Volume 3 | Issue 3 | 2015
Power Management
Solutions for Modern
Electronic Devices
Dan Goodhew – Applications Engineer, Central Applications, Intersil
Integrated circuits (ICs) are a vital component in almost all fields of the
modern world. As a result, power management in these ICs has
become more and more critical. From consumer products to industrial
applications such as medical equipment, portable instruments and
fitness equipment, modern electronic devices require efficient power
management solutions. Some of the key requirements of today’s
power management solutions include less power consumption under
various load conditions, less space, high reliability and wide input
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Volume 3 | Issue 3 | 2015
voltage. These requirements are driving the need for highly efficient,
wide VIN, low quiescent current (IQ) switching regulators in a broad
range of applications.
Device Selection: Efficiency
Low dropout (LDO) voltage regulators are frequently used in low
power designs due to their simplicity, low external component count,
low electrical noise and low IQ. For low load currents, their power
dissipation is manageable and their efficiency is approximately
VOUT/VIN. If the source decreases in voltage with use, such as with a
battery, the efficiency of an LDO will increase as the difference
between the input voltage and output voltage reduces until the
dropout voltage is reached. However, at higher load currents or when
the input voltage is significantly higher than the output voltage, the
power dissipation can be unmanageable due to excessive heat and too
much power drain on the rest of the system.
“
"Some of the key requirements of today’s power
management solutions include less power consumption
under various load conditions, less space, high reliability and
wide input voltage."
Switching regulators are traditionally known to be slightly more
complex and costly to design with but have high overall efficiencies.
However, switching regulators tend to have higher quiescent current
than LDOs. IQ is the current necessary to maintain an active output
voltage when there is no external load. Modern switching regulators
have done much to improve on their historical shortcomings. Today’s
product offering has developed to the point that switching regulators
are available with integrated pulse width modulation (PWM) control,
power MOSFET, compensation network, protection and monitoring
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Volume 3 | Issue 3 | 2015
circuitry in tiny packages. Switching regulators provide efficient,
compact and cost-effective power conversion. Designing them into a
circuit is nearly as easy as with an LDO voltage regulator. More
advanced devices have the ability to switch between PWM and pulse
frequency modulation (PFM) mode to increase the efficiency at low
load current levels and reduce their required IQ, This allows modern
switching regulators to deliver superior efficiency across the entire
operation range. Figures 1 and 2 contrast the efficiency levels in PWM
and PFM mode on a device with 3.3 V output and several input
voltages.
Figure 1. ISL85410 Efficiency with PFM (VOUT=3.3V)
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Volume 3 | Issue 3 | 2015
Figure 2. ISL85410 Efficiency with PWM (VOUT=3.3V)
High Integration: Protection and Timing
When looking at cost, additional consideration must be given to the
integrated features. One highly valuable integrated feature set found
in switching regulators is protection and control logic circuitry that
features overcurrent protection (OCP), overvoltage protection (OVP)
and overtemperature protection (OTP). It ensures a robust system able
to run under severe operating conditions. To provide OCP for example,
the device may monitor the current through the upper FET during
PWM on-time and compare it to the peak over-current limit. If the
current reaches the limit and persists, the regulator will begin its
hiccup sequence. In this case, both FETs will be turned off to protect
the device and a fault condition will be set. Ideal monitoring should
detect even if the output is shorted during soft-start. If VOUT is shorted
very quickly, the regulator recognizes this condition and begins to
lower its switching frequency proportional to the voltage so that
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Volume 3 | Issue 3 | 2015
under no circumstance (even with VOUT near 0 V) will the inductor
experience current runaway. External circuitry to protect the system
in a similar manner could cost more than the switching regulator by
itself, not to mention require more board space. Similar circuitry exists
to detect and discharge negative currents, and the FETs can be turned
off in response to temperatures unsafe for operation.
Another valuable feature found
in integrated switching regulators is their
power start-up and sequencing circuitry.
Correct power up sequencing prevents
possible system damage, and systems with
digital components are particularly
sensitive to power sequencing because an
incorrect power up can latch up the digital
devices. Adjustable soft-start avoids large
in-rush currents by slowly increasing VOUT
at startup to its final regulated value. The
monotonic rise in voltage is especially
important for devices with power-on reset.
Soft-start time is determined by the
capacitor placed from the given pin
connection to ground. Switching regulators with soft-start may include
a power good pin, which goes high when the output voltage reaches
its set value, and can be used for power supply sequencing. The pin
goes low when it’s outside the acceptable tolerance level, thereby
providing fault detection.
“
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'Another valuable feature found in integrated switching
regulators is their power start-up and sequencing circuitry.'
Copyright © 2015 Avnet, Inc. | All rights reserved.
“
Volume 3 | Issue 3 | 2015
Finally, highly integrated switching regulators may offer internal
compensation and the option to use external compensation to achieve
fast transient performance. They also provide synchronization control
to minimize input voltage ripple and reduce EMI when using multiple
devices, and their adjustable switching frequency enables better
control over the design size and efficiency.
Conclusion
Power management systems for modern electronic devices require
less power consumption under various load conditions, offer higher
efficiency, high reliability and a wide input voltage range. Newer
switching regulators on the market, such as Intersil’s ISL85410/15/18
family, offer high efficiency, flexibility, low quiescent current and
robust stability over a wide range of VIN and output conditions. These
devices are highly reliable with complete protection features, making
them ideal for highly efficient, compact power conversions in
industrial, infrastructure, consumer and automotive applications.
Dan Goodhew
Dan Goodhew is an Applications Engineer in Central
Applications at Intersil Corp. He joined Intersil in 2010 and
specializes in precision analog components as well as
designing low power data-acquisition systems. Mr.
Goodhew holds a B.S. in Electrical Engineering from the
University of Central Florida.
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