Part Number: LM5119
I am using an LM5119 to produce a single output (i.e. interleaved operation), circuit attached. The input voltage spec is 24 - 65V, the output voltage is variable from ~5 to 12V, set by an external DAC feeding into the FB node via a 2.2k resistor. The circuit generally works well, has good output current capability, accurate output voltage across the full range, tolerates a short circuit, works across the full input voltage range.
The problem I am seeing is occasional catastrophic device failure. Flash of light from the LM5119 followed by small puff of smoke and the LM5119 is no more. No other device in the circuit seems to be damaged during the failure, although I did have a high-side FET die simultaneously on one occasion. I do not believe this has anything to do with the LM5119; it is entirely my fault but I'm not sure what is causing the failure because it happens unpredictably and also quite fast. I did provoke this failure on one occasion by making a DAC output have a step change from 4 to 0V. This should have caused the corresponding output voltage to go from 4 to 12V, but instead the IC blew.
I should add that this circuit is one of many largely identical circuits powered from a common HV bus. They have clocks that are synchronised but phase offset from each other to spread the current draw evenly across time. There is a total of 160uF of ceramic (X7R) capacitance on the HV bus. There is also a 60V TVS, doing pretty much nothing it would seem.
Do you have any thoughts on what might be causing my LM5119s to blow?Servo Switcher-Servo A Switcher.pdf
Do you know the Vin and Iout condition when the failure happened? Below is my thought.
1. LM5119 Vin rate is 65V. If your input voltage is up to 65V, the transient Vin voltage during switching may exceed 65V and damage the IC.
2. Another possibility is the high voltage spike on switching node. Can you check use oscilloscope probe to check SW voltage spike?
3. LM5119 internal LDO is used to supply gate drive circuit. When VIN is high, the power loss on IC could be large. Can you check if the IC temperature is very high at high Vin condition?
4. If the failiure happens during Vout transition, can you slow down the transition slew rate and see if the failiure is related to Vout slew rate?
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