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TPS92633-Q1: TPS92633

Rohit Joshi
Prodigy 20 points
Part Number: TPS92633-Q1

Tool/software:

Hello,

I am using the TPS92633-Q1 in a 24V battery operation (16V - 32V).

I have connected 4 LEDs in series (for checking behaviour with 2 LEDs short)

My problem lies with open-LED behaviour.

I am providing open LED on one string.

At voltage < 26V the device is operating well - fault pin goes to 0 when detect open LED

But at higher voltage > 26V till 32V - fault pin not going completely 0 but the voltage at fault pin is nearly around 2,7V.

Can you please tell me the reason for such behaviour?

Is it because of external resistor i am using and drawing maximum current through these resistors?

  • 0
    TI__Intellectual 890 points

    Hi Rohit,

    Are you utilizing the one-fails-all fails feature by connecting FAULT_DI to other ICs? The minimum internal pulldown on the fault bus is 2mA.

    If you are externally pulling up to 26-32V with multiple fault pins tied together, the ~1mA seen from each 33k resistor may be opposing the fault pulldown to where the voltage does not reach the logic low threshold (0.7V).

    In this case you can use a zener diode on the pullup to clamp the fault line voltage. The diode will pulldown current to ground when the breakdown voltage is reached, limiting the amount of pulldown current needed for the fault bus to be low. 

    Please let me know if this is the case.

    Best,
    Isaiah

  • 0 in reply to Isaiah Atsedewoin
    Prodigy 20 points

    Hi Isaiah,

    Yes i have connected two ICs together with the same configuration.

    But even if i checked the open LED behaviour with single IC (seconf IC not active and Fault pins not connected) then also i am facing the same issue.

    Thanks

    Rohit Joshi

  • 0 in reply to Rohit Joshi
    TI__Intellectual 890 points

    Hi Rohit,

    Okay, I see your concern. Is the open fault being detected and only weakly pulling down fault pin? What is the measured voltage on the fault pin prior to the open LED condition with just one IC?

    What is your measured Vout in normal operation and again with your LED open? I want to check the case with >26V supply voltage if the Vin-Vout measurement is still > V_Open_th_rising. 

    I also noticed additional resistors R121 and R122 on Out1 and Out2. What is the reasoning for this? 

    Best, 
    Isaiah