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TPSM64406: External SYNC frequency

Saadya M.
Prodigy 40 points
Part Number: TPSM64406

Tool/software:

In the datasheet for the TPSM64406, it says to keep the external SYNC frequency between +/- 20% of the modulation frequency set by the Rt resistor. What if we need to use it up to +/- 35% of the modulation frequency ?

For a design (under consideration), we have Vin = 12 V, Vout needed 6 V (single output) , Iout about 2.5 A,  and a variable SYNC freq from 1 to 2 MHz. Would this be OK? how would this SYNC range Fmod +/- 33% or so affect the performance ?

  • 0
    TI__Mastermind 24115 points

    Hi,

    When utilizing the SYNC frequency (external), it is recommended that the RT pin resistance be set such that the internal frequency of the device is close to the external sync signal. This way, in the case that synchronization is lost, the device is still able to operate properly. 

    Wildly differing these two frequencies, SYNC and the RT, can potentially cause increased voltage ripple and unstable outputs in certain conditions. Your switching frequency has an affect on your loop stability, as well as your inductor current ripple, which may further affect your stability. 

    My advice would be to test the device at your minimum and maximum switching frequencies as dictated by your system. As long as your stability and application requirements are satisfied at both these frequencies, there should be no issue. If this is not the case, you will need to modify your application components so that all your conditions are satisfied. The design calculator tool here: https://www.ti.com/tool/download/TPSM6440X-DESIGN-CALC should be able to help you get started with this. Set your RT resistor such that your device operates at its preferred switching frequency in the case the external clock signal is corrupted or in-operational in some way as your fail-safe.

    Thank you,

    Joshua Austria