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Entering mosfet data into MyParts

maxthestork
Intellectual 390 points

Hi All,

 I am trying to put in some MOSFET data into switcher pro and I am having some trouble determining some of the values that have been asked for.

 

Resistance at 2.5V : this is not available in any data sheet I looked at.  For example the Vishay si4470EY datasheet does not have this value listed.  This part is in the TI database and it along as most other parts have a value of 10000 asigned.  Is this a default to be used if the value is not available.

Rds on ratio : Again for the Vishay si4470EY, the Rds on goes from ~1 to ~1.6 from 25 deg to 125 deg.  Doesn't that mean the ratio should be 1.6?  Most of the values in the TI database are 1 for the Rds on ratio

Fall time : is the unit picoseconds? It appears to be from comparing the datasheet (again the si4470EY).  The label on the tool is ms

Reverse recovery charge : I am sorry if this is a dumb question but what is this and where in the datasheet is it specified?

Max power loss: I guess this means maximum power dissipation .

Gate resistance : If not explicitly noted in the datasheet, is there a guide to specifying this.  The component I am looking to enter is the ST, STD12NF06T4.

http://www.st.com/stonline/products/literature/ds/8431/std12nf06t4.pdf

Thanks for any responses

cheers

Peter

 

 

 

  • 0
    TI__Intellectual 2710 points

    Hello Peter,

    I will get you the explanation for all fields for entering MosFET.next week.

    Thanks,

    Hetal.

  • 0 in reply to Hetal
    Intellectual 390 points

    Thanks Hetal,

     

     Look forward to it.  Just to point out, there is an error in the specs for the Panasonic EEEFP1V331AP capacitor.  It is actually rated for 35V but (probably due to a typo) is listed as being rated for 53V in version 3.4.  This could cause it to be selected or accepted for designs that were not right.

    cheers

    Peter

  • 0 in reply to maxthestork
    Intellectual 390 points

    Hi Hetal,

     

     any luck with getting clarifications on entering part data?

     

    cheers

    Peter

  • 0
    TI__Intellectual 1280 points

    Here's some information on the available fields for entering mosfets in SwitcherPro.

    For Rdson values (these are really important) and frequently you'll need to review a graph of Rdson vs Gate Voltage to get the correct values.

    For curves that don't include a value at 2.5V (example the mosfet doen't turn on until 4V on the gate.  You need to put in a large resistance, like 1000 mOhms.   this will ensure that SP will not attempt to select that mosfet for designs where gate voltage might be close to 2.5V or 3V.  

    Rds(On) ratio 125C to 25C is the ratio that describes how much rdson increase will be present as you go to 125degC from 25degC.  Typically this would be about 1.3.  Currently a bug in the grid is rounding this value to an integer for display (so it always shows 1)
    for the Vishay si4470EY, you are correct it should be 1.6

    Fall time is stored in nano seconds, that's a type-O on the form.  Typically this might be like 10-100ns.

    For Reverse Recovery Charge, this may or may not be specified in every manufacturers datasheet.  this field is used in the efficiency calculation for a Synchronous Rectifier only.  The loss is calculated like ReverseRecoveryLoss = charge*Vin*FreqSw.  

    Sometimes the manufacturer will specify the reverse recovery time instead of charge.  This is the case of the Vishay si4470EY.  It gives 40ns as the Trr (from 3A to 0A) so I just used my current = charge/time formula, solving for charge, charge = current * time =  40ns * 3A = 120nC so I'd put 120nC as my Qrr. 


    Max power loss is the same as max power dissapation which is not a very handy spec for a FET but we have it anyway.
    If the data sheet doesn't contain gate resistance, i'd put in like 1 or 2 ohms.

    I hope this helps

    Thanks

  • 0 in reply to maxthestork
    TI__Intellectual 2710 points

    Hi Peter,

    We do not have this panasnic cap 'EEEFP1V331AP' in our system parts library. Did you mean any other cap?

    Thanks,

    Hetal.

  • 0 in reply to Hetal
    TI__Intellectual 1280 points

    Some questions have come up about fall time and dead time in the specifications for adding mosfets.  These fields can typically be found in the table section of most mosfet datasheets.  For the Vishay part in question "SI4470EY" page 2 of the datasheet lists fall time as "tf" 30ns.  For Dead time we used 16ns, that comes from the "Turn-On Delay" time of this datasheet.

    Fall time is used in SwitcherPro in the efficiency calculations.  We use fall time along with Switching Frequency to help calculate a swiching loss for a high side mosfet in a non-rectifier role. 

    whereas on the Low Side mosfet we ignore the switching loss and check the "Dead Time" the time when current is conducting through the body diode to calculate a body diode conduction loss.

    Those fields are only used in these calculations in SwitcherPro.