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TLC5944 Iref-pin

tsutomu ueno
Intellectual 520 points
Other Parts Discussed in Thread: TLC5944, TLC5943, TLC5948A

Hi  members

This is BEN.

My customer   elect   this device that will be use to LED message board for station.
The LED light control for Iref-pin  voltage level  0.1～1.6V.

《Q》
　　Is　it  safe  to use in  Iref-pin　voltage　level:0.1～1.6V?
     Example, opposite voltage.

　※　I think safe that datesheet  P2: Covered Absolute maximum　Vin.

Best　regard
BEN

  • 0
    TI__Prodigy 395 points

    Hello Ueno-san,

    Thanks for your interests on our LED drivers.

    I think you are trying to manupulate IREF pin voltage outside to adjust output current.
    And I need to tell you that this won't work.

    For almost all TLC59xx LED video display / signage drivers, IREF pin is a tiny LDO (constand voltage regulator) and, inside IC, we mirror its output current into RIREF as a reference of constant current driver block.
    If you force IREF pin voltage, you will have huge ouput current (<1.2V) or zero current (>1.2V).
    (Just like forcing LDO output "short to current limit" or "pulling to VCC to stop".)

    For your output current adjustment, TI offers various methods (but please don't force IREF pin voltage):

    1. TLC5944 provides dot-correction, by sending logic codes, you can change amplitude of output current.
      You need to send dot-correction code to all output channels.
    2. By adding a clock divider between your clock source and GSCLK pin, you can change output current in PWM manner. (I think a simple clock divider IC is lower cost than ICs you planned to force IREF pin voltage.)
    3. Family IC like TLC5943, TLC5948A..., has a function called brightness correction and you can change amplitude of output current with one code for whole IC.

    I hope this will help and give us your opinion.  We are happy to provide further support for your better appliation design.

    best regards,
    Masashi