LM20333EVAL National Semiconductor, LM20333EVAL Datasheet

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LM20333EVAL

Manufacturer Part Number
LM20333EVAL
Description
EVALUATION BOARD FOR THE LM20333
Manufacturer
National Semiconductor
Series
PowerWise®r
Datasheets

Specifications of LM20333EVAL

Main Purpose
DC/DC, Step Down
Outputs And Type
1, Non-Isolated
Voltage - Output
3.3V
Current - Output
3A
Voltage - Input
4.5 ~ 25V
Regulator Topology
Buck
Board Type
Fully Populated
Utilized Ic / Part
LM20333
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
Power - Output
-
Frequency - Switching
-
© 2008 National Semiconductor Corporation
LM20333 Evaluation Board
Introduction
This evaluation board provides a solution to examine the full
featured LM20333 buck switching regulator that is capable of
driving up to 3A of load current. This device features a clock
synchronization input that allows the switching frequency to
be synchronized to an external clock source. The flexibility to
synchronize the switching frequency from 250 kHz to 1.5 MHz
allows the size of the power stage components to be reduced
while still allowing for high efficiency. The LM20333 is capable
of down converting from an input voltage between 4.5V and
36V. Fault protection features include cycle-by-cycle current
limit, output power good, and output over-voltage protection.
The dual function soft-start/tracking pin can be used to control
the startup response of the LM20333, and the precision en-
able pin can be used to easily sequence the LM20333 in
applications with sequencing requirements.
Evaluation Board Schematic
300513
National Semiconductor
Application Note 1791
Dennis Hudgins
October 1, 2008
The LM20333 evaluation board has been optimized to work
from 4.5V to 25V achieving a balance between overall solu-
tion size with the efficiency of the regulator. The evaluation
board measures just under 2” x 2” on a four layer PCB, and
exhibits a thermal characteristic of 27 °C/W with no air flow.
The power stage and compensation components of the
LM20333 evaluation board have been optimized for an input
voltage of 12V, but for testing purposes, the input can be var-
ied across the entire operating range. The output voltage of
the evaluation board is nominally 3.3V, but this voltage can
be easily changed by replacing one of the feedback resistors
(R5 or R6).
www.national.com
30051301

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LM20333EVAL Summary of contents

Page 1

... The dual function soft-start/tracking pin can be used to control the startup response of the LM20333, and the precision en- able pin can be used to easily sequence the LM20333 in applications with sequencing requirements. Evaluation Board Schematic © 2008 National Semiconductor Corporation National Semiconductor Application Note 1791 Dennis Hudgins October 1, 2008 The LM20333 evaluation board has been optimized to work from 4 ...

Page 2

Powering and Loading Considerations Read this entire page prior to attempting to power the evalu- ation board. QUICK SETUP PROCEDURE Step 1: Set the input source current limit to 3A. Turn off the input source. Connect the positive output of ...

Page 3

Performance Characteristics EFFICIENCY PLOTS Figure 1 shows the conversion efficiency versus output cur- rent for a 5V and 12V input voltage. FIGURE 1. TURN-ON WAVEFORM When applying power to the LM20333 evaluation board a soft-start sequence occurs. Figure 2 shows ...

Page 4

Bill of Materials The Bill of Materials is shown below, including the manufacturer and part number. DESIGNATOR QTY PART NUMBER C1 1 GRM32ER61E226KE15 C2 GRM21BR61E475KA12L C5 1 GRM188R71A105KA61D C4 C1608X7R1H104K C7 1 C1608C0G1H100J C8 1 C1608C0G1H152J ...

Page 5

Component Selection This section provides a walk-through of the design process of the LM20333 evaluation board. Unless otherwise indicated all equations assume units of amps (A) for current, farads (F) for capacitance, henries (H) for inductance, and volts (V) for ...

Page 6

For stability purposes the device should be compensated for the maximum output current expected in the application. OPTIONAL COMPENSATION CAPACITOR second compensation capacitor C7 can be used in some designs to improve noise immunity for low duty cycle ...

Page 7

PCB Layout Top Layer Mid Layer1 30051330 30051331 7 30051332 Mid Layer2 30051333 Bottom Layer www.national.com ...

Page 8

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