In this technical deep dive, we examine the CH340 USB-to-serial converter and a curious V3 pin configuration used. While the CH340 datasheet specifies tying V3 to VCC in 3.3V mode, some implementations connect it only to a capacitor—seemingly a violation. Through bench tests, we found the internal LDO enters dropout mode at 3.3V, allowing V3 to stay near VCC as long as no external current is drawn. This explains why these implementations CH340 design remains reliable. We validate these designs and confirm its safe use in our own CH340C-based products, including our latest USB-UART Bridge.
This is a companion discussion topic for the original entry at https://community.robotshop.com/tutorials/show/non-compliant-use-of-ch340-v3-pin-deep-dive-for-engineers