First let’s find out what is PPS.
PPS (Programmable Power Supply) programmable power supply, a type of Power Supply supported by USB PD3.0, is a power supply that can realize voltage and current regulation using USB PD protocol output. The PPS specification integrates current high-voltage low-current, low-voltage and high-current charging modes. In addition, the PPS specification reduces the voltage regulation range to 20mV, which is one-tenth of the QC3.0 standard, and the voltage regulation is more precise. There are two types of USB PD3.0:
USB PD3.0 does not have PPS (pure USB PD2.0 protocol upgrade, version number is REV 3.0);
USB PD3.0 with PPS.
Note that PPS is certified with USB PD3.0 and belongs to one branch of the company. USB-IF USB PD authentication is USB PD2.0, USB PD3.0, USB PD3.0 (PPS). It can be seen that not all USB PDs support PPS. However, USB PD3.0 is backward compatible with 2.0.
Some laptops released in the early days, PPS has not seen at that time, such as USB PD protocol chip ADC accuracy is not enough or the system does not have online upgrade capability, USB PD protocol chip will work according to the original design specifications.
This PPS charger is not compatible with some laptops, not just one case; the coming charger with PPS will continue to encounter compatibility problems when charging the laptops, and the probability will increase. This is a legacy of history, because PPS came out late; Apple and other brands publish other laptops early, USB-IF has not yet defined PPS by then.
The reason for the incompatibility is that some laptops are made up of protocol chips. When designing the laptops in the early days, the USB PD2.0 specification did not say how to be compatible with PPS. The space that this manufacturer can freely play is relatively large.
Analysis by Charger LAB UW001 shows that this type of Host has a feature that the host can not resolve the correct USB PD3.0, once the charger with PPS function will refuse to charge.
Furthermore, USB PD is negotiated charging. The protocol chip on the host side does not select Fixed PDO, which is the fixed voltage of 5, 9, 15, 20V. It is directly judged that PPS is a non-standard charger and uses a reset charger. Thereby rejecting the charge protection itself. For example, the notebook replacement protocol handshake detection process first selects the Fixed PDO and skips the PPS, so that the charging compatibility problem will be solved. In addition, the charger can turn off the PPS, which can also solve the charging compatibility problem. This requires upgrading the protocol chip firmware, and the white user cannot operate.
Famous laptop brands always sold laptops with their original USB PD charger; and the warranty card instructions usually recommend friendly certification of the original power adapter, the use of third-party problems is not responsible.
Speaking of this, the laptop is a valuable item, if the charger can not charge the laptops; people’s first reaction is there is a problem with the charger, instead of the laptop itself. In fact, the charger is not broken, but the USB PD handshake protocol of the laptop does not match the charger, resulting in the failure to charge.
Laptop manufacturers are giants. They warn consumers to use original accessories in the warranty card and manual to get the best performance, but consumers have demand for third-party accessories. How to do it? There are two solutions.
1. The third-party charger does not use USB PD3.0, and uses the protocol of pure USB PD2.0 to interact;
2. Add a system judgment strategy to the charger. When the charger finds such a phenomenon, after passive reset, the USB PD2.0 protocol is re-issued to support such devices.
In this way, PPS can continue to be used in the case of interconnecting QC4.0/PPS mobile phones.