LMK04832-SP: LMK04832-SP vs. LMX2615-SP

LMK04832-SP only supports up to 3255MHz output frequency. So use LMX2615-SP.

Regards,
Hao

Hi Rajan,

In that case you can only use one LMK04832-SP and one LMX2615-SP for each of the output.

Regards,
Hao

Sorry I didn't see the previous question. For LMK04832, there should be registers CLKoutx_FMT (for example, CLKout3_FMT) that have "powerdown" option.

LMK04832 provides max current for some use cases: 

Simply multiply that number by supply voltage to get max power consumption.

I'm afraid LMX2615 doesn't guarantee max current. Only typical values are provided.

Regards,

Hao

Hi Rajan,

For question:

can both devices be controlled using SPI as the design does not have sufficient I/O to support parallel I/O.

for the LMX2615, if I use the SPI, can the FSx pins be left floating

Yes both devices support SPI. Check out "Pin functions" table for more information.

Check out table 11 for pin connections when unused.

For questions:

1. Can the LMK04832 output a 3 GHz differential clock, a.c. couple and then input this to the LMX2615 to produce a phase-coherent 6 GHz output?

2. Can I directly a.c. couple the differential 6 GHz output from the LMX2615 to supply a DAC with its differential clock input?

3. For the LMX2615, it's odd that VIH max for the digital control inputs is 1.6V max. Are both devices intended to interface with 1V8 logic, i.e. SPI interface and CS.

4. Can I use a FPGA to control both devices via SPI?

I have to enter the loop filters and a input reference source to the LMK04832, and then would like to share my schematic sheet with you please for any obvious errors

1. No. Check out max reference frequency on page 8.

2. If the DAC has internal biasing then it's fine, only one decoupling capacitor is needed between the output of LMX2615 and DAC. Note that pull up resistors/inductors are needed for the output of LMX2615. Refer to the datasheet for details of output configuration.

3. This one I'm not sure. I'll get back to you tomorrow.

4. Yes.

You can use PLLatinum sim to design your loop filter: http://www.ti.com/tool/PLLATINUMSIM-SW?keyMatch=pllatinum%20sim&tisearch=Search-EN-Products

Regards,

Hao

For question:

the LMK04832 contains an internal VCO which I would prefer to use rather than external reference: if I use its internal reference, will I be able to generate outputs at 250 MHz, 750 MHz, 3 GHz and delayed versions of 750 MHz and 3 GHz. Will the internal VCO have to be set to a specific frequency to produce the desired frequencies?

I don't quite understand this one. Yes it has internal VCO for PLL2 but it doesn't have internal reference. User still needs to provide external reference.

Regards,

Hao