Measuring RDsON in Power MOSFET

  1. ragraymond
    Hello Friends Im new to the whole Power Management and Analog Design sphere .
    I am working on a simple Synchronous Buck Converter for a Portable Charger .
    I use SABER for simulation.
    To simulate a particular MOSFET model i have been reading its datasheet and using the device specs in the SABER model library.
    But Measuring the RDSon is still not clear.
    Although Theoretically Rdson is Delta V/Delta Idrain. My simulation shows me very high values and a significant drop.
    How do you actually measure RDson(Note the temperature affect on the MOSFET is not included in the Model hence its taken constant.)
    Any opinion would be greatly appreciated.


    Raghu.I. Menon
  2. leo_o2
    Don't use (delta V)/(delta I). Please try V/I for RDSon
    In Synchronous Buck Converter, the drain node of the P-type Power FET and the N-type Power FET (that is connected to the inductor) is always switching.

    To calculate the Rdson of the P-type Power FETs:
    1) Disconnect the inductor
    2) Connect the Drain between the two Power FETs to VSS (Ground)
    3) Pull the Gate down to VSS (For turning the PFET ON)
    4) Measure the current flowing through the PFET, Ids
    5) VDD / Ids will give the PFET on resistance

    For N-type Power FET connect the drain node to VDD and pull the NFET gate to VDD as well (to turn it ON) and do the same

    You can also measure the the Rdson during transient analysis .... you have to measure the inductor peak current and then the Rdson = VDD / Inductor_Peak_Current

    Hope this will help !!! :)
  4. Hatim Ameziane
    Hatim Ameziane
    exemple power management project
    I need a theoretical part of a voltage regulator(Low dropOut)-based technology CMOS ?
    plz HELP ?
Results 1 to 4 of 4