Tool/software:
Hi,
We are currently using your product, "LM5155DSSR," in our circuit design and have observed the following phenomena. We would appreciate it if you could provide guidance on the possible causes and solutions.
Observations
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Abnormal oscillations related to the noise filter (R51, C39) in the current detection line
- When C39 is 100pF or less, the circuit operates normally. However, when C39 is 220pF or more, abnormal oscillations occur.
- The datasheet calculation suggests that C39 should operate properly if it is less than 778pF. Could you help us understand the discrepancy between the calculated range and the observed behavior?
-
Abnormal oscillations are more likely at lower input voltages (around 5.3V or below)
- This behavior becomes more prominent under conditions of high load current (e.g., 3A).
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Behavior during abnormal oscillations
- The FET does not turn OFF during abnormal oscillations. Instead, it appears that the duty cycle limit is triggered, eventually leading to overcurrent protection activation and circuit shutdown.
Questions
- Could you please provide insight into the possible causes of the abnormal oscillations mentioned above?
- Are there specific considerations we should be aware of when designing the noise filter for the current detection line or configuring the control loop?
Below is the waveform information.
We would greatly appreciate your assistance in resolving this issue.
Thanks,
Conor
