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PCA9555: pca9555

Jithin potu
Prodigy 70 points
Part Number: PCA9555
Other Parts Discussed in Thread: PCF8575, , TCA9555

WE used earlier pcf8575 part number but when we do power on all pins become high , so because of this our power supply become on . ( can we do this high pins low initially ?? )

So for initially if we want to I/O pins off  when we give the power , we can use part pca9555 for this purpose ??  

At power on, the I/Os are configured as inputs. at this time we get voltage in output or not ??

  • 0
    TI__Mastermind 47008 points

    Hi Jithin,

    PCF8575 powers ON with GPIO's HIGH due to active current source (IOH). Initially this cannot be changed unless the device is written to to change the GPIO's to output logic LOW. However, if the input is driven externally HIGH, this could allow for a large current sink and could damage the device if adequate resistance is not applied. 

    PCA9555 has actual registers unlike the PCF8575. PCA9555 powers on with high-Z inputs. It is recommended to have a pull-up or pull-down resistor connected to p-ports if the pins are left as inputs. Voltage output will not be present upon power up. To set PCA9555 GPIO's to outputs, this must be done via the configuration register via i2c write commands. 

    Regards,

    Tyler

  • 0
    TI__Mastermind 47008 points

    Jithin,

    One more thing. I would recommend switching from PCA9555 to TCA9555. TCA9555 is the p2p upgrade to the PCA9555 device, and is more capable speeds up to 400kHz, wider supply voltage range, and fixes a power-on reset issue and interrupt errata. 

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    Prodigy 70 points

    hi tyler ,

    i connect io expander IO pin connect tps7a8300rgwt Enable pin and adp7104rdz Enable Pin. and PCF8575 I2C channel connect to ARTY A7 FPGA.

    At Power On FPGA config Some Time(1-2 sec) with Flash and this time IO expander Pin On and All TPS and ADP power supply Generate. 

    pull-up or pull-down resistor connected to p-ports need?

  • 0 in reply to Jithin potu
    Prodigy 70 points

    hi tyler ,

    i connect io expander IO pin connect tps7a8300rgwt Enable pin and adp7104rdz Enable Pin. and PCF8575 I2C channel connect to ARTY A7 FPGA.

    At Power On FPGA config Some Time(1-2 sec) with Flash and this time IO expander Pin On and All TPS and ADP power supply Generate. 

    pull-up or pull-down resistor connected to p-ports need?

    and i also Try NXP PCA9555 Ic this IC reset condition or power On all Pin are input but output voltage available. NXP PCA9555 Ic datasheet write At reset, the device's ports are inputs with a pull-up to VDD.  NXP PCA9555 not Resolved My probelm.

    i will used texas instruments PCA9555 or TCA9555 Resolved My problem. 

  • 0 in reply to Jithin potu
    TI__Mastermind 47008 points

    Hi Jithin, 

    I don't know if you are asking questions or found a solution. 

    P-ports if left as inputs should be connected to a pull-up or pull-down resistor so that the input is not left floating. Floating inputs can cause a variety of issues, please see this app note concerning floating cmos inputs here.

    P-ports configured to outputs can be left floating. 

    PCA9555 / TCA9555 power's ON with p-ports configured as floating inputs. Please abide by the two configurations I mentioned above when using this IO expander. 

    I am glad that PCA9555 or TCA9555 resolved the issue. Please let me know if there are any additional questions. 

    Regards,

    Tyler