LMX2594EVM: LMX2594EVM

Hi Michael,

Let's do some simple debug first.

After Vcc power up, if you program the POWERDOWN bit = 1, do you see a current drop? This test is to verify the SPI communication.

If there is no problem with the SPI interface, then after Vcc power up and full programming, do you see any output signal?

Hi Noel,

We verified that after Vcc power up we are able to toggle the bit and we see a 280 mV drop as we toggle it.  After the power up we do not see any signal or sync.  

Mike

Hi Michael,

OK, the SPI programming is through. Then after Vcc power up, after loading all registers, did you mean you see no signal at all? Or you see some garbage signals? If you change the output power setting  OUTx_PWR, do you see a change in current consumption? What is the Vtune voltage? Compare the DC voltage on the following pins between good and bad EVM:

pin 3, 10, 27, 29, 33, 36 and 38. 

in addition, check the RFout SMA connectors for cold soldering, we have seen this problem before. 

Hi Noel,

After we expanded the bandwidth on the VSA we can see the signal but it’s not at the frequency that we programmed. We programmed 5750 MHZ , but see the output at 5800 MHz, it seems to be 50 MHz off and it is not syncing to 100MHz clock.  We used the same Ref Pro board with 100MHz to program both a good EVM board and the "defective" board, it works on one but not the other.  We have also added a 0 Ohm resistor to r29 on the defective EVM to try the other ref clock input and we still see the same issue, the frequency is off by 50MHz. Lock Led is always off.

After Vcc power up, after loading all registers, did you mean you see no signal at all?    Correct we did not see any signal until we expanded the bandwidth at which point, we did see the signal but the output was off by 50MHz, and the lock LED is off.

If you change the output power setting, OUTx_PWR, do you see a change in current consumption?    Yes, when the OUTx_PWR is set to 0 the current = 316mA, when it is set to 63 the current=399mA .  

RFout SMA/ REF_CLK SMA connectors cold solder?    There does not appear to be any cold solder, all the SMA connections are fine.

DC voltage comparison between good and bad EVM

Mike

Hi Mike,

Everything seems good except that it locked to a wrong frequency. What was the Vtune voltage? I expect it should be off from 1.3V. 

Could you also do a register readback for the following registers?

R110, R111 and R112.

Compare them with a good device, I want to see if the unlock is due to calibration.

...

Hi Noel,

Here is the register readback and the Vtune voltage

Thanks,

Mike

Hi Michael,

The calibration is fine, both devices return similar calibration data.

Vtune is zero voltage, maybe there is some connection problem with the loop filter, would you take a look on the loop filter?

Hi Noel,

We checked the loop filter, and everything looks ok, we also checked the charge pump, U1 pin 12 and there was no voltage there.

Hi Micheal,

Noel is currently on chinese new year holiday. Please allow us a bit more time to comment further on your question.

Regards,

Julian

Hi Michael,

Please check if you have a valid supply voltage at pin 11 (VccCP). 

If the supply voltage is good, then I don't have a good explanation to the failure.

Hi Noel,

We checked the supply voltage on Pin 11 of a good unit and the bad unit.  On the good unit the voltage is reading 3.25V on the bad one it is reding 3.15V.

Mike

Hi Michael,

3.15V is fine, I don't know what went wrong with the chip.