I am planning to use a simple overvoltage protection IC DS9801. Now, looking at the datasheet I see the typical application schematic attached and I just cannot give any explanation to the added resistor on the input side.

I would say that the capacitor is meant to be a bypass capacitor, but isn't ESR considered harmful in that case? Unfortunately the datasheet gives no hint on that.

Any ideas?

Thanks.

 

In this particular application it may be beneficial to limit the initial infush current. The application where ESR is critical is in the output filter for an SMPS converter. There you typically want a smaller value.

 

Could you provide a link to the datasheet?

 

Could you provide a link to the datasheet?

Here it is: https://datasheet.lcsc.com/lcsc/2305091657_DSTECH-DS9801AS6_C5795659.pdf

 

In this particular application it may be beneficial to limit the initial infush current. The application where ESR is critical is in the output filter for an SMPS converter. There you typically want a smaller value.

I am planning to put this right at the output of my own designed SMPS hence the need for OVP . This device has soft start function, could it be related to that somehow?.. I don't know.

 

Here it is: https://datasheet.lcsc.com/lcsc/2305091657_DSTECH-DS9801AS6_C5795659.pdf

Unfortunately, I don't read Chinese.

 

In this case, when in doubt go with the manufacturer's recommendation. Later, you can experiment with variations.

 

Sometimes an aluminium electrolytic with its higher ESR works better than a low ESR capacitor. It acts as a snubber, whereas a low-ESR capacitor reflects high frequency signals elsewhere in the circuit.

 

At one time it was very common to put a low value resistor in series with tantalum capacitors because they use to go short circuit without warning.

Datasheet in English: https://datasheet.lcsc.com/lcsc/2306301043_DSTECH-DS9801BS6_C5884224.pdf

 

Sometimes an aluminium electrolytic with its higher ESR works better than a low ESR capacitor. It acts as a snubber, whereas a low-ESR capacitor reflects high frequency signals elsewhere in the circuit.

My first thought was exactly like that, so just to use an electrolytic capacitor and that is it. But the device will sit just right on top of my SMPS output capacitors, so I do not think it would make sense anyway.

 

To my surprise I received a response from the manufacturer. They said the resistor is indeed against inrush currents (as Papabravo said) during hot-plug events. Most likely as a result of connection wire inductance, they experienced a spike of double the input voltage during their tests.

So it is quite a special situation. A high voltage (like 20V instead of 5V) and a hot-plug event is required with some cable. While I may have high voltage (when my SMPS fails), no cable and hot-plug in my case, so it looks safe to just ignore it.

Thank You all for your responses.