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akidder

1519 Posts
Posted - 05 Dec 2003 :  11:49:32  Show Profile  Email Poster
SMBus and ADS devices

SMBus (System Management Bus) is a protocol developed by Intel that is similar to I2C. Some laptop and desktop computers use SMBus to manage system power using the ACPI standards. A subset of SMBus, the Smart Battery protocol, uses SMBus to communicate with "intelligent" batteries and chargers.

Key differences between I2C and SMBus include the following:
  • Bus speed
    The SMBus clock rate must be between 10 kHz and 100 kHz, while I2C can run between DC and 400 kHz.

  • Timeout
    SMBus slave devices time out and reset their communication interfaces if there is more than a 35 ms delay in the clock. I2C doesn't have a timeout.

  • Current draw on bus
    SMBus devices must draw between 100 and 350 mA; I2C devices can draw up to 3 mA.
    • The AGX and BitsyX implementation of I2C will work with most SMBus devices. The most likely point of conflict is in the AGX I2C bus current draw (see the pull-up resistor specifications in your product's user manual). If your configuration will use I2C as an SMBus controller, contact us to discuss the configuration you'll require.

    Source: Maxim app note 356


Additional Reading:
SMBus.org
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