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Original question:

LM63615-Q1: Pre-bias start up

LM63615-Q1: tolerance of switching frequency includes SSCG modulation?

Shinji Tsuji
Genius 14169 points
Part Number: LM63615-Q1

Hi team,

I would like to set the switching frequency no lower than 1.8MHz.

When I set RT=GND, minimum switching frequency is 1.85MHz, but I concern if this includes +/-5% of Spread spectrum clocking.

1. Does the switching frequency tolerance includes this SSCG's 5% modulation?

Or minimum switching frequency might drops to 1.7575MHz(1.85MHz -5%)?

2. How much is the switching frequency tolerance when I put RT=7.5kohm?

fADJ2 only specifies typical value. Could you give me the minimum value?

regards,

  • 0
    TI__Mastermind 28020 points

    Hi Shinji,

    1. The switching frequency tolerance does NOT include the spread spectrum modulation. There are both spread spectrum and non-spread spectrum devices if spread spectrum is not needed.

    2. Setting the frequency to 2.2MHz would have a minimum value of 1.95MHz.

    Also, the device can be synchronized to a fixed frequency using the SYNC function.

    Regards, Jason

  • 0 in reply to J Arrigo
    TI__Genius 14169 points

    Hi Jason,

    Could you advise the tolerance of the switching frequency if I use external RT register?

    Can I use -11%(min 1.95MHz for 2.2MHz setting) for other switching frequency too?

    For example, if I select 2.0MHz, then the minimum frequency will be 1.77MHz?

    I would like to know the tolerance of "15770" constant in equation (1) in the datasheet. 

    regards,

  • 0 in reply to Shinji Tsuji
    TI__Mastermind 28020 points

    Hi Shinji,

    If using an external RT resistor, the tolerance can be +/-10%.

    If selecting 2.0MHz, design for a minimum of 1.8MHz.

    Regards, Jason