I have a problem on approx 75% of my first batch of prototype PCBs where the CC3200 is holding the reset low (20 prototypes).
The circuit is very close to the "launch pad" with very good grounding and the same (recommended) components as the application notes, except the following:
A) Lower cost 32KHz Crystal (still meets the spec 150ppm, and <50KESR (I have tried a few different crystals).
B) Circuit runs of a regulated 2.5V power supply (>1.5A), so I can also tie VDD_ANA2 (pin 47) to 2.5V - Not using pin 45, and 46.
C) uses the lower cost Walsum RFANT5220110A2T antenna (see application notes).
The PCBs works fine on the good PCBs, (WiFi range better than the Simple Link - using the Walsim antenna). In fact initially more than 50% of the PCBs worked like this, however the problem is intermittent and now only 25% work.
Symptoms observed so far:
1) Reset pin is held low by the processor (normally it is released and then the 32KHz starts).
2) 32Kz is not running, however some of the 75% faulty PCBs do release the reset, but the 32KHz does not start (may be a different problem, as I understand that the chip must release reset first).
3) I do see the CC3200 releasing reset occasionally (randomly), however as it rises (to approx 500mV) it immediately pulls the reset back down again. This is intermittent and sometimes does not release it for more than a few seconds. The chip does not release the reset long enough to see the 32Khz start to oscillate.
4) The CC3200 dc-dc converters/regulators are running OK - providing expected DC voltages.
5) It does not matter if the SOP0 pin is high or low.
6) The 2.5V VIN is rock solid.
Some thoughts:
I was surprised to see that the CC3200 can even drive the Reset Pin low, as I thought it was an input. There is no mention on why the CC3200 may pull the reset pin low in the data sheet??? Can anyone explain under what conditions it will release the reset pin?????
Some of these PCBs worked well initially, but now do not (I was replacing the RF filter to the specified one, and around that time I found this strange reset behavior). Not I was not observing this anomaly while working on the RF Filter replacement with a hot rework station (I was chasing RF issues), - Did I damage the ICs? But the original 5% that have never worked have not had any re-work.
They are soldered well, observation under the microscope. The Circuit is 4 later with a ground plane, very similar to the launch pad. it is very small in size.
I have some new CC3200 on order, and can hopefully successfully replace them.
I am scared to go into volume production, because of this issue, until I determine what it is... But I am stumped what to logically check for next.
Any Ideas????
