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TCA9535: Supply current

Kanava Sait Abdul Kathar
Prodigy 60 points
Part Number: TCA9535

I am going to use this device with Aardvark which can source 5V 50mA. Is that sufficent to power up this device. 

IOs will be used to control FET Gate pins

  • 0
    Guru 297900 points

    The static power consumption of CMOS devices is negligible. (Ensure that the TCA's supply is properly decoupled.)

    Ensure that 50 mA is enough for all the loads (current through the I²C pull-ups, and whatever current is needed to (dis)charge those transistor gates).

  • 0
    TI__Mastermind 37473 points

    Hi Kanava,

    Please see Clemens recommendations. I agree with him. 

    Looks like there are several loads on the output side of the IO expander. The combined load needs to be calculated to ensure that 50mA is enough for the required loads as well as current for the digital core inside the device. The main source of current requirement however is from the GPIO side. 10kohm pull-up resistors see like small enough loads that even if you had VCC = 5V, then.

    5V / 10kohm = 0.5mA

    24 outputs

    24 x 0.5mA = 12 mA. 

    A 5V 50mA supply from Aardvark should be sufficient. 

    Regards,

    Tyler

  • 0 in reply to Clemens Ladisch
    Prodigy 60 points

    Thanks for the response, what is the operating current of TCA. I hope the FET gate (dis)charge current will in uA.

  • 0 in reply to Tyler Townsend
    Prodigy 60 points

    Tyler, Thanks for the response, the PUs are on different board, connected with different power rail. The IOs from TCA are connected to FET gate pin only.

  • 0 in reply to Kanava Sait Abdul Kathar
    Guru 297900 points

    ICC is specified as < 40 µA.

    A FET gate can be modelled as a capacitor. Input capacitances less than about 70 pF are negligible; for larger gates, a noticeable current can flow when switching.

  • 0 in reply to Kanava Sait Abdul Kathar
    TI__Mastermind 37473 points

    Hi Kanava, 

    Clemens is correct here. ICC can be as low as 0.4 uA, but due to switching current ICC can be max of 40uA in the operating mode. 

    This is just for operation of TCA9535. Any load that is sinking or sourcing current from the output side will also account for increases in total ICC current on top of the 40uA. I would suggest starting out with the load requirements on the GPIO first as this will be a majority of the current sink through ICC. 

    Regards,

    Tyler