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LMK00804B-Q1: Buffer IC Clock pins input connections and different voltage level output realization from single buffer IC

Arshad Mughal
Prodigy 40 points
Part Number: LMK00804B-Q1
Other Parts Discussed in Thread: LMK00804B, LMK04828

Hello,

I have three queries regarding LMK00804B.

Following is the circuit I have been using to provide input from 25MHz TCXO (output impedance 200ohm typ) to the LMK00804B.

1. Can I directly connect the TCXO (LVCMOS) output with an output impedance of 200 ohm to LMK00804B LVCMOS_CLK input (pin 8) as shown below? Considering driver and transmission line impedance will be different? 

2 Or I can connect 4:1 step down BALUN at the output of TCXO (LVCMOS) and the BALUN balanced output (differential) connect to the LMK00804B buffer CLK_P and CLK_N inputs (pin5 and pin 6) as shown below?  

OR I should use Thevenin termination circuit as given in the datasheet (shown below) at the output of BALUN pin 1 and connect both pin 2 and 3 of BALUN to GND?

3. I need to have 2 buffered CLK output, one is for 1.8V DSP CORE CLK and other is 3.3V clock input to LMK04828 TI Clock Synth. Can I get 2 different level (1.8V and 3.3V) outputs from the same LMK00804B buffer IC or I have to use 2 LMK00804B buffer IC's to provide those two clock inputs?

Thank you,

Arshad 

  • 0
    TI__Genius 10395 points

    Hello Arshad,

    I'll get back to you by the end of this week.

    Best,

    Andrea

  • +1 in reply to Arshad Mughal
    TI__Genius 10395 points

    Hello Arshad,

    Arshad Mughal said:
    1. Can I directly connect the TCXO (LVCMOS) output with an output impedance of 200 ohm to LMK00804B LVCMOS_CLK input (pin 8) as shown below? Considering driver and transmission line impedance will be different? 

    That should be fine while you make sure the internal resistance of the TCXO and an external resistor (if needed) add up to 50Ω.

    Arshad Mughal said:
    OR I should use Thevenin termination circuit as given in the datasheet (shown below) at the output of BALUN pin 1 and connect both pin 2 and 3 of BALUN to GND?

    That figure is only needed if the input LVCMOS driver is in tristate condition. If not, then that topology is not needed. However, if you choose to use that topology, then the balun is also not needed. Only the caps and resistors shown are needed.

    Arshad Mughal said:
    3. I need to have 2 buffered CLK output, one is for 1.8V DSP CORE CLK and other is 3.3V clock input to LMK04828 TI Clock Synth. Can I get 2 different level (1.8V and 3.3V) outputs from the same LMK00804B buffer IC or I have to use 2 LMK00804B buffer IC's to provide those two clock inputs?

    Unfortunately, this part wont work since it combines its output supply voltage rails to all outputs. Hope this helps!

    Good luck,

    Andrea

  • 0 in reply to Andrea Vallenilla
    Prodigy 40 points

    Thank you Andrea for the reply.

    Regards,
    Arshad