Maximize power density with buck-boost charging and USB Type-C PD technology

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Maximize power density with buck-boost charging and USB Type-C PD technology [Copy link]

Buck - boost chargers have become increasingly popular in recent years because they can charge a battery from nearly any input source, whether the input voltage is above or below the battery voltage.

One of the key advantages of USB Type-C ’s widespread adoption is that it is considered to be the ideal solution for achieving universal adapters and reducing the corresponding electronic waste . Although the USB Type-C interface is unified, the power ratings and voltages of different adapters still vary greatly, including traditional 5 V USB adapters and USB PD adapters that can provide a voltage range of 5 V to 20 V. In addition, the number of batteries in series may also vary from portable device to portable device. This requires the battery charger integrated circuit ( IC ) to adopt a buck - boost topology to adapt to these arbitrary changes in input voltage and battery voltage . Buck - boost charging chips with high power density can not only integrate universal charging function modules, but also other components in the USB PD charging system, such as load switches and DC/DC converters, to simplify system design, reduce bill of materials ( BOM ) costs, and maintain a small overall solution size. Figure 1 shows the system block diagram of the USB PD charging solution.

Figure 1 System block diagram of a USB PD charging solution.

To support the mobile USB OTG charging specification, when the adapter is not present, the battery is discharged through the DC/DC converter and a constant voltage is output on V _BUS to power external devices . If the USB Type-C port needs to support the fast role swap ( FRS ) function , the DC/DC converter must be turned on and always in standby mode, even if the adapter is plugged into the USB Type-C port. When the adapter is disconnected, the back-to-back MOSFETs in the discharge power path are quickly turned on to pass the U3 output voltage to V _BUS and keep the V _BUS voltage from dropping . In this process, keeping the DC/DC converter turned on all the time actually causes additional quiescent current loss to the entire system.

The fully integrated buck - boost charger chip shown in Figure 2 can simplify the system-level design of USB PD charging solutions. First, the input current detection circuit is integrated into the chip . With the input current detected by this circuit , the charger provides input current regulation and input current overcurrent protection to avoid adapter overload. Second, as part of the input overvoltage and overcurrent protection circuit, the control logic and drive circuit of the external back-to-back MOSFET are also integrated into the charger. These functions make it possible to eliminate the units that support input power path management and input current detection from the block diagram .

By implementing bidirectional operation of the buck - boost converter of four FETs , the charging chip itself can support OTG mode. When the adapter is plugged into the USB port , the charging chip operates in forward charging mode and power flows from V _BUS to the battery. When the adapter is disconnected, power flows from the battery to V _BUS . The OTG output voltage at V _{BUS covers the} full USB PD voltage range from 2.8 V to 22 V with a 10mV programmable step size, which is compatible with the USB PD 3.0 specification.

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Figure 2 Fully integrated buck - boost charging chip .

To support the FRS function of the USB Type-C port , this integrated buck - boost charger chip implements a new backup mode. In this article, the backup mode refers to the fast transition of the buck - boost charger chip from the forward charging mode to the reverse OTG mode to avoid the bus voltage drop . Looking at the application block diagram in Figure 3 , the adapter is connected to the USB port, powers the system, and charges the battery through the buck - boost power stage. At the same time, the adapter can power system accessories from the PMID output of the charger. If the buck - boost charger chip does not support the backup mode, when the adapter is removed , the battery can still power the system through the FET inside the chip . However, the accessory power supply on the PMID may be powered off.

After the charger chip enables the backup mode, it can monitor the V _BUS voltage. The V _BUS voltage falling below the preset threshold can be used as a signal that the adapter has been removed . Once the charger chip detects that the adapter has been removed, it will quickly switch from the forward charging mode to the reverse OTG mode, using the energy of the battery discharge to maintain the V _BUS voltage and implement FRS by itself . When the adapter is removed , the power supply of the system itself and system accessories can be seamlessly switched from the adapter to the battery, which can eliminate the DC/DC converter used for OTG mode and FRS from the block diagram .

Figure 4 shows the test waveform of the charger chip used as a standby mode to support FRS. A 9 V adapter is connected at USB1 as the input power source. When the adapter is plugged in, the charger chip turns on ACFET1-RBFET1 to connect the adapter to V _BUS . The test condition of this waveform is that there is a 1 A current at PMID to power system accessories and a 1 A charging current at BAT . When the 9 V adapter voltage ( V _AC ) is removed , the charger chip quickly switches from forward charging mode to reverse OTG mode, and can still maintain PMID and V _BUS at 5 V while continuously powering the 1 A PMID load.

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Figure 3 Implementing USB Type-C FRS with a single buck - boost charger .

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Figure 4 Buck - boost charger FRS from V _BUS sink to V _BUS source .

All the functions described above help simplify the system-level design of USB PD charging solutions, and TI has implemented them in the new buck - boost charging chips BQ25790 and BQ25792 . These charging chips support 1 to 4 series battery charging with an input voltage range from 3.6 V to 24 V , covering the entire USB PD voltage range .

These features are available in a 2.9 mm × 3.3 mm wafer-size package or a 4 mm × 4 mm quad flat leadless package. The entire charging solution is capable of delivering 45 W of power with a power density of approximately 100 W/in ² (150 mV/mm ² ) , twice that of similar products on the market .

宋元浩

Thanks for sharing

qwqwqw2088

USB PD charging is explained in detail

alan000345

qwqwqw2088 posted on 2020-7-7 17:41 USB PD charging is explained in great detail

Yeah, good information.

alan000345

Song Yuanhao posted on 2020-7-7 09:05 Thanks for sharing