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ADS127L18: ERROR pin sink capabilities. Driving a LED from this open drain output.

Diogo Costa
Prodigy 20 points

Part Number: ADS127L18
Other Parts Discussed in Thread: SN74AUP1G07, SN74LV1T125

Tool/software:

Hi,

I would like to drive a LED to indicate an error, from the ERROR pin. I understand he pin is open drain with a 100k pullup resistor to IOVDD, but can this pin sink enough current to light a LED? In the datasheet I found this:

Is the sink current capability for this pin only 1uA? If so, this isn't enough current, can you provide any suggestions to drive a LED (from 3.3V separate supply).

Thank you, 

Diogo Costa

  • 0
    TI__Guru 51550 points

    Hello Diogo,

    The sink capability (logic output 0, current flowing into the pin) is 2mA with OUT_DRV=0 and 1mA with OUT_DRV=1, with a maximum voltage of 0.36V.

    This maximum current should be more than enough to drive an LED for an Error indication.

    Please note that all digital pins are relative to 1.8V, and the LED would need to be pulled up to 1.8V, not 3.3V, which will limit the available LEDs that can be used.  If you need to drive an LED up to 3.3V (more common voltage), then you will need to use a buffer, similar to SN74AUP1G07.

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0 in reply to Keith Nicholas
    Prodigy 20 points

    Thank you Keith.

    I have available a SN74LV1T125. Can I power it from 3.3V, tie the input (A) to 1.8V (or 3.3V) and connect the ERROR pin from the ADC to the OE pin of the buffer, as it is active low? This would drive the LED from 3.3V, correct?

  • +1 in reply to Diogo Costa
    TI__Guru 51550 points

    Hi Diogo,

    Yes, this part should work just as well.  Correct, power from 3.3V, connect input A to 1.8 (or 3.3) and connect ERROR pin to OE pin.  When the Error flag is set (active low) the buffer will be enable and will drive the output to 3.3V, which can then drive an LED.

    Regards,
    Keith