TPS54240-Q1 How to Interface to RT/CLK Pin

tateo yamashiro

Other Parts Discussed in Thread: TPS54240-Q1

Hi,

My customer has question about TPS54240-Q1.
Could you tell me about questoin?

[Question]
You recommend AC-coupling the synchtonization signal through a 10-pF ceramic capacitor to RT/CLK pin and a 4-kohm series resistor in datasheet.
Why is it 10-pF and 4-kohm? My customer want to use 4.7-kohm. How much is maximum value of resistor?

Best Regards,

tateo

over 8 years ago

0 Akeem Whitehead over 8 years ago

TI__Mastermind 27780 points

The appropriate Applications Engineer has been assigned to respond accordingly. Thank you for your patience.

0 Karl Westerberg | Field Application Engineer over 8 years ago

TI__Prodigy 700 points

Hello Tateo,

your customer will be fine by using a 4.7k Ohm resistor!

There are no specified limit for the resistor, but we recommend to use a for 4k Ohm resistor or something close to that value.

Regards,
Karl

0 tateo yamashiro over 8 years ago in reply to Karl Westerberg | Field Application Engineer

Guru 10890 points

Thank you for your reply.

My customer want to know more detail. We know 4-kohm reduces PH jitter in heavy load applications when synchronizing to an external clock and in applications which transition from synchronizing to RT mode. Why does 4-kohm reduce PH jitter? Could you explain about this method?

Best Regards,

tateo

0 Karl Westerberg | Field Application Engineer over 8 years ago in reply to tateo yamashiro

TI__Prodigy 700 points

Yes,

The resistor is added to attenuate the signal passing through the ac coupling or high pass filter. In heavy load application will the environment become more noisy and also affect the clock signal. The noise will pass through the high pass filter and be attenuated by the resistor, resulting in that the jitter is reduced.

As long as you are changing the resistance around 4k will your customer be fine.

Please let me know if you need a more detailed description.

Regards,
Karl

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TPS54240-Q1 How to Interface to RT/CLK Pin