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LM5032: The external synchronizing pulse generation circuit.

user1375311
Prodigy 170 points
Part Number: LM5032


According to the data sheet, the LM5032 can be synchronized to an external sync signal, but the sync signal conditions are complicated.

Please give me an example of a circuit for generating sync signal as simple as possible.

Thank you in advance.

  • 0
    TI__Genius 13660 points

    Hello,

    If the LM5032 is to be synchronized to an external clock, that signal must be coupled into the RT/SYNC pin through a 100 pF capacitor. The external synchronizing frequency must be at least 4% higher than the free running frequency set by the RT resistor and no higher than twice the free running frequency. The RT/SYNC pin voltage is nominally regulated at 2.0V and the external pulse amplitude should lift the pin to between 3.8V and 5.0V on the low-to-high transition. The synchronization pulse width should be between 15 and 150 ns. The RT resistor is always required, whether the oscillator is free running or externally synchronized.

    For your reference:

    Regards,

    Teng

  • 0 in reply to Teng Feng
    Prodigy 170 points 
    Hello,
    Thank you for showing me an easy-to-understand figure.
    I don't know the impedance of the RT / SYNC pin, 
    so I wanted to know a specific example of a circuit that generates a 2 to 3V pulse.
    Is the following pulse generator circuit all right? 
    For example, a microcomputer output port that operates with a power supply voltage of 2 to 3V.
    Or an open-collector comparator output with a pull-up resistor of about 10 kΩ.
    In this case, is 10kΩ too high? What is the optimum resistance value?
    Regards,
  • 0 in reply to user1375311
    TI__Genius 13660 points

    Hello,

    They are both ok,  It doesn't need large driver ability of source to driver sync pin. You also can get a voltage from IO port with resister divider. but the resister shouldn't be very large, generally less than 10 k. since there is parasitic parameters.

    Please ensure there is no signal distortion at sync pin.

    Regards,

    Teng

  • 0 in reply to Teng Feng
    Prodigy 170 points

    Hello,


    Thank you for the advice.

    I understand that.

    Now I can design with confidence.


    Thank you very much.