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Original question:

AMC6821-Q1: RPM mode and DCY mode response time

AMC6821: AMC6821

Stephanie Hibler
Prodigy 725 points
Part Number: AMC6821

Hello Sensors team,

In the AMC6821 datasheet, the I2C timing is described as follows:

 

 

https://www.ti.com/lit/ds/symlink/amc6821.pdf?ts=1687500081885

 

Is this timing what the AMC will provide back to the I2C controller (master) device or is this what it needs to receive from the I2C controller? 

 The I2C specification has MUCH faster timing than this, and if AMC6821 needs to receive that setup and hold time I do not see how this device is I2C compliant .

Thanks for helping clarify!

  • 0
    TI__Mastermind 43785 points

    Hi Stephanie,

    The AMC6821 is designed for SMBus 2.0. These setup and hold specifications on AMC6821 are aligned with the SMBus 2.0 standard. You are correct that I2C has a lower minimum spec, but that doesn't prevent devices from being cross-compatible. These two standards have co-existed for two decades. 

    As written, the AMC6821 requires the minimum setup and hold times shown from the controller. As a target-only device, the AMC6821 has limited ability to control setup and hold of its SDA output when it responds. This is because the controller drives the SCL. 

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    TI__Prodigy 725 points

    Hi Ren, 

    It looks like the AMC6821 does not meet SMBus 2.0 specification though. 

    The specification is 350ns and 250ns… not 350ns and 350ns. So it seems that the AMC does not meet any specification. 

    Can you explain what would be the expected outcome if those timing windows are not met? Is there a window where the data will be rejected or not latched? 

  • 0 in reply to Stephanie Hibler
    TI__Mastermind 43785 points

    We don't have reports of timing issues with AMC6821 and have not investigated it. On other products, failure to meet the minimum hold time causes the target device to misunderstand its I2C address and NACK. For this reason, no communication is able to complete successfully.

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    TI__Prodigy 725 points

    What is your response to SMBus 2.0 data hold time min being 250ns, where the AMC6821 has a min 350 hold time?

  • +1 in reply to Stephanie Hibler
    TI__Mastermind 43785 points

    The SMBus 2.0 data hold time is 300ns, not 250ns. The AMC6821 was released in 2007. I don't have insight into decisions that were made at that time.

    ren