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.