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PCA9557: Parameter Questions for I2C Interface Timing Requirements

Jon WANG
Intellectual 970 points

Part Number: PCA9557

My customer want to use TI PCA9557 to replace NXP PCA9557BS,but they find some Dynamic characteristics are difference.For example, when the Tbuf parameter is in Standard mode, the minimum value for NXP PCA9557BS is 4.7us, while the maximum value for TI PCA9557 is 4.7us.

Could you pls help check whether PCA9557 can replace PCA9557BS? and are these Dynamic characteristics of TI PCA9557 right? Thanks.

NXP PCA9557BS.png

PCA9557 I2C Dynamic characteristics.png

PCA9557.png

  • 0
    TI__Guru 63958 points

    Hi Jon,

    This seems like a definition problem. The devices are compatible in timing and both abide by the I2C standard for standard and fast mode speeds. 

    Whether Tbuf is a min or max spec could be up to debate. The I2C standard itself lists it as a minimum condition. You should have atleast 4.7 us or 1.3 us (standard mode vs. fast mode) for the bus free time between a stop and start condition to be compliant to the standard. Our PCA9557 will behave the same whether you have 4.7us bus free, or 10 us bus free. 

    Regards,

    Tyler