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TPS7H1101A-SP: Current limit and foldback

Jill Burnham
Prodigy 30 points
Part Number: TPS7H1101A-SP

The datasheet states " It is not recommended to use overcurrent limit activation thresholds of less than 500 mA due to internal bias offset currents representing a larger percentage of total IPCL current and therefore additional error."  

Could you quantify what this error is if I set the limit to 500mA using typical CSR ?   

The CSR range over temperature seems to be the variable that changes the most when choosing to set the limit.    

Also,   if the device enters foldback is there a way that the regulator would exit foldback without a power cycle ?      

  • 0
    TI__Genius 12080 points

    Hi Jill,

    Unfortunately, the variation of the offset is not characterized in the Electrical Characteristics so I don't have a quick answer for quantifying what the error could look like under those conditions. I can check if there is a nominal approximation of the error value to help quantify it. I'll update you here soon.

    Thanks,

    Sarah

  • 0 in reply to Sarah Koch
    Prodigy 30 points

    Hi Sarah,

    Were you able to locate the approximation of the error ?   What are the internal offset bias currents ?  Is it not recommended to set the current limit to 500mA ?

  • 0 in reply to Jill Burnham
    TI__Genius 12080 points

    Hi Jill,

    Apologies for the delay, the Designer of this device was out of office.

    Based on the datasheet Electrical Characteristics spec, the current limit setting can be set as low as 200mA. 

    The recommendation to not set it lower than 500mA is simply because the offset term in the equation for the current limit resistor becomes a larger component of the denominator when ICL is a smaller value. This means any part-to-part variation in the offset currents of actual devices begins to have a larger impact on the accuracy of the current limit setting. 

    I have not been able to acquire the expected variation of the offset value, however, there is some data available in the TID Report for this device that can be referenced. If you search this document for the term "current limit" you will see data showing the measured current limits for a batch of devices pre- and post-radiation at room temp. The 26.0 test is using a 100kOhm PCL resistor and the 26.1 test is using a 47kOhm PCL resistor. 

    The current limit variation of the 100kOhm test (current limit set below 500mA) is larger as a percentage of the average value than it is for the 47kOhm test (current limit set above 500mA).

    The variation shown in these tests is for the current limit itself and not the offset. It is impacted by the variation of VREF, CSR, and the PCL resistor, but overall it should give you a rough idea of the variation for the offset term as well.

    This post is a bit long, so please let me know if there is anything else I can clarify or help with.

    Thanks,

    Sarah