Other Parts Discussed in Thread: LM3102, LM25011, LM3100
Hi, I have an urgent issue about the LM25085:
Circuit Description: LM25085, as the first-stage Buck chip, is connected to the supercapacitor through the MOS driven by the LM74701 ideal diode controller to charge the supercapacitor.
Function Description: At the beginning, the supercapacitor is charged from 0V through the body diode of the MOS (Q4 in the schematic diagram), and the MOS (Q4) is turned off; later, when the output voltage of the LM25085 rises to the turn-on threshold of the MOS (about 3V), the MOS is turned on, and the charging path is switched from the body diode to the MOS.
Phenomenon Description: However, in the customer's application, it is found that when the path is switched from the body diode to the MOS, the circuit does not work normally, the circuit enters a similar hiccup mode (current-limiting mode), and the MOS drive waveform driven by the LM25085 is also abnormal. However, after a period of time, the system returns to the normal state, exits the hiccup mode (current limiting mode), and the supercapacitor voltage continues to rise. And during the hiccup mode, the switching state of LM25085's MOS seems abnormal. Even though the inductor current has been reduced to 0, LM25085 still does not return to the switching state, and restarts after about 100-200us.
The key waveforms are given below:
Channel 1: The output voltage (Capacitor Node) of LM25085; Channel 4: The waveform of the inductor current. It can be found that there is a period of abnormal state (like hiccup mode/ current limiting mode)
Channel 1: The output voltage (SW Node) of LM25085; Channel 4: The waveform of the inductor current. It can be found that even though the inductor current has been reduced to 0, LM25085 still does not return to the switching state, and restarts after about 100-200us.
Thus, my questions can be concluded that:
1.Why there is an abnormal transition period of the LM25085 when the path is switched from the body diode to the MOS.
2.Why even though the inductor current has been reduced to 0, LM25085 still does not return to the switching state, and restarts after about 100-200us. (Which should be restarted immediately)
