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PCF8575: Using PWM

Yigal BenZeev
Prodigy 30 points
Part Number: PCF8575
Other Parts Discussed in Thread: LP5009

Tool/software:

Can the PCF8575 generate PWM? 

Does it have internal clock?

I assume it is possible to generate something like PWM in software, yet this will not be accurate and require a lot of CPU resources.

  • 0
    Guru 316440 points

    No, the PCF's internal state machine is controlled entirely by I²C accesses.

    The are LED drivers like the LP5009 that can generate PWM signals, but they are designed to sink a constant current. What is your application?

  • 0 in reply to Clemens Ladisch
    Prodigy 30 points

    it is a small robot car, based on ESP32. The PCF8575 will bring more IOs, yet PWM could be helpful because of the DC motor controls, and the servo motors. 

    One more question about the PCF8575: Is it possible to verify it's existence by software? In order to to do power up checks, the software needs to verify the units are connected and alive. Is there a software command like status read? 

  • 0 in reply to Yigal BenZeev
    Guru 316440 points

    In general, such PWM signals are generated directly by the microcontroller.

    The only way to check for the existence of the PCF is to try to read from it.

  • +1 in reply to Yigal BenZeev
    TI__Mastermind 46888 points

    Hi Yigal,

    PCF8575 does not have internal clock. 

    PWM would need to be generated via constant I2C writes to control the output. 

    In addition to Clemens' comments, we also offer the TCA6507 'which does have internal clock and is I2C controlled. 

    Clemens is correct about the existence of the IO expander on the bus. You would need to send a read with correct I2C address of the device to see if it ACK's as a presence detect. 

    Also, feel free to email me at t-townsend@ti.com to talk more about the use case you are defining. I am interested in the small robot car application. 

    Regards,

    Tyler