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LMX2572LP: Termination of unwanted pins

Part Number: LMX2572LP

Hi,

Good day. I hope you are well.

Our customer is using the LMX2572LP and they have some question about it. Kindly refer to their question below.

"We are using LMX2572LP Device in our design and it is in design stage. We just want PLL functionality and neither FSK nor ramp calibration.so we are not using RampDir and RampClk pins from the package. But is it okay if those pins are left floating?
Other than this there is a 12 Kohm resistor n series for all other programming pins why it is required?
Doesnt CSB pin require pull up resistor?"

I hope you could help us with this matter. Thank you.


Regards,

Cedrick

  • Hi Cedrick,

    Datasheet section 8.1.9 has the recommendation for unused pins. 

    The EVM was design to support both 5V and 3.3V digital interface, so there were some 12kΩ + 10kΩ resistors reserved to divide down 5V signal. In normal use case, I suggest use 33Ω series resistors to limit possible current flow.

    CSB pin does not need pull-up resistor, you can make it LOW all the time if you are not programming the device.