Silicon Labs CP210x: In the self-powered reference circuit, the VBUS pin input voltage is divided, but why is a voltage dividing resistor necessary?

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Silicon Labs CP210x: In the self-powered reference circuit, the input voltage on the VBUS pin is divided down. Why do we need a voltage divider resistor?

CP21xx

In the self-powered reference circuit for some devices such as the CP2104 and CP2109, the input voltage to the VBUS pin is set to 3.3V by a voltage divider resistor.

Article header self powered%e6%99%82%e3%81%ae%e6%8e%a8%e5%a5%a8%e5%9b%9e%e8%b7%af%e3%81%a7%e3%80 %81vbus%e3%83%94%e3%83%b3%e3%81%ae%e5%85%a5%e5%8a%9b%e9%9b%bb%e5%9c%a7%e3%81%8c %e5%88%86%e5%9c%a7%e3%81%95%e3%82%8c%e3%81%a6%e3%81%84%e3%81%be%e3%81%99%e3 %81%8c%e3%80%81%e3%81%aa%e3%81%9c%e5%88%86%e5%9c%a7%e6%8a%b5%e6%8a%97%e3%81 %8c%e5%bf%85%e8%a6%81%e3%81%a7%e3%81%99%e3%81%8b%ef%bc%9f 1

For example, for the CP2104, the absolute maximum rating of the VBUS pin is

5.8V when VIO > 2.2V
VIO+3.6V when VIO < 2.2V

stipulated in
This means that when VIO is 0V, the absolute maximum rating of the VBUS pin is 3.6V.

When Self-Powered, it is assumed that the CP2104 is not powered but the USB signal is coming. Since the VBUS signal is 5V, if it is supplied to the CP2104 as it is, it will exceed the absolute maximum rating of 3.6V.

Of course, even if it is self-powered, depending on the circuit or system design, it may be possible to use it within the absolute maximum ratings without using the above voltage dividing resistors.・Please judge unnecessary.

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