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PCA9544A: I2C sink current

Danilo A.
Mastermind 26450 points
Part Number: PCA9544A

Hi Team,

A customer wants to confirm if the I2C lines of PCA9544APW can sink 8mA. They have 2 PCB stacked with a total of 3 pull ups on the SDA and SCL lines. The resistors are: 10K, 2.8K and 523Ohms. Equivalent resistance is 422 ohms. The supply voltage of the microcontroller is 3.3V

Regards,

Danilo

  • 0
    TI__Guru 57820 points

    Hey Danilo,

    This seems like something I'll have to double check with our design team to verify. My initial guess is that the Io absolute maximum spec in the datasheet covers the SDA/SCL pins and the typical IoL in the electrical char state 10mA for a VoL of 0.6V so this should be a strong yes to the question.

    -Bobby

  • 0 in reply to BOBBY
    TI__Mastermind 26450 points

    Hi Bobby,

    At Section 6.5 Electrical Characteristics table, it shows that there are 4 values of IOL. When the VOL is 0.4V it will fail the customer's requirement of 8mA sink current if the pull-up resistors at SCL and SDA lines is 422 ohms but will pass if the VOL is 0.6V. Is 0.4V the minimum value of VOL for SCL and SDA lines?

    Regards,

    Danilo

  • 0 in reply to Danilo A.
    TI__Guru 57820 points

    Hey Danilo,

    I assumed your question was can our SDA (SCL is not an output) sink 8mA without damage. If so, the answer is yes SDA can sink 8mA.

    The VoL spec you reference in the datasheet is voltage you should expect when you sink that amount of current. Meaning that the average number found was 7mA for generated a VoL on SDA at 0.4V. The 3mA value means we guarantee that the device will push a voltage of 0.4V or less at 3mA (though since this is actually a I2C standard spec we designed for, we made sure to give higher margin to ensure we meet I2C spec at 3mA).

    -Bobby

  • 0 in reply to BOBBY
    TI__Mastermind 26450 points

    Hi Bobby,

    Thank you for the clarification on the sink current and VoL of SDA pin. I will now resolve this inquiry.

    Regards,

    Danilo