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TLC59281: Straightforward, reliable way to use current sink output to drive high-Z logic level input of another device?

Jonathan Bender
Expert 7895 points
Part Number: TLC59281
Other Parts Discussed in Thread: SN74CBTLV3257, , TLV7031

Hello,

I use TLC59281 for controlling LEDs on my board, and I have an unused output that I'd like to control a local switch's SEL pin (SN74CBTLV3257). It looks like the output voltage on TLC59281 is variable depending on the current sink setting and the source. Ideally, I would simply size a pull-up resistor to 3.3V to match the programmed sink current (10 mA) and get V_OL < 0.5V when the TLC59281 turns the channel 'on'.

My concern is that the V_IL threshold of the switch is 0.8V max, so I need V_OUTn of TLC59281 to be below that with sufficient margin.

Have you used a pull-up resistor, or some other small basic circuit, to accomplish this 'logic output function' with current sink output LED drivers like TLC59281? If there's not an easy way to guarantee V_OUTn be < 0.8V with just a pull-up resistor, then I may need to look into using a small comparator like TLV7031 to interface between the LED driver and the switch.

Thanks,

Jonathan

  • 0
    TI__Expert 7895 points

    Hello,

    After further offline discussion, it was determined that a high enough pull-up resistance on the output should ensure the V_OUTn will be quite low, likely around 0.1V, as the TLC59281 drives the output stage in an attempt to make the channel current match the R_IREF setpoint. So a 4.7 kohm pull-up to 3.3V would sink ~700 uA, and provide the necessary logic high and low thresholds for the downstream device.

    Thanks,

    Jonathan