We have used the evaluation boards Eval-adf4007 for more than two years without problems. However, since two weeks ago we observed the output level of charge pump is incorrect for two of our evaluation boards. It should have been at 5V when the RFin frequency (after N-counter) is higher than REFin (after R counter), but we observed zero volt in one board, and about 2V in the other board.
I will describe our parameters and tests we’ve done:
1. The signal for RFin at 1144MHz, 7dBm before being connected to the board (it should be about 1dBm sent to ADF4007), the N-counter is to divide by 16; REFin at 143MHz, 1dBm. Our custom made loop filter is a 100 ohm in series with a 10 nF (we do not use the loop filter on the board).
2. We have tested the two problematic boards: the N-counter and R-counter are working, but we do not see current pulses at charge pump output when we change the loop filter to a 100 ohm resister (to convert the current to voltage). When we use another working board, we do observe pulses at PFD frequency and the charge pump output does have 5V value with a loop filter.
Now, my questions are:
1. What could be possible reasons that make the two boards fail around the same time? We didn’t change anything in our setup. The only thing I can think of is we have (once or twice) left the charge pump output open while the evaluation board is still powered by 15V during the tests. Will this do something?
2. Is our way to test the charge pump output OK (attaching a resistor)?