Sharing on the serious problem of LM2611 output voltage heating

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Sharing on the serious problem of LM2611 output voltage heating [Copy link]

question:

Use the LM2611 chip to convert 5V to -5V to power the op amp. Refer to the circuit design in the manual.

The actual designed circuit is shown in the figure:

During the chip testing process, the output voltage was only -2V. When testing the NFB pin, the voltage was less than -1V, and the chip heated up severely.

I would like to ask whether this is due to chip damage or circuit design problems. I replaced two chips and got the same test results.

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Answer 1: It is recommended to first confirm whether the selected power inductor saturation current is sufficient, especially L5.
If the power inductor saturation current is sufficient under the confirmed maximum output current, then confirm the layout, and pay attention to the power loop as small as possible. And the input capacitor as close to the input end of L5 as possible.

After replacing the inductor with a higher saturation current, the effect described in the manual still cannot be achieved. Is there a negative voltage conversion chip with similar parameters that can convert 5V voltage to -5V output?

Answer 2: I have used this chip before. It was 12V to -12V and I did not encounter any problems. First, I suggest you confirm whether the current output is within the normal chip specifications.

Replace the inductors of L5 and L6, try 22uF, and increase the value of C16;

In addition, add a 10uF capacitor and a 100nF small capacitor at the input end.

Answer 3: Buck chips can convert positive voltage to negative voltage. As long as the input voltage range exceeds 10V and the load capacity exceeds 0.6A, the buck chip can be used (please remember to leave some buffer,

Efficiency and other factors must also be considered. After negative pressure is created, the load capacity drops to 1-D times)

What tube does the D12 use?

Can you please upload the input waveform? SW waveform?

Found the reason. Cin and Cout were replaced by 22uF polar capacitors. The polarity capacitor at the -5V end was connected in reverse. After changing the circuit, it was correct.

kuo751676292

May I ask the OP, I also want to use this chip recently, but some of its data sheets are not clear, such as what is the calculation formula for the output voltage and what is the voltage drop, none of them are written clearly, do you know?

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kuo751676292 posted on 2021-9-26 12:11 May I ask the OP, I also want to use this chip recently, but some of its data sheets do not indicate, such as what is the calculation formula for the output voltage, the voltage drop...

The manual does not specifically calculate the partial pressure.

Instructions in the manual

3. The description says that the input voltage range is 2.7V to 14V and the output voltage range is -(36-VinMAX)

The following figures show that the voltage divider should be adjusted according to RFB2.