National Semiconductor LM22679 Technical data
October 17, 2008
LM22679
5A SIMPLE SWITCHER®, Step-Down Voltage Regulator
with Adjustable Soft-Start and Current Limit
LM22679 5A SIMPLE SWITCHER®, Step-Down Voltage Regulator with Adjustable Soft-Start and
Current Limit
General Description
The LM22679 series of regulators are monolithic integrated
circuits which provide all of the active functions for a stepdown (buck) switching regulator capable of driving up to 5A
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® concept provides for an easy to
use complete design using a minimum number of external
components and National’s WEBENCH® design tool.
National’s WEBENCH® tool includes features such as external component calculation, electrical simulation, thermal simulation, and Build-It boards for easy design-in. The switching
clock frequency is provided by an internal fixed frequency oscillator which operates at 500 kHz. The LM22679 series also
has built in thermal shutdown and current limiting. The current
limit threshold can be adjusted using an external resistor. An
adjustable soft-start feature is provided by selecting an appropriate external soft-start capacitor.
Features
Wide input voltage range: 4.5V to 42V
■
Internally compensated voltage mode control
■
Stable with low ESR ceramic capacitors
■
100 mΩ N-channel MOSFET
■
Output voltage options:
■
-ADJ (outputs as low as 1.285V)
-5.0 (output fixed to 5V)
±1.5% feedback reference accuracy
■
Switching frequency of 500kHz
■
-40°C to 125°C operating junction temperature range
■
Adjustable soft-start
■
Adjustable current limit
■
Integrated boot diode
■
Fully WEBENCH® enabled
■
Step-down and inverting buck-boost applications
■
Package
TO-263 THIN (Exposed Pad)
■
Applications
Industrial Control
■
Telecom and Datacom Systems
■
Embedded Systems
■
Automotive Telematics and Body Electronics
■
Conversions from Standard 24V, 12V and 5V Input Rails
■
Simplified Application Schematic
30072301
© 2008 National Semiconductor Corporation 300723 www.national.com
Connection Diagram
LM22679
7-Lead Plastic TO-263 THIN Package
NS Package Number TJ7A
30072302
Ordering Information
Output Voltage Order Number Package Type NSC Package Drawing Supplied As
ADJ LM22679TJE-ADJ
ADJ LM22679TJ-ADJ 1000 Units in Tape and Reel
5.0 LM22679TJE-5.0 250 Units in Tape and Reel
5.0 LM22679TJ-5.0 1000 Units in Tape and Reel
TO-263 THIN Exposed Pad TJ7A
250 Units in Tape and Reel
Pin Descriptions
Pin Name Description Application Information
1 SW Switch pin Attaches to the switch node
2 VIN Source input voltage Input to the regulator. Operates from 4.5V to 42V
3 BOOT Bootstrap input Provides the gate voltage for the high side NFET
4 GND System ground Provide good capacitive decoupling between VIN and this pin
5 IADJ Current Limit Setting pin A resistor attached between this pin and GND can be used to set the current limit threshold.
Pin can be left floating and internal setting will be default.
6 FB Feedback pin Inverting input to the internal voltage error amplifier.
7 SS Soft-start pin An external capacitor and an internal 50 µA current source set the time constant for the rise
of the error amplifier reference. Pin can be left floating and internal soft-start will be default.
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LM22679
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
VIN to GND 43V
SS, IADJ Pin Voltage -0.5V to 7V
SW to GND (Note 2) -5V to V
IN
Boot Pin Voltage VSW + 7V
FB Pin Voltage -0.5V to 7V
Power Dissipation Internally Limited
Junction Temperature 150°C
Electrical Characteristics Limits in standard type are for T
Soldering Information
Vapor Phase (75 sec.) 219°C
Infrared (10 sec.) 240°C
Wave (4 sec.) 260°C
ESD Rating (Note 3)
Human Body Model ±2 kV
Storage Temperature Range -65°C to +150°C
Operating Ratings (Note 1)
Supply Voltage (VIN)
Junction Temperature Range -40°C to +125°C
= 25°C only; limits in boldface type apply over the
J
4.5V to 42V
junction temperature (TJ) range of -40°C to +125°C. Minimum and Maximum limits are guaranteed through test, design, or statistical
correlation. Typical values represent the most likely parametric norm at TA = TJ = 25°C, and are provided for reference purposes
only. Unless otherwise specified: VIN = 12V.
Symbol Parameter Conditions Min
(Note 5)
Typ
(Note 4)
Max
(Note 5)
LM22679-5.0
V
FB
Feedback Voltage VIN = 8V to 42V 4.925/4.9 5.0 5.075/5.1 V
LM22679-ADJ
V
FB
Feedback Voltage VIN = 4.7V to 42V 1.266/1.259 1.285 1.304/1.311 V
All Output Voltage Versions
I
V
ADJ
I
CL
I
CLADJ
I
Q
L
Quiescent Current VFB = 5V 3.4 6 mA
Current Limit Adjust Voltage 0.65 0.8 0.9 V
Current Limit 6.0/5.75 7.1 8.4/8.75 A
Current Limit Adjust
IADJ Resistor = 56.2 kΩ
0.4 0.7 1 A
Output Leakage Current VIN = 42V, SS Pin = 0V, VSW = 0V 32 60 µA
VSW = -1V 31 75 µA
R
DS(ON)
T
OFFMIN
T
ONMIN
I
BIAS
I
T
f
SS
O
SD
Switch On-Resistance 0.10 0.14/0.2
Oscillator Frequency 400 500 600 kHz
Minimum Off-time 300 ns
Minimum On-time 100 ns
Feedback Bias Current VFB = 1.3V (ADJ Version Only) 230 nA
Soft-start Current 30 50 70 µA
Thermal Shutdown
150 °C
Threshold
θ
JA
Thermal Resistance Junction to ambient temperature
22 °C/W
resistance (Note 6)
Units
Ω
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 those indicated in
the recommended Operating Ratings is not implied. The recommended Operating Ratings indicate conditions at which the device is functional and should not be
operated beyond such conditions.
Note 2: The absolute maximum specification of the ‘SW to GND’ applies to DC voltage. An extended negative voltage limit of -10V applies to a pulse of up to 50
ns.
Note 3: ESD was applied using the human body model, a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin.
Note 4: Typical values represent most likely parametric norms at the conditions specified and are not guaranteed.
Note 5: Min and Max limits are 100% production tested at 25°C. Limits over the operating temperature range are guaranteed through correlation using Statistical
Quality Control (SQC) methods. Limits are used to calculate National’s Average Outgoing Quality Level (AOQL).
Note 6: The value of θJA for the TO-263 THIN (TJ) package of 22°C/W is valid if package is mounted to 1 square inch of copper. The θJA value can range from
20 to 30°C/W depending on the amount of PCB copper dedicated to heat transfer. See application note AN-1797 for more information.
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Typical Performance Characteristics Unless otherwise specified the following conditions apply: Vin =
12V, TJ = 25°C.
LM22679
Efficiency vs I
V
= 3.3V
OUT
OUT
and V
IN
30072327
Current Limit vs Temperature
30072303
Normalized Switching Frequency vs Temperature
30072304
Normalized Feedback Voltage vs Temperature
Feedback Bias Current vs Temperature
30072305
Normalized R
vs Temperature
DS(ON)
30072307
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30072308
LM22679
Normalized Feedback Voltage vs Input Voltage
30072309
Current Limit vs IADJ Resistor
Soft-start Current vs Temperature
30072311
30072313
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