MCP6271R Microchip Technology Inc., MCP6271R Datasheet - Page 36

• Manufacturer Part Number: MCP6271R
• Description: 170 ?a, 2 Mhz Rail-to-rail Op Amp
• Manufacturer: Microchip Technology Inc.

Designing With Low Dropout Regulators In Embedded Applications
By Qi Deng, Microchip Technology Inc.
Low dropout regulators (LDOs) are a mainstay of embedded
microcontroller based applications. For designs where simplicity,
flexibility, footprint and cost concerns are primary, LDOs are still
the power sources of choice. These target applications include
industrial and enterprise applications such as industrial controls,
switch mode power supply (SMPS) post regulators, server boards
and consumer products such as video/audio systems and Set
Top Boxes (STBs).
A common characteristic of embedded applications is they
are AC powered by either high voltage multiphase industrial or
110V/220V 50 Hz/60 Hz consumer AC sources. The AC voltage
is then rectified to a high DC voltage such as 12V or 24V, which
is further converted down to a low DC voltage. This DC/DC
conversion is typically done by a step-down switching regulator
to maximize power conversion efficiency. The low DC voltage,
with 3.3V and 5.0V as the most common values, is the top level
DC power source, or “system rail,” for the embedded circuitry. A
majority of embedded microcontrollers these days are powered
by a DC voltage ranging between 1.8V and 5.0V, which is typically
converted from the “system rail” by a cost effective LDO device.
In addition to executing application level functions, the
embedded microcontroller also acts as a “system supervisor,”
performing tasks such as power condition monitoring and
power management. Because of this, the LDO also needs to
provide relevant power condition information to the embedded
microcontroller to help it make system control decisions, and be
controllable by the embedded microcontroller to react to system
status changes.
Therefore, in addition to the load current, which is always the first
parameter for designer to consider, several LDO specifications
and features are considered critical in an embedded application,
including dropout voltage, a power condition indicator output to
the microcontroller, such as power good output, and a control
feedback feature, such as shutdown.
It is always a good design practice to choose a LDO with the
smallest dropout voltage for it offers the highest fl exibility and
fault tolerance. For example, in many embedded applications, a
3.3V system rail is converted down to 2.5V, leaving only 800 mV
maximum dropout headroom over a wide temperature range
(e.g., -40°C to 125°C). This means the typical dropout voltage
under a normal condition (25°C) cannot be much more than
300 mV.
Power good indicator output is also critical because the
embedded microcontroller needs to perform certain system
housekeeping functions as a direct response to power level
fl uctuation. In an embedded application that converts a 3.3V
system rail to 2.5V, if the system rail drops to, say, 2.8V, there
is not enough dropout headroom to keep the regulation at
2.5V. When such a condition occurs, the power good output is
asserted to notify the embedded microcontroller. Because the
most likely response of the embedded microcontroller is to reset
the system, a programmable delay on the power good output is
desirable to optimize time setting of the system reset.
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Analog and Interface Guide – Volume 2
Miscellaneous Articles
Another critical LDO feature is the need to be shut down by
either the embedded microcontroller or some other system
level intelligence. This is because that when the embedded
microcontroller decides to switch off the system either voluntarily
or as a response to fault conditions, the LDO needs to be shut
down to preserve power or prevent damage.
Putting this all together, an ideal LDO for a typical embedded
application should have the following critical features included in
a single package:
• High load current, up to 1A
• Low dropout voltage, less than 300 mA typical
• Power good output with programmable delay
• Shutdown input
One example of an ideal LDO solution is the MCP1726 from
Microchip Technology. The MCP1726 is the first LDO in the
industry specifically designed for embedded applications with all
the above features incorporated on one chip, including 1A load
current, 150 mV typical dropout voltage, Power Good output with
User Programmable Delay and Shutdown.
In addition, the MCP1726 offers other desirable features for
numerous applications, such as small and thermal capable
DFN (3 mm x 3 mm) package, stability with 1 μF ceramic output
capacitor, low 140 μA typical supply current and low 0.001 μA
typical leakage current during shutdown. The standard output
voltages for the MCP1726 include 0.8V, 1.2V, 1.8V, 2.5V, 3.3V,
5.0V, as well as adjustable, covering a complete input voltage
range of embedded microcontroller. The MCP1726 is also
available in more traditional SOIC package.
With the MCP1726, system designers no longer have to use
up to three devices to perform all necessary power monitoring,
conversion and management tasks. The simplicity, flexibility,
footprint and cost advantages of the MCP1726 make it the top
choice for embedded applications.
For more information on LDOs or the MCP1726, please visit
Microchip’s web site at: www.microchip.com