Synthesizer Not Working

Synthesizer still not working.  I checked that there aren’t any shorts between the exposed paddle underneath the IC and any of its pins.  Ground and power is everywhere it should be.  The loop filter is pulled up to 3.3V though it should be around 1.8V when it’s locked in.  It’s not shorted to 3.3V so it’s the synthesizer that’s driving it up.

I noticed that the evaluation board needs the command sent to it twice to set the frequency which is odd.  At first I thought it was me hitting Load and then OK but it won’t take without Load/OK, Load/Load, or OK/OK.  I checked from power on to RF out with the logic analyzer to see if there is any reason why it would need to be commanded twice but found nothing.  For the hell of it, I commanded it twice (and more) on my board to no avail.

I’ve used the sister part before, the ADF4360-0, and had no trouble with it at all, proving that not all siblings have the same temperament.

Update: 7:33 PM

I’ve got a support request into Analog Devices so I’m waiting to hear back from them.  What I’ve found is that there is no output from MUX pin when set to “N Divider Output” and there should be a 500 kHz pulse train which explains why the loop filter is at 3.3V.  The N Divider and R Counter are fed into a phase comparator and its output passes through the loop filter to tune in the frequency.  So with no N Divider signal, it’s pulled all the way up as it tries to tune.

So far, what I’ve checked is:

  • There are no shorts between any pins, power, or ground.
  • Power and ground present where they should be.
  • CE enable line is HIGH.
  • 10 MHz reference input is present at pin.
  • Serial data was checked with a logic analyzer against an ADF-4360-xEBZ1 Rev. D4 evaluation board and all serial and enable signals are identical from power up to output. My serial clock is 1.4MHz; slowing it did not help.
  • MUX set to “Serial Data Out” properly parrots back serial data in, delayed by 24 bits.
  • Mux set to “Open Drain Lock Detect” goes HIGH for approx. 100us then low upon setting the latches.
  • Output stages are pulled up to Vvco with 47nH inductor.
  • Voltage at Rset pin is 0.52V with 4.7k resistor.
  • Time between setting Control Latch and N Latch is greater than 10ms.

The output is connected directly to a spectrum analyzer and there are no signals from DC to 2GHz. My latches for testing are configured as follows:

  • R Latch: 0x300051
  • Control Latch: 0x4FF180
  • N Latch: 0x006C32

R Latch is set first, Control Latch second, and N Latch last.