DC-DC boost to 5V abnormal

yaoquan5201314

DC-DC boost to 5V abnormal [Copy link]

 

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My boost circuit diagram is as follows:

My BAT input is three AA batteries, and the DC-DC boost chip used is PT1311. The following figure is a partial introduction to PT1311:

My boost output is 5V. Now the problem is that if I input three AA batteries and the voltage is less than 4V, U4 outputs 5V normally, and the output voltage signal of the driven resistive sensor signal modulation circuit is also normal and stable without fluctuation.

If the three AA dry batteries are new and the voltage is greater than 4.5V, it is normal for U4 to output 5V. However, the output voltage signal of the driven resistive sensor signal debugging circuit is abnormal and unstable, with a fluctuation of several mV.

This strange problem has never occurred in so many DC-DC boost circuits I have used before. I hope the big guys in the forum can help me analyze what is going on. Thank you!

yaoquan5201314

I think there must be something wrong with my power wiring, because another product uses the same boost circuit and it works fine. Then I connected the 5V output of that product to the board that has the abnormality, and the output was also normal.

yaoquan5201314

This is my 5V circuit diagram

maychang

"The output voltage signal of the driving resistor sensor signal debugging circuit is abnormal and unstable, with a few mV fluctuations."

What you mean by "the output voltage signal of the driven resistive sensor signal debugging circuit" is the VGG in the figure?

yaoquan5201314

maychang posted on 2022-5-25 11:45 "The output voltage signal of the driving resistance sensor signal debugging circuit is abnormal and unstable, with a few mV fluctuations. ' What do you mean by "driving electric...

No, it is the sensor signal modulation circuit driven by U4 output VCC5V.

yaoquan5201314

maychang posted on 2022-5-25 11:45 "The output voltage signal of the driving resistance sensor signal debugging circuit is abnormal and unstable, with a few mV fluctuations. ' What do you mean by "driving electric...

This circuit is my sensor output modulation circuit, J1J2 is my sensor resistance output, EXT_ADC is the modulated signal output, when J1J2 resistor is fixed, my EXT_ADC, output voltage should also be fixed, now BAT power supply voltage is below 4V, EXT_ADC output is stable in the figure, BAT voltage is above 4.5V, EXT_ADC has fluctuations and is unstable in the figure. VCC5V in these two cases is also measured, no problem, use an oscilloscope to capture the ripple, the ripple is also small.

maychang

yaoquan5201314 Published on 2022-5-25 13:28 This circuit is my sensor output modulation circuit, J1J2 is my sensor resistance output, EXT_ADC is the modulated signal output, when J1J2 is...

The lower end of C34 and the right end of R44 should be connected together, but there may be a "dot" missing.

yaoquan5201314

maychang posted on 2022-5-25 14:07 The lower end of C34 and the right end of R44 should be connected together, but there may be a "dot" missing.

Hmm, there is a point missing here in the schematic diagram. There is a flying wire connection on the board. If this point is not connected, the signal output will have no voltage, so the existing tests are all done by connecting this point with a flying wire.

yaoquan5201314

maychang posted on 2022-5-25 11:45 "The output voltage signal of the driving resistance sensor signal debugging circuit is abnormal and unstable, with a few mV fluctuations. ' What do you mean by "driving electric...

I short-circuited J1 and J2. When BAT was above 4.5V, the EXR_ADC voltage not only fluctuated by several MV, but was also about 30mv larger than normal. The whole machine current was 13ma less than when BAT was less than 4V.

maychang

yaoquan5201314 posted on 2022-5-25 15:20 I short-circuited J1J2. When BAT was above 4.5V, the EXR_ADC voltage not only fluctuated by several MV, but was also about 30mv larger than normal, and...

"I short-circuited J1 and J2. When BAT was above 4.5V, the EXR_ADC voltage not only fluctuated by several MV, but was also about 30mv higher than normal."

When J1 and J2 are short-circuited, the DC voltage at EXR_ADC increases, which is completely normal.

maychang

yaoquan5201314 posted on 2022-5-25 15:20 I short-circuited J1J2. When BAT was above 4.5V, the EXR_ADC voltage not only fluctuated by several MV, but was also about 30mv larger than normal, and...

As for the larger ripple at EXR_ADC when the battery voltage is higher, I can't figure out the reason for this.

yaoquan5201314

maychang posted on 2022-5-25 15:31 "I short-circuited J1J2, and when BAT was above 4.5V, the EXR_ADC voltage not only fluctuated by several MV, but was also about 30mv higher than normal." ...

I may not have written it clearly. What I meant is that when J1 and J2 are shorted, when the BAT power supply voltage is above 4.5V, the EXT_ADC voltage is 30mv higher than when the BAT power supply voltage is below 4V. In both cases, J1 and J2 are shorted, but the BAT power supply voltage is different.

yaoquan5201314

maychang posted on 2022-5-25 15:32 As for the larger ripple at EXR_ADC when the battery voltage is higher, I can't think of the reason for this.

OK, when the BAT power supply voltage is high, the EXT_ADC voltage not only has ripples, but is also too large. I have tried various methods but still cannot find the reason.

vincentc543

C10, C11 覺得應該用 uF 等級的電容, 用PF 等級應該不足以給後端供電做穩壓.

yaoquan5201314

vincentc543 发表于 2022-5-27 13:00 C10, C11 覺得應該用 uF 等級的電容, 用PF 等級應該不足以給後端供電做穩壓.

C10 is 475P-4.7uF, C11 is 104P=0.1uF.

yaoquan5201314

vincentc543 published on 2022-5-27 13:00 I think uF level capacitors should be used for C10 and C11. Using PF level capacitors should not be enough to stabilize the backend power supply.

C10=475P=4.7uF,C11=104P=0.1uF

vincentc543

yaoquan5201314 发表于 2022-5-27 13:33 C10=475P=4.7uF,C11=104P=0.1uF

應該至少是10uF, 22uF, 等級的吧

yaoquan5201314

vincentc543 发表于 2022-5-27 15:57 應該至少是10uF, 22uF, 等級的吧

These capacitor values are the reference values written in the manual, and 10uf, 22uf, and 47uf have all been tried, but they all fail.

vincentc543

yaoquan5201314 posted on 2022-5-27 16:07 These capacitor values are the reference capacitor values written in the manual, and 10uf, 22uf, and 47uf have all been tried, and they all fail.

但C10典型應用是1uF ~ 22uF.

我覺得你應該量一下VGG 的電壓狀況.

另外R5 有些設計會並聯一個 幾pF的電容來降低漣波問題. 可以試試

vincentc543

剛看了一下PT1311 spec,

PT1311 輸入建議0.85~4.2V ,

PT1311 輸出規格是3.3V 跟 5V, 但你 U4 又加上 5V的LDO,

你使用上好像超過他的輸入規格還有 輸出設計方式不對了