Can RCout pin of ADUM5000 connect to some small capacitor?
thank you very much~
The RC out pin should not be connected to the capacitors as you have shown in your circuit, as this may load the RCout pin. The RC out pin is meant to drive an RC in pin of a slave device such as another ADuM5000, which should be a high impedance input, in order to regulate the Viso of that device. If not used, the RC out should be left open.
Why did you want to add these two 22nF capacitors to RCout?
I found the similar question and answer as follow.
I add a question.
Regarding this answer, I assume as follow.
Is this right?
RCout is “Regulation Control Output of VIOS” pin.
The voltage curve of RCout is changed if the capacitor is connected to RCout pin of ADUM5000W.
And the voltage of VISO is unstable (For example increase ripple etc.)
So, RCout pin should be opened.
I explain about the reason for adding a capacitors to RCOUT instead of EVAN.
The reason for adding a capacitors to RCOUT is to improve the conduction emission noise for low frequencies range.
The customers need to improve noise for low frequency at conducted emission test to D-FIX ADuM5000.
Conduction emission test was failed mainly at about 550 kHz.
They assume that this frequency is similar to the frequency of PWM control in ADuM5000.
I understand that adding capacitors at RCOUT is not recommended for you.
My thinking for general theory is as follow.
Is my thinking right?
In general, it is theory to add a capacitor to improve the off surge of FET at the feedback loop of the fly back controller.
Or could you give me a idea if there is a way to improve noise at low frequency range?
In addition, they passed radiated emission noise test with AN-0971.
I assume that this method written in AN-0971 is for high frequency (about 180, 360 MHz).
Noza: I have asked the designer your question and will give you the response when I receive it.
This case is a little emergency.
As Nozawa san said, our customer failed in CE test and they want to solve this issue this week.
Customer has tried to connect RCOUT with 1nF or 3.3nF capacitor to GND, and it is helpful.
Do you think 1nF or 3.3nF capacitor still not be recommended?
Please reply me ASAP.
Thank you for your support!
Evan & Noza: In the past I have asked this question to the designer and this is the respone:
The PWM signal on RCout pin is used to turn on/off the LC oscillator (Turing on LC oscillator is generating the power), that is why you see adding in the capacitance or resistance can improve the EMI performance (slope control: slow down the turn on/off LC oscillator). But this will degrade the efficiency.
We didn’t do this kind of experiment previously, so we can’t recommend an exact resistor/capacitor value for customers. But I think as long as the dc/dc converter can work and the customer can accept the degraded efficiency, the customer can add the value relatively arbitrarily.
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