DAC37J84: about DAC3XJ8XEVM-SCH_D SYSREF TERMINATION

user5983069

Part Number: DAC37J84
Other Parts Discussed in Thread: LMK04828, , DAC38J84

We try to connect SYSERF SIGNAL between LMK04828 and DAC37J84 as LVPECL DC coupling connection which shows in DAC3XJ8XEVM-SCH_D SYSREF TERMINATION.

But we cannot understand the effect of (R98,R89) / (R106.R105)/(R115,R116)

Would you please show us what for?

thank you

over 3 years ago

0 Kang Hsia over 3 years ago

TI__Guru 66054 points

Hi,

R98, R89 form the necessary pull-down bias resistors needed for the LCPECL driver. R106/R105 and R115/R116 forms the resistor divider to divide down the common mode to 0.5V necessary to the DAC38J84 sysref receiver circuit.

The overall impedance (Thevinin looking back into the SYSREF driver) is close to 100ohm differential. This creates the source impedance needed to match the DAC38J84 SYSREF load termination of 100ohm.

-Kang

0 user5983069 over 3 years ago in reply to Kang Hsia

Intellectual 320 points

Hi Kang

I understood.

thank you very much.

-Takeshi

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DAC37J84: about DAC3XJ8XEVM-SCH_D SYSREF TERMINATION