LMX2541: Using Two PLL on the Same Micowire Bus

TI-CSC

Part Number: LMX2541
Other Parts Discussed in Thread: LMX2592

Hello E2E Experts,

Good day.

We use two PLL LMX2541SQ3740E on the same Microwire bus and use the chip in "Full Chip Mode".
Programming is done only once.

On page 37, the following information is written:

• After the programming is complete, the CLK, DATA, and LE signals should be returned to a low state.

• When using the part in Full Chip Mode with the Integrated VCO, LE should be kept high no more than 1 us

after the programming of the R0 register. Failure to do so may interfere with the digital VCO calibration.

Now came the question up how to use the CLK, Data and Lacth enable signal correctly if we program both PLL1 and PLL2 in sequence.

Is it fine if we keep LE1 low if we start programming the second PLL2 or is it better to pull LE1 high during the programming of the second chip with LE2? We thought, bringing LE1 high would avoid clocking new data into PLL1.

Thank you in advance for your support.

Regards,

CSC

over 2 years ago

0 Andrea Vallenilla over 2 years ago

TI__Genius 10975 points

Hello TI-CSC,

LMX2541 should be similar to our LMX2592 in configuring the microwire bus; therefore, you can use this thread as guidance:

https://e2e.ti.com/support/clock-timing-group/clock-and-timing/f/clock-timing-forum/654132/lmx2592-multiple-lmx2592-pll-over-spi-not-getting-confugred/2403199#2403199

In summary, you can program both PLLs in the Microwire both either in sequence or simultaneously; however, whichever you choose there are certain considerations you have to make.

If you program the PLLs in sequence, you can connect the SCK and SDI pins together but the CSB pins must be separated. If you choose to program them simultaneously, then you can connect all the SPI interface together but make that the SPI driver has enough strength so that signal integrity is kept. Hope this helps.

Good Luck,

Andrea

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LMX2541: Using Two PLL on the Same Micowire Bus