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LM74722-Q1: Questions - OV pin, Zener, Inrush CdVdT Cal

Part Number: LM74722-Q1

Hi team,

Regarding LM74722-Q1 - 

  1. If OV pin is not used, how should I connect this pin? Can I connect it to ground via a pull-down resistor and what is the recommended pull-down resistor? 
  2. Regarding Zener usage, if the selected MOSFET has VGS,max = 20V, do I still need to put the Zener to protect VGS <14V? Or I can just remove it? 

 

  1. Regarding inrush current limit capacitor CdVdT, using equation (1) in datasheet, based on IPD_DRV = 50uA, Cload = 470uF, Iinrush = 250mA in datasheet example, the calculated CdVdT is 94nF (or round up to 100nF) instead of 10nF in datasheet. Is the equation wrong or the example is wrong? 

  

  • Hi PY,

    1. If OV pin is unused, you can directly connect it to GND.

    2. For  Blocking MOSFET, if the FET Vgs rating is +/- 20V, then you can avoid using an external zener across FET gate-source, But even with +/-20V FET Vgs rating, the  Load Disconnect MOSFET driven by PD requires a 18V Zener across PD to FET source. 

    3. Your calculations are correct. For IPD_DRV = 50uA and Cout = 470uF, the required Cdvdt to limit inrush current to 250mA is 94nF.

    There is a typo in the datasheet - the calculations in datasheet where considering Cout = 47uF and IPD_DRV = 55uA. initially before characterization of the device the IPD_DRV was 55uA and not 50uA. Hence this confusion. We will get this updated in the datasheet. Thanks for pointing this out.