TI中文支持网Part Number:LM27402
Hello TI team
I encountered several problems during the testing process. The first is that the chip will have abnormal waveforms when operating at 300kHz, and the gate oscillation is obvious. The second is that the maximum load current 20A cannot be reached. The last one is the intermittent rest of the chip when it is unloaded.
Hope you can give some good solutions, thank you very much.
Guojia Mu：
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Johnsin Tao：
Hi
从你描述看很可能是layout不好，特别是带载能力下降，要特别注意功率回路尽量小，以及电流保护走线。
layout建议严格参考datasheet第36~40页描述来做。
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Guojia Mu：
I have done according to the datasheet, but there will still be concussion problems, what other possible reasons
I really need your help,thanks
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Johnsin Tao：
HI
将电路放上来看看？ 或者你借助芯片官网在线仿真webench确认一下电路。
一般不建议芯片和MOS电感等分别放在板子正反两面，从你描述看仍重点确认layout。
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Guojia Mu：
Hello, this is a designed circuit, drawn according to the datasheet. The PCB is also designed according to the datasheet, with the MOS inductor on top and the chip on the back.
Besides LAYOUT, are there any other possible causes for these phenomena？
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Johnsin Tao：
HI
完全参照datasheet的电路，说明不是电路问题，剩下的主要就是确认功率电感没有质量问题，饱和电流足够。如果这些都没有问题，剩下就只有layout。
从你上面的波形看，驱动出现大小波吗？ 而且空载出现异常，具体异常能说详细说下。
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Guojia Mu：
At 300kHz, large and small waves appear, and the other frequencies are only the gate oscillation is more obvious. The anomaly in no-load is that the waveform has a radian after power-on, and then the waveform disappears for a period of time, but during this period the output is still normal, as if the chip is working intermittently. In addition, even 0.1A load current will lead to abnormal output and waveform disorder.
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Johnsin Tao：
HI
建议重新layout一版看看。
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Guojia Mu：
Then how do I need to improve the Layout? This version is already drawn according to the datasheet. In addition, I would like to ask whether it is possible to cut off the DCR detection loop. I suspect that DCR has caused concussion feedback on the gate. Can the CS- and CS+ ports of the chip be suspended?
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Johnsin Tao：
HI
上面top layer和你的板子差异还是很大的，建议严格参照。
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Guojia Mu：
So whether it is possible to cut off the DCR detection loop. I suspect that DCR has caused concussion feedback on the gate. Can the CS- and CS+ ports of the chip be suspended?
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Johnsin Tao：
Hi 通过排除法，电路没有问题，所以偏向layout问题。
反馈可以根据datasheet里面的算法再确认下。
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Guojia Mu：
Ok, thank you for your help. I'll try my best.
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Johnsin Tao：
Hi
好的。
