Hello,
in the actual development of a new control system we use three switching regulators LMZ12002 for generating the internal voltages of 3.3 V / 1.5 V / 1.2 V. All 3 switching regulators are fed by a central DC/DC converter with 15 V.
The typical loads are as follows:
- 3.3 V: 1000 mA
- 1.5 V: 600 mA
- 1.2 V: 400 mA
The schematic with the 3 switching regulators is available, all capacitors are ceramic. The 15 V from the DC/DC converter is also buffered via an electrolytic capacitor. The soldering was done by reflow with maximum 240 ° C.
The switching regulators behave very well, less ripple, etc. but we have now 3 losses by a total of 30 switching regulators:
- 1 x switching regulator without function after reflow soldering
- 1 x switching regulator switches its input supply voltage on the output (short-circuit)
- 1 x switching regulator properly worked about 5 days and fall out spontaneous
Our question is, what can be the reason for the failures?
- Are there any irregularities/faults of this LMZ12002 or the LMZ1200x family known?
- Can you see anything is wrong or bad in the schematic that could damage the switching regulator? (The schematic was attachted with the SR# 1-875797236)
- Is it permitted that the input voltage falls below the output voltage (Uoutput > Uinput) by power down? (Is there an external diode of the output to the input necessary?)
- Is the multiple reflow soldering of the LMZ12002 permitted?
We must find and solve these effects promptly; otherwise the LMZ12002 can’t be used in the series. We therefore appreciate your promptly feedback and are available for questions.
Best regards
