With mobile equipment manufacturers
demanding ever smaller
and lighter handheld systems,
the trend is to create smaller ICs
that offer greater functionality.
However, meeting those functionality,
size, and weight
requirements becomes a more
difficult proposition in power-oriented applications.
For instance, switching regulators must be very efficient, particularly
when multiple switchers are integrated into an IC. Battery-
charger circuits must be efficient. Also, chip layout must
ensure that there are no "hot spots" and electromagnetic interference
(EMI) is controlled. On top of that, many handhelds
operate from a single lithiumion/
polymer cell. Despite these difficult
design issues, many IC manufacturers
have responded with
devices that meet the system
requirements.
Take Linear Technology's
LTC3555, the first in a family of
multifunction power-management
solutions for Li-ion/polymer
battery applications. It integrates
a switching PowerPath
manager, a standalone battery
charger, an ideal diode, I2C control,
three high-efficiency synchronous
buck regulators, and
an always-on low-dropout regulator
(LDO) (Fig. 1).
The LTC3555's PowerPath control seamlessly manages
power flow between an ac wall adapter or USB port, Li-ion
battery, and system load while its "instant-ON" operation
ensures system load power even with a dead or missing battery.
For fast charging, the LTC3555's switching input stage
converts nearly all of the 2.5 W available from the USB port to
charging current.
This enables up to 700 mA from a 500-mA limited USB supply
and up to 1.5 A when wall-powered. An internal 180-mV
ideal diode plus optional external ideal diode controller provide
a low-loss power path, further minimizing heat generation
and maximizing efficiency.
The LTC3555's three integrated synchronous buck regulators
feature 100% duty-cycle operation and can deliver
1-A/400-mA/400-mA outputs, respectively, with adjustable
output voltages down to 0.8 V. The internal low-RDS(ON)
switches deliver efficiency as high as 94%, maximizing battery
run time.
In addition, Burst Mode operation optimizes efficiency at
light loads with a quiescent current of 35 mA per regulator
(<1 mA in shutdown). The 2.25-MHz switching frequency
allows use of tiny low-cost capacitors and inductors less
than 1 mm in height. Furthermore, the regulators are stable
with ceramic output capacitors, achieving very low output
voltage ripple.
The LTC3555 features USB-compatible programmable current
limiting to 100 mA/500 mA/1 A, while its Bat-Track adaptive
output control enables high-efficiency charging and reduces
power dissipation. Standalone autonomous operation simplifies
design, eliminating the need for an external microprocessor for
charge termination. To preserve battery energy, the LTC3555
draws <23 mA from the battery in suspend mode. The charger
is compatible with inputs up to 5.5 V (7-V absolute maximum
transient for added robustness).
The powerwise interface
National Semiconductor's
LP5552 is a PowerWise Interface (PWI) 2.0-compliant
energy management unit (EMU) for applications such as
baseband processors in mobile phones and other portable
equipment (Fig. 2). It operates cooperatively with processors
using an advanced power controller (APC) to provide
adaptive voltage scaling (AVS), which significantly
improves processor efficiencies over conventional powerdelivery
methods.
The LP5552 is intended for use in a voltage scaling system
that lowers the system's power dissipation. Scaling supply
voltage with the clock frequency of a processor is a
huge power saver. Also, the device supports two types of
voltage scaling - dynamic voltage scaling (DVS) and AVS.
DVS systems switch between pre-characterized voltages,
which are paired to clock frequencies used for frequency scaling
in the processor. AVS systems track the processor performance
and optimize the supply voltage to the required
performance. AVS is a closed-loop system that provides
process and temperature compensation to deliver the minimum
supply voltage for any given processor, temperature, or
clock frequency.
To support DVS and AVS, the LP5552 is programmable
via the low-power, two-wire PWI. This serial interface controls
the various voltages and states of all regulators in the
LP5552. Both slaves in the LP5552 support the full PWI
command set, other than the optional extended register
read and write, as described in the PWI 2.0 specification:
core voltage adjust, reset, sleep, shutdown, wakeup, register
read, register write, and authenticate.
The PowerWise technology is an advanced energy-management
solution for energy-constrained digital devices, like
mobile phones, PDAs, handheld gaming consoles, and personal
navigators. Developed by National Semiconductor in
collaboration with ARM, it enables longer battery life, more
features, and improved user experience by reducing the energy
consumption in digital processors by up to 70%.
Operating from a 2.7- to 4.8-V input, it's compatible with
single-cell Li-ion batteries. The LP5552 contains two 88%
efficiency, switching dc-dc buck converters that are programmable
from 0.6- to 1.235-V outputs. Switching frequency is
3.6 MHz, and output current measures
800 mA per switcher. They supply
two voltage scaling domains,
and five digitally programmable
LDOs are available for supplying
additional support circuitry.