included, unlike you application.

    Let me know if you have any questions.

    -Francis Houde