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TCA9555: May I have some question regarding TCA9555?

TAlex Wu
Expert 1200 points
Part Number: TCA9555
Other Parts Discussed in Thread: PCA9554, PCA9555, PCA9554A, TCA9535

Dear Sir:

May I have some question regarding TCA9555?

Regarding the TCA9555PWR, can pins P00 through P17 be configured only as Input (I) or Output (Open Drain) only, or can they also be configured as Input(I) or Output (O) and Output (Open Drain)? 

Double confirming below mention Is that correct? :

If config Output (O) because TCA9555PWR pins P00 through P17 is push pull,therefore no need external pull resistor.

If config Output (Open Drain) TCA9555PWR pins P00 through P17will need external pull resistor.

 

Thanks

  • 0
    TI__Guru 53928 points

    Hi TAlex, 

    TCA9555 does not have true open-drain outputs. You can create pseudo open-drain outputs by writing to the configuration register. This application note describes this method in more detail: 

    https://www.ti.com.cn/cn/lit/an/slvafl2/slvafl2.pdf?ts=1722876123872&ref_url=https%253A%252F%252Fwww.google.com%252F

    TAlex Wu said:
    If config Output (O) because TCA9555PWR pins P00 through P17 is push pull,therefore no need external pull resistor.

    If you configure the Pxx pins to OUTPUT through the configuration register, then these are push-pull outputs. Therefore, no need for external pull up resistors. 

    TAlex Wu said:
    If config Output (Open Drain) TCA9555PWR pins P00 through P17will need external pull resistor.

    If you write to the configuration register by switching it from OUTPUT to INPUT, you can create a pseudo open-drain output (as described in the app note). If you do this method of open-drain outputs, then you will need an external pull-up resistor if the 100k internal pull-up resistor of the TCA9555 is too weak for your load requirement. 

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    Expert 1200 points

    Dear SIR:

    Thanks for your reply.

    May I double confirming regarding you mention the "https://www.ti.com.cn/cn/lit/an/slvafl2/slvafl2.pdf?ts=1722876123872&ref_url=https%253A%252F%252Fwww.google.com%252F"

    The pseudo open-drain output (as described in the app note),Besides the TCA9555, do the products listed in Section 5, References, on pages 4 and 5 of that document also apply (meaning, can they also use this method)? For example: TCA9535, PCA9554A, PCA9554, PCA9555.

    May I double confirming other question,regarding TCA9555 default high,but when During power up, and before any control has been initiated, will there be any unknown states that could affect downstream inputs? 

    Thanks

  • 0 in reply to TAlex Wu
    TI__Guru 53928 points

    Hi TAlex,

    TAlex Wu said:
    The pseudo open-drain output (as described in the app note),Besides the TCA9555, do the products listed in Section 5, References, on pages 4 and 5 of that document also apply (meaning, can they also use this method)? For example: TCA9535, PCA9554A, PCA9554, PCA9555.

    These devices all work with the app note: 

    TAlex Wu said:
    TCA9535, PCA9554A, PCA9554, PCA9555.

    TAlex Wu said:
    May I double confirming other question,regarding TCA9555 default high,but when During power up, and before any control has been initiated, will there be any unknown states that could affect downstream inputs? 

    During power up and after the TCA9555 hits a power-on reset threshold, the device will power up with all Pxx pins as CMOS inputs. The TCA9555 has internal 100k PU resistors on each Pxx pin, so each pin will be pulled high. So no unknown states here on power-up. 

    Regards,

    Tyler