If the recent 5G smartphones have larger screens, larger lithium-ion battery capacity, and "fast charging" (fast charging), which is predicting the future development of mobile phones, then the USB type-c PD 3.0 specification, especially the Programmable Design Power Supply (PPS), will become the preferred choice for USB power supply.

Since its inception in 1996, USB has held an unprecedented leadership position in the standardization of data transmission, charging, and power supply for mobile products. The greatest progress in USB technology occurred from 2013 to 2016, when the USB committee unanimously approved:

1: USB 3.1 Super Speed+Gen 1 (5Gbps) and Gen 2 (10Gbps) data communication

2: Power Delivery 2.0 or PD, up to 100W or 20V/5A

3: Type-C connector (version 1.2)

Figure 1: The evolution of the USB type-c connector has 24 contact points (12 contact points in each row), designed to handle currents up to 100W, 20V/5A, and provides a very compact exterior size (only 2.4mm high) that can be inserted in both forward and backward directions for plug insertion and accessory direction detection, bringing hope for abandoning the tangled "rat nest" style traditional cable that we all dislike.

100W... really

The transition from 7.5W charging (USB3.0) to 100W charging (USB3.1) is a significant breakthrough. Perhaps someone may ask, who really needs 100W when most mobile devices use 15W-45W chargers to function properly? However, if past events can indicate future trends, future innovation will consume 100W faster than we imagine.

Charging and power supply are very similar to supply and demand economics. This is a symbiotic relationship. If demand does not increase, supply will not increase, but if supply does not increase, demand cannot be met. Raising the USB power supply from 7.5W to 100W will only allow more devices to charge through the USB.

The USB-C PD power contract protocol identifies the USB charging port through non data messages on the D+and D-terminals before using the USB 3.1 and type-c connectors. Although this method still works well at power levels up to 7.5W, a more precise and powerful method is still needed to securely transmit up to 100 W (20V/5A) of power between the USB source and the USB sink.

USb3.1, PD 2.0 and Type C connectors jointly import two-way and Single Wire Protocol through the CC line between source and sink, across the CC line between source and sink (Figure 2), and have a comprehensive message transmission function. One purpose of this PD message transmission is to negotiate electricity contracts. The agreement for an electricity contract is much like ordering food from a restaurant on a menu. After using an implicit contract (up to 15W) to connect source and sink, if both ports have PD functionality, an explicit contract or PD power contract (up to 100W) must be established.

Figure 2: All compliant>3A type-c cables in the USB-C/PD power contract must include electronically labeled cables or emarkers. Therefore, if an emarker is detected in the cable, the first thing a signal source with>3A capability may need to do is send a "Discover Identity" or SVID message to the emarker. Sources and Sinks will respond to the SOP (Start of Packet) when they start receiving messages. In order to avoid conflicts, the emarker responds to the SOP at the beginning of receiving the message.

Once Sources learns whether the cable supports>3A capability, it will advertise its V/I function, just like ordering a menu in a restaurant. Then, sink requests one of the advertising functions, similar to restaurant guests. If the request is acceptable, Sources will provide the contracted electricity. Every time a message is sent, the recipient will send a "Good CRC" message to the sender, notifying them that the message has been received without error.

USB-C PD 2.0 vs. PD 3.0PD 2.0 allows up to 7 power data objects (PDOs), which are used to reveal the power capacity of the source port or the power demand of the sink, and are transmitted in the PD message through USB Type C and CC pins. In contrast, PD 3.0 and PPS provide the "voltage and current range" PDO shown in Figure 3. The advantage of PPS is that compared to fixed PDO, sink can request voltage/current at a finer granularity. This helps optimize the charging efficiency between source and sink.

Figure 3: PD 2.0 vs. 3.0 Comparison of 5G smartphone battery size. The recently released 5G smartphone is equipped with a 6.9 inch large screen and a 5000mAh lithium-ion battery, which increases capacity by 25% compared to previous models. The screen size and 5G both play a certain role in increasing the battery size. A 25% increase in battery size means that the AC-DC travel adapter (TA) needs to provide more power in order to continue promoting the 'fast charging' capability. And USB-C PPS is the first choice to achieve this function.

Quickly charge, lithium-ion charging is safely completed at a charging rate of 0.7 (C-rate is simply the charging current divided by the battery capacity). For example, a charging current of 0.7 C-rate is 700mA for a 1000mAh battery. However, it usually takes about 45 minutes (Figure 4) to charge an empty battery from 0% to 50% state of charge (SoC). This is not so fast, and you cannot simply improve TTC by increasing the current. When a battery's data sheet indicates a charging rate of 0.7 C-rate, charging at 1C-rate can lead to premature battery aging or potentially permanent damage. According to its data sheet, lithium-ion batteries must retain at least 80% of their original capacity after at least 500 charging cycles.

Faster TTC means more battery capacity. In order to improve TTC, battery manufacturers are designing rechargeable batteries with a rate greater than 1 C-rate or faster charging. This is mainly to reduce the internal impedance of the battery, in order to extend the time that the charging curve remains in constant current (CC) mode before the battery voltage reaches its maximum voltage and the charging curve transitions to constant voltage (CV) mode (assuming you start charging from an empty battery). As shown in Figure 5, for 0-50% SoC TTC, charging at 1 C-rate can shorten 15 minutes compared to 0.7 C-rate, and charging at 1.5 C-rate can even be faster, up to 22 minutes. However, the 1.5 C-rate of a 5000 mAh battery requires 7.5A charging and 32.6W (4.35V x 7.5A) peak charging power, which is a lot of power in a small space.

Figure 4: Charging Rate and Time Although the actual charging situation inside the recently released 5G smartphone is not known, it is indeed equipped with a 25W PPS charger and accepts 45W PPS charger accessories. If you want to use a 45W travel adapter and assume that the energy efficiency from the wall to the battery is around 80%, approximately 36W of electricity will enter the battery. This is not significantly different from the calculated charging time of 22 minutes and 0% to 50% SoC required for 32.6W, as shown in Figure 5.

It is worth mentioning that due to the maximum current of the USB-C connector being 5A, in order to achieve 7.5A IBAT, a "2-frequency" charging pump is required between the type-c connector inside the 5G phone and the battery charger (Figure 5). For example, TA may output 10V/4A, while the charge pump will output 5V/8A (assuming ideal power loss). Sometimes referred to as high voltage, low current (HVLC). As physics tells us, power dissipation is I2R, so transferring power from TA to mobile phones (~1m cable), HVLC has a more "energy efficiency advantage" than low-voltage high current (LVHC). With the advent of type-c connectors, the USB-C PD increased the maximum voltage of VBUS from 5V to 20V, promoting the HVLC approach.

Figure 5: 5G Smartphone Probe Laptop PD 2.0 Traffic You may not be able to measure the actual IBAT current between the 5G smartphone's internal battery charger and battery, but you can use the Total Phase PD detector (sniffer) to measure the VBUS voltage and current (IBUS) between TA and 5G smartphones. But before performing this operation, you can spy on VBUS/IBUS PD 2.0 between the laptop and FUSB3307 60 W Evaluation Board (EVB) Source, as shown in Figure 6.

In this display, a 5A cable is used between the laptop PD 2.0 sink and the FUSB3307 EVB PD 3.0 Source. The Total Phase detector is inserted in series with FUSB3307 EVB and 5A cables. After connection, FUSB3307 EVB announces its source capability in the form of four fixed PDOs and three PPS (enhanced) PDOs. The laptop requests a fixed PDO of 20V/3 A, but only a maximum of 1.5A is required. FUSB3307 accepts the request from the laptop and completes the power contract. In Figure 7, you can see that VBUS (red) increases from 5V to 20V, and as the laptop starts (starting from an empty battery), the dynamic IBUS current (blue) increases to~1.3A or~30W.

From Figure 8 and Figure 9, it can be seen that switching from a laptop to a 5G smartphone and source to a 100 W FUSB3307 PD 3.0 PPS EVB is the first step in exploring the 5G smartphone PD 3.0 PPS traffic. The 5G smartphone initially requested and obtained a 5V fixed PDO, but about 7 seconds later, the 5G smartphone requested and obtained a PPS (3V to 21V/5A) PDO. The 5G smartphone immediately enters an "algorithm" that increments its requested voltage (red) from 8V to 9.28V every 210 milliseconds, in steps of 40mV, while increasing the current (blue) from 2A to 4A in approximately 7 seconds. Throughout the entire charging process, the 5G smartphone continuously communicates with the FUSB3307 source.

PPS current limit (CL) alarm safety is an important aspect of power supply (PD). In Figure 10, when the 5G phone increases the requested power supply voltage (red) from 8V to 9.28V, the maximum working current requested is 4A. The FUSB3307 100W source sends an "Alert" message to the phone informing it that the 4A "current limit" (CL) has been reached.

Figure 10: Comparison of PPS Current Limit Alarm (CL) 5G Mobile Phone PD 3.0 and Pen PD 2.0 Traffic The PD 2.0 traffic displayed by laptops, although effective, is relatively simple. In the first second of connection, a 20V/1.5A power contract was negotiated and awarded, and no further PD flow was observed. 5G smartphones with PPS perform completely differently. The 5G smartphone is the master controller of precision algorithms, which continuously communicates with the FUSB3307 source to instruct it to change the voltage output. In fact, PPS includes a regulation that there is a maximum 15 second 'stay active' time between source and sink information transmission. Therefore, during the operation of PPS, the source and sink maintain stable digital communication at the CC contact point.

The 5G smartphone/FUSB3307 observed a peak power of 37.68W (9.6V/3.925A) approximately 60 seconds after connection. This is not much different from the estimated power required to charge the battery with a 1.5 C-rate, or the power required to charge the battery is 32.6W to achieve a fast TTC (0% to 50% SoC) of about 22 minutes.

The efficient and fast charging of "A, B, C" and PPS5G, as well as larger screens, are driving the increase in smart phone batteries. In addition, customers' expectations for "fast charging" have led to higher power requirements for travel adapters, reaching 45W. However, the increase in power dissipation will be tracked in the form of heat. Therefore, energy efficiency has become increasingly crucial, which is the role of PPS.

If we review the general "Wall to Battery" lithium-ion charging block diagram in Figure 11, the goal is to power the system through PMIC and charge the 1S battery from empty charge (~3V) to full charge (4.35V) through power path FET. Regardless of the technology used (switch, linear, or bypass), if the input voltage (B) of the battery charger is slightly higher than its output voltage (C) or VBAT, the battery charger will always operate with higher energy efficiency. Moreover, VBAT has always been a target of change for two reasons:

1) The battery voltage will rise during the charging curve from empty to full charge;

2) The battery voltage rises and falls with the variation of asynchronous load.

In order to optimize energy efficiency, the voltage output (A) of the travel adapter (TA) needs to be strictly controlled by Sink's MCU, which now becomes the "charging algorithm master". Between reading VBAT through an electricity meter and detecting charge pump VOUT, the MCU Policy Manager can strictly control TA VOUT with PD protocol messages at a particle size of 20mV (PPS) through CC pins.

After adding PPS, mobile devices can now charge larger batteries faster, safer, and more efficiently. For example, Onsemi Semiconductor's FUSB3307 Evaluation Board (EVB) supports the precise PPS charging algorithm for 5G smart phones.

Figure 11: The evaluation board FUSB3307 EVB with DC input for efficient and fast charging A, B, and C accepts 4.5V to 32V DC input and provides 5V to 20V USB PD output, complying with PD 2.0 and PD 3.0 specifications, including programmable design power supply (PPS). FUSB3307 is a state machine based PD controller and a type c port controller. Therefore, there is no need for MCU or firmware development. The absence of firmware also means Tamper resistance, which is beneficial in medical applications. Simply weld it in and it can run autonomously. The FUSB3307 state machine includes the PD Policy Manager, and uses the FUSB3307 CATH output pin to drive the Comp input to control the NCV81599 step-down and step-up of Onsemi Semiconductor. FUSB3307 also independently controls VBUS FET.

Figure 12: FUSB3307 EVB with DC input FUSB3307 EVB with AC input Additionally, FUSB3307 can be used as a PD 3.0 source with AC input. FUSB3307 is a USB-C PD 3.0 port controller based on a state machine, which adjusts VBUS (5 V to 20 V) by controlling NCP1568 FB input with CATH output through FODM8801BV optocoupler. Similarly, FUSB3307 autonomously controls VBUS FET.

summary

PPS has everything: power, safety, and high energy efficiency. The ultra fine V/I granularity of USB C interface/PD 3.0, up to 100W (20V/5A) PPS, can achieve higher energy efficiency, and is used for fast charging of 5G smartphones (0 to 50% SoC for about 22 minutes). PPS also supports the "Wall to Battery" control loop architecture, in which the USB-C/PD sink uses the bidirectional Single Wire Protocol on the CC contact of the Type C connector and the smart slave travel adapter to become the master controller of the precise and safe charging algorithm. PPS source operates in constant voltage (CV) mode (default) or current limiting (CL) mode, and notifies sink through alarm information when changing mode. The fact that 5G smartphones use PPS clearly indicates that PPS is the preferred choice and will continue to exist.