Electronic Design

Where Are We?

Looking at the last few months of battery-chip product announcements reveals some trends. In terms of chargers for handheld devices, chip makers are responding to customer pressure to accommodate both ac-adapter and USB charging. In fact, the OEMs want to use the USB port for connection to either USB or an ac charger.

Thus, we find Microchip Technology announcing its USB-compatible MCP73811 and MCP73812 charge-management controllers. The MCP73811 has a digital input and selectable USB charge currents of either 85 mA or 450 mA. The MCP73812 offers a user-programmable charge current via an external resistor. Both come in a five-pin SOT-23 package, and both integrate the pass transistor and provide current sense, reverse battery protection, and thermal regulation. The MCP73811 is priced at $0.57 each, and the MCP73812 at $0.59 each, in 10,000-unit quantities.

Maxim Integrated Products' MAX8804Y/MAX8804Z, 2- by 6-mm, dual-input, standalone, USB/ac-adapter chargers for one-cell lithium-ion (Li-ion) batteries play to the demand for small footprint. The "Z" version incorporates a prequalification charging stage to bring the battery voltage to 2.5 V, while the "Y" version starts fast-charging without the precharging stage. Both have intelligent USB/dc-input circuitry that automatically selects between either a USB or ac-adapter input source. Using integrated FETs, they deliver up to 700 mA of fast-charging current (from the ac adapter), and when they aren't charging, they put only 2 mA of drain on the battery.

For safety, they shut off charging when the input voltage exceeds 7.5 V, but they can withstand voltages as high as 30 V dc on from an ac adapter or 16 V on the USB input. The chargers also employ Maxim's proprietary thermal-regulation and constant-current, constant-voltage (CCCV) circuitry to eliminate overheating during fast charging. Prices start at $1.40 (2500- up, FOB USA).

In the battle for ever smaller gas-gauge chips, Maxim also announced the DS2784, a standalone fuel gauge that integrates a one-cell Li-ion protector and SHA-1 authentication in a 3- by 5-mm TDFN package. The objective of the shrink was to make the device small enough to mount on the cell itself, rather than on a board in the end product. Prices start at $2.94 (1000- up, FOB USA).

I've already mentioned TI and impedance tracking. Last September, the company introduced the first gas-gauge chips expressly designed to mount on the system board, rather than in the battery pack. The bq24314 and bq24316 come in 2- by 2-mm packages and cost $0.75 each in 1000-piece lots.

For those who want a custom USB/ac-adapter charger, Summit Microelectronics announced earlier this month its SMB137 programmable chips. These are the first chips, to my knowledge, that explicitly support USB On-The-Go (USB-OTG) power and the new China USB charging spec. USB-OTG is a scheme that lets two USB clients, such as a camera phone and an MP3 player, communicate directly without a server as an intermediary.

Customization is accomplished on a development platform with files sent to Summit for programming. The SMB137 comes in a 3.3- by 3.6-mm package and costs $2.30 each in quantities of 10,000.

A new trend is mixing battery charging with general power-management functions, which is just the case regarding Linear Technology's LTC3557 power-management and battery-charger IC. The chip also includes three adjustable synchronous step-down switching regulators and a high-voltage buck-regulator output controller with a proprietary scheme that allows for efficient charging from supplies as high as 38 V. The step-down regulators, which can be programmed for output voltages down to 0.8 V, can be used to power a microcontroller's core, I/O, and memory rails. The LTC3557 costs $3.95 each in 1000-unit lots.

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