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MC33063A: spec check

GARETH OU
Guru 11365 points
Part Number: MC33063A

Hi

I have a question: The picture below is the circuit in Spec.

1. Does this circuit use a switching frequency of KHz? ? 

2. For the CT mounted on Pin3-4, what is the basis for selecting 1500pF?

3. Formula table in Spec: What is the value of Vsat?

  • 0
    TI__Mastermind 19595 points

    Hello Gareth,

    Thanks for reaching out to us via e2e.

    The CT capacitor defines the frequency of the oscillator.
    Please look at the application note, section 1.2, 3.2 and 3.4: https://www.ti.com/lit/pdf/slva252 
    1500pF is just an example.

    VSAT depends on the configuration (Darlington when pins 1 and 8 are connected, or non-Darlington), see table 7.6.
    But it also depends on the Collector current.
    Therefore, please use figure 3 - upper line for Darlington - to derive VSAT.

    All information in this correspondence and in any related correspondence is provided “AS IS” and “with all faults” and is subject to TI’s Important Notice (www.ti.com/.../important-notice.shtml).

    Best regards
    Harry

  • 0 in reply to Harry Hofner
    Guru 11365 points

    Hi Harry

    Could you help check the MC33063A schematic and any need to adjust Thanks

    1. Is the sensitivity of L2 enough? (Currently 100uH)

    2. The output current is planned to be 80mA. What value should be placed in R6?

    3. The desired switching frequency is around 40KHz. How much should C14 be?

    4. Can C14 only contain 150pF?

  • 0 in reply to GARETH OU
    TI__Mastermind 19595 points

    Hello Gareth,

    An FAE should be able to use the equations of section 9.2.1.2 to calculate all necessary values.
    Adding some margin to the desired average output current (100mA instead of 80mA), I get the following:
    C14: 750pF
    I peak: 800mA
    R6: 390Milliohm
    L2: 100uH
    For the chosen Cout of 79uF you will end up with a ripple of 170mV

    All information in this correspondence and in any related correspondence is provided “AS IS” and “with all faults” and is subject to TI’s Important Notice (www.ti.com/.../important-notice.shtml).

    Best regards
    Harry