Texas Instruments | Linear power for automated industrial systems | Application notes | Texas Instruments Linear power for automated industrial systems Application notes

Texas Instruments Linear power for automated industrial systems Application notes
Linear power for automated
industrial systems
Jose Gonzalez
Linear Power – LDO
Product Marketing Engineer
Texas Instruments
Designing a robust power management system for
industrial automated equipment requires thorough
understanding of the surroundings and conditions
that affect the functionality.
During the past few decades, industrial and factory automation systems have become
more robust, intelligent and connected, which has drastically increased the footprint for
semiconductor components. This change has created an amalgamation of different designs
and system structures. As a result, engineers were required to retain the tried and true designs
and interface them with modern or newer designs in order to enable better functionality.
Out with the old, in with the new?
systems benefit from high-power efficiency DC/DC
architectures in order to achieve a lower voltage,
Although designs are improving and a vast number
there is a great demand for linear regulators (LDOs)
of systems are being updated, the environment
to provide voltage regulation to other semiconductor
and the conditions surrounding these devices have
systems in charge of metering, sensing and to
not changed much. Unlike many of the electronic
control major motor functions. This paper reviews
devices we interface with on a day-to-day basis,
the requirements for linear regulators intended for
systems within an industrial environment require
use within industrial or factory automation systems
working within high temperatures, high-voltage
and their benefits.
conditions, and various external factors that can
cause wear, tear and stress.
This means that in order to support the microcontroller, sensors and other devices mounted on
the PCBs, power management must be able to
fully operate in these conditions. At the same time,
there must be a steady supply of power, efficiency
and reliability for very long periods of time, even
decades. Note that many designs created today
must interact directly or indirectly with a lot of
Industrial automation systems
and high voltages
previous generation or high-voltage systems and
machinery. Therefore, it is also very important to
identify and address the faults and events that
A standard industrial automation system consists of
may cause harm to any sensitive electronics
a CPU or central controller, analog and digital inputs
components.
and outputs that interact with all subsystems, a
When it comes to power management there is a
communications protocol that allows very long wire
wide variety of topologies that can be employed.
lengths, and branching or stacked I/O modules for
However, in automation systems it is common
added functionality. Figure 1 shows a very popular,
to find a high DC voltage already being used for
very simplified programmable logic controller
a motor or in the system’s control lines, most
(PLC) configuration currently being used in many
commonly 12V or 24V. While a large number of
automated structures.
Texas Instruments: Linear power for automated industrial systems
2
July 2017
linear regulators have a very low output voltage
Digital BUS/24V Power
BUS
ripple because none of its internal elements are
Power
Supply
CPU
Multichannel
Analog
I/O
Multichannel
Digital
I/O
switching on and off. They can also have a very
high bandwidth with very little electromagnetic
COMMS
(Ethernet,
RS485, etc.)
interference (EMI) in the system. Furthermore, low
I/O Module
drop-out (LDO) linear regulator devices are much
simpler and easier to use. Most of them are 3 to 4 pin
110V
220V
devices with very small packages and do not require
Figure 1: Standard 24V PLC system.
external inductors in order to function (Figure 2).
VIN
In most cases the devices in each block or section
ON/OFF
can be powered directly from the main supply
while others can take advantage of the 24V rail and
VREF
1.23V +
regulate what is needed. This scenario requires
R1
the designer to take into consideration all possible
R2
devices that are or may be connected, as the
VOUT
Overcurrent/
Overtemperature
Protection
power supply needs to compensate or have power
GND
to spare. Also, as more and more devices are
Figure 2: Standard linear regulator.
connected to the power BUS, noise on the line
increases and, thus, the noise in the subsystems.
High temperature compatibility
Note that while the standard PLC functions at
Motors in most systems, whether mechanical
12V and 24V, there is always the possibility that
or electrical, dissipate a great deal of power
one of the system’s devices, boards or interfaced
through heat. This heat is dissipated through the
peripherals needs to operate beyond this range. In
housing which, in most cases, is made of metal.
such a case, the required power supply must be
This means that in order to survive and function
able to reach these high voltages that often are in
properly, all internal electronics must be rated
the range 40V or higher.
for very high temperatures – even up to 125°C.
Linear versus a switching regulator
This range has now become the new standard of
ambient temperature for semiconductors intended
In a plethora of automated systems, condition
for industrial systems. This also works well in the
sensing, communications and precision analog-to-
opposite manner where equipment intended for
digital conversion are key factors and the base of
use outdoors is faced with temperatures well
functionality. These converters and communication
below freezing, such as –40°C. Although it is not
devices, for the most part, are sensitive to noise.
always the case that both conditions are met, many
For these noise-sensitive devices it is important to
devices have to be tested at both extremes in order
minimize the supply noise as this ultimately affects
to comply.
the accuracy or stability of the communication or
One drawback for a linear regulator is the amount
conversion [1].
of power dissipated through the system almost
Switching regulators can change the input voltage
entirely as heat [2]. The power dissipated by a linear
by turning or switching on and off an internal
regulator can be determined as follows:
element. However, this creates an output voltage
ripple that can be seen by the receiving component
as noise or a fluctuation in the input voltage,
PD = (VIN – VOUT )• IOUT
thus, affecting their functionality. Alternatively,
Texas Instruments: Linear power for automated industrial systems
3
(1)
July 2017
This means that the higher the voltage difference
the power dissipated may increase unexpectedly.
between your input and output voltages, the greater
Many linear regulators and LDOs feature internal
the heat that will be dissipated, and the higher the
thermal shutdown structures that can turn off
temperature around the LDO. In such cases, a
the device whenever junction temperature is
better way to dissipate this system heat is by using
exceeded as shown previously in Figure 2. In
a pad or contact. The designer can benefit from
a standard linear regulator, thermal protection
regulators fitted with ON/OFF switches to control
disables the output when the junction temperature
the length of time the device is active. Other devices
rises to approximately 170°C, allowing the device
also can be fitted with over temperature shutdown
to cool. When the junction temperature cools
functionality to prevent the device from reaching
to approximately 150°C, the output circuitry is
unsafe temperatures. Another way to compensate
enabled allowing for regulation to resume. This
for power dissipation is to choose a very low-
protection circuitry is not intended to replace proper
voltage dropout regulator and keep the VOUT as
heatsinking, but allows for additional protection.
close to VIN as possible. This is the most common
scenario for low-current power within the range of
100mA or less.
Risk conditions and faults
While heat, voltage and power are important factors
for the power management design in an automated
system such as in vehicle assembly sites (Figure 3),
other factors may be present that can significantly
impact the system, particularly when integrating
motors in the design. If a given motor within the
system gets shut or stuck, it draws more current
into the system, increasing the power demand on
Figure 3: Automated vehicle assembly.
the regulators. While many discrete solutions can be
used to dissipate this current through the electrical
available today that can sense the output current
Current limit and short circuit
protection
and shutdown in an event of exceeded current. In
Similar to a rise in operating temperature, an
many instances this causes the device to overheat,
unexpected rise in output current in power
in which case over temperature can help. The
management may lead to severe damage that
increase in heat is progressive while the increase in
could transmit across the entire power rail. Multiple
current demand is almost immediate.
conditions could lead to an increase in output
ground, there are a variety of linear regulators
current ranging from stalled motors, too many
Over-temperature conditions
nodes attached to the power rail and even short
Although we can compensate and design around
circuits from electrically and physically damaged
thermal and power dissipation, faults may exist
equipment. This increase in supply current is
where the load exceeds our set parameters. It is
harmful to most electronic systems as well as the
recommended to have a way of shutting down
host power management circuit and can cause
the system to prevent permanent damage in case
irreparable damage to very expensive machinery or
Texas Instruments: Linear power for automated industrial systems
4
July 2017
production delays. Selecting an LDO with internal
will sample this and take control of the output to
protection from short circuit and current limit can
maintain this current within its safe operation. Once
help prevent this harmful effect from transmitting
the current limit is reached, the output voltage is
and provide additional protection to the overall
no longer regulated and will be defined by the load
power management.
impedance:
Internal
Current
VREF
VOUT= ILIMIT x RLOAD
VIN
Current
Source
ILOAD
The pass transistor will continue this operation
and will dissipate power as long as the thermal
IS = ILOAD / β
VADJ
Ref
Current
Sensing
resistance (θJA) allows for healthy power
dissipation (TJ < 125 °C).
Conclusion
A great deal of consideration and precaution
must be taken when designing a power supply for
Figure 4: Internal LDO current Llimit structure.
any type of automated industrial/factory system.
Current limit in a linear regulator (LDO) is defined
However, many features have been widely adopted
by establishing an upper boundary for the current
supplied. This is achieved through internal circuitry
which controls the output stage transistors inside
the LDO as seen in Figure 4. The internal current
measures and mimics the output current so that
when the output load’s current increases, so will
in linear regulator designs that make them a great, if
not perfect, fit for all environments. While there is no
one-size fits all, there is definitely a linear regulator
that can meet all the requirements for any particular
system while remaining an easy-to-use and costeffective power management solution.
the sensed current. Finally the internal comparator
References
1. F. Barzegr, S. Cuk, and R.D. Middlebrook, ” Using Small Computers to Model and Measure Magnitude and Phase of Regulator Transfer Functions and Loop Gain,” Proceedings of Powercon 8, April 1981
2. Bruce Hunter and Patrick Rowland, Linear Regulator Design Guide For LDOs, Application Report (SLVA118A),
Texas Instruments, June 2008
Here’s more information about linear regulators Download these datasheets: TPS709, TPS7A16 and TPS7A4001
Important Notice: The products and services of Texas Instruments Incorporated and its subsidiaries described herein are sold subject to TI’s standard terms
and conditions of sale. Customers are advised to obtain the most current and complete information about TI products and services before placing orders. TI
assumes no liability for applications assistance, customer’s applications or product designs, software performance, or infringement of patents. The
publication of information regarding any other company’s products or services does not constitute TI’s approval, warranty or endorsement thereof.
The platform bar is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
© 2017 Texas Instruments Incorporated
SLYY067
IMPORTANT NOTICE FOR TI DESIGN INFORMATION AND RESOURCES
Texas Instruments Incorporated (‘TI”) technical, application or other design advice, services or information, including, but not limited to,
reference designs and materials relating to evaluation modules, (collectively, “TI Resources”) are intended to assist designers who are
developing applications that incorporate TI products; by downloading, accessing or using any particular TI Resource in any way, you
(individually or, if you are acting on behalf of a company, your company) agree to use it solely for this purpose and subject to the terms of
this Notice.
TI’s provision of TI Resources does not expand or otherwise alter TI’s applicable published warranties or warranty disclaimers for TI
products, and no additional obligations or liabilities arise from TI providing such TI Resources. TI reserves the right to make corrections,
enhancements, improvements and other changes to its TI Resources.
You understand and agree that you remain responsible for using your independent analysis, evaluation and judgment in designing your
applications and that you have full and exclusive responsibility to assure the safety of your applications and compliance of your applications
(and of all TI products used in or for your applications) with all applicable regulations, laws and other applicable requirements. You
represent that, with respect to your applications, you have all the necessary expertise to create and implement safeguards that (1)
anticipate dangerous consequences of failures, (2) monitor failures and their consequences, and (3) lessen the likelihood of failures that
might cause harm and take appropriate actions. You agree that prior to using or distributing any applications that include TI products, you
will thoroughly test such applications and the functionality of such TI products as used in such applications. TI has not conducted any
testing other than that specifically described in the published documentation for a particular TI Resource.
You are authorized to use, copy and modify any individual TI Resource only in connection with the development of applications that include
the TI product(s) identified in such TI Resource. NO OTHER LICENSE, EXPRESS OR IMPLIED, BY ESTOPPEL OR OTHERWISE TO
ANY OTHER TI INTELLECTUAL PROPERTY RIGHT, AND NO LICENSE TO ANY TECHNOLOGY OR INTELLECTUAL PROPERTY
RIGHT OF TI OR ANY THIRD PARTY IS GRANTED HEREIN, including but not limited to any patent right, copyright, mask work right, or
other intellectual property right relating to any combination, machine, or process in which TI products or services are used. Information
regarding or referencing third-party products or services does not constitute a license to use such products or services, or a warranty or
endorsement thereof. Use of TI Resources may require a license from a third party under the patents or other intellectual property of the
third party, or a license from TI under the patents or other intellectual property of TI.
TI RESOURCES ARE PROVIDED “AS IS” AND WITH ALL FAULTS. TI DISCLAIMS ALL OTHER WARRANTIES OR
REPRESENTATIONS, EXPRESS OR IMPLIED, REGARDING TI RESOURCES OR USE THEREOF, INCLUDING BUT NOT LIMITED TO
ACCURACY OR COMPLETENESS, TITLE, ANY EPIDEMIC FAILURE WARRANTY AND ANY IMPLIED WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT OF ANY THIRD PARTY INTELLECTUAL
PROPERTY RIGHTS.
TI SHALL NOT BE LIABLE FOR AND SHALL NOT DEFEND OR INDEMNIFY YOU AGAINST ANY CLAIM, INCLUDING BUT NOT
LIMITED TO ANY INFRINGEMENT CLAIM THAT RELATES TO OR IS BASED ON ANY COMBINATION OF PRODUCTS EVEN IF
DESCRIBED IN TI RESOURCES OR OTHERWISE. IN NO EVENT SHALL TI BE LIABLE FOR ANY ACTUAL, DIRECT, SPECIAL,
COLLATERAL, INDIRECT, PUNITIVE, INCIDENTAL, CONSEQUENTIAL OR EXEMPLARY DAMAGES IN CONNECTION WITH OR
ARISING OUT OF TI RESOURCES OR USE THEREOF, AND REGARDLESS OF WHETHER TI HAS BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.
You agree to fully indemnify TI and its representatives against any damages, costs, losses, and/or liabilities arising out of your noncompliance with the terms and provisions of this Notice.
This Notice applies to TI Resources. Additional terms apply to the use and purchase of certain types of materials, TI products and services.
These include; without limitation, TI’s standard terms for semiconductor products http://www.ti.com/sc/docs/stdterms.htm), evaluation
modules, and samples (http://www.ti.com/sc/docs/sampterms.htm).
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2017, Texas Instruments Incorporated
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertising