For many handhelds, lithium-ion
(Li-ion) batteries have become
the power source of choice. In
response, IC manufacturers are
developing devices that operate
properly using the normal output
voltage of these batteries. In other words,
the nominal Li-ion output of 4.2 V will drop
down as low as about 3 V as it's used. An
IC then should be able to work with an
input voltage of at least 3 to 5 V so it can
accommodate a single Li-ion cell.
National Semiconductor's LM3671
step-down switching-regulator IC for singlecell Li-ion applications can operate with an
input voltage range of 2.7 to 5.5 V (). It can handle up to a 600-mA load
over the entire input voltage range. Also,
it's available as an adjustable output version as well as in 10 fixed output versions
supplying 1.2 to 3.3 V.
Optimized for these applications, it
includes automatic intelligent switching
between pulse-width modulation (PWM)
and pulse-frequency modulation (PFM),
reducing current consumption. In the
PWM mode, it operates at a fixed 2 MHz
(typical). The hysteretic PFM mode
extends battery life by reducing the quiescent current to a typical 16 µA during light
load and standby operation.
Internal synchronous rectification provides high efficiency during PWM mode
operation. In the shutdown mode, the IC
turns off and reduces battery drain to 0.01 µA (typical). Housings are SOT23-5
and five-bump micro surface-mount packages in lead-free and leaded versions.
The LM3671 is the first in the switching-regulator IC family with similar and
expanded capabilities. The LM3674 is a
PWM-only version of the LM3671 that
produces lower output ripple. The
LM3670 and the LM3673 are lower-current versions. Coming in the first quarter
of 2007 is a version with a 3-MHz switching frequency. This allows the use of a 1µH chip inductor, which results in a 20mm2 switching regulator circuit.
The ADP2105, ADP2106, and
ADP2107 run from input voltages of 2.7
to 5.5 V, enabling single Li+/Li– polymer
cell, multiple alkaline/NiMH (nickel-metal-hydride) cells, PCMCIA, and other standard power sources. The output voltage
of the ADP2105, ADP2106, and
ADP2107-ADJ is adjustable from 0.8 V to
the input voltage, while the ADP2105,
ADP2106, and ADP2107-xx are available
in preset output voltage options of 3.3,1.8, 1.5, and 1.2 V. Each variation is
available in three maximum current levels, 1 A (ADP2105), 1.5 A (ADP2106), and 2 A (ADP2107).
The power switch and synchronous rectifier are integrated for minimal external part count and high efficiency. During
logic-controlled shutdown, the input is
disconnected from the output, and it
draws less than 0.1 µA from the input
source. Other key features include undervoltage lockout to prevent deep-battery
discharge and programmable soft-start
to limit inrush current at startup.
The ADP2105, ADP2106, and
ADP2107 are low-quiescent-current, synchronous, step-down dc-to-dc converters
in a compact 4- by 4-mm LFCSP/QFN
package. At medium-to-high load currents, they use a current-mode, constantfrequency PWM control scheme for excellent stability and transient response. To
ensure the longest battery life in portable applications, the
ADP2105, ADP2106,
and ADP2107 use a
PFM control scheme
under light load conditions that reduces
switching frequency to
save power.
Operating from a 2.7- to 5.5-V input, Maxim's MAX8581 and MAX8582 high-frequency step-down converters are optimized to dynamically power the power amplifier (PA) in CDMA handsets. They integrate a high-efficiency
PWM step-down converter for mediumand low-power transmission and a 60mΩ (typical) bypass mode to power the
PA directly from the battery during high
power transmission.
Also, they employ an analog input driven by an external digital-to-analog converter (DAC) to control the output voltage
linearly for continuous PA power adjustment. The MAX8581 and MAX8582 use
an internal feedback network, and the
switching frequency is internally set to 2.5 and 1.5 MHz, respectively.
Fast switching (up to 2.5 MHz) and fast soft-start make it possible to use ceramic 2.2-µF input and output capacitors while
maintaining low voltage ripple. The small
1.5- to 3.3-µH inductor size can be optimized for efficiency. These ICs are available in 10-pin, 3- by 3-mm TDFN packages with a 0.8-mm max height.
Texas Instruments' TPS7510x LED
drivers feature a 2.7- to 5.5-V input range
that suits single-cell Li-ion batteries. The
TPS75100, TPS75105, and TPS75103
have nominal default output currents of
10, 5, and 3 mA, respectively. This lowdropout (LDO) matching LED current
source is optimized for low-power keypad
and navigation pad LED backlighting
applications.
The IC provides a constant current to
up to four unmatched LEDs organized in
two banks of two LEDs, each in a common-cathode topology. Without an external resistor, the current source defaults
to factory-programmable, preset current
level with µ0.5% accuracy (typical). An optional external resistor can be used to
set initial brightness to user-programmable values with higher accuracy.
Brightness can be varied from off to full
brightness by inputting a PWM signal on
each Enable pin. Each bank has independent enable and brightness control, but current matching is done to all four channels
concurrently. TPS7510x is available in a
nine-ball, 0.4-mm, ball-pitch wafer chipscale package (WCSP) and a 3- by 3-mm
quad flat no-lead (QFN) package.