we have recently experienced a number of return of synthesizers build with ADF4153 and ADF4106.
These circuits use 2 supplies of +5V (VCO and PLL) supply and 15-20V (Vtune).
The PLL supply of 3.3V comes from the +5V through a low noise regulator. The VP is tied to +5V of VCO.
The charge-pump pin 20 is connected to the negative input of an OpAmp (used as integrator for the PLL filter).
The OpAmp supply is 15-20V to GND.
All these cases exhibit low impedance on the charge-pump pin (Pin 20).
I have removed (un-soldered) the ADF4153 from the PCB and I checked the impedance with a multimeter (set for diode/continuity measurement).
The following is the result of the measurement:
|Measurement||Returned ADF4153||Good ADF4153|
|CP (pin20) -> GND||28 Ohm||Open|
|GND -> CP (pin20)||28 Ohm||0.569V (ESD diode)|
|Vp (Pin18) -> GND||1.5V||Open|
|GND -> VP (Pin18)||0.57V||0.565V|
|Rset (pin 19)-> GND||2.01V||Open|
|GND-> RSET (pin 19)||0.585V||0.569V|
Please note that the 28Ohm impedance to ground was observed also when the ADF4153 was soldered on PCB. The good-working PCBs do not exhibit this short.
The answer to the following question will be appreciated:
Q1. In your opinion, what could cause such behavior?
Q2. Is it possible to investigate the failure on the damaged device?
Q3. What FIB houses could provide such investigation?
Q4. How much would cost the failure investigation ?