Charging Handshake: How PD and QC “Talk” to Your Phone
Introduction: The Silent Conversation You Never Knew Existed Every time you plug your smartphone, tablet, or laptop into a charger, a complex digital negotiation takes place in milliseconds. This is called the “handshake.” Without this handshake, your expensive 100W GaN charger is nothing more than a glorified 5W brick. The handshake determines how much voltage and current your device receives, dictating whether you wait 30 minutes for a full charge or three hours. In the world of fast charging, there are two dominant “languages” for this handshake: USB Power Delivery (PD) and Qualcomm Quick Charge (QC) . While both achieve the same goal—faster charging—their handshake processes are entirely different. One uses physical voltage pulses on data wires; the other uses sophisticated digital data packets on a dedicated pin. This article dissects the anatomy of both handshakes, explains why they fail, and reveals how the new PPS standard is rewriting the rules of communication. What Exactly is a Charging “Handshake”? In electrical engineering terms, a handshake is the initial negotiation protocol between a power source (charger) and a power sink (device). Its primary purposes are: If the handshake succeeds, the charger ramps up from the default 5 Volts to 9V, 12V, 15V, or even 20V. If it fails, the charger remains locked at 5V—the universal “safe mode” used for basic USB charging. Part 1: The QC (Quick Charge) Handshake – “Morse Code” Over Data Lines Qualcomm Quick Charge is the older, more established standard. It was born during the Micro-USB era, long before USB-C existed. Because Micro-USB had no dedicated pins for power negotiation, Qualcomm
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