Hello,
I recently designed a circuit which is powered by small 3.3V fixed voltage regulator (TPS70933DBVR) and draws only 9mA. 10 units have been built as part of engineering evaluation.
In front of TPS70933DBVR, I have a diode CRS09(TE85L,Q), followed by two shunt capacitors (100nF and 10nF) and TPS70933DBVR IC.
On its output, there are 3x100nF capacitors, 1x10nF and 1x470uF capacitor followed by two small ICs.
According to the datasheet, TPS70933DBVR should be able to withstand input voltages up to 30V.
I run into a problem when part of my design requirement called for input voltage test between 4V and 28V.
I first tested the circuit at 12V & 4V without any surprise. I then increased the input voltage to 28V and TPS70933DBVR failed almost immediately (dropped output current to approximately .4V and started sinking over 400mA on my current limited analog PS).
I replaced the defective IC and then tried again, the circuit failed again after a few seconds and a few brief connect/disconnect power cycles.
I powered second, third, and forth unit and experienced an identical problem; the circuit powers up fine at first but if you briefly power cycle the unit, it fails immediately (starts drawing large input current).
I then removed the large 470uF capacitor on the output hoping that would solve the problem (as there may have been large current flowing from TPS70933DBVR output to input). The problem is still present.
Last experiment I’d performed was I gradually increased voltage from 12V (1V at the time) and power cycled the circuit and everything worked fine until I reached 20V at which point TPS70933DBVR failed again.
Can you please explain what may be causing this issue?
Is this IC supposed to operate up to 18V?
Should I dump this voltage regulator and pick a different supplier?