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UC1846: To Slave IC i have a question in paralell push pull operation.

Eduardo Vasques
Prodigy 30 points
Part Number: UC1846

Hello,

what i need to do with the IC 1846 used to be the Slave in a paralell operation with the Master?

The pins 3 and 4 (currente sense) it will necessary install the current sense resistor? How a used at the Master circuit? Both i"ll need to conect to ground?

At the data sheet from UC1846 don't speak about these.

  • 0
    Prodigy 30 points
    can use 2.5V at the NI input (+ E/A) ? At the datasheet is used Vref = 5.1V. I need to use 2.5V because I'll use a opto-coupler to control at the inverter input of the error amplifier. At this case i will be able to change the voltage by opto transitor around 2.5V. If a used 5.1V the opto transistor will be at maximum value 5.1 minus Vce sat of the transistor.
  • 0 in reply to Eduardo Vasques
    TI__Mastermind 20045 points
    Hello Eduardo,

    In figure 7 on page 13 of the UC1846 datasheet you can see a schematic of the device in parallel operation. I realize that pin 3 and 4 are not shown. I believe that a separate current sense resistor should be used to measure the current of each inductor (i.e. there will be two current sense resistors, one for each IC). I will look into this and see if I can confirm.

    I don't believe there is any issue if you use 2.5V instead of the 5.1V at the NI input. I will again investigate and let you know if I find out differently.

    Thanks,
    Kyle
  • 0 in reply to Kyle Rakos
    Prodigy 30 points

    Kyle,

    Thanks a lot.

    But i am still doubtfull about this.

    Because the Master will be the limit function with it's shunt resistor. And if operating in limitatin the pulse width will be reduced by Master CI. Then, the compensation input voltage (pin 7 ) will reduced and the Slave IC will do the same because this pines are connected together.

    Is this true?

    Best Regards,

    Eduardo Vasques.

  • 0 in reply to Eduardo Vasques
    TI__Mastermind 20045 points
    Hello Eduardo,

    I just wanted to let you know that I am still researching your question and hope to have a better answer for you by the beginning of next week.
    Thanks,
    Kyle
  • 0 in reply to Eduardo Vasques
    TI__Mastermind 20045 points

    Hello Eduardo,

    I still believe you need to use 2 sense resistors and the reason for that is that each controller is sensing the current for each inductor, which ideally should be half of the total current. Therefore, each controller is equivalent to operating by itself to half the total current and therefore each needs to have its own current sense resistor for peak current limiting purposes.

    The compensation network is the part that takes into account the fact that one is driving the other (by connecting the COMP pins together). Therefore, I believe the adjusted compensation value (by a factor of 2) will be compared to each current limit in the current comparator. The factor of 2 in the compensation calculation accounts for the adjustment in the comparison threshold used in the current comparator.

    Thanks,
    Kyle