Greetings all:
I'm experiencing some inexplicable behavior with the TPS73433 (DDC).
The regulator powers a (PIC18) microcontroller and a (Murata) ISM radio. I designed the circuit, and my partner (at another location) hand-solders the PCBs.
Everything's been working perfectly (for about a year) -- until now.
Recently he reported that on several of the PCBs, the regulator outputs are wrong, ranging from about 1.5V to input voltage (4.2V).
He tells me his solder temp is about 270C, and that he uses anti-static wrist strap religiously.
He gave me several of the failed units to look at.
With 4.2V input, all give different outputs; for example:
One starts at 2.1V and rises,
Another starts at 3.8V and falls.
Another starts at input and stays there.
Other than the one equal to input, none of the outputs are stable.
He bought a new batch of 100 regulators, and still gets incorrect results (with no other components mounted).
Capacitor used are:
Input
CAP CER 0.1UF 25V 20% X7R 0603
www.digikey.com/.../2093726
NR
CAP CER 10000PF 25V 20% X7R 0603
www.digikey.com/.../2093716
Output
CAP CER 2.2UF 10V 20% X7R 0603
www.digikey.com/.../2444000
Attached is a snapshot of the Gerber showing the pads and traces for the regulator and caps.
I've annotated the regulator and capacitor pads.
Many of these PCB have worked perfectly, now many don't (from same manufacturing batch).
Does anyone have any ideas for how to determine the cause of this unexpected failure?
Thanks,
-Mike
