Enabling universal battery charging and compliance

Enabling universal battery charging and compliance

New battery charging solutions maximize energy efficiency and minimize waste

BY SHADI HAWAWINI and GEORGE PAPARRIZOS
Summit Microelectronics, Sunnyvale, CA
http://www.summitmicro.com

A number of new industry standards on battery charging have hit the market over the last couple of years. These new initiatives are attempting to increase portable device users’ satisfaction by increasing safety, enabling slim form factors and simplifying battery charging.

While compliance introduces significant long-term benefits for both consumers and manufacturers, system designs need to undergo extensive modifications, which very often means delayed time to market, increased number of components, and higher system cost. This article introduces some of the key new standards/regulations and discusses their benefits and challenges as well as potential solutions.

The IEEEP1725 standard

The IEEE Standards Association Corporate Program introduced a new standard for rechargeable batteries for cellular phones in March 2006. The goal of this standard is to allow cellular phone designs to provide the increasing power and complexity required by the consumer, while ensuring robust and reliable operation.

Among other items, the IEEEP1725 establishes criteria for reliability of rechargeable Li-ion and Li-ion-polymer batteries for mobile telephone applications. The standard also regulates battery pack electrical and mechanical construction, packaging technologies, pack and cell level charge and discharge controls, and overall system considerations. As demonstrated in Fig. 1 , the IEEEP1725 looks at the whole chain to proactively address reliability and safety risks.

Fig. 1. The IEEEP1725 safety chain.

Some of the requirements and recommendations that may affect battery-charging design, and consequently the selection of battery-charging and management IC solutions, are listed below:

• Redundant overcurrent protection.

• Indefinitely withstanding of a faulty adapter’s voltage and subsequent protection of the system from cascade failures.

• Redundant charge current limiting.

• Battery pack temperature monitoring.

• Safety timer protection.

• Redundant battery overvoltage protection.

• Battery preconditioning.

USB Battery Charging Specification 1.0

Another major specification that has garnered a lot of attention is the USB Battery Charging Specification 1.0, which became available by the USB Implementer’s Forum (USB-IF) in March 2007. The idea behind this spec is to provide the means to standardize battery charging while using different power sources with the same physical USB connector to optimize battery charging under different scenarios and to allow portable devices to transition to a standardized USB micro connector.

The USB Battery Charging Specification provides various methods for source detection, that is, identifying if the portable device is connected to a dedicated (wall adapter), a USB host/hub or a host/hub charger. This new specification also introduces the concept of “dead-battery condition.” This condition allows the device to charge with a maximum of 100 mA, until the system powers up, at which point it must connect.

One of the problems of the dead-battery condition is that with a deeply discharged battery, the system might need up to 30 min to wake up while charging at 100 mA. This is where *accurate detection of the power source is critical (see Fig. 2 ); when a wall adapter is connected, faster charging and therefore faster system power-up is possible.

A new challenge arising from this standard is the ability for the system to differentiate among all the different dedicated chargers (wall adapters), and their current capability (500 mA to 1.8 A), and to allow for optimized (fastest) but also reliable battery charging. This issue is difficult to compensate for, even when the system is on, and requires the use of advanced detection algorithms.

Fig. 2. Charging a portable device from a USB-compliant wall adapter.

Chinese standard CCSA YD/T 1591-2006

In parallel with the USB-IF activities, the China Ministry of Information Industry (MII) also developed a specification to standardize cellular phone charging in the Chinese market. This spec also defines the detection of a wall adapter with a USB physical interface (USB type A) via the shorting of the D+ and D- USB signal lines. It also allows the wall adapter to provide a current as low as 300 mA, further complicating matters.

Another major difference between this standard and USB Charging Specification 1.0 is that while USB-IF promotes a USB micro connector to be used on the handheld devices, the China specification imposes the USB type A connector on the wall adapter, but allows proprietary connectors on the cellular phone side. CCSA YD/T 1591-2006 provides mostly information on mechanical, reliability, electrical and testing information, as these apply on the device’s charging interface, wall adapter, and connecting cable.

Consumer, OEM, and carrier benefits

Standardization has many important benefits for manufacturers, including the use of an industry-standard connector which helps bring costs down and allows the development of slimmer consumer electronics with the use of the USB micro connector. Additionally, the need for OEMs to package a wall-wart does not really exist anymore because consumers will probably already have their own, thereby saving significant cost in terms of the wall-wart itself, as well as associated packaging and shipping costs.

Consumers have many benefits as well. The use of a standardized connector allows a particular user that may have to travel with his/her laptop, cell phone, and digital camera, the ability to bring a single USB cable to charge directly from his/her laptop, or from a USB wall adapter.

Additionally, because many consumer electronics may begin adopting the USB connector for charging, users can use existing charging adapters and do not have to continually throw away old chargers, or buy new ones. This will dramatically increase consumer satisfaction, and contribute to a truly unified, universal mobile experience.

Finally, with so many companies focusing on various global green initiatives or being environmentally friendly, the use of a standardized connector helps reduce landfill waste. Generally when a consumer gets a new portable device, the old adapter is obsolete and is thrown away, adding to landfill waste. Also, to a lesser degree, the amount of packaging saved can help reduce waste, and consequently the smaller volume of the box can reduce shipping costs and greenhouse gases related to shipping.

Solution that enables compliance

There are many challenges in achieving compatibility with the various standards discussed in this article, but these can be alleviated by using modern battery-charging solutions, such as the SMB339 battery charger IC. For the case of the USB battery-charging specification, particularly the difficulties associated with dead-battery charging, the SMB339 incorporates an algorithm to virtually eliminate the need for the system to intervene when an input is applied.

The SMB339 also has the ability to virtually “snoop” the D+ and D- USB signal lines to determine whether the input is a USB port, or a dedicated charger, and then make a decision to charge at and draw an input current of 100 mA (USB2.0 compatibility), or to charge at full-charge current and get out of the dead-battery condition faster. The SMB339’s TurboCharge operation allows for current multiplication of the input current, thereby enabling faster charging from a 100-mA input or other limited inputs; this is very important for lower battery voltages below the dead-battery threshold.

A 1-s holdoff timer is also provided to prevent the battery from beginning to charge until 1 s after the SMB339 detects a valid USB input. The SMB339 also has independent input and output current limiting, including input current limits of 100 mA, and 500 mA for USB2.0 compliance.

One of the major challenges of universal charging is ensuring reliable operation, given that consumer behavior becomes unpredictable. Users can connect any portable device to any “compliant” wall adapter with a high probability of trying to draw more current from a source that it can provide, thereby entering a “non-charging” mode.

Such events can significantly damage OEM brand recognition, increase carriers’ cost (many service calls) and frustrate consumers. The SMB339 eliminates these issues, by automatically “matching” wall adapter current capability to the device’s battery charging current.

In addition to industry-standard safety features, the SMB339 also provides unique protection mechanisms for maximum system reliability. These include secondary battery over-voltage protection, watchdog timers and a wide range of status and fault registers that allow the handheld device to retrieve real-time operational data. Last, but not least, the device’s high-efficiency, switch-mode operation reduces wasted power and contributes to the industry’s effort for more green power management solutions.

The great popularity of portable devices over the last few years has driven a new wave of industry initiatives that target consumer satisfaction, product reliability, and reduced electronic waste. Meeting all these new standards introduces major challenges both in terms of design complexity and system cost and size.

Innovative charging solutions are entering the marketplace that off-load these new requirements from the system and achieve full compatibility. These new solutions maximize energy efficiency and minimize waste by reducing power dissipation while also eliminating the need for proprietary ac/dc adapters for every portable device, thereby enabling true universal USB charging. ■

References

1. IEEEP1725 Standard (grouper.ieee.org/groups/1725/)

2. USB Charging Specification 1.0 (www.usb.org/developers/devclass_docs)

3. CCSA YD/T 1591-2006 (www.ccsa.org.cn/)

4. SMB339 Product Information (www.summitmicro.com)