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Difference between the LTC4300 and the LTC4300A.

Category: Datasheet/Specs
Product Number: LTC4300A

Please tell me the difference between the LTC4300 and the LTC4300A.

In the LTC4300 datasheet, "Figure 3: Bus Requirements for 3.3V Systems" shows the relationship between the recommended pull-up resistors and CBUS.
(www.analog.com/.../430012fb.pdf)

The LTC4300A datasheet does not mention it, but is there any limit to the value of the pull-up resistor as long as it is lower than the maximum resistance listed on page 10?

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  • Hi, 

    The LTC4300-1 and LTC4300-2 are an early product in the bus buffer line. These buffers could stick in a permanent logic low oscillation state if the (RBUS * CBUS) product was too light (that is, high frequency) on one or both buses. See the “Minimum SDA and SCL Capacitance Requirements” text and corresponding Figures 3 and 4 on page 10 of the LTC4300 -1/LTC4300 -2 datasheet for details.

    The LTC4300A-1 and LTC4300A-2 addressed that issue, so I would recommend using these parts instead for new designs. 

    There is a selection guide that summarizes the features available in the bus buffer family here: Serial Bus Buffers, Extenders, and Accelerators

    Regards,

    Jason

  • Hi Jason,

    Sorry. I have one more additional question.
    Why does the LTC4300 have this problem, which seems to be different from the I2C specification?
    Can you please tell me more about the mechanism of sticking to the persistent logic LOW oscillation state?

    Regards.

  • Hi Takahiro,

    The LTC4300-1 / LTC4300-2 family of bus buffers use special analog amplifiers to implement their buffering function.  If the amplifiers in the LTC4300-1 or LTC4300-2 are not sufficiently capacitively loaded as described in the datasheet, they may become unstable with the end result of the part not functioning correctly.

    The LTC4300A-1/LTC4300A-2 (and our other bus buffers) have improved amplifiers which have a wider stability region and so do not have the bus loading requirements of the LTC4300-1 / LTC4300-2. 

    As you mentioned, the pull up resistors should be less than the maximum discussed in the data sheet on page 10.  They also need to be large enough so that the current when the I2C bus line is pulled down does not exceed the maximum pull-down current rating of the _weakest_ device on the I2C bus.  Normally, in order to maximize the system benefit of the LTC4300A's rise time accelerator, you would want to select a larger valued pull-up resistor so as to minimize the supply current load when an I2C device is pulling the bus low.

    Eric

Reply
  • Hi Takahiro,

    The LTC4300-1 / LTC4300-2 family of bus buffers use special analog amplifiers to implement their buffering function.  If the amplifiers in the LTC4300-1 or LTC4300-2 are not sufficiently capacitively loaded as described in the datasheet, they may become unstable with the end result of the part not functioning correctly.

    The LTC4300A-1/LTC4300A-2 (and our other bus buffers) have improved amplifiers which have a wider stability region and so do not have the bus loading requirements of the LTC4300-1 / LTC4300-2. 

    As you mentioned, the pull up resistors should be less than the maximum discussed in the data sheet on page 10.  They also need to be large enough so that the current when the I2C bus line is pulled down does not exceed the maximum pull-down current rating of the _weakest_ device on the I2C bus.  Normally, in order to maximize the system benefit of the LTC4300A's rise time accelerator, you would want to select a larger valued pull-up resistor so as to minimize the supply current load when an I2C device is pulling the bus low.

    Eric

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