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TPS1H100-Q1: How to detect a open load in the off state for the B version and why CS pin will pull up to Vcs,h?

Ted Zhang
Intellectual 2280 points
Part Number: TPS1H100-Q1

Hi

The datasheet mentioned when an open load/short to battery happen in the off state, the CS pin will pull up to Vcs,h. Why will the CS pin been pull up to Vcs,h considered the CS pin is a reflection of the current flow through the the channel and equals to zero when a open load happened?

Can you help me to understand below circuit and help elaborate on how this circuit is functioning here? I don't not really understand the datashee here, See below datasheet comments and my questions.

Thus, TI recommends an external pullup resistor to offset the leakage current. -- How this pull up resistor will help to offset the leakage current?

This pullup current should be less than output load current to avoid misdetection in the normal operation mode.  -- I don't understand.

To reduce the standby current, TI recommends to always use a switch for the pullup resistor. TI recommends Rpu ≤ 15 kΩ. -- I don't understand either.

  • 0
    TI__Mastermind 28200 points

    Hi Ted,

     

    CS pin in B version has dual function. The voltage CS pin is a reflection of the channel current but this only occurs in the ON state. In off state when IN is low, the CS pin is internally clamped to Vcs,h in open load.

    On this version of the device, the CS pin also acts as a logic pin to indicate faults. V_cs(h) is usually higher than the linear range to differentiate it between normal condition and fault condition.

     

    The open load detection function in off state is based on comparator. The comparator measures the voltage across the FET (VS – VOUT) and compare it to a reference voltage Vol,off. If the voltage across the FET (VS –VOUT) < Vol,off, the comparator report a fault through CS pin.

     

    How the pull up resistor helps to offset the current? Check the attached file for detail explanation.

     

    The pull up resistor is connected to Vs pin which is the battery voltage. Due to OUT sinking current of 50uA in off state, the pull up resistor provides a current path and draws additional 50uA from the battery. A switch, in series with the pull up resistor can be implemented, that connects the pull up only in the in the OFF state. With the additional switch, the standby current is within the datasheet spec.

     

    Regards3755.Output voltage level in any state.docx