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Power Management ICs Forum Discussions

Fantastic
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Hello, we would like to know whether the RST pin will send multiple reset signals when the power IC works at the voltage before the starting voltage, and how can we improve this phenomenon?

(Example: BAT=4V RST is not reset, BAT=3.9V RST is reset several times, BAT=3.8V RST is reset once)

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Kevin_Wu
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Hi there,

  according to your information, several times reset caused by  the undervoltage detection threshold are different, when the voltage increasing and decreasing.

Kevin_Wu_0-1661320771742.png

according to this table, for example, when voltage high than 4.8V,  there will be no reset; when voltage less than 4.7V, there are will a reset; when voltage between 4.7V to 4.8V, and voltage not stable to increasing or decreasing, most likely cause several times reset.

Thanks, Kevin

 

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Kevin_Wu
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Moderator First like received 5 solutions authored 10 replies posted
Moderator

Hi there,

  according to your information, several times reset caused by  the undervoltage detection threshold are different, when the voltage increasing and decreasing.

Kevin_Wu_0-1661320771742.png

according to this table, for example, when voltage high than 4.8V,  there will be no reset; when voltage less than 4.7V, there are will a reset; when voltage between 4.7V to 4.8V, and voltage not stable to increasing or decreasing, most likely cause several times reset.

Thanks, Kevin

 

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Fantastic
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Fantastic_0-1661321707624.png

您好,这个表里的参数是指 V5V引脚而不是BAT引脚,目前给BAT引脚电压为4.7V,测试到V5V引脚的电压为4.57V,此时RST引脚会出现反复复位情况。请问一下RST多次复位现象是否可以通过外部电路设计来进行优化?

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Kevin_Wu
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Moderator First like received 5 solutions authored 10 replies posted
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Hi there,

  Vbat 的电压决定了V5V的电压,所以问题还是出现在V5V的低电压复位。

可以考虑让Vbat不要在这个区间,如增加boost电路,或V5V要保持稳定,纹波电压要尽量的小,参考DS,用陶瓷电容取典型值。

Kevin_Wu_0-1661325047255.pngKevin_Wu_1-1661325103146.png

Thanks, Kevin

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Fantastic
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Fantastic_0-1661327901335.png

您好,首先谢谢您提供的解决方法,对于这个4.7-4.8V范围还是有些疑问,表格内给的是V5V的欠压阈值,VBAT电压此时为4.7-4.8V范围内会出现RST引脚多次复位情况,但是此时的V5V电压值是在4.5V附近,理论上来说不会出现多次复位情况。希望您可以帮忙解答这个疑惑,谢谢!

下图为VBAT在4.7V情况下V5V红色以及RST绿色的电压波形,可以看到V5V在RST拉高的情况下会有一个拉低的电压。

Fantastic_1-1661328442903.png

 

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Kevin_Wu
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Moderator First like received 5 solutions authored 10 replies posted
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Hi there,

  关于“对于这个4.7-4.8V范围还是有些疑问”问题,我只是给了你一个例子,其实V5V低电压复位是个范围,从4.45V到4.7或4.8V,而且都有磁滞问题。

Kevin_Wu_0-1661329101717.png

表中显示磁滞电压最小是10mv,典型是50mv。所以如果电压不稳定,而且处在临界复位电压附件就很容易出现多次复位。每个芯片的临界复位电压都有所不同,表中只是给了范围。

Thanks, Kevin

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Fantastic
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谢谢您,我明白了,多谢您的解惑 :)

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Fantastic
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您好,增加boost电路的话,有典型的电路推荐么

我们在V5V上增加20uF、40uF甚至是220uF,都不能在VBAT复位阈值时有效的控制V5V的电压稳定

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Kevin_Wu
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Moderator First like received 5 solutions authored 10 replies posted
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Hi,

  boost 电路没有典型的推荐,要求是保证电压高于复位电压;

  关于电容的问题:首先要使用陶瓷电容,即电容的ESR值满足DS中给定值;电解电容是不起作用的!其次要在Vbat,V5V,V6V,sensor供电处都需要加上相应的陶瓷电容。最后是电容的位置要尽量接近芯片的管脚并有良好的接地!请认真地阅读DS并和有经验的HW工程师一起处理。按照我们的建议是可以解决问题的。

 

thanks, Kevin

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