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AFE4490 with LED strings

Marko Pavlin75965
Prodigy 140 points
Other Parts Discussed in Thread: AFE4490

Hello. I would like to use AFE4490 in reflective application. For reflective operation to be effective, more than one LED should be used. I could use Tx in Common Anode LED Configuration with external LED supply. There are four LEDs per channel. Here's idea for schematics: 

http://pavlin.si/foto/v/tech/afe4490.JPG.html

Is this OK? Are there any suggestions? "VLED" supplying LED strings would be 4xVfLED+1,4V. What about LED fault detection ?

  • 0
    TI__Mastermind 49956 points

    Hello,

    Can you explain more about your application and why do you think you need 4 LEDs?

    Whenever putting 4 LED’s in series, the LED Vf will need to be considered. 

    For common anode configuration, voltage at TXP and TXN pins must not exceed TX_CTRL_SUP voltage i.e., (External supply to LED strings - (4* VfLED) - Vcable ) <= TX_CTRL_SUP

    Another option would be to use higher power led to get the desired light intensity. 

    As for the diagnostics: LED S/C, TXP S/C to Gnd and TXN S/C to Gnd should still work. LED Open should still work provided the LED chain satisfies.

  • 0 in reply to Praveen Aroul
    Prodigy 140 points

    Hi  Praveen,

    thank you for your answer. I would like to assemble reflective photometric sensor with photodiode in the center surrounded with LED ring.

    Are there any references on using AFE4490 in reflective applications? 

    Marko

  • 0 in reply to Marko Pavlin75965
    TI__Mastermind 49956 points

    Hello Marko,

    There are reference designs on using AFE4490 for reflective applications.
    Unfortunately they are customer specific designs and we will not be able to share that information.