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Original question:

PCF8574: Three questions: I2C speed, timing, faster alternatives

PCF8574: PCF8574 for reset pulse generation

Juan Journade
Prodigy 60 points
Part Number: PCF8574
Other Parts Discussed in Thread: TCAL6416, TCAL9539

Tool/software:

Hello I have a pcb design using a PCF8574 to generate a reset pulse for DRV8243 wake up.

Is it possible to get a 30 micro second with this io expander?

If not, is there some i2c alternative with same footprint SSOP?

Regards

  • 0
    TI__Guru 52918 points

    Hi Juan,

    Can you elaborate on the following statement? 

    Juan Journade said:
    Is it possible to get a 30 micro second with this io expander?

    What needs to be 30 us? Can you be more specific here? 

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    Prodigy 60 points

    Hello Tyler, below a figure from your TI DRV8243 mosfet.

    To wake up a sequence is required at "SLEEP" pin. A 30 us reset pulse (pin low) is required put this device active.

    As I don't have micro controller GPIOs available I tried with this io expander.

    If you need some more detail let me know.

    Regards,

    Juan

  • 0 in reply to Juan Journade
    TI__Guru 52918 points

    Hi Juan,

    You might need to write I2C FM+ in order to get a tRESET pulse < 30 us. The clocking period for 1 MHz i2c is 1 us. If you use 100kHz or 400kHz I2C bus, it will be too slow to change the output in time for a tRESET pulse. 

    A device like TCAL6416 or TCAL9539 might be better for this application. 

    Regards,

    Tylerh