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TPS929120-Q1: LED open circuit fault, one of the conditions {V(SUPPLY) > V(ADCLOWSUPTH)}, V(ADCLOWSUPTH) value setting problem.

Dimon Y
Prodigy 20 points
Part Number: TPS929120-Q1

Tool/software:

TPS929120-Q1 Operating voltage V(SUPPLY) 7.5V power supply, and V(ADCLOWSUPTH) register set 7V; The condition V(SUPPLY) > V(ADCLOWSUPTH) is valid, but the open circuit fault cannot be read; V(ADCLOWSUPTH) register value set 5V, 6V can read open circuit faults. May I ask the V(ADCLOWSUPTH) register value set 7V, the condition is true can not read the open circuit fault cause?

  • +1
    TI__Genius 15730 points

    Can you measure SUPPLY pin and OUTx PIN VOLTAGE when opens and read status registers content? thanks. 

  • +1 in reply to Xiaoguang
    Prodigy 20 points

    I can measure.

  • +1 in reply to Xiaoguang
    Prodigy 20 points

    SUPPLY pin for 7.28v，V(ADCLOWSUPTH) register set 7V，fault pin voltage equals SUPPLY pin, faulty pin cannot read open circuit fault. what is the reason?

  • 0 in reply to Dimon Y
    TI__Genius 15730 points

    Can you help check if FLAG_ADCLOWSUP is set to 1? 

    The TPS929120-Q1 uses its internal ADC to monitor supply voltage V(SUPPLY). TPS929120 ADC is 8 bit and it's not very high resolution, INL is +/2LSB, which is +/- 0.16V for SUPPLY voltage.

    In this case, SUPPLY & V(ADCLOWSUPPTH) are too close. If there is ripple/noise or dynamic response, it is possible to trig ADCLOWSUP. 

    The LED open-circuit and single LED short circuit detection is disabled if the supply voltage is below threshold to avoid LED open circuit and to prevent the single LED short-circuit fault from being mis-triggered. Refer to Programmable Low Supply Warning in datasheet 

    You may either increase input voltage or set lower V(ADCLOWSUPTH)