• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Subscribers 63 subscribers
  • Views 1125 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Question about LM5085 Drive:FET and TINA-TI

Satoshi
Guru 19485 points
Other Parts Discussed in Thread: LM5085, UCC27322-Q1, LM5085-Q1, UCC27322, UCC27323, TINA-TI

Please let me know four points below about the drive of LM5085.

[Background]

・Circuit configuration LM5085-Q1 ⇒ UCC27322-Q1 ⇒ SQM40P10-40L

・Vin:16～24V, Vout:16V, 30W (1.875A)

------------------------------------------------

[Question]

・Since Qgs of SQM40P10-40L is large(134nC), it is due to drive by UCC27322.

Is this composition right?

And, is electric supply right below?

　・LM5085・・・Vin:16～24V

　・UCC27323・・・VDD,IN:16V

・About calculation of power dissipation 

　When connecting UCC27323, which calculation does power dissipation use the following?

　・Datasheet 　　 P14 (14) 

　　Pdiss=Vin × ((Qg × Fs) + Iin) 

　・The formula currently examined 　　

　　Pdiss=Vcc(reg) × Qg × Fs + Vin × Iin 　　

　　　　　※Vcc(reg)_max:8.5V

　　～For example～ 　

　　Vin=24V, Iin =1.8 mA, Qg=134nC (SQM40P-40L), Vcc(reg) =8.5V 　　

　　・Datasheet

　　　1.01W = 24 × ((134/1000000000 × 300 × 1000) + 1.8/1000) 　　

　　・Examination 　

　　　 0.385W = 8.5 × ((134/1000000000 × 300 × 1000) + 24 × 1.8/1000

・Is the power dissipation of Pch-MOSFET connected to LM5085 the following formulas?

　P = C × V2 × f 　　= Qg × V × f

・About TINA-TI

　Is there any TINA-TI model of SQM40P10-40L or SQD40P10-40?

　※Although the customer using TINA-TI, in order that there may be no data of above-mentioned FET, 　

　　　the simulation is carried out by product FDMC5614P made from FAIRCHILD.

　And, above-mentioned FET has a difference in Qg, what kind of change occur by the difference in Qg?

　(Power loss, switching frequency and other...)

------------------------------------------------

 

Best regards,

Satoshi

  • 0
    Guru 19485 points

    How about the situation of content which questioned the other day?

    Please teach if there are spec and information necessary to confirm.

    I will confirm it.

    Best regards,

    Satoshi

  • 0 in reply to Satoshi
    Guru 19485 points

    The request of the reminder came from the customer.

    First of all, It is OK only the known point, please answer.

    Especially, A customer is wanting to get to know the point of "About calculation of power dissipation" early.

    Best regards,

    Satoshi

  • 0 in reply to Satoshi
    Guru 19485 points

    I'm sorry. The mistake occurred about the question.

    ・Mistake : UCC27323 　

    ⇒Right : UCC27322

    Best regards,

    Satoshi

  • 0 in reply to Satoshi
    Prodigy 10 points

    Dear Satoshi,

    if you got any reply from TI? I would like to clrify the same question as yours - how to use the external driver with LM5085.

    Please let me know if it was clarified,

    Thanks,

    Dmitry.

  • 0
    TI__Genius 11490 points

    Hi Satoshi,

    The big FET issue is usually related to the delay of the FET turn on. This in my estimate is eating into the blanking time of the current sense. If the turn on was faster this issue can be avoided. The second limitation is the VCC current capability which provides the driver average current.

    Since I have not tested the circuit with an exteranl driver, all these are educated guesses only.

    The driver is likely to speed up the FET turn on. So should work. But the driver will add its own propogation delay.

     

  • 0 in reply to Vijay86929
    TI__Genius 11490 points

    The power dissipation equation is only calculating the IC power. This is the static current + gate drive current.

    Since you will be powering the external drivers from the VCC of the IC. This power dissipation still happens in the IC.

  • 0 in reply to Vijay86929
    TI__Genius 11490 points

    No, the power dissipation in the mosfet has many components. The QG component is only gate driver related. And it actually does not happen in the mosfet. It happens in the driver circuit. Which in this case is LM5085 IC VCC circuit.