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LM5122-Q1: LM5122-Q1 does not start properly when connected to load

Benjamin ZHANG
Prodigy 50 points
Part Number: LM5122-Q1
Other Parts Discussed in Thread: LM5122EVM-2PH

I used the LM5122-Q1 to make a 12V to 48V, maximum 1.5A output DC-DC, and now I have the following two problems:
1. During debugging, it is found that the board can start normally when it is not connected to the load, and then the load can work normally. However, when the board is started after the load is connected, it cannot be started normally, and the output will be limited to about 32 V. What is the reason for this?
2. Figure 1 shows the waveform of the LM5122EVM-2PH driven by high and low MOS transistors without load. Figure 2 shows the waveform of my board without load. Is this difference a problem? How can I improve it?
I look forward to your reply and wish you a happy life!

  • 0
    TI__Guru* 78430 points
    Hi Benjamin,

    Thanks. Like I replied to your other post, you need to completely disconnect the second phase by removing Q3 and Q4 and U2. Please refer to that post and wish you good luck.

    Please let us know if you still see problems.

    Best Regards,
    Youhao Xi, Applications Engineering