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TPS1HTC30EVM: TPS1HTC30-Q1 on TPS1HTC30EVM - minimum load required?

Kent Suzuki
Prodigy 40 points
Part Number: TPS1HTC30EVM
Other Parts Discussed in Thread: TPS1HTC30-Q1,

Tool/software:

Dear Sir/Madam,

I'm evaluating the TPS1HTC30-Q1 part on the TPS1HTC30EVM board, and I'm seeing very strange behavior.  J3 is the 3-pin header where the EN pin can be connected to 3.3V or GND.  I have the 3.3V LDO enabled on this EVM, and I've confirmed that I'm getting 3.3V.  When I jumper EN to GND, it's supposed to turn off the high side switch.  If I have no load on the output, the input voltage on J11 shows up on J13, regardless of the EN pin connection.  If I put a small load (10k on 14V, drawing 1.4mA), then the EN pin does switch the output, but only down to 1.04V.  Our application requires the output to be at (or very close to) 0V when the high side switch is disabled.  I didn't see a minimum load requirement in the datasheet.  Could you elaborate, so that I can design this part in with enough margin for production?  I can put a nominal load on the output to make sure the output does stay at 0V, but I would want to know what's going on in the IC, and make sure the load I have on it will guarantee the output will be 0V.  

In addition, we're using this in a 48V system.  I understand the TPS1HTC30-Q1 is good to 60V, but the TPS1HTC30EVM specifies the max voltage to be 48V.  What's the limitation for the TPS1HTC30EVM that caps the voltage at 48V?

Thanks and best regards,

Kent  

  • +1
    TI__Expert 7881 points

    Hi Kent,

    The EVM overlay just states the nominal conditions for use. I am assuming that DIAG_EN is high in your set-up; please correct me if it is not. If DIAG_EN is high and the device is powered, the output voltage should be close to the input voltage for an open-load situation when EN is off because there is an internal pull-up resistor from VOUT to VS. Please see below and section 8.3.5.2 Open-Load Detection in the datasheet for more information about the mechanism. 

    For the 1.04V shift - it could possibly be due to leakage from diagnostics. If you turn DIAG_EN and EN are off, you should see 0V on the output. Can you please confirm this and also that there is not a general offset due to the measuring equipment being used? 

    There is technically no minimum load requirement, but accuracies are better at higher load currents compared to really small ones. 

    Best Regards,

    Rishika Patel 

  • 0 in reply to Rishika Patel
    Prodigy 40 points

    Brilliant, Rishika!  

    That's exactly what it was.  DIAG_EN was high in my setup, and once I switched it low, the output voltage went to 0V.  Thank you for pointing out the pull-up resistor.

    Thanks and best regards,

    Kent