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OPA4277-EP: Failure Modes

Elisha Tarroza71
Expert 3700 points
Part Number: OPA4277-EP
Other Parts Discussed in Thread: OPA4277,

We are having one design using OPA4277. In our application, we use +6V/-6V power supply to OPA4277, it's a simple DC inverter and level shifting circuit. Due to heavily capacitance (0.2uF) load applied at OP output (VVA_VP and VVA_VS see the schematic), it has instability issue (oscillation), and caused high current (up to 35mA). We realize it's a design error. Unfortunately we already made some units and shipped, and we need provide worst case and impact analysis.

Our thermal engineer is doing junction temperature analysis for different operation condition. We hope the device will work below the max junction temperature limiting.

Since we don’t have the OPA4277 internal schematic, we want to know, assume if the junction temperature exceed the max limit of +125ºC, what failure mode will be? Will it fail in shorting or open mode in +6V/-6V rail?

  • 0
    Guru 140200 points

    Hi Elisha,

    hhm, wouldn't it be a much better idea to replace the circuit with the design mistake by a proper one??

    Kai

  • 0
    TI__Guru* 93105 points

    Hello Elisha,

    The OPA4277-EP uses an all NPN output stage that will current limit as related in the datasheet Figure 17, "Output Voltage Swing vs Output Current" curves. Fortunately, the graph shows that with increased temperature the output current limits at lower current level than it does at room and cold temperatures. This may help keep the output from going into a thermal run away condition where the transistors become so hot that they melt and are destroyed.

    Should the output transistors become so hot that they melt, then the expected failure would be a short circuit rather than an open circuit. However, if a short does occur and high current is available the silicon or the aluminum metal that carries the high current may open. Therefore, we cannot say with certainty that the output would appear as a short, or an open. It comes down to the individual failure case.

    Regards, Thomas

    Precision Amplifiers Applications Engineering