LMK04828: output abnormal problem

Amelie Zheng

Part Number: LMK04828
Other Parts Discussed in Thread: LMK04808

Hi Team,

My customer meets an output abnormal problem.
Configure the hardware to a single-loop mode according to the requirements, and the signal amplitude of the differential output becomes lower and lower with the frequency. There is basically no signal output when it reaches 1G.

could you help for this？

over 4 years ago

0 Noel Fung over 4 years ago

TI__Guru** 107190 points

Hi Amelie,

What is the clock output format?

0 Amelie Zheng over 4 years ago in reply to Noel Fung

TI__Genius 10865 points

Hi Noel,

format is Lvpecl

The external clock is 100MHz and input is osin output 2500M
Could you please kindly help to check?
Thanks!!

0 Noel Fung over 4 years ago in reply to Amelie Zheng

TI__Guru** 107190 points

Hi Amelie,

there should not be a problem to support 1GHz with LVPECL.

From datasheet Figure 27, the output power is -2.4dBm at 983MHz.

With LVPECL output, make sure to have the 240Ω shunt resistors populated at the output pins, similar to Figure 21.

0 Amelie Zheng over 4 years ago in reply to Noel Fung

TI__Genius 10865 points

Noel,

Do you have the calculation of resistance? Because customer now output clock is 2.5GHz. Is it also add 240 ohm register?

0 Noel Fung over 4 years ago in reply to Amelie Zheng

TI__Guru** 107190 points

Hi Amelie,

Please refer to LMK04808 datasheet section 6.7, there are some plots showing the voltage swing vs frequency vs shunt resistors.

Clock & timing

Clock & timing forum

LMK04828: output abnormal problem