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LM25066I: What will happen when CL or CB or Timer or Vref open before power on?

Jan Bob
Intellectual 280 points
Part Number: LM25066I

Hi Experts,

We want to know what will happen when following four pin open or short before power on?

1. CL

2. CB

3. Timer

4. Vref

Can it output normally? or what function will be affected?

We need to evaluate the necessity of ICT test points...

  • 0
    TI__Guru 57737 points

    Hi Jan Bob,

    A short on CL and CB Pins will set the overcurrent limit threshold at 25mV and circuit breaker trip point to 1.8 times the overcurrent limit. So, there is no problem here. 

    Vref is Internally generated precision 2.73-V reference used for analog to digital conversion. A short on Vref would effect the functionality of the digital section (PMBus telemetry) of the IC.

    A short on the timer means that the voltage on the timer pin would never build up. This means that the during fault conditions the controller wouldn't pull the gate low as it keeps on waiting for the timer to reach its threshold. This will damage the FET's.

    When you mean open on these pins, are these pins floating ?

  • 0 in reply to Praveen GD
    Intellectual 280 points

    Hi Praveen,

    Yes, "open" means pin floating.

  • 0 in reply to Jan Bob
    TI__Guru 57737 points

    Hi Jan Bob,

    I need to work on this before giving you and answer. I will come back to you by mid next week.

    Hope this timeline is fine.

  • 0 in reply to Praveen GD
    TI__Guru 57737 points

    HI Jan Bob,

    When Timer pin is left floating, it charges to its maximum value very fast as the parasitic cap on the pin would be negligible. This means the timer duration is almost zero. If there is any condition which forces the timer to activate like current limit or power limit, the device would turn OFF immediately as the timer duration is almost negligible. This can cause the device to fail startup if the device starts in current limit or power limit.

    When the Vref Pin is left floating, the voltage on the Vref pin will have a ripple on its voltage as there is no decoupling Capacitor to filter it out. As Vref is the reference voltage to internal digital circuits, you can expect errors in telemetry readings. 

    When CL and CB pins are left floating, these pins seems to be pulled low internally and hence act as connected to GND and act accordingly. I can confirm to you on this point in a couple of days.

  • 0 in reply to Praveen GD
    TI__Guru 57737 points

    Hi Jan Bob,

    Do you have any other questions ?