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LM22673, LM22673-Q1
SNVS586O – SEPTEMBER 2008 – REVISED NOVEMBER 2014
LM22673/-Q1 42 V, 3 A SIMPLE SWITCHER®, Step-Down Voltage Regulator
with Features
1 Features
3 Description
•
•
•
•
•
The LM22673 switching regulator provides all of the
functions necessary to implement an efficient high
voltage step-down (buck) regulator using a minimum
of external components. This easy to use regulator
incorporates a 42 V N-channel MOSFET switch
capable of providing up to 3 A of load current.
Excellent line and load regulation along with high
efficiency (> 90%) are featured. Voltage mode control
offers short minimum on-time, allowing the widest
ratio between input and output voltages. Internal loop
compensation means that the user is free from the
tedious task of calculating the loop compensation
components. Fixed 5 V output and adjustable output
voltage options are available. A switching frequency
of 500 kHz allows for small external components and
good transient response. An adjustable soft-start
feature is provided through the selection of a single
external capacitor. In addition, the switch current limit
can be programmed with a single external resistor,
allowing solution optimization. The LM22673 device
also has built-in thermal shutdown, and current
limiting to protect against accidental overloads.
1
•
•
•
•
•
•
•
•
•
•
•
Wide Input Voltage Range: 4.5 V to 42 V
Internally Compensated Voltage Mode Control
Stable with Low ESR Ceramic Capacitors
120 mΩ N-Channel MOSFET PFM Package
100 mΩ N-Channel MOSFET SO PowerPAD
Package
Output Voltage Options:
-ADJ (Outputs as Low as 1.285 V)
-5.0 (Output Fixed to 5 V)
±1.5% Feedback Reference Accuracy
Switching Frequency of 500 kHz
–40°C to 125°C Operating Junction
Temperature Range
Adjustable Soft-Start
Adjustable Current Limit
Integrated Boot-Strap Diode
Fully Webench® Enabled
LM22673-Q1 is an Automotive Grade Product
that is AEC-Q100 Grade 1 Qualified (–40°C to
+125°C Junction Temperature)
SO PowerPAD (Exposed Pad)
PFM (Exposed Pad)
The LM22673 device is a member of Texas
Instruments' SIMPLE SWITCHER® family. The
SIMPLE SWITCHER® concept provides for an easy
to use complete design using a minimum number of
external components and the TI WEBENCH® design
tool. TI's WEBENCH® tool includes features such as
external component calculation, electrical simulation,
thermal simulation, and Build-It boards for easy
design-in.
2 Applications
•
•
•
•
Industrial Control
Telecom and Datacom Systems
Embedded Systems
Conversions from Standard 24 V, 12 V and 5 V
Input Rails
Device Information(1)
PART NUMBER
LM22673,
LM22673-Q1
PACKAGE
BODY SIZE (NOM)
HSOP (8)
4.89 mm x 3.90 mm
TO-263
10.16 mm x 9.85 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Simplified Application Schematic
VIN
VIN
FB
LM22673-ADJ
BOOT
VOUT
IADJ
SS
GND
SW
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LM22673, LM22673-Q1
SNVS586O – SEPTEMBER 2008 – REVISED NOVEMBER 2014
www.ti.com
Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
4
6.1
6.2
6.3
6.4
6.5
6.6
6.7
4
4
4
4
4
5
6
Absolute Maximum Ratings ......................................
Handling Ratings.......................................................
Handling Ratings: LM22673-Q1................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Typical Characteristics ..............................................
Detailed Description .............................................. 7
7.1 Overview ................................................................... 7
7.2 Functional Block Diagram ......................................... 8
7.3 Feature Description................................................... 8
7.4 Device Functional Modes........................................ 10
8
Applications and Implementation ...................... 13
8.1 Application Information............................................ 13
8.2 Typical Application .................................................. 14
9 Power Supply Recommendations...................... 17
10 Layout................................................................... 17
10.1 Layout Guidelines ................................................. 17
10.2 Layout Examples................................................... 18
10.3 Thermal Considerations ........................................ 19
11 Device and Documentation Support ................. 20
11.1
11.2
11.3
11.4
11.5
Documentation Support ........................................
Related Links ........................................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
20
20
20
20
20
12 Mechanical, Packaging, and Orderable
Information ........................................................... 20
4 Revision History
Changes from Revision N (April 2013) to Revision O
Page
•
Added Pin Configuration and Functions section, Handling Rating table, Thermal Information table, Feature
Description section, Device Functional Modes, Application and Implementation section, Power Supply
Recommendations section, Layout section, Device and Documentation Support section, and Mechanical,
Packaging, and Orderable Information section ..................................................................................................................... 1
•
Deleted Inverting Regulator Application .............................................................................................................................. 13
Changes from Revision M (April 2013) to Revision N
•
2
Page
Changed from National format toTI format ............................................................................................................................ 1
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Product Folder Links: LM22673 LM22673-Q1
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SNVS586O – SEPTEMBER 2008 – REVISED NOVEMBER 2014
5 Pin Configuration and Functions
8-Pin
HSOP
Top View
BOOT
1
8
SW
NC
2
7
VIN
IADJ
3
6
GND
FB
4
5
SS
Exposed Pad
Connect to GND
7-Pin
PFM
Top View
7 SS
6 FB
5 IADJ
4 GND
3 BOOT
2 VIN
1 SW
Exposed Pad
Connect to GND
Pin Functions
PIN
TYPE
DESCRIPTION
APPLICATION INFORMATION
NAME
SO
PowerPAD
PFM
BOOT
1
3
I
Bootstrap input
Provides the gate voltage for the high side NFET.
NC
2
—
—
Not Connected
Pin is not electrically connected inside the chip.
Pin does function as thermal conductor.
IADJ
3
5
I
Current limit adjust input 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.
FB
4
6
I
Feedback input
Feedback input to regulator.
SS
5
7
Soft-Start pin
Used to increase soft-start time. See Soft-Start
section of data sheet.
GND
6
4
—
Ground input to regulator;
system common
System ground pin.
VIN
7
2
I
Input voltage
Supply input to the regulator.
SW
8
1
O
Switch output
Switching output of regulator.
EP
EP
EP
—
Exposed Pad
Connect to ground. Provides thermal connection
to PCB. See Thermal Considerations.
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6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)
MIN
MAX
VIN to GND
SS, IADJ Pin Voltage
SW to GND (1)
V
–0.5
7
V
–5
VIN
V
VSW + 7
V
7
V
150
°C
Boot Pin Voltage
FB Pin Voltage
–0.5
Power Dissipation
UNIT
43
Internally Limited
Junction Temperature
For soldering specifications, refer to Application Report Absolute Maximum Ratings for Soldering (SNOA549).
(1)
The absolute maximum specification of the ‘SW to GND’ applies to dc voltage. An extended negative voltage limit of –10 V applies to a
pulse of up to 50 ns.
6.2 Handling Ratings
Tstg
Storage temperature range
V(ESD)
Electrostatic discharge
(1)
Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, all
pins (1)
MIN
MAX
UNIT
–65
150
°C
–2
2
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
6.3 Handling Ratings: LM22673-Q1
Tstg
Storage temperature range
V(ESD)
(1)
Electrostatic discharge
Human body model (HBM), per AEC Q100-002
MIN
MAX
UNIT
–65
150
°C
–2
2
kV
(1)
AEC Q100-002 indicates HBM stressing is done in accordance with the ANSI/ESDA/JEDEC JS-001 specification.
6.4 Recommended Operating Conditions
VIN
MIN
MAX
Supply Voltage
4.5
42
UNIT
V
Junction Temperature
–40
125
°C
6.5 Thermal Information
LM22673
THERMAL METRIC
RθJA
(1)
4
(1)
Junction-to-ambient thermal resistance
DDA
NDR
8 PINS
7 PINS
60
22
UNIT
°C/W
For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report (SPRA953).
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SNVS586O – SEPTEMBER 2008 – REVISED NOVEMBER 2014
6.6 Electrical Characteristics
Typical values represent the most likely parametric norm at TA = TJ = 25°C, and are provided for reference purposes only.
Unless otherwise specified: VIN = 12 V.
PARAMETER
TEST CONDITIONS
MIN (1)
TYP (2)
MAX (1)
4.925
5.0
5.075
UNIT
LM22673-5.0
VFB
Feedback Voltage
VIN = 8 V to 42 V
VIN = 8 V to 42 V, –40°C ≤ TJ ≤ 125°C
4.9
5.1
V
LM22673-ADJ
VFB
Feedback Voltage
VIN = 4.7 V to 42 V
1.266
VIN = 4.7 V to 42 V, –40°C ≤ TJ ≤ 125°C
1.259
1.285
1.304
1.311
V
ALL OUTPUT VOLTAGE VERSIONS
IQ
Quiescent Current
VADJ
Current Limit Adjust Voltage
ICL
Current Limit
VFB = 5 V
3.4
VFB = 5 V, –40°C ≤ TJ ≤ 125°C
6
0.8
–40°C ≤ TJ ≤ 125°C
0.65
–40°C ≤ TJ ≤ 125°C
3.35
3.4
PFM Package
RDS(ON)
Switch On-Resistance
0.9
4.2
5.5
0.12
PFM Package, –40°C ≤ TJ ≤ 125°C
SO PowerPAD Package
0.10
Oscillator Frequency
TOFFMIN
Minimum Off-time
TONMIN
Minimum On-time
IBIAS
Feedback Bias Current
ISS
Soft-start Current
TSD
Thermal Shutdown
Threshold
(1)
(2)
0.16
A
Ω
0.20
500
–40°C ≤ TJ ≤ 125°C
400
–40°C ≤ TJ ≤ 125°C
100
600
200
VFB = 1.3 V (ADJ Version Only)
EN Input = 0 V
EN Input = 0 V, –40°C ≤ TJ ≤ 125°C
V
0.16
0.22
SO PowerPAD Package, –40°C ≤ TJ ≤ 125°C
fO
5.3
mA
300
kHz
ns
100
ns
230
nA
50
30
70
150
µA
°C
MIN and MAX limits are 100% production tested at 25°C. Limits over the operating temperature range are ensured through correlation
using Statistical Quality Control (SQC) methods. Limits are used to calculate TI's Average Outgoing Quality Level (AOQL).
Typical values represent most likely parametric norms at the conditions specified and are not ensured.
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6.7 Typical Characteristics
Vin = 12 V, TJ = 25°C (unless otherwise specified)
Figure 1. Efficiency vs IOUT and VIN
VOUT = 3.3 V
Figure 2. Current Limit vs Temperature
Figure 3. Normalized Switching Frequency vs Temperature
Figure 4. Feedback Bias Current vs Temperature
1.5
NORMALIZED RDS(ON)
1.4
PFM Package
1.3
1.2
1.1
1.0
SO Package
0.9
0.8
0.7
0.6
–50 –25
0
25
50
75
100 125
TEMPERATURE (°C)
Figure 5. Normalized Feedback Voltage vs Temperature
6
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Figure 6. Normalized RDS(ON) vs Temperature
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Typical Characteristics (continued)
Vin = 12 V, TJ = 25°C (unless otherwise specified)
Figure 7. Normalized Feedback Voltage vs Input Voltage
Figure 8. Soft-Start Current vs Temperature
Figure 9. Current Limit vs IADJ Resistor
7 Detailed Description
7.1 Overview
The LM22673 device incorporates a voltage mode constant frequency PWM architecture. In addition, input
voltage feedforward is used to stabilize the loop gain against variations in input voltage. This allows the loop
compensation to be optimized for transient performance. The power MOSFET, in conjunction with the diode,
produce a rectangular waveform at the switch pin, that swings from about zero volts to VIN. The inductor and
output capacitor average this waveform to become the regulator output voltage. By adjusting the duty cycle of
this waveform, the output voltage can be controlled. The error amplifier compares the output voltage with the
internal reference and adjusts the duty cycle to regulate the output at the desired value.
The internal loop compensation of the -ADJ option is optimized for outputs of 5V and below. If an output voltage
of 5V or greater is required, the -5.0 option can be used with an external voltage divider. The minimum output
voltage is equal to the reference voltage, that is, 1.285 V (typ).
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7.2 Functional Block Diagram
VIN
VIN
BOOT
Vcc
INT REG, EN,UVLO
EN
ILimit
PWM Cmp.
FB
TYPE III
COMP
+
+
-
LOGIC
Error Amp.
VOUT
SW
OSC
1.285V
&
Soft-Start
RT/SYNC
GND
7.3 Feature Description
7.3.1 UVLO
The LM22673 also incorporates an input undervoltage lock-out (UVLO) feature. This prevents the regulator from
turning on when the input voltage is not great enough to properly bias the internal circuitry. The rising threshold is
4.3 V (typ) while the falling threshold is 3.9 V (typ).
7.3.2 Soft-Start
The soft-start feature allows the regulator to gradually reach steady-state operation, thus reducing start-up
stresses. The internal soft-start feature brings the output voltage up in about 500 µs. This time can be extended
by using an external capacitor connected to the SS pin. Values in the range of 100 nF to 1 µF are recommended.
The approximate soft-start time can be estimated from Equation 1.
TSS » 26 ´103 × CSS
(1)
Soft-start is reset any time the part is shut down or a thermal overload event occurs.
8
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Feature Description (continued)
7.3.3 Boot-Strap Supply
The LM22673 incorporates a floating high-side gate driver to control the power MOSFET. The supply for this
driver is the external boot-strap capacitor connected between the BOOT pin and SW. A good quality 10 nF
ceramic capacitor must be connected to these pins with short, wide PCB traces. One reason the regulator
imposes a minimum off-time is to ensure that this capacitor recharges every switching cycle. A minimum load of
about 5 mA is required to fully recharge the boot-strap capacitor in the minimum off-time. Some of this load can
be provided by the output voltage divider, if used.
7.3.4 Internal Compensation
The LM22673 has internal loop compensation designed to provide a stable regulator over a wide range of
external power stage components. The internal compensation of the -ADJ option is optimized for output voltages
below 5 V. If an output voltage of 5 V or greater is needed, the -5.0 option with an external resistor divider can be
used.
Ensuring stability of a design with a specific power stage (inductor and output capacitor) can be tricky. The
LM22673 stability can be verified using the WEBENCH Designer online circuit simulation tool. A quick start
spreadsheet can also be downloaded from the online product folder.
The complete transfer function for the regulator loop is found by combining the compensation and power stage
transfer functions. The LM22673 has internal type III loop compensation, as detailed in Figure 10. This is the
approximate "straight line" function from the FB pin to the input of the PWM modulator. The power stage transfer
function consists of a dc gain and a second order pole created by the inductor and output capacitor(s). Due to
the input voltage feedforward employed in the LM22673, the power stage dc gain is fixed at 20 dB. The second
order pole is characterized by its resonant frequency and its quality factor (Q). For a first pass design, the
product of inductance and output capacitance should conform to Equation 2.
(2)
Alternatively, this pole should be placed between 1.5 kHz and 15 kHz and is given by Equation 3.
(3)
The Q factor depends on the parasitic resistance of the power stage components and is not typically in the
control of the designer. Of course, loop compensation is only one consideration when selecting power stage
components (see the Applications and Implementation section for more details).
COMPENSATOR GAIN (dB)
40
35
-ADJ
-5.0
30
25
20
15
10
5
0
100
1k
10k
100k
1M
FREQUENCY (Hz)
10M
Figure 10. Compensator Gain
In general, hand calculations or simulations can only aid in selecting good power stage components. Good
design practice dictates that load and line transient testing should be done to verify the stability of the application.
Also, Bode plot measurements should be made to determine stability margins. AN-1889 How to Measure the
Loop Transfer Function of Power Supplies (SNVA364) shows how to perform a loop transfer function
measurement with only an oscilloscope and function generator.
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7.4 Device Functional Modes
7.4.1 Current Limit
The LM22673 has current limiting to prevent the switch current from exceeding safe values during an accidental
overload on the output. This peak current limit is found in the Electrical Characteristics table under the heading of
ICL. The maximum load current that can be provided, before current limit is reached, is determined from
Equation 4.
(4)
Where:
L is the value of the power inductor.
When the LM22673 enters current limit, the output voltage will drop and the peak inductor current will be fixed at
ICL at the end of each cycle. The switching frequency will remain constant while the duty cycle drops. The load
current will not remain constant, but will depend on the severity of the overload and the output voltage.
For very severe overloads ("short-circuit"), the regulator changes to a low frequency current foldback mode of
operation. The frequency foldback is about 1/5 of the nominal switching frequency. This will occur when the
current limit trips before the minimum on-time has elapsed. This mode of operation is used to prevent inductor
current "run-away", and is associated with very low output voltages when in overload. Equation 5 can be used to
determine what level of output voltage will cause the part to change to low frequency current foldback.
(5)
Where:
Fsw is the normal switching frequency.
Vin is the maximum for the application.
If the overload drives the output voltage to less than or equal to Vx, the part will enter current foldback mode. If a
given application can drive the output voltage to ≤ Vx, during an overload, then a second criterion must be
checked. Equation 6 gives the maximum input voltage, when in this mode, before damage occurs.
(6)
Where:
Vsc is the value of output voltage during the overload.
fsw is the normal switching frequency.
NOTE
If the input voltage should exceed this value, while in foldback mode, the regulator and/or
the diode may be damaged.
It is important to note that the voltages in Equation 4 through Equation 6 are measured at the inductor. Normal
trace and wiring resistance will cause the voltage at the inductor to be higher than that at a remote load.
Therefore, even if the load is shorted with zero volts across its terminals, the inductor will still see a finite voltage.
It is this value that should be used for Vx and Vsc in the calculations. In order to return from foldback mode, the
load must be reduced to a value much lower than that required to initiate foldback. This load "hysteresis" is a
normal aspect of any type of current limit foldback associated with voltage regulators.
The safe operating area, when in short circuit mode, is shown in Figure 11. Operating points below and to the
right of the curve represent safe operation.
10
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Device Functional Modes (continued)
45
INPUT VOLTAGE (v)
40
35
30
25
SAFE OPERATING AREA
20
15
10
5
0.0
0.2
0.4
0.6
0.8
1.0
SHORT CIRCUIT VOLTAGE (v)
1.2
Figure 11. SOA
7.4.2 Current-Limit Adjustment
A key feature of the LM22673 is the ability to adjust the peak switch current limit. This can be useful when the full
current capability of the regulator is not required for a given application. A smaller current limit may allow the use
of power components with lower current ratings, thus saving space and reducing cost. A single resistor between
the IADJ pin and ground controls the current limit in accordance with Figure 12. The current limit mode is set
during start-up of the regulator. When VIN is applied, a weak pullup is connected to the IADJ pin and, after
approximately 100 µs, the voltage on the pin is checked against a threshold of about 0.8V. With the IADJ pin
open, the voltage floats above this threshold, and the current limit is set to the default value of 4.2A (typ). With a
resistor present, an internal reference holds the pin voltage at 0.8 V; the resulting current sets the current limit.
The accuracy of the adjusted current limit will be slightly worse than that of the default value, that is, +35% /
–25% is to be expected. Resistor values should not exceed the limits shown in Figure 12.
Figure 12. Current Limit vs IADJ Resistor
7.4.3 Thermal Protection
Internal thermal shutdown circuitry protects the LM22673 should the maximum junction temperature be
exceeded. This protection is activated at about 150°C, with the result that the regulator will shutdown until the
temperature drops below about 135°C.
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Device Functional Modes (continued)
7.4.4 Duty-Cycle Limits
Ideally the regulator would control the duty cycle over the full range of zero to one. However due to inherent
delays in the circuitry, there are limits on both the maximum and minimum duty cycles that can be reliably
controlled. This in turn places limits on the maximum and minimum input and output voltages that can be
converted by the LM22673. A minimum on-time is imposed by the regulator in order to correctly measure the
switch current during a current limit event. A minimum off-time is imposed in order the re-charge the bootstrap
capacitor. Equation 7 can be used to determine the approximate maximum input voltage for a given output
voltage.
(7)
Where:
Fsw is the switching frequency.
TON is the minimum on-time.
Both parameters are found in the Electrical Characteristics table.
Nominal values should be used. The worst case is lowest output voltage. If this input voltage is exceeded, the
regulator will skip cycles, effectively lowering the switching frequency. The consequences of this are higher
output voltage ripple and a degradation of the output voltage accuracy.
The second limitation is the maximum duty cycle before the output voltage will "dropout" of regulation. Equation 8
can be used to approximate the minimum input voltage before dropout occurs.
(8)
Where:
The values of TOFF and RDS(ON) are found in the Electrical Characteristics table.
The worst case here is largest load. In this equation, RL is the dc inductor resistance. Of course, the lowest input
voltage to the regulator must not be less than 4.5 V (typ).
12
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8 Applications and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
The LM22673 device is a step down dc-to-dc regulator. It is typically used to convert a higher dc voltage to a
lower dc voltage with a maximum output current of 3 A. Detailed Design Procedure can be used to select
components for the LM22673 device. Alternately, the WEBENCH® software may be used to generate complete
designs. When generating a design, the WEBENCH® software utilizes iterative design procedure and accesses
comprehensive databases of components. Go to WEBENCH Designer for more details. This section presents a
simplified discussion of the design process.
8.1.1 Output Voltage Divider Selection
For output voltages between about 1.285 V and 5 V, the -ADJ option should be used, with an appropriate voltage
divider as shown in Figure 13. Equation 9 can be used to calculate the resistor values of this divider.
(9)
A good value for RFBB is 1 kΩ. This will help to provide some of the minimum load current requirement and
reduce susceptibility to noise pick-up. The top of RFBT should be connected directly to the output capacitor or to
the load for remote sensing. If the divider is connected to the load, a local high-frequency bypass should be
provided at that location.
For output voltages of 5 V, the -5.0 option should be used. In this case no divider is needed and the FB pin is
connected to the output. The approximate values of the internal voltage divider are as follows: 7.38 kΩ from the
FB pin to the input of the error amplifier and 2.55 kΩ from there to ground.
Both the -ADJ and -5.0 options can be used for output voltages greater than 5 V, by using the correct output
divider. As mentioned in the Internal Compensation section, the -5.0 option is optimized for output voltages of 5
V. However, for output voltages greater than 5 V, this option may provide better loop bandwidth than the -ADJ
option, in some applications. If the -5.0 option is to be used at output voltages greater than 5 V, Equation 10
should be used to determine the resistor values in the output divider.
(10)
A value of RFBB of about 1 kΩ is a good first choice.
Vout
RFBT
FB
RFBB
Figure 13. Resistive Feedback Divider
A maximum value of 10 kΩ is recommended for the sum of RFBB and RFBT to maintain good output voltage
accuracy for the -ADJ option. A maximum of 2 kΩ is recommended for the -5.0 option. For the -5.0 option, the
total internal divider resistance is typically 9.93 kΩ.
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Application Information (continued)
In all cases the output voltage divider should be placed as close as possible to the FB pin of the LM22673,
because this is a high impedance input and is susceptible to noise pick-up.
8.1.2 Power Diode
A Schottky-type power diode is required for all LM22673 applications. Ultra-fast diodes are not recommended
and may result in damage to the IC due to reverse recovery current transients. The near ideal reverse recovery
characteristics and low forward voltage drop of Schottky diodes are particularly important for high input voltage
and low output voltage applications common to the LM22673. The reverse breakdown rating of the diode should
be selected for the maximum VIN, plus some safety margin. A good rule of thumb is to select a diode with a
reverse voltage rating of 1.3 times the maximum input voltage.
Select a diode with an average current rating at least equal to the maximum load current that will be seen in the
application.
8.2 Typical Application
8.2.1 Typical Buck Regulator Application
Figure 14 shows an example of converting an input voltage range of 5.5 V to 42 V, to an output of 3.3 V at 3 A.
RFBB
976:
VIN 4.5V to 42V
+
C2
22 PF
C1
6.8 PF
C6
1 PF
FB
VIN
C3
LM22673-ADJ
10 nF
SS
BOOT
IADJ
R3
GND
RFBT
1.54 k:
L1
8.2 PH
SW
D1
60V, 5A
VOUT 3.3V
C4
120 PF
+
GND
GND
Figure 14. Typical Buck Regulator Application
8.2.1.1 Design Requirements
DESIGN PARAMETERS
EXAMPLE VALUE
Driver Supply Voltage (VIN)
5.5 to 42 V
Output Voltage (VOUT)
3.3 V
RFBT
Calculated based on RFBB and VREF of 1.285 V.
RFBB
1 kΩ to 10 kΩ
IOUT
3A
8.2.1.2 Detailed Design Procedure
8.2.1.2.1 External Components
The following guidelines should be used when designing a step-down (buck) converter with the LM22673.
14
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8.2.1.2.2 Inductor
The inductor value is determined based on the load current, ripple current, and the minimum and maximum input
voltages. To keep the application in continuous conduction mode (CCM), the maximum ripple current, IRIPPLE ,
should be less than twice the minimum load current.
The general rule of keeping the inductor current peak-to-peak ripple around 30% of the nominal output current is
a good compromise between excessive output voltage ripple and excessive component size and cost. Using this
value of ripple current, the value of inductor, L, is calculated using Equation 11.
(11)
Where:
Fsw is the switching frequency.
Vin should be taken at its maximum value, for the given application.
The formula in Equation 11 provides a guide to select the value of the inductor L; the nearest standard value will
then be used in the circuit.
Once the inductor is selected, the actual ripple current can be determined by Equation 12.
(12)
Increasing the inductance will generally slow down the transient response but reduce the output voltage ripple.
Reducing the inductance will generally improve the transient response but increase the output voltage ripple.
The inductor must be rated for the peak current, IPK, in a given application, to prevent saturation. During normal
loading conditions, the peak current is equal to the load current plus 1/2 of the inductor ripple current.
During an overload condition, as well as during certain load transients, the controller may trip current limit. In this
case the peak inductor current is given by ICL, found in the Electrical Characteristics table. Good design practice
requires that the inductor rating be adequate for this overload condition.
NOTE
If the inductor is not rated for the maximum expected current, it can saturate resulting in
damage to the LM22673 and/or the power diode.
This consideration highlights the value of the current limit adjust feature of the LM22673.
8.2.1.2.3 Input Capacitor
The input capacitor selection is based on both input voltage ripple and RMS current. Good quality input
capacitors are necessary to limit the ripple voltage at the VIN pin while supplying most of the regulator current
during switch on-time. Low ESR ceramic capacitors are preferred. Larger values of input capacitance are
desirable to reduce voltage ripple and noise on the input supply. This noise may find its way into other circuitry,
sharing the same input supply, unless adequate bypassing is provided. A very approximate formula for
determining the input voltage ripple is shown in Equation 13.
(13)
Where:
Vri is the peak-to-peak ripple voltage at the switching frequency.
Another concern is the RMS current passing through this capacitor. Equation 14 gives an approximation to this
current.
(14)
The capacitor must be rated for at least this level of RMS current at the switching frequency.
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All ceramic capacitors have large voltage coefficients, in addition to normal tolerances and temperature
coefficients. To help mitigate these effects, multiple capacitors can be used in parallel to bring the minimum
capacitance up to the desired value. This may also help with RMS current constraints by sharing the current
among several capacitors. Many times it is desirable to use an electrolytic capacitor on the input, in parallel with
the ceramics. The moderate ESR of this capacitor can help to damp any ringing on the input supply caused by
long power leads. This method can also help to reduce voltage spikes that may exceed the maximum input
voltage rating of the LM22673.
It is good practice to include a high frequency bypass capacitor as close as possible to the LM22673. This small
case size, low ESR, ceramic capacitor should be connected directly to the VIN and GND pins with the shortest
possible PCB traces. Values in the range of 0.47 µF to 1 µF are appropriate. This capacitor helps to provide a
low impedance supply to sensitive internal circuitry. It also helps to suppress any fast noise spikes on the input
supply that may lead to increased EMI.
8.2.1.2.4 Output Capacitor
The output capacitor is responsible for filtering the output voltage and supplying load current during transients.
Capacitor selection depends on application conditions as well as ripple and transient requirements. Best
performance is achieved with a parallel combination of ceramic capacitors and a low ESR SP™ or POSCAP™
type. Very low ESR capacitors such as ceramics reduce the output ripple and noise spikes, while higher value
electrolytics or polymers provide large bulk capacitance to supply transients. Assuming very low ESR,
Equation 15 gives an approximation to the output voltage ripple.
(15)
Typically, a total value of 100 µF, or greater, is recommended for output capacitance.
In applications with Vout less than 3.3 V, it is critical that low ESR output capacitors are selected. This will limit
potential output voltage overshoots as the input voltage falls below the device normal operating range.
8.2.1.2.5 Boot-Strap Capacitor
The bootstrap capacitor between the BOOT pin and the SW pin supplies the gate current to turn on the Nchannel MOSFET. The recommended value of this capacitor is 10 nF and should be a good quality, low ESR
ceramic capacitor. In some cases it may be desirable to slow down the turn-on of the internal power MOSFET, in
order to reduce EMI. This can be done by placing a small resistor in series with the Cboot capacitor. Resistors in
the range of 10 Ω to 50 Ω can be used. This technique should only be used when absolutely necessary, because
it will increase switching losses and thereby reduce efficiency.
8.2.1.3 Application Curve
Figure 15. Efficiency vs IOUT and VIN
VOUT = 3.3 V
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9 Power Supply Recommendations
The LM22673 device is designed to operate from an input voltage supply range between 4.5 V and 42 V. This
input supply should be well regulated and able to withstand maximum input current and maintain a stable
voltage. The resistance of the input supply rail should be low enough that an input current transient does not
cause a high enough drop at the LM22673 supply voltage that can cause a false UVLO fault triggering and
system reset. If the input supply is located more than a few inches from the LM22673, additional bulk
capacitance may be required in addition to the ceramic bypass capacitors. The amount of bulk capacitance is not
critical, but a 47 μF or 100 μF electrolytic capacitor is a typical choice.
10 Layout
10.1 Layout Guidelines
Board layout is critical for the proper operation of switching power supplies. First, the ground plane area must be
sufficient for thermal dissipation purposes. Second, appropriate guidelines must be followed to reduce the effects
of switching noise. Switch mode converters are very fast switching devices. In such cases, the rapid increase of
input current combined with the parasitic trace inductance generates unwanted L di/dt noise spikes. The
magnitude of this noise tends to increase as the output current increases. This noise may turn into
electromagnetic interference (EMI) and can also cause problems in device performance. Therefore, care must be
taken in layout to minimize the effect of this switching noise.
The most important layout rule is to keep the ac current loops as small as possible. Figure 16 shows the current
flow in a buck converter. The top schematic shows a dotted line which represents the current flow during the FET
switch on-state. The middle schematic shows the current flow during the FET switch off-state.
The bottom schematic shows the currents referred to as ac currents. These ac currents are the most critical
because they are changing in a very short time period. The dotted lines of the bottom schematic are the traces to
keep as short and wide as possible. This will also yield a small loop area reducing the loop inductance. To avoid
functional problems due to layout, review the PCB layout example. Best results are achieved if the placement of
the LM22673, the bypass capacitor, RFFB, RFBT, the Schottky diode and the inductor are placed as shown in the
example. In the layout shown, R1 = RFBB and R2 = RFBT. It is also recommended to use 2 oz copper boards or
heavier to help thermal dissipation and to reduce the parasitic inductances of board traces. See AN-1229
SIMPLE SWITCHER ® PCB Layout Guidelines (SNVA054) for more information.
Figure 16. Current Flow in a Buck Application
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10.2 Layout Examples
Figure 17. PCB Layout Example for PFM Package
Figure 18. PCB Layout Example for SO PowerPAD Package
18
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SNVS586O – SEPTEMBER 2008 – REVISED NOVEMBER 2014
10.3 Thermal Considerations
The components with the highest power dissipation are the power diode and the power MOSFET internal to the
LM22673 regulator. The easiest method to determine the power dissipation within the LM22673 is to measure
the total conversion losses then subtract the power losses in the diode and inductor. The total conversion loss is
the difference between the input power and the output power. An approximation for the power diode loss is
shown in Equation 16.
(16)
Where:
VD is the diode voltage drop.
An approximation for the inductor power is determined by Equation 17.
(17)
Where:
RL is the dc resistance of the inductor.
The 1.1 factor is an approximation for the ac losses.
The regulator has an exposed thermal pad to aid power dissipation. Adding multiple vias under the device to the
ground plane will greatly reduce the regulator junction temperature. Selecting a diode with an exposed pad will
also aid the power dissipation of the diode. The most significant variables that affect the power dissipation of the
regulator are output current, input voltage and operating frequency. The power dissipated while operating near
the maximum output current and maximum input voltage can be appreciable. The junction-to-ambient thermal
resistance of the LM22673 will vary with the application. The most significant variables are the area of copper in
the PC board, the number of vias under the IC exposed pad and the amount of forced air cooling provided. A
large continuos ground plane on the top or bottom PCB layer will provide the most effective heat dissipation. The
integrity of the solder connection from the IC exposed pad to the PC board is critical. Excessive voids will greatly
diminish the thermal dissipation capacity. The junction-to-ambient thermal resistance of the LM22673 SO
PowerPAD package, and the PFM package, are specified in the Electrical Characteristics table. See AN-2020
Thermal Design By Insight, Not Hindsight (SNVA419) for more information.
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11 Device and Documentation Support
11.1 Documentation Support
11.1.1 Related Documentation
• AN-2020 Thermal Design By Insight, Not Hindsight (SNVA419)
• AN-1229 SIMPLE SWITCHER ® PCB Layout Guidelines (SNVA054)
• AN-1894 LM22673 Evaluation Board (SNVA367)
• AN-1889 How to Measure the Loop Transfer Function of Power Supplies (SNVA364)
• AN-1797 TO-263 THIN Package (SNVA328)
11.2 Related Links
The table below lists quick access links. Categories include technical documents, support and community
resources, tools and software, and quick access to sample or buy.
Table 1. Related Links
PARTS
PRODUCT FOLDER
SAMPLE & BUY
TECHNICAL
DOCUMENTS
TOOLS &
SOFTWARE
SUPPORT &
COMMUNITY
LM22673
Click here
Click here
Click here
Click here
Click here
LM22673-Q1
Click here
Click here
Click here
Click here
Click here
11.3 Trademarks
SIMPLE SWITCHER, WEBENCH are registered trademarks of Texas Instruments.
All other trademarks are the property of their respective owners.
11.4 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
11.5 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
12 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
20
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PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LM22673MR-5.0/NOPB
ACTIVE SO PowerPAD
DDA
8
95
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 125
L22673
5.0
LM22673MR-ADJ/NOPB
ACTIVE SO PowerPAD
DDA
8
95
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 125
L22673
ADJ
LM22673MRE-5.0/NOPB
ACTIVE SO PowerPAD
DDA
8
250
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 125
L22673
5.0
LM22673MRE-ADJ/NOPB
ACTIVE SO PowerPAD
DDA
8
250
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 125
L22673
ADJ
LM22673MRX-5.0/NOPB
ACTIVE SO PowerPAD
DDA
8
2500
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 125
L22673
5.0
LM22673MRX-ADJ/NOPB
ACTIVE SO PowerPAD
DDA
8
2500
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 125
L22673
ADJ
LM22673QMR-5.0/NOPB
ACTIVE SO PowerPAD
DDA
8
95
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 125
L22673
Q-5.0
LM22673QMR-ADJ/NOPB
ACTIVE SO PowerPAD
DDA
8
95
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 125
L22673
QADJ
LM22673QMRE-5.0/NOPB
ACTIVE SO PowerPAD
DDA
8
250
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 125
L22673
Q-5.0
LM22673QMRE-ADJ/NOPB
ACTIVE SO PowerPAD
DDA
8
250
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 125
L22673
QADJ
LM22673QMRX-5.0/NOPB
ACTIVE SO PowerPAD
DDA
8
2500
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 125
L22673
Q-5.0
LM22673QMRX-ADJ/NOPB
ACTIVE SO PowerPAD
DDA
8
2500
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 125
L22673
QADJ
LM22673QTJ-5.0/NOPB
ACTIVE
TO-263
NDR
7
1000
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
LM22673
QTJ-5.0
LM22673QTJ-ADJ/NOPB
ACTIVE
TO-263
NDR
7
1000
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
LM22673
QTJ-ADJ
LM22673QTJE-5.0/NOPB
ACTIVE
TO-263
NDR
7
250
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
LM22673
QTJ-5.0
LM22673QTJE-ADJ/NOPB
ACTIVE
TO-263
NDR
7
250
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
LM22673
QTJ-ADJ
LM22673TJ-5.0/NOPB
ACTIVE
TO-263
NDR
7
1000
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
LM22673
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
Orderable Device
10-Dec-2020
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
TJ-5.0
LM22673TJ-ADJ/NOPB
ACTIVE
TO-263
NDR
7
1000
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
LM22673
TJ-ADJ
LM22673TJE-5.0/NOPB
ACTIVE
TO-263
NDR
7
250
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
LM22673
TJ-5.0
LM22673TJE-ADJ/NOPB
ACTIVE
TO-263
NDR
7
250
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
LM22673
TJ-ADJ
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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