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LM5108: HI/LI internal connections and leakage paths

Kannan Sockalingam
Intellectual 1905 points
Part Number: LM5108

Hi team, working with a customer on this device, had a few questions on the internals:

  1. Why don’t we measure any resistance on the LI and HI pins?  Can you tell us the value of the resistors circled in red?
  2. When the EN pin is pulled low the VDD still provides current following the arrow shown.  Is this accurate per the design?  Do you have any plans to remove this current path with a shutdown pin in any future parts?
  3. Is there a leakage current path in the opposite direction of the arrow shown?

 

  • 0 in reply to Kannan Sockalingam
    TI__Guru**** 189401 points

    Hi, Kannan,

    Great to hear from you!

    Those resistors are spec'd as 250 kohms in the data sheet.

    This device has an ENable pin, not a shutdown pin. If you require low-current shutdown, please use a power switch or LDO with enable for the VDD supply.

  • 0 in reply to Don Dapkus
    Prodigy 120 points

    To: Don Dapkus,

    1. There is no spec. that tells the resistance on the LI and HI pins, only the EN pin.  Also when we measure the resistance of the pins on the IC with a DMM we see the 250kohm on the EN pin but not the other two pins.

    2.  Also can you tell me if there is a leakage path that allows current to flow from the HS pin to the VDD pin.  I suspect there is a 100V diode blocking this current flow but could you please confirm this?

    Thank you,

    Anthony D'Andrea

    Cubic Corporation

     

  • 0 in reply to user6299704
    TI__Mastermind 23155 points

    Hello Anthony,

    For the LM5108 there is a specification called RIN in the parameter table, INPUT section, that is 250K Ohms typical. This is the input pulldown resistance of the driver input pins, LI and HI. In some cases, there may be a fixed voltage drop, or Vf before you see the resistance so it may be with a DVM there is not enough voltage for the meter voltage measurement.

    I would suggest applying 5V to the input pins and see if the current correlates to the expected ~250k Ohms.

    There is also a spec in the datasheet that refers to the current path from HS with high voltage applied. In the supply currents section there is a ILK spec with VHS=VHB=110V that is 2.0uA typical. This would include any leakage to ground and VDD, and the current is very low.

    Confirm if this addresses your questions, or you can post additional questions on this thread.

    Regards,