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MC33063A-Q1: Crossover Frequency

Muwei Zheng
Intellectual 1560 points
Part Number: MC33063A-Q1

Hi team,

Could you provide the Crossover Frequency for MC33063A-Q1?

My customer have been using this device for production while the initial design did not consider crossover frequency, so they would like to check the value which is not on the datasheet.

Thank you,

Muwei Zheng

  • 0
    TI__Genius 10385 points

    Hi Zheng,

    Thank you for using E2E forums, regarding your query what do you mean by Crossover frequency of the device, it is not something specific to the IC but something related to the schematic design or PCB itself. you basically have to measure the open loop response of the design and from there you will get your cross over frequency, Phase margin and gain margin by reading the bode plot of your loop response.

    Hope this helps.

    BR,

    Haroon

  • 0 in reply to Haroon Wardak
    TI__Intellectual 1560 points

    Hi Haroon,

    My understanding is MC33063A-Q1 uses hysteretic control, thus there is no external compensation circuit as usual buck converter. Is that correct?

    Thanks,

    Muwei Zheng 

  • 0 in reply to Muwei Zheng
    TI__Genius 10385 points

    Hi Zheng,

    Yes this device does not have any external compensation circuit.

    BR,

    haroon

  • 0 in reply to Haroon Wardak
    TI__Intellectual 1560 points

    Hi Haroon,

    If the device does not have any external compensation circuit, does it mean the crossover frequency will depend on the IC itself? Sorry I am not quite familiar with hysteretic control buck converter. 

  • 0 in reply to Muwei Zheng
    TI__Genius 10385 points

    Hi Zhang,

    Yes it does not have any external circuitry for compensation, and there is no information in the datasheet on what this Fco depends on, but my guess would be as you said dependent on the device itself and maybe oscillator frequency.

    Hope this helps.

    BR,

    haroon

  • 0 in reply to Haroon Wardak
    TI__Intellectual 1560 points

    Hi Haroon,

    Just for double check, oscillator frequency in the datasheet is the crossover frequency of MC33063A-Q1? 

    Customer mentioned Fco should be specified for this device, so please confirm if it's correct.

  • 0 in reply to Muwei Zheng
    TI__Mastermind 19595 points

    Hello Zheng, 


    Due to Easter vacation all colleagues are on vacation right now. 
    We will come back to you by mid of next week.

    Best regards,

    Harry

  • 0 in reply to Harry Hofner
    TI__Mastermind 19595 points

    Hello Zheng,

    It is not possible to specify the cross-over frequency for the device itself.
    As Haroon had initially indicated, it depends on external components.
    The cross-over frequency equals to the bandwidth with which the system can follow a transient.
    It is correct that there is no compensation network, but the bandwidth is still limited by external components: inductor, output capacitors, current limit which is defined by the sense resistor, parasitic inductances of the PCB, and so on.
    Therefore, the achievable cross-over frequency will be lower than the switching frequency.

    My question would be: Why is the cross-over frequency important to you?
    In a system with a pretty stable input voltage and load current, this parameter is not so important.
    But if you want to use the converter e.g. for a dynamically changing load, I would propose using a different converter which can react better to such an environment.

    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