Sunday, April 12, 2009

Linear Battery-Charger ICs

NiCd/NiMH Battery
Fast-Charge Controllers

The MAX712/MAX713 fast-charge Nickel Metal Hydride
(NiMH) and Nickel Cadmium (NiCd) batteries from a DC
source at least 1.5V higher than the maximum battery
voltage. 1 to 16 series cells can be charged at rates up
to 4C. A voltage-slope detecting analog-to-digital converter,
timer, and temperature window comparator determine
charge completion. The MAX712/MAX713 are powered
by the DC source via an on-board +5V shunt regulator.
They draw a maximum of 5µA from the battery when not
charging. A low-side current-sense resistor allows the
battery charge current to be regulated while still
supplying power to the battery’s load.
The MAX712 terminates fast charge by detecting zero
voltage slope, while the MAX713 uses a negative
voltage-slope detection scheme. Both parts come in 16-
pin DIP and SO packages. An external power PNP transistor,
blocking diode, three resistors, and three
capacitors are the only required external components.
The evaluation kit is available: Order the MAX712EVKITDIP
for quick evaluation of the linear charger.

♦ Fast-Charge NiMH or NiCd Batteries
♦ Voltage Slope, Temperature, and Timer
Fast-Charge Cutoff
♦ Charge 1 to 16 Series Cells
♦ Supply Battery’s Load While Charging
(Linear Mode)
♦ Fast Charge from C/4 to 4C Rate
♦ C/16 Trickle-Charge Rate
♦ Automatically Switch from Fast to Trickle Charge
♦ Linear Mode Power Control
♦ 5uA (max) Drain on Battery when Not Charging
♦ 5V Shunt Regulator Powers External Logic

Cost-Saving Multichemistry
Battery-Charger System

The MAX846A is a cost-saving multichemistry batterycharger
system that comes in a space-saving 16-pin
QSOP. This integrated system allows different battery
chemistries (Li-Ion, NiMH or NiCd cells) to be charged
using one circuit.

In its simplest application, the MAX846A is a standalone,
current-limited float voltage source that charges
Li-Ion cells. It can also be paired up with a low-cost
microcontroller (µC) to build a universal charger capable
of charging Li-Ion, NiMH, and NiCd cells.
An internal 0.5%-accurate reference allows safe charging
of Li-Ion cells that require tight voltage accuracy.
The voltage- and current-regulation loops used to control
a low-cost external PNP transistor (or P-channel
MOSFET) are independent of each other, allowing more
flexibility in the charging algorithms.
The MAX846A has a built-in 1%, 3.3V, 20mA linear regulator
capable of powering the µC and providing a reference
for the µC’s analog-to-digital converters. An
on-board reset notifies the controller upon any unexpected
loss of power. The µC can be inexpensive, since
its only functions are to monitor the voltage and current
and to change the charging algorithms.
- Multichemistry Charger System (Li-Ion, NiMH, NiCd)
- Independent Voltage and Current Loops
- ±0.5% Internal Reference for Li-Ion Cells
- Lowers Cost:
—Stands Alone or Uses Low-Cost µC
—Built-In 1% Linear Regulator Powers µC
—Linear Regulator Provides Reference to µC ADCs
—Built-In µC Reset
—Controls Low-Cost External PNP Transistor or
P-Channel MOSFET
- Space-Saving 16-Pin QSOP
- Charging-Current-Monitor Output
- <1µa>

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