LMK00334: Impact of Output Clock mapping to devices with different logic levels

Yasar Maheen Seenath

Part Number: LMK00334
Other Parts Discussed in Thread: AM6442

Hello Team,

Could you please help on below query asap.

I am using LMK00334 clock buffer in one of our design to configure 3x HCSL outputs.
Input CLK is HCSL and 3x outputs also required in HCSL
I tied the VCCOA,VCCOB pins to 3.3V.
My design requirement is as follows.
1) CLKoutA0 & CLKoutA0* will be mapped to a device whose REF_CLK input is compatible to 0V to 2.7V.
2) CLKoutB0 & CLKoutB0* will be mapped to a device whose REF_CLK input is compatible to 1.8V.
3) CLKoutB1 & CLKoutB1* will be mapped to another device whose REF_CLK input is compatible to 1.8V.

Will there is any issue, when mapping the 3.3V compatible output clocks of LMK00334 to devices which is compatible to either 2.7V or 1.8V?

NOTE:-If there is any issue, please suggest some recommendation to overcome this issue with same configuration needs.

4 months ago

0 Michael Srinivasan 4 months ago

TI__Genius 17791 points

Hi Yasar,

The output supplies (VCCOA/B) can take 2.5V to accommodate a 2.5V output. With regards to a 1.8V output, a voltage divider or decreased output termination may be the best way to ensure that the individual stages of your signal path will be compatible.

Thanks,

Michael

0 Yasar Maheen Seenath 4 months ago

Prodigy 250 points

Hi Michael,

Thanks for your quick feedback.

Please help to clarifiy below for a re-confirmation.

The output characteristic of LMK00334 HCSL differential output are on page no:7 of datasheet which mentions the voltage swing as 520mV(Min) to 920mV(Max).

In this case, Is there any compatibility issue if we connect the outputs clocks directly to the 3 devices (The devices are 2x AM6442 and 1 x PCI12000), without any voltage divider or any discrete output terminations?

On a quick inspection, since LMK00334 is specifically targeted for PCIe Gen 1 to Gen7 applications and AM6442 and PCI12000 are also PCIe compliant, will LMK00334 work for our AM6442 and PCI12000 devices without any voltage divider or any discrete output terminations?

0 Michael Srinivasan 4 months ago in reply to Yasar Maheen Seenath

TI__Genius 17791 points

Hi Yasar,

50 Ohms shunt terminations to GND are required at the output of the device in order to achieve the swing (HCSL is a current-based driving standard). Beyond that, as long as the output swing range satisfies the VIH and VIL requirements of the other devices, then there should be no issues routing the output straight into the devices.

Thanks,

Michael