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LM25066A I2C support and timing

Rajan Sundar
Prodigy 10 points
Other Parts Discussed in Thread: LM25066A

Hi -

I wanted to know if I can use an I2C master to talk to the LM25066A. The datasheet mentions SMBus/PMBus, but it also says that the device can be clocked to 400KHz. The I2C master will be a 3.3V master, so and will be pulled up (at the master) with a ~1.5K resistor.

I am was also interested in the 100ns data setup and 300ns data hold requirements - what are the general expectations of the master - which edges should it use to generate/sample data? With the eval board, does the FTDI chip run standard I2C at 3.3V, or is there some special firmware written to guarantee that it works with the LM25066A? Does it run at 400KHz?

Thanks!

  • 0
    TI__Genius 13485 points

    Hi Rajan,

    The eval. board runs at 100 kHz but the device will have no problems at 400 kHz.  The FTDI chip is programmed to act like an PMBus master.  PMBus is basically an extended command set of SMBus, and SMBus is a subset of generic I2C.  To my knowledge, most things that are SMBus-compliant will work with generic I2C.

    Changing the FTDI clock rate is not possible right now, it would require significant software changes.

    As far as the clocking goes, the device will sample the data on the rising edge, so the data needs to be stable just before the clock rising edge, and the data cannot change while the clock is high otherwise you may get a stop condition.  The setup and hold times were taken from the SMBus/PMBus specifications and aren't necessarily particular to this device.

    Give me a call if that doesn't answer your questions. Regards,

    Mike Hartshorne, 520-751-2363