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TCA9509 Current Sink Clarification

Vini
Intellectual 895 points
Other Parts Discussed in Thread: TCA9509

Hi,

As per datasheet for TCA9509, low level output current (IOL) is given as max 10uA only on A side as shown below.

It is given that no external pull ups are required on A side. What will happpen if there is an external pull up also present on I2C lines on A side? As per my understanding, this device sinks 1mA through internal 200Ohm pull down when driving the I2C lines Low on A side driving the lines to ~0.2V and if I have an external pull up also, current sink through this resistor will increase and V(OL) level may increase.

But due the specs given in datasheet max current is 10uA and I am not sure if extra current due to external pull ups will damage the IC.

Actually I have bought OVERO FIRE COM for OMAP from Gumstix which has 4.7k pull ups on I2C lines and I can not remove those resistors on all COMs especially during production.

Can anyone from TI tell me that extra pull ups of 4.7K to 1.8V (~0.38mA current) can damage the IC or not

VIni

  • 0
    Intellectual 895 points

    Hi,

    I have tested TCA9509 with 4.7K pull-up resistor to 1.8V on A side and it is working pretty well.

    But still it will be good to have a confirmation from TI why this is not recommended and how will it affect the chip?

    The only limitation I can think about is the allowed power dissipation for internal 200Ohm pull down. Can external pull up resistor shorten chip life?

    Regards,

    Vini

  • 0 in reply to Vini
    TI__Intellectual 1930 points

    the effect of pull up resistor on the A-side is mainly the Vol level. when there is an external pull up on teh A-side the Vol level will be higher than specified on teh DS.

    unfortunately, The device is not characterized for what the maximum current sink can be with external resistors.. so we cannot say for sure what this level is but it should be ok if it is already working in your application. I don't think there would be lifetime related issues.