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

Since its inception in 1996, USB has provided unprecedented leadership in the standardization of data communication, charging, and power supply for mobile products. The biggest leap in USB technology occurred from 2013 to 2016, when the USB committee collectively 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 (Revision 1.2)

Figure 1: Evolution of USB Type-C connector with 24 contacts (12 contacts in each row), designed to handle currents up to 100 W, 20V/5A, providing plug insertion and accessory direction detection in a very compact form factor (only 2.4mm high), and promising to give up the entanglement of traditional cables that we all love and hate.

100 W... really?

The transition from 7.5W charging (USB 3.0) to 100W charging (USB 3.1) is a significant leap. Some people may ask, who really needs 100W when most mobile devices can function properly with a 15 W to 45 W charger? However, if past events can indicate future trends, tomorrow's 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. On the contrary, if supply does not increase, demand will stagnate. Increasing the USB power supply from 7.5W to 100W only allows more devices to charge through USB.

USB-C PD Power Agreement

Before using the USB 3.1 and type-c connectors, the USB charging device identifies the USB charging port through non data signaling on the D+and D-terminals. Although this method can work normally up to 7.5W, a more precise and powerful method is needed to safely provide up to 100W (20V/5A) of power between the USB source and USB sink.

In general, USB 3.1, PD 2.0 and type-c connectors introduce a two-wire, Single Wire Protocol that spans the CC line between source and sink (Figure 2) and has a comprehensive messaging function. One purpose of this PD messaging is to negotiate power agreements. The power agreement is much like ordering restaurant food from a menu. After connecting source and sink based on an implicit protocol (up to 15 W), if both ports have PD functionality, an explicit protocol or PD power protocol (up to 100 W) must be established.

Figure 2: All compliant cables greater than 3A type-c in the usb-c/PD power protocol must contain electronically labeled cables or emarkers. Therefore, if an emarker in the cable is detected, the first thing a source device with a capacity greater than 3A may do is send a "Discover Identity" or SVID message to the emarker. Sources and Sinks will respond to an SOP (Start of Packet) when receiving a message. To avoid conflicts, the emaker responds to the SOP 'when receiving the message at the beginning.

Once Source learns whether the cable has a capacity greater than 3A, it will advertise its V/I function, just like a restaurant menu. Then, sink requests one of the power supply capability options announced by the source device, similar to restaurant customers. If the request is acceptable, Source will provide the agreed power. 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 3.0

PD 2.0 allows up to 7 power options (PDOs) to reveal the power capacity of the source port or the power demand of the sink, transmitted in PD messages 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 with more precise step values. This helps optimize the charging efficiency between source and sink.

Figure 3: PD 2.0 vs. 3.0

5G smartphone battery size

A recently released 5G smartphone is equipped with a 6.9 inch large screen and a 5000 mAh lithium-ion battery, which increases the battery capacity by 25% compared to previous models. Both screen size and 5G have an impact on the increase in 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" feature. USB c PPS is the preferred solution for achieving this function.

Fast charging

Traditionally, lithium-ion charging is safely completed at a charging rate of 0.7 (C-rate simply refers to the charging current divided by the battery capacity). For example, a charging current of 0.7C-rate is 700 mA for a 1000 mAh battery. However, in general, it takes approximately 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 increase the current to improve TTC., When a battery's data sheet states that its charging rate is 0.7 C-rate, charging at 1 C-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 uses.

Faster charging time (TTC) means more battery

In order to improve TTC, battery manufacturers are designing rechargeable batteries larger than 1 C-rate or faster charging solutions. This mainly requires reducing the internal impedance of the battery 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 a 0-50% SoC TTC, charging at 1 C-rate can shorten the time by 15 minutes compared to charging at 0.7 C-rate, while charging at 1.5 C rate can be faster, shortening it to 22 minutes. However, the 1.5 C-rate of a 5000 mAh battery requires 7.5 A charging and 32.6W (4.35 V x 7.5 A) peak charging power. This is a lot of electricity in a small space.

Figure 4: 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 "half voltage" charge 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). This is sometimes referred to as high voltage, low current (HVLC). As physics tells us, power dissipation is I2R, so transferring power from TA to a mobile phone (~1 meter 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: Half pressure charge pump inside a 5G smartphone

Analyzing the Traffic of Laptop PD 2.0

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

In this demonstration setup, a 5 A cable is used between the laptop PD 2.0 sink and FUSB3307 EVB PD 3.0 Source. The Total Phase analyzer is connected 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 20 V/3 A, but only a maximum of 1.5 A. FUSB3307 accepts the request from the laptop and the power agreement is completed. In Figure 7, you can see that VBUS (red) increases from 5 V to 20 V, and as the laptop starts (starting from an empty battery), the dynamic IBUS current (blue) increases to~1.3 A or~30 W.

Figure 6: Laptop Demonstration

Figure 7: According to the design shown in Figure 6, VBUS and IBUS for laptops

Analyze the traffic of 5G smartphone PD 3.0 PPS

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

Figure 8: 5G mobile phone demonstration settings

Figure 9: According to the design shown in Figure 8, VBUS IBUS for 5G mobile phones

PPS current limit (CL) alarm

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

Figure 10: PPS current limit alarm (CL)

Comparative analysis of 5G smartphone PD 3.0 and laptop PD 2.0 traffic

The PD 2.0 traffic displayed by laptops, although effective, is relatively simple. In the first second of connection, the 20V/1.5A power protocol was negotiated and granted, and no further PD flow was observed. The performance of 5G smartphones with PPS is completely different. The 5G smartphone is the master controller of precision algorithms, constantly communicating with the FUSB3307 source to instruct it to change its voltage output, thus cleverly increasing its load current. In fact, PPS includes a regulation that there is a maximum 15 second 'stay active' time between source and sink information transmission. Therefore, during PPS operation, the source and sink maintain constant digital communication at the CC contact.

The peak power observed on the 5G smartphone/FUSB3307 was 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 1.5 Crate, or the power required to charge the battery is 32.6W, in order to achieve a fast TTC (0% to 50% SoC) of about 22 minutes.

Efficient and fast charging details, as well as PPS

5G and larger screens are driving the increase in smartphone batteries, coupled with customers' expectations for "fast charging", resulting in higher power requirements for travel adapters, reaching 45W. However, the increase in power dissipation will follow this increase in power 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 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. More complex, VBAT is always a flowing target for two reasons:

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

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

To optimize energy efficiency, the output (A) voltage 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 the electricity meter and detecting charge pump VOUT, the MCU Policy Manager can provide strict control of TA VOUT with a control accuracy of 20 mV (PPS) using PD protocol messages through the CC pin.

After adding PPS, mobile devices can now charge larger batteries faster, safer, and more efficiently. The FUSB3307 evaluation board of Onsemi Semiconductor supports the precise PPS charging algorithm of 5G smart phones.

Figure 11: Detailed explanation of efficient and fast charging

 summarize

PPS combines power, safety, and efficiency. USB-C/PD 3.0 has extremely fine V/I stepping and a programmable power supply (PPS) of up to 100W (20V/5A), which can achieve higher energy efficiency and is used for fast charging of 5G smartphones (0 to 50% SoC for about 22 minutes). PPS also realizes the control loop architecture of "from wall to battery", in which USB-C/PD sink uses the bidirectional Single Wire Protocol on the CC contact of the type c connector and the intelligent 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 with alarm information when changing mode. The fact that 5G smartphones use PPS clearly indicates that PPS is the preferred choice and will continue to be used.