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LM61460: Synchronisation

Franz Haselsteiner
Prodigy 20 points
Part Number: LM61460

Is the possible synchronisation frequency independent from resistor on RT?

For example wth RT=33k2 nominal switching frequency would be 400kHz. Can the oscillator be synchronized to 300kHz or 540kHz?

We want to change the frequency depending on running system application between these values.

Thanks

  • 0
    TI__Guru 50120 points

    Hi Franz,

    The EN/SYNC feature of this device allows external synchronization. Please refer to Section 8.3.2 for more information. 

    You can have the RT resistor set the initial startup switching frequency. Once the start-up sequence is properly initialized, an external clock can be injected through an AC coupling capacitor into the EN/SYNC pin of the device to dynamically control the switching frequency. This external clock should then override the RT resistor. 

    Regards,

    Jimmy

  • 0 in reply to Jimmy Hua
    Prodigy 20 points

    There is no restriction on synchronisation frequency, depending on RT?

    So I can use RT=33k2 and synchronize after start up to 1MHz.

    Or I can use RT=6k and synchronize to 300kHz.

    Is this correct?

  • 0 in reply to Franz Haselsteiner
    TI__Guru 50120 points

    Hi Franz,

    The external synchronization can be between 200kHz and 2.2MHz as stated in the datasheet. If the external synchronization is removed, the RT resistor should set the internal clock back to the set RT value. 

    Regards,

    Jimmy