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Designing interoperable battery chargers

July 02, 2019

anshulgulati-July 02, 2019

Enter USB Type-C and USB Power Delivery

To overcome the challenge of incompatible charging standards, most manufacturers are now adopting the USB Type-C connector that supports the new USB Power Delivery standard, aiming to unify the charger world to a single standard. This is a reversible connector which can be plugged in either orientation (facing up or facing down). This connector resolves the most annoying orientation issue with the USB Type-A and USB Type-B connectors. It is a small connector with dimensions of only 8.4 mm (0.33 in) by 2.6 mm (0.10 in), allowing it to be nicely fitted in ultra-thin notebooks, tablets and mobile phones.

By standardizing the power connector for all the portable devices and accessories on USB Type-C; the need of carrying different chargers and cables is minimized. One charger with the USB Type-C cable can charge one’s mobile phone, laptop, tablet, and other portable device, eliminating confusion and incompatibility forever.

USB Power Delivery

USB Power Delivery (PD) is one the new USB standards for power delivery over the USB Type-C connector. It delivers up to 100 Watts and a voltage/current as high as 20 V/5 A over VBUS. USB PD 2.0 supports fixed voltage profiles ranging from 5 V to 20 V. Next-generation PD 3.0 supports these as well as programmable power supplies in the range from 3.3 V to 21 V in 20 mV steps.

Two Communication Channel (CC) lines – CC1 and CC2 – are used to negotiate the power delivery contract between the charger (power provider) and a device (power consumer). The provider communicates a Source Capabilities[1] message to the consumer. In response, the consumer returns a Request[2] message based on its power requirements. The provider gets into an explicit contract after accepting the request and then sets the desired voltage; this process is termed “power delivery negotiation”. The power delivery negotiation uses PD Messages (as specified in the USB-PD specification).

To illustrates the incompatibility among different charging standards and the need for a universal standard, a series of tests were conducted using several popular smart phones, including Google Pixel 2 XL, Apple iPhone 7, and Samsung Galaxy S8 phones and their associated fast chargers.

The graphs below show the battery percentage vs charging time for all three phones.

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Figure 1: Google Pixel 2 XL Charging time

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Figure 2: iPhone Battery Charging time

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Figure 3: Samsung Galaxy S8 Charging time

The test results reveal some interesting facts and expected outcome:

  • These chargers do not support all charging standards.

  • To reduce charging time for particular phone, a charger supporting the compatible charging standard is required.

While standardizing all mobile phones and chargers to the universal USB PD standard is the future, there is still a huge incompatible installed base that will continue to exist for years to come. This is where a programmable charging solution can be deployed to deal with both the new and old standards. With a programmable solution, developers can implement different charging standards without modifying the hardware and without compromising battery charge-time for consumers. The programmability also helps to keep the solution updated in the field if necessary to keep pace with the changes of all supported charging standards.

The most important components of a battery charger system are:

  1. Power Converter

  2. USB PD Controller and

  3. USB Type-C receptacle

Designing a Universal Mobile Phone Charger

A mobile phone charger becomes programmable if the USB PD controller in the charger is programmable. Such USB PD controller contains a processor and Flash to execute and store firmware and hardware components like Timers, ADC, GPIOs and Communication blocks that can be configured by firmware. Figure 4 shows a block diagram of a generic programmable implementation.

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Figure 4: Programmable Battery Charger Block diagram

An example of a programmable USB charging solution is Cypress Semiconductor’s EZ-PD CCG3PA controller. The CCG3PA is Cypress’ third-generation USB Power Delivery solution and it is a highly integrated controller for all USB-C charger and power bank applications. The CCG3PA has an integrated 32-bit Arm® Cortex®-M0 processor, 64KB flash, 8KB RAM, a built-in USB Type-C transceiver, 2 ADCs, 2 programmable communication interfaces, 4 Timer modules, integrated feedback control circuitry for voltage (VBUS) regulation, and other hardware blocks as shown in Figure 5.

Chargers designed using the programmable CCG3PA controller can be updated/customized easily to support the latest USB PD 3.0 and a long list of legacy charging standards, thus reducing the time to market for charger manufacturers and eliminating confusion for consumers. In this way, a single charger is all a user needs to charge any of his or her mobiles, all at the shortest possible charging time. At the same time, OEMs will benefit from the flexibility of being able to use a single hardware architecture to address the various charging standards. This will simplify design, reduce inventory size, eliminate costs, and improve profitability.

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Figure 5: CCG3PA Power Adapter Block diagram

Footnotes

[1] A Source Port reports its capabilities in a series of 32-bit Power Data Objects as part of a SourceCapabilities Message. Power Data Objects are used to convey a Source Port’s capabilities to provide power.

[2] Message is sent by a Sink to request power, during the request phase of a power negotiation. The Request Data Object is returned by the Sink making a request for power.


Anshul Gulati is currently working on customer/reference designs on USB Type-C and USB PD applications like Car Chargers and Power Banks. She has over 16 years of experience in Embedded System designs and has worked on applications ranging from USB, BLE, HBLEDs to Solar Charger Controllers. She has a degree in Electrical and Electronics Engineering.

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