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UCC28881: Question minimum Vout ,maximum Iout and simulation

Masaharu Takahashi
Expert 4170 points
Part Number: UCC28881

Hi, Team.

could you answer for below quesiton?

1.how to calc the minimum vout IC can ?

->I tried to calc by using Vin x (minimum Ton/Tsw) but it seems like that this IC switching frequency would vary depends on load current and it has burst also.

how do we know the minimum output voltage ?(Ton_max and Ton_off would be almost same which means duty is 50%).

so, Vin x (1/2) = estimated output voltage as possible?

2.how much load current can IC work?

-> i know it depends on how much current ripple on inducter and whether it hits current limit or not though,

(i basically use power stage designer but it can not be applied on this IC since power stage designer can not work in this case)

AC200V

Vout:48V

Iout:200mA

can we know whether it is ok or not?

3.i can't use the TINA file on ti,com as below, could you give me the file.

  • 0
    TI__Expert 8210 points

    Takahashi-san

    The way UCC28881 works is that it operates at a fixed frequency of 50% duty cycle at 62kHz.  To regulate the output voltage it goes into a burst mode where it disables PWM operation for period of time to allow the voltage to reach the target level.  This is described in section 8.4.3 PWM Controller (page 13) of the datasheet.  What this means for the maximum output voltage, the highest D that can be achieved is 50%, so the max output voltage UCC28881 can support is 0.5*Vin.

    In buck mode the maximum load current for UCC28881 is 225mA.  This comes from the cycle by cycle current limit ILIMIT that UCC28881 regulates thru the integrated power FET. 

    UCC28881 can work at your operating conditions of 200VAC input, 48V/200mA output.

    If you need to simulate a design with UCC28881 we recommend that you use PSpice with our PSpice model that's available here http://www.ti.com/lit/zip/slum501.  This model is encrypted, so if you are looking to import it into a TINA you need an unencrypted model.  

    Best Regards,

    Eric

  • 0 in reply to Eric Faraci
    TI__Expert 4170 points

    Hi, Eric-san.

    thanks your reply.

    for simulation model, i tried to use .LIB file via TINA TI function as "New Macro Wizard".

    but i couldnt import it.

    do you know how we could import it smoothly?

    are there any specific way to import the file which is encrypted file into TINA TI?

  • 0 in reply to Masaharu Takahashi
    TI__Expert 8210 points

    Takahashi-san

    You cannot import an encrypted SPICE file into TINA.  I have sent you an email on how to get access to an unencrypted model.

    Best Regards,

    Eric