Objective: Understand how a linear or low-dropout regulator
delivers a regulated output voltage. Know the difference
between linear and low-dropout regulators.
Length: 45 minutes
Published Date: Jul 30, 04
Step(s) to complete
- View online seminar
- Complete the suggested assignments
- Complete the online test to receive a certificate from
Bob Pease
Online Seminar: The evolution of voltage regulators with focus on LDO's
 About the
Presentor: Muna Acosta is an application manager
with National Semiconductor Standard Analog Group in Santa
Clara, California.
This seminar discusses the details of linear voltage
regulators and the evolution of the Low Dropout Voltage (LDO)
regulator topology.
About the Instructor: Wanda Garrett is the Technical Communications
Manager in the Web Business Group at National Semiconductor
Corp. in Santa Clara, California. With 20 years experience in
the design and application of DC/DC converters and related
power management products, as well as being a key trainer on
this subject, she is now a primary developer of National's
Knowledge Base, the Online Seminar series, and other online
technical tools. Before joining National in 1983, she received
a BSEE from Washington State University. |
Reading
Assignments:
To understand how the three types of regulators
provide control for the regulated output voltage, and to
see how the differences in control method affect the
frequency response of the regulators, read AN-1148 , "Linear Regulators: Theory of Operation and
Compensation."
For additional information, consult the Knowledge
Base using the following queries:
Research
Assignments:
Using the datasheets for LP3985 (150mA), LM3480 (100mA), and LM340L (100mA), compare their performance and limitations (for
the 5V output versions) -
- Identify which is the standard (NPN) regulator,
which is the quasi-LDO regulator, and which is the LDO
regulator.
- Which packages are the devices available in?
- What type of pass device is used in each?
Compare specifications:
- Which allows highest supply voltage?
- Which allows lowest supply voltage (while
maintaining regulated output)?
- Which is lowest cost (check at http://www.national.com/ )?
- Which has the lowest max. quiescent (no load)
supply current?
- How does the dropout voltage of the LM3480 and the
LP3985 vary with temperature?
Check the LP3985 Application Hints:
- What is the function of the LP3985 Bypass pin?
- What type of output capacitor should be used for
most applications?
Check thermal performance of LP3985 (with Vin=3.0V,
Vout=2.8V, Iout=150mA, Ignd=140uA):
- What is the power dissipation of the LP3985?
- What is the regulator efficiency?
- If the thermal resistance qJA of the SOT23-5
package is 220oC/W, then what is the LP3985 junction
temperature with an ambient temperature of 40oC?
CHECK ALL ANSWERS HERE
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