LM22672EVAL National Semiconductor, LM22672EVAL Datasheet

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LM22672EVAL

Manufacturer Part Number
LM22672EVAL
Description
Manufacturer
National Semiconductor
Datasheet
1.LM22672EVAL.pdf (18 pages)

Specifications of LM22672EVAL

Lead Free Status / Rohs Status
Not Compliant
© 2010 National Semiconductor Corporation
1A SIMPLE SWITCHER®, Step-Down Voltage Regulator
with Features
General Description
The LM22672 series of regulators are monolithic integrated
circuits which provide all of the active functions for a step-
down (buck) switching regulator capable of driving up to 1A
loads with excellent line and load regulation characteristics.
High efficiency (>90%) is obtained through the use of a low
ON-resistance N-channel MOSFET. The series consists of a
fixed 5V output and an adjustable version.
The SIMPLE SWITCHER
use complete design using a minimum number of external
components and National’s WEBENCH
National’s WEBENCH
nal component calculation, electrical simulation, thermal sim-
ulation, and Build-It boards for easy design-in. The switching
clock frequency is provided by an internal fixed frequency os-
cillator which operates at 500 kHz. The switching frequency
can also be adjusted with an external resistor or synchronized
to an external clock up to 1MHz. It is also possible to self-
synchronize multiple regulators to share the same switching
frequency. The LM22672 series also has built in thermal shut-
down, current limiting and an enable control input that can
power down the regulator to a low 25 µA quiescent current
standby condition. An adjustable soft-start feature is provided
by selecting an appropriate external soft-start capacitor.
Simplified Application Schematic
®
tool includes features such as exter-
®
concept provides for an easy to
300767
®
design tool.
LM22672
Features
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Package
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Applications
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Wide input voltage range: 4.5V to 42V
Internally compensated voltage mode control
Stable with low ESR ceramic capacitors
200 mΩ N-channel MOSFET
Output voltage options:
±1.5% feedback reference accuracy
Switching frequency of 500 kHz, adjustable between 200
kHz and 1 MHz
-40°C to 125°C operating junction temperature range
Precision enable pin
Integrated boot diode
Adjustable soft-start
Fully WEBENCH
Step-down and inverting buck-boost applications
PSOP-8 (Exposed Pad)
Industrial Control
Telecom and Datacom Systems
Embedded Systems
Automotive Telematics and Body Electronics
Conversions from Standard 24V, 12V and 5V Input Rails
-ADJ (outputs as low as 1.285V)
-5.0 (output fixed to 5V)
®
enabled
30076701
September 10, 2010
www.national.com

LM22672EVAL Summary of contents

Page 1

... An adjustable soft-start feature is provided by selecting an appropriate external soft-start capacitor. Simplified Application Schematic © 2010 National Semiconductor Corporation LM22672 Features ■ Wide input voltage range: 4.5V to 42V ■ ...

Page 2

Connection Diagram Ordering Information Output Voltage Order Number ADJ LM22672MR-ADJ ADJ LM22672MRE-ADJ ADJ LM22672MRX-ADJ 5.0 LM22672MR-5.0 5.0 LM22672MRE-5.0 5.0 LM22672MRX-5.0 Pin Descriptions Pin Name Description 1 BOOT Bootstrap input 2 SS Soft-start pin 3 RT/SYNC Oscillator frequency adjust pin or ...

Page 3

... Absolute Maximum Ratings If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VIN to GND EN Pin Voltage SS, RT/SYNC Pin Voltage SW to GND (Note 2) BOOT Pin Voltage FB Pin Voltage Power Dissipation Electrical Characteristics junction temperature (T ) range of -40° ...

Page 4

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur, including inoperability and degradation of device reliability and/or performance. Functional operation of the device and/or non-degradation at the Absolute Maximum Ratings or other conditions beyond ...

Page 5

Feedback Bias Current vs Temperature Standby Quiescent Current vs Input Voltage Normalized Feedback Voltage vs Input Voltage Normalized Enable Threshold Voltage vs Temperature 30076705 Normalized Feedback Voltage vs Temperature 30076706 Switching Frequency vs RT/SYNC Resistor 30076709 5 30076710 30076707 30076713 ...

Page 6

Soft-start Current vs Temperature www.national.com 30076742 6 ...

Page 7

Typical Application Circuit and Block Diagram FIGURE 1. 3. 600 kHz OUT 7 30076714 www.national.com ...

Page 8

Detailed Operating Description The LM22672 switching regulator features all of the functions necessary to implement an efficient high voltage buck regu- lator using a minimum of external components. This easy to use regulator integrates a 42V N-Channel switch with an ...

Page 9

FIGURE 2. Output Current in Foldback vs. Nominal Duty Cycle The percentage of output current limit fold back is affected by duty cycle, inductance, and switching See Figure 2 for details. The current limit will only protect the inductor from ...

Page 10

Self Synchronize It is also possible to self-synchronize multiple LM22672 reg- ulators to share the same switching frequency. This can be done by attaching the RT/SYNC pins together and putting a 1 kΩ resistor to ground. The diagram in this ...

Page 11

F is the switching frequency which is 500 kHz without an external frequency set resistor or external sync signal ap- plied to the RT/SYNC pin. If the switching frequency is set higher than 500kHz, the inductance value may not ...

Page 12

FIGURE 5. Resistive Feedback Divider A maximum value of 10 kΩ is recommended for the sum of R1 and R2 to keep high output voltage accuracy for the –ADJ option. A maximum of 2 kΩ is recommended for the -5.0 ...

Page 13

The junction-to-ambient thermal resistance of the LM22672 will vary with the application. The most signifi- cant variables are the area of copper in the PC board, the number of ...

Page 14

PCB Layout Example www.national.com 14 30076741 ...

Page 15

Schematic for Buck/Boost (Inverting) Application See AN-1888 for more information on the inverting (buck- boost) application generating a negative output voltage from a positive input voltage. 30076726 15 www.national.com ...

Page 16

Physical Dimensions www.national.com inches (millimeters) unless otherwise noted 8-Lead Plastic PSOP-8 Package NS Package Number MRA08B 16 ...

Page 17

Notes 17 www.national.com ...

Page 18

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