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LMX2492 EVM PLL will not lock

Prodigy 120 points

Replies: 2

Views: 691

Iv'e set up the EVM for a Flat top Frequency Sweep per SAU160a.pdf section 6.2 also see data sheet LMX2492-q1.pdf section 9.2.4.

The Board is power and the voltages appear at all test points and all parts for the high frequency VCO are populated. (can add a resistor to Fast lock pin).

Code Loader4 appears to download the configuration file to the IC, see flags and leds toggle as requested.

Probe the Charge pump output (see Test point) appear constant at low level but the sweep flag appear to work. The VCO output appears to be stuck at 8.9GHz and is not sweeping per App note.

When I enable three Fast Lock bits the VCO the Charge Pump output appears to non-linear ramps up from 0 to .330V and reset back to zero and repeats the ramp.

Can you help me.

Thank you.

2 Replies

  • Jeffry,

    The fact that you can toggle the LEDs indicates that you can communicate with the part.

    The next thing would be to do is establsh a lock.   If you go to the default mode, then this should lock for this condition.   Although there is a 100 MHz XO on this board, it is not hooked up so that this can be driven by an external signal generator.  Could this be the issue?

    REgards,

    Dean

  • In reply to Dean Banerjee:

    Dean,

    Thanks for you fast response. But... the VCO doesn't lock in non-ramp mode either. The on board 100MHz works since I can probe it and also see the ramp flag (which I have enabled on the MUX_out port). My board is serial #1, was it tested at the factory?

    Can you send me a "tested" ramp file and default file that was verfied to work on a your working board.

    Jeff

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