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PCA9535: Remote 16-BIT I2C and SMBus Low-Power I/O Expander With Interrupt Output and Configuration Registers

Finbarr Long
Prodigy 130 points
Part Number: PCA9535
Other Parts Discussed in Thread: TCA9535

HI

In order to hardware reset the PCA9535 registers to default state we are looking to cycle its VCC supply voltage pin resulting in a POR.

Given that all I/O pins will default to high impedance "inputs" is it OK that some of these inputs may be driven by VCC levels whilst the the supply voltage pin is 

being cycled from VCC to GND to VCC.

Similarly the I2C interface signals, the address pins and the INT# output pins will/may be pulled to VCC via resistors whilst the supply pin cycling is occurring.

Can you see any issue with doing this?

Regards

Finbarr

  • 0
    Guru 303830 points

    At the Pxx pins, the recommended operating conditions allow input voltages above VCC, up to 5.5 V (also see section 8.2.2). At the I²C pins, the absolute maximum ratings allow voltages above VCC.

  • 0 in reply to Clemens Ladisch
    Prodigy 130 points

    HI 

    So , just to be clear. When VCC supply pin is connected to GND , which will apply a Power On Reset to the PCA9535 can we drive the Pxx, Axx and the I2C pins with signals at 3.3V ?

    Regards

    Finbarr

  • 0
    TI__Mastermind 39763 points

    Hi Finbarr,

    PCA9535 supports powered off impedance for the GPIO and address pins. Recommended maximum voltage for input pins is 5.5V, absolute maximum of 6V. 

    It looks like SDA/SCL say input max voltage is VCC in the recommended operating conditions, but I doubt there is a leakage path from SDA/SCL to VCC when VCC is 0V. I don't believe there is a diode from pin to VCC in design. Only diode present from GND to pin. Absolute maximum voltage is 6V however. 

    /INT pin is an output. No concern here with this pin being pulled to VCC via resistor while power cycling. 

    When power cycling it is recommended to power VCC all the way to ground. After power to GND is it important to stay there for a substantial length of time (ms range). THis is due to an existing power on reset issue present in the PCA9535 silicon. The work around is what I suggested here, or to move to the TCA9535 which is the p2p compatible upgrade to the PCA9535. TCA9535 fixes this PoR issue. 

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    Prodigy 130 points

    Thanks Tyler for the comprehensive response. 

    Regards

    Finbarr