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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.
LM2594
,
LM2594HV
SNVS118E DECEMBER 1999REVISED MAY 2020
LM2594, LM2594HV SIMPLE SWITCHER
®
Power Converter 150-kHz 0.5-A Step-Down
Voltage Regulator
1
1 Features
1 New product available: LMR36506 3-V to 65-V
0.6-A ultra-small synchronous buck converter
3.3-V, 5-V, 12-V, and adjustable output versions
Adjustable version output voltage range: 1.2 V to
37 V (57-V for the HV version), ±4% maximum
over line and load conditions
Available in 8-pin surface-mount SOIC and 8-pin
PDIP packages
Ensured 0.5-A output current
Input voltage range up to 60 V
Requires only four external components
150-kHz Fixed-frequency internal oscillator
TTL shutdown capability
Low power standby mode, IQtypically 85 μA
High efficiency
Uses readily-available standard inductors
Thermal shutdown and current-limit protection
Start WEBENCH design with LM2594HV
2 Applications
Simple high-efficiency step-down (buck) regulator
Efficient preregulator for linear regulators
On-card switching regulators
Positive-to-negative convertor
3 Description
The LM2594xx series of regulators are monolithic
integrated circuits that provide all the active functions
for a step-down (buck) switching regulator, capable of
driving a 0.5-A load with excellent line and load
regulation. These devices are available in fixed output
voltages of 3.3 V, 5 V, 12 V, and an adjustable output
version, and are packaged in a 8-pin PDIP and a 8-
pin surface-mount SOIC package.
Requiring a minimum number of external
components, these regulators are simple to use and
feature internal frequency compensation, a fixed-
frequency oscillator, and improved line and load
regulation specifications.
The new product, LMR36506, offers reduced BOM
cost, higher efficiency, and smaller solution size with
many other features. See the Device Comparison
Table to compare specs. Start WEBENCH Design
with LMR36506.
Device Information(1)
PART NUMBER PACKAGE BODY SIZE (NOM)
LM2597, LM2597HV SOIC (8) 4.90 mm × 3.91 mm
PDIP (8) 9.81 mm × 6.35 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Typical Application
Fixed Output Voltage Versions
2
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,
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Table of Contents
1 Features.................................................................. 1
2 Applications ........................................................... 1
3 Description............................................................. 1
4 Revision History..................................................... 2
5 Description (continued)......................................... 3
6 Pin Configuration and Functions......................... 3
7 Specifications......................................................... 4
7.1 Absolute Maximum Ratings ...................................... 4
7.2 ESD Ratings.............................................................. 4
7.3 Recommended Operating Conditions....................... 4
7.4 Thermal Information.................................................. 4
7.5 Electrical Characteristics 3.3 V.............................. 5
7.6 Electrical Characteristics 5 V................................. 5
7.7 Electrical Characteristics 12 V............................... 5
7.8 Electrical Characteristics Adjustable...................... 6
7.9 Electrical Characteristics All Output Voltage
Versions..................................................................... 6
7.10 Typical Characteristics............................................ 7
8 Detailed Description............................................ 10
8.1 Overview................................................................. 10
8.2 Functional Block Diagram....................................... 10
8.3 Feature Description................................................. 10
8.4 Device Functional Modes........................................ 14
9 Application and Implementation ........................ 15
9.1 Application Information............................................ 15
9.2 Typical Applications ................................................ 22
10 Power Supply Recommendations ..................... 29
11 Layout................................................................... 30
11.1 Layout Guidelines ................................................. 30
11.2 Layout Example .................................................... 30
11.3 Thermal Considerations........................................ 31
12 Device and Documentation Support................. 33
12.1 Related Links ........................................................ 33
12.2 Support Resources ............................................... 33
12.3 Trademarks........................................................... 33
12.4 Electrostatic Discharge Caution............................ 33
12.5 Glossary................................................................ 33
13 Mechanical, Packaging, and Orderable
Information........................................................... 33
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision D (May 2016) to Revision E Page
Added information on LMR36506 to Features and Description ............................................................................................. 1
Changes from Revision C (April 2013) to Revision D Page
Added ESD Ratings 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
Removed all references to design software Switchers Made Simple ................................................................................... 1
Changes from Revision B (April 2013) to Revision C Page
Changed layout of National Semiconductor Data Sheet to TI format .................................................................................. 31
Not to scale
1NC 8 Output
2NC 7 +VIN
3NC 6 Ground
4Feedback 5 ON/OFF
3
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,
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(1) I = INPUT, O = OUTPUT
5 Description (continued)
A standard series of inductors (both through-hole and surface-mount types) are available from several different
manufacturers optimized for use with the LM2594xx series. This feature greatly simplifies the design of switch-
mode power supplies.
Other features include an ensured ±4% tolerance on output voltage under all conditions of input voltage and
output load conditions, and ±15% on the oscillator frequency. External shutdown is included, featuring typically
85-μA standby current. Self-protection features include a two stage frequency reducing current limit for the output
switch and an overtemperature shutdown for complete protection under fault conditions.
The LM2594HV is for applications requiring an input voltage up to 60 V.
6 Pin Configuration and Functions
D or P Package
8-Pin SOIC or PDIP
Top View
*No internal connection, but must be soldered to PCB for best heat transfer.
‡Patent Number 5,382,918.
Pin Functions(1)
PIN I/O DESCRIPTION
NO. NAME
1, 2, 3 NC No connection
4 Feedback I Senses the regulated output voltage to complete the feedback loop.
5 ON/OFF I
Allows the switching regulator circuit to be shut down using logic level signals, thus dropping
the total input supply current to approximately 80 μA. Pulling this pin below a threshold
voltage of approximately 1.3 V turns the regulator on, and pulling this pin above 1.3 V (up to
a maximum of 25 V) shuts the regulator down. If this shutdown feature is not needed, the
ON/OFF pin can be wired to the ground pin or it can be left open, in either case, the
regulator is in the ON condition.
6 Ground Circuit ground
7 +VIN IThis is the positive input supply for the IC switching regulator. A suitable input bypass
capacitor must be present at this pin to minimize voltage transients and to supply the
switching currents needed by the regulator.
8 Output O Internal switch. The voltage at this pin switches between (+VIN VSAT) and approximately
0.5 V, with a duty cycle of VOUT/VIN. To minimize coupling to sensitive circuitry, the PCB
copper area connected to this pin must be kept to a minimum.
4
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(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
(2) If Military/Aerospace specified devices are required, please contact the TI Sales Office/ Distributors for availability and specifications.
7 Specifications
7.1 Absolute Maximum Ratings(1)(2)
MIN MAX UNIT
Supply voltage LM2594 45 V
LM2594HV 60
ON/OFF pin input voltage 0.3 25 V
Feedback pin voltage 0.3 25 V
Output voltage to ground (steady state) 1 V
Power dissipation Internally limited
Lead temperature D8 package Vapor phase (60 s) 215 °CInfrared (15 s) 220
P package (soldering, 10 s) 260
Maximum junction temperature 150 °C
Storage temperature, Tstg 65 150 °C
(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
(2) The human-body model is a 100-pF capacitor discharged through a 1.5k resistor into each pin.
7.2 ESD Ratings VALUE UNIT
V(ESD) Electrostatic discharge Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1)(2) ±2000 V
7.3 Recommended Operating Conditions MIN MAX UNIT
Supply voltage LM2594 4.5 40 V
LM2594HV 4.5 60 V
Temperature 40 125 °C
(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
(2) The package thermal impedance is calculated in accordance to JESD 51-7.
(3) Thermal resistances were simulated on a 4 -layer, JEDEC board.
7.4 Thermal Information
THERMAL METRIC(1) LM2594, LM2594HV
UNITD (SOIC) P (PDIP)
8 PINS 8 PINS
RθJA Junction-to-ambient thermal resistance(2)(3) 150 95 °C/W
5
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(1) Typical numbers are at 25°C and represent the most likely norm.
(2) All limits ensured at room temperature and at temperature extremes. All room temperature limits are 100% production tested. All limits at
temperature extremes are specified via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to
calculate Average Outgoing Quality Level (AOQL).
(3) External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect
switching regulator system performance. When the LM2594xx is used as shown in the Figure 35 test circuit, system performance is as
shown in the system parameters.
7.5 Electrical Characteristics 3.3 V
Specifications are for TJ= 25°C, VINmax= 40 V for the LM2594 and 60 V for the LM2594HV (unless otherwise noted).
PARAMETER TEST CONDITIONS MIN TYP(1) MAX(2) UNIT
SYSTEM PARAMETERS(3) (see Figure 35 for test circuit)
VOUT Output voltage 4.75 V VIN VINmax,
0.1 A ILOAD 0.5 A
TJ= 25°C 3.432 3.3 3.168 V
Over full operating temperature
range 3.465 3.135
ηEfficiency VIN = 12 V, ILOAD = 0.5 A 80%
(1) Typical numbers are at 25°C and represent the most likely norm.
(2) All limits ensured at room temperature and at temperature extremes. All room temperature limits are 100% production tested. All limits at
temperature extremes are specified via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to
calculate Average Outgoing Quality Level (AOQL).
(3) External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect
switching regulator system performance. When the LM2594xx is used as shown in the Figure 35 test circuit, system performance is as
shown in the system parameters.
7.6 Electrical Characteristics 5 V
Specifications are for TJ= 25°C (unless otherwise noted).
PARAMETER TEST CONDITIONS MIN TYP(1) MAX(2) UNIT
SYSTEM PARAMETERS(3) (see Figure 35 for test circuit)
VOUT Output voltage 7 V VIN VINmax,
0.1 A ILOAD 0.5 A TJ= 25°C 4.8 5 5.2 V
Over full operating temperature range 4.75 5.25
ηEfficiency VIN = 12 V, ILOAD = 0.5 A 82%
(1) Typical numbers are at 25°C and represent the most likely norm.
(2) All limits ensured at room temperature and at temperature extremes. All room temperature limits are 100% production tested. All limits at
temperature extremes are specified via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to
calculate Average Outgoing Quality Level (AOQL).
(3) External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect
switching regulator system performance. When the LM2594/LM2594HV is used as shown in the Figure 35 test circuit, system
performance is as shown in the system parameters.
7.7 Electrical Characteristics 12 V
Specifications are for TJ= 25°C (unless otherwise noted).
PARAMETER TEST CONDITIONS MIN TYP(1) MAX(2) UNIT
SYSTEM PARAMETERS(3) (see Figure 35 for test circuit)
VOUT Output voltage 15 V VIN VINmax,
0.1 A ILOAD 0.5 A TJ= 25°C 11.52 12 12.48 V
Over full operating temperature range 11.4 12.6
ηEfficiency VIN = 25 V, ILOAD = 0.5 A 88%
6
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,
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(1) Typical numbers are at 25°C and represent the most likely norm.
(2) All limits ensured at room temperature and at temperature extremes. All room temperature limits are 100% production tested. All limits at
temperature extremes are specified via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to
calculate Average Outgoing Quality Level (AOQL).
(3) External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect
switching regulator system performance. When the LM2594/LM2594HV is used as shown in the Figure 35 test circuit, system
performance is as shown in the system parameters.
7.8 Electrical Characteristics Adjustable
Specifications are for TJ= 25°C (unless otherwise noted).
PARAMETER TEST CONDITIONS MIN TYP(1) MAX(2) UNIT
SYSTEM PARAMETERS(3) (see Figure 35 for test circuit)
VFB Feedback voltage
4.5 V VIN VINmax,
0.1 A ILOAD 0.5 A,
VOUT programmed for 3 V,
Circuit of Figure 35
TJ= 25°C 1.193 1.23 1.267
V
Over full operating temperature range 1.18 1.28
ηEfficiency VIN = 12 V, ILOAD = 0.5 A 80%
(1) Typical numbers are at 25°C and represent the most likely norm.
(2) All limits ensured at room temperature and at temperature extremes. All room temperature limits are 100% production tested. All limits at
temperature extremes are specified via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to
calculate Average Outgoing Quality Level (AOQL).
(3) The switching frequency is reduced when the second stage current limit is activated. The amount of reduction is determined by the
severity of current overload.
(4) No diode, inductor or capacitor connected to output pin.
(5) Feedback pin removed from output and connected to 0 V to force the output transistor switch ON.
(6) Feedback pin removed from output and connected to 12 V for the 3.3-V, 5-V, and the adjustable version, and 15 V for the 12-V version,
to force the output transistor switch OFF.
(7) VIN = 40 V for the LM2594 and 60 V for the LM2594HV.
7.9 Electrical Characteristics All Output Voltage Versions
Specifications are for TJ= 25°C, VIN = 12 V for the 3.3-V, 5-V, and adjustable version, and VIN = 24 V for the 12-V version,
ILOAD = 100 mA (unless otherwise noted).
PARAMETER TEST CONDITIONS MIN TYP(1) MAX(2) UNIT
DEVICE PARAMETERS
IbFeedback bias current Adjustable version only, VFB =
1.3 V TJ= 25°C 10 50 nA
Over full operating temperature range 100
fOOscillator frequency See(3) TJ= 25°C 127 150 173 kHz
Over full operating temperature range 110 173
VSAT Saturation voltage IOUT = 0.5 A(4)(5) TJ= 25°C 0.9 1.1 V
Over full operating temperature range 1.2
DC Max duty cycle (ON) See(5) 100%
Min duty cycle (OFF) See(6) 0%
ICL Current limit Peak current(4)(5) TJ= 25°C 0.65 0.8 1.3 A
over full operating temperature range 0.58 1.4
ILOutput leakage current Output = 0 V(4)(6)(7)
Output = 1 V 50 μA
2 15 mA
IQQuiescent current See(6) 5 10 mA
ISTBY Standby quiescent
current
ON/OFF pin = 5 V (OFF)(7) 85 μA
LM2594 TJ= 25°C 200 μA
Over full operating temperature range 250
LM2594HV TJ= 25°C 140 250 μA
Over full operating temperature range 300
ON/OFF CONTROL (see Figure 35 for test circuit)
ON/OFF pin logic input 1.3 V
VIH Threshold voltage Low (regulator ON), over full operating temperature range 0.6 V
VIL High (regulator OFF), over full operating temperature range 2 V
IHON/OFF pin input
current VLOGIC = 2.5 V (regulator OFF) 5 15 μA
ILVLOGIC = 0.5 V (regulator ON) 0.02 5 μA
7
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7.10 Typical Characteristics
Figure 1. Normalized Output Voltage Figure 2. Line Regulation
Figure 3. Efficiency Figure 4. Switch Saturation Voltage
Figure 5. Switch Current Limit Figure 6. Dropout Voltage
8
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Typical Characteristics (continued)
Figure 7. Quiescent Current Figure 8. Standby Quiescent Current
Figure 9. Minimum Operating Supply Voltage Figure 10. ON/OFF Threshold Voltage
Figure 11. ON /OFF Pin Current (Sinking) Figure 12. Switching Frequency
9
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Typical Characteristics (continued)
Figure 13. Feedback Pin Bias Current
10
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8 Detailed Description
8.1 Overview
The LM2594 SIMPLE SWITCHER®regulator is an easy-to-use, nonsynchronous step-down DC-DC converter
with a wide input voltage range from 45 V to up to 60 V for a HV version. The regulator is capable of delivering
up to 0.5-A DC load current with excellent line and load regulation. These devices are available in fixed output
voltages of 3.3-V, 5-V, 12-V, and an adjustable output version. The family requires few external components, and
the pin arrangement was designed for simple, optimum PCB layout.
8.2 Functional Block Diagram
8.3 Feature Description
8.3.1 Delayed Start-Up
The circuit in Figure 14 uses the ON/OFF pin to provide a time delay between the time the input voltage is
applied and the time the output voltage comes up (only the circuitry pertaining to the delayed start-up is shown).
As the input voltage rises, the charging of capacitor C1 pulls the ON/OFF pin high, keeping the regulator off.
Once the input voltage reaches its final value and the capacitor stops charging, the resistor R2pulls the ON/OFF
pin low, thus allowing the circuit to start switching. Resistor R1is included to limit the maximum voltage applied to
the ON/OFF pin (maximum of 25 V), reduces power supply noise sensitivity, and also limits the capacitor, C1,
discharge current. When high input ripple voltage exists, avoid long delay time, because this ripple can be
coupled into the ON/OFF pin and cause problems.
This delayed start-up feature is useful in situations where the input power source is limited in the amount of
current it can deliver. It allows the input voltage to rise to a higher voltage before the regulator starts operating.
Buck regulators require less input current at higher input voltages.
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Feature Description (continued)
Figure 14. Delayed Start-Up
8.3.2 Undervoltage Lockout
Some applications require the regulator to remain off until the input voltage reaches a predetermined voltage.
Figure 15 shows an undervoltage lockout feature applied to a buck regulator, while Figure 16 and Figure 17
apply the same feature to an inverting circuit. The circuit in Figure 16 features a constant threshold voltage for
turnon and turnoff (Zener voltage plus approximately 1 V). If hysteresis is needed, the circuit in Figure 17 has a
turnon voltage which is different than the turnoff voltage. The amount of hysteresis is approximately equal to the
value of the output voltage. If Zener voltages greater than 25 V are used, an additional 47-kΩresistor is needed
from the ON/OFF pin to the ground pin to stay within the 25 V maximum limit of the ON/OFF pin.
Figure 15. Undervoltage Lockout
for Buck Regulator
8.3.3 Inverting Regulator
The circuit in Figure 18 converts a positive input voltage to a negative output voltage with a common ground. The
circuit operates by bootstrapping the regulators ground pin to the negative output voltage, then grounding the
feedback pin, the regulator senses the inverted output voltage and regulates it.
This circuit has an ON/OFF threshold of approximately 13 V.
Figure 16. Undervoltage Lockout for Inverting Regulator
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Feature Description (continued)
This circuit has hysteresis
Regulator starts switching at VIN = 13 V
Regulator stops switching at VIN = 8 V
Figure 17. Undervoltage Lockout With Hysteresis for Inverting Regulator
CIN 68-μF, 25-V Tant. Sprague 595D
120-μF, 35-V Elec. Panasonic HFQ
COUT 22-μF, 20-V Tant. Sprague 595D
39-μF, 16-V Elec. Panasonic HFQ
Figure 18. Inverting 5-V Regulator With Delayed Start-Up
This example uses the LM2594-5 to generate a 5-V output, but other output voltages are possible by selecting
other output voltage versions, including the adjustable version. Because this regulator topology can produce an
output voltage that is either greater than or less than the input voltage, the maximum output current greatly
depends on both the input and output voltage. Figure 19 provides a guide as to the amount of output load current
possible for the different input and output voltage conditions.
The maximum voltage appearing across the regulator is the absolute sum of the input and output voltage, and
this must be limited to a maximum of 40 V. For example, when converting 20 V to 12 V, the regulator would see
32 V between the input pin and ground pin. The LM2594 has a maximum input voltage specification of 40 V (60
V for the LM2594HV).
Additional diodes are required in this regulator configuration. Diode D1 is used to isolate input voltage ripple or
noise from coupling through the CIN capacitor to the output, under light or no load conditions. Also, this diode
isolation changes the topology to closely resemble a buck configuration thus providing good closed loop stability.
TI recommends a Schottky diode for low input voltages (because of its lower voltage drop), but for higher input
voltages, a fast recovery diode could be used.
Without diode D3, when the input voltage is first applied, the charging current of CIN can pull the output positive
by several volts for a short period of time. Adding D3 prevents the output from going positive by more than a
diode voltage.
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Feature Description (continued)
Figure 19. Inverting Regulator Typical Load Current
Because of differences in the operation of the inverting regulator, the standard design procedure is not used to
select the inductor value. In the majority of designs, a 100-μH, 1-A inductor is the best choice. Capacitor
selection can also be narrowed down to just a few values. Using the values shown in Figure 18 provides good
results in the majority of inverting designs.
This type of inverting regulator can require relatively large amounts of input current when starting up, even with
light loads. Input currents as high as the LM2594 current limit (approximately 0.8 A) are needed for at least 2 ms
or more, until the output reaches its nominal output voltage. The actual time depends on the output voltage and
the size of the output capacitor. Input power sources that are current limited or sources that can not deliver these
currents without getting loaded down, may not work correctly. Because of the relatively high start-up currents
required by the inverting topology, the delayed start-up feature (C1, R1and R2) shown in Figure 18 is
recommended. By delaying the regulator start-up, the input capacitor is allowed to charge up to a higher voltage
before the switcher begins operating. A portion of the high input current needed for start-up is now supplied by
the input capacitor (CIN). For severe start-up conditions, the input capacitor can be made much larger than
normal.
8.3.4 Inverting Regulator Shutdown Methods
To use the ON/OFF pin in a standard buck configuration is simple; pull it below 1.3 V (at 25°C, referenced to
ground) to turn regulator ON and pull it above 1.3 V to shut the regulator OFF. With the inverting configuration,
some level shifting is required, because the ground pin of the regulator is no longer at ground, but is now setting
at the negative output voltage level. Two different shutdown methods for inverting regulators are shown in
Figure 20 and Figure 21.
Figure 20. Inverting Regulator Ground Referenced Shutdown
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Feature Description (continued)
Figure 21. Inverting Regulator Ground Referenced Shutdown Using Opto Device
8.4 Device Functional Modes
8.4.1 Discontinuous Mode Operation
The selection guide chooses inductor values suitable for continuous mode operation, but for low current
applications and high input voltages, a discontinuous mode design can be a better choice. Discontinuous mode
would use an inductor that is physically smaller, and would need only one half to one third of the inductance
value needed for a continuous mode design. The peak switch and inductor currents are higher in a discontinuous
design, but at these low load currents (200 mA and below), the maximum switch current is still less than the
switch current limit.
Discontinuous operation can have voltage waveforms that are considerably different than a continuous design.
The output pin (switch) waveform can have some damped sinusoidal ringing present (see Figure 33). This
ringing is normal for discontinuous operation, and is not caused by feedback loop instabilities. In discontinuous
operation, there is a period of time where neither the switch nor the diode are conducting, and the inductor
current has dropped to zero. During this time, a small amount of energy can circulate between the inductor and
the switch or diode parasitic capacitance causing this characteristic ringing. Normally this ringing is not a
problem, unless the amplitude becomes great enough to exceed the input voltage, and even then, there is very
little energy present to cause damage.
Different inductor types and core materials produce different amounts of this characteristic ringing. Ferrite core
inductors have very little core loss and, therefore, produce the most ringing. The higher core loss of powdered
iron inductors produce less ringing. If desired, a series RC can be placed in parallel with the inductor to dampen
the ringing.
Figure 22. Post Ripple Filter Waveform
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9 Application 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.
9.1 Application Information
9.1.1 Input Capacitor (CIN)
A low ESR aluminum or tantalum bypass capacitor is required between the input pin and ground pin. The
capacitor must be located near the regulator using short leads. This capacitor prevents large voltage transients
from appearing at the input, and provides the instantaneous current needed each time the switch turns on.
The important parameters for the input capacitor are the voltage rating and the RMS current rating. Because of
the relatively high RMS currents flowing in the input capacitor of the buck regulator, this capacitor must be
chosen for its RMS current rating rather than its capacitance or voltage ratings, although the capacitance value
and voltage rating are directly related to the RMS current rating.
The RMS current rating of a capacitor could be viewed as a power rating of the capacitor. The RMS current
flowing through the capacitors internal ESR produces power which causes the internal temperature of the
capacitor to rise. The RMS current rating of a capacitor is determined by the amount of current required to raise
the internal temperature approximately 10°C above an ambient temperature of 105°C. The ability of the capacitor
to dissipate this heat to the surrounding air determines the amount of current the capacitor can safely sustain.
Capacitors that are physically large and have a large surface area typically has a higher RMS current ratings. For
a given capacitor value, a higher voltage electrolytic capacitor is physically larger than a lower voltage capacitor,
and thus be able to dissipate more heat to the surrounding air, and therefore has a higher RMS current rating.
The consequences of operating an electrolytic capacitor above the RMS current rating is a shortened operating
life. The higher temperature speeds up the evaporation of the electrolyte of the capacitor, resulting in eventual
failure.
Selecting an input capacitor requires consulting the manufacturers data sheet for maximum allowable RMS ripple
current. For a maximum ambient temperature of 40°C, a general guideline would be to select a capacitor with a
ripple current rating of approximately 50% of the DC load current. For ambient temperatures up to 70°C, a
current rating of 75% of the DC load current would be a good choice for a conservative design. The capacitor
voltage rating must be at least 1.25 times greater than the maximum input voltage, and often a much higher
voltage capacitor is needed to satisfy the RMS current requirements.
Figure 23 shows the relationship between an electrolytic capacitor value, its voltage rating, and the RMS current
it is rated for. These curves were obtained from the Nichicon PL series of low-ESR, high-reliability electrolytic
capacitors designed for switching regulator applications. Other capacitor manufacturers offer similar types of
capacitors, but always check the capacitor data sheet.
Standard electrolytic capacitors typically have much higher ESR numbers, lower RMS current ratings and
typically have a shorter operating lifetime.
Because of their small size and excellent performance, surface-mount solid tantalum capacitors are often used
for input bypassing, but several precautions must be observed. A small percentage of solid tantalum capacitors
can short if the inrush current rating is exceeded. This can happen at turnon when the input voltage is suddenly
applied, and of course, higher input voltages produce higher inrush currents. Several capacitor manufacturers do
a 100% surge current testing on their products to minimize this potential problem. If high turnon currents are
expected, it may be necessary to limit this current by adding either some resistance or inductance before the
tantalum capacitor, or select a higher voltage capacitor. As with aluminum electrolytic capacitors, the RMS ripple
current rating must be sized to the load current.
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Application Information (continued)
Figure 23. RMS Current Ratings for Low-ESR Electrolytic Capacitors (Typical)
9.1.2 Output Capacitor (COUT)
An output capacitor is required to filter the output and provide regulator loop stability. Low impedance or low ESR
Electrolytic or solid tantalum capacitors designed for switching regulator applications must be used. When
selecting an output capacitor, the important capacitor parameters are; the 100-kHz Equivalent Series Resistance
(ESR), the RMS ripple current rating, voltage rating, and capacitance value. For the output capacitor, the ESR
value is the most important parameter.
The output capacitor requires an ESR value that has an upper and lower limit. For low output ripple voltage, a
low ESR value is needed. This value is determined by the maximum allowable output ripple voltage, typically 1%
to 2% of the output voltage. But if the ESR of the selected capacitor is extremely low, there is a possibility of an
unstable feedback loop, resulting in an oscillation at the output. Using the capacitors listed in the tables, or
similar types, provides design solutions under all conditions.
If very low output ripple voltage (less than 15 mV) is required, see Output Voltage Ripple and Transients for a
post-ripple filter.
An aluminum electrolytic capacitor's ESR value is related to the capacitance value and its voltage rating. In most
cases, Higher voltage electrolytic capacitors have lower ESR values (see Figure 24). Often, capacitors with much
higher voltage ratings may be needed to provide the low ESR values required for low output ripple voltage.
The output capacitor for many different switcher designs often can be satisfied with only three or four different
capacitor values and several different voltage ratings. See Figure 30 and Table 7 for typical capacitor values,
voltage ratings, and manufacturers capacitor types.
Electrolytic capacitors are not recommended for temperatures below 25°C. The ESR rises dramatically at cold
temperatures and typically rises three times at 25°C and as much as ten times at 40°C (see Figure 25).
Solid tantalum capacitors have a much better ESR specifications for cold temperatures and are recommended
for temperatures below 25°C.
Figure 24. Capacitor ESR versus Capacitor Voltage Rating (Typical Low-ESR Electrolytic Capacitor)
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Application Information (continued)
Table 1. Output Capacitor and Feedforward Capacitor Selection Table
OUTPUT
VOLTAGE
(V)
THROUGH-HOLE OUTPUT CAPACITOR SURFACE-MOUNT OUTPUT CAPACITOR
PANASONIC HFQ
SERIES (µF/V) NICHICON PL
SERIES (µF/V) FEEDFORWARD
CAPACITOR AVX TPS SERIES
(µF/V) SPRAGUE 595D
SERIES (µF/V) FEEDFORWARD
CAPACITOR
1.2 220/25 220/25 0 220/10 220/10 0
4 180/25 180/25 4.7 nF 100/10 120/10 4.7 nF
6 82/25 82/25 4.7 nF 100/10 120/10 4.7 nF
9 82/25 82/25 3.3 nF 100/16 100/16 3.3 nF
12 82/25 82/25 2.2 nF 100/16 100/16 2.2 nF
15 82/25 82/25 1.5 nF 68/20 100/20 1.5 nF
24 82/50 120/50 1 nF 10/35 15/35 220 pF
28 82/50 120/50 820 pF 10/35 15/35 220 pF
9.1.3 Catch Diode
Buck regulators require a diode to provide a return path for the inductor current when the switch turns off. This
must be a fast diode and must be located close to the LM2594 using short leads and short printed-circuit traces.
Because of their very fast switching speed and low forward voltage drop, Schottky diodes provide the best
performance, especially in low output voltage applications (5 V and lower). Ultra-fast recovery, or high-efficiency
rectifiers are also a good choice, but some types with an abrupt turnoff characteristic may cause instability or
EMI problems. Ultra-fast recovery diodes typically have reverse recovery times of 50 ns or less. Rectifiers such
as the 1N4001 series are much too slow and must not be used.
Figure 25. Capacitor ESR Change versus Temperature
Table 2. Diode Selection Table
VR
1-A DIODES
SURFACE MOUNT THROUGH HOLE
SCHOTTKY ULTRA FAST RECOVERY SCHOTTKY ULTRA FAST RECOVERY
20 V
All of these diodes are rated to
at least 60 V.
1N5817
All of these diodes are rated to
at least 60 V.
SR102
MBRS130 1N5818
30 V SR103
11DQ03
MBRS140 MURS120 1N5819 MUR120
40 V 10BQ040 10BF10 SR104 HER101
10MQ040 11DQ04 11DF1
50 V
or
more
MBRS160 SR105
10BQ050 MBR150
10MQ060 11DQ05
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Table 2. Diode Selection Table (continued)
VR
1-A DIODES
SURFACE MOUNT THROUGH HOLE
SCHOTTKY ULTRA FAST RECOVERY SCHOTTKY ULTRA FAST RECOVERY
MBRS1100 MBR160
10MQ090 SB160
SGL41-60 11DQ10
SS16
9.1.4 Inductor Selection
All switching regulators have two basic modes of operation: continuous and discontinuous. The difference
between the two types relates to the inductor current, whether it is flowing continuously, or if it drops to zero for a
period of time in the normal switching cycle. Each mode has distinctively different operating characteristics,
which can affect the regulators performance and requirements. Most switcher designs operates in the
discontinuous mode when the load current is low.
The LM2594 (or any of the SIMPLE SWITCHER family) can be used for both continuous or discontinuous modes
of operation.
In many cases the preferred mode of operation is the continuous mode. This mode offers greater output power,
lower peak switch, inductor, and diode currents, and can have lower output ripple voltage. However, the
continuous mode requires larger inductor values to keep the inductor current flowing continuously, especially at
low output load currents and high input voltages.
To simplify the inductor selection process, an inductor selection guide (nomograph) was designed (see Figure 27
through Figure 30). This guide assumes that the regulator is operating in the continuous mode, and selects an
inductor that allows a peak-to-peak inductor ripple current to be a certain percentage of the maximum design
load current. This peak-to-peak inductor ripple current percentage is not fixed, but is allowed to change as
different design load currents are selected. (See Figure 26).
Figure 26. (ΔIIND) Peak-to-Peak Inductor Ripple Current
(as a Percentage of the Load Current) versus Load Current
By allowing the percentage of inductor ripple current to increase for low load currents, the inductor value and size
can be kept relatively low.
When operating in the continuous mode, the inductor current waveform ranges from a triangular to a sawtooth
type of waveform (depending on the input voltage), with the average value of this current waveform equal to the
DC output load current.
Inductors are available in different styles such as pot core, toroid, E-core, bobbin core, and so forth, as well as
different core materials, such as ferrites and powdered iron. The least expensive, the bobbin, rod or stick core,
consists of wire wrapped on a ferrite bobbin. This type of construction makes for a inexpensive inductor;
however, because the magnetic flux is not completely contained within the core, it generates more Electro-
Magnetic Interference (EMl). This magnetic flux can induce voltages into nearby printed-circuit traces, thus
causing problems with both the switching regulator operation and nearby sensitive circuitry, and can give
incorrect scope readings because of induced voltages in the scope probe (see Open Core Inductors).
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The inductors listed in the selection chart include ferrite E-core construction for Schott ferrite bobbin core for
Renco and Coilcraft, and powdered iron toroid for Pulse Engineering.
Exceeding the maximum current rating of the inductor can cause the inductor to overheat because of the copper
wire losses, or the core can saturate. If the inductor begins to saturate, the inductance decreases rapidly and the
inductor begins to look mainly resistive (the DC resistance of the winding). This can cause the switch current to
rise very rapidly and force the switch into a cycle-by-cycle current limit, thus reducing the DC output load current.
This can also result in overheating of the inductor and the LM2594. Different inductor types have different
saturation characteristics, and this must be kept in mind when selecting an inductor.
The inductor manufacturers data sheets include current and energy limits to avoid inductor saturation.
For continuous mode operation, see the inductor selection graphs in Figure 27 through Figure 30.
Figure 27. LM2594xx 3.3-V Figure 28. LM2594xx 5-V
Figure 29. LM2594xx 12-V Figure 30. LM2594xx Adjustable Voltage
Table 3. Inductor Manufacturers Part Numbers
INDUCTANCE
(μH) CURRENT
(A)
SCHOTTKY RENCO PULSE ENGINEERING COILCRAFT
THROUGH
HOLE SURFACE
MOUNT THROUGH
HOLE SURFACE
MOUNT THROUGH
HOLE SURFACE
MOUNT SURFACE
MOUNT
L1 220 0.18 67143910 67144280 RL-5470-3 RL1500-220 PE-53801 PE-53801-S DO1608-224
L2 150 0.21 67143920 67144290 RL-5470-4 RL1500-150 PE-53802 PE-53802-S DO1608-154
L3 100 0.26 67143930 67144300 RL-5470-5 RL1500-100 PE-53803 PE-53803-S DO1608-104
L4 68 0.32 67143940 67144310 RL-1284-68 RL1500-68 PE-53804 PE-53804-S DO1608-68
L5 47 0.37 67148310 67148420 RL-1284-47 RL1500-47 PE-53805 PE-53805-S DO1608-473
L6 33 0.44 67148320 67148430 RL-1284-33 RL1500-33 PE-53806 PE-53806-S DO1608-333
L7 22 0.60 67148330 67148440 RL-1284-22 RL1500-22 PE-53807 PE-53807-S DO1608-223
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Table 3. Inductor Manufacturers Part Numbers (continued)
INDUCTANCE
(μH) CURRENT
(A)
SCHOTTKY RENCO PULSE ENGINEERING COILCRAFT
THROUGH
HOLE SURFACE
MOUNT THROUGH
HOLE SURFACE
MOUNT THROUGH
HOLE SURFACE
MOUNT SURFACE
MOUNT
L8 330 0.26 67143950 67144320 RL-5470-2 RL1500-330 PE-53808 PE-53808-S DO3308-334
L9 220 0.32 67143960 67144330 RL-5470-3 RL1500-220 PE-53809 PE-53809-S DO3308-224
L10 150 0.39 67143970 67144340 RL-5470-4 RL1500-150 PE-53810 PE-53810-S DO3308-154
L11 100 0.48 67143980 67144350 RL-5470-5 RL1500-100 PE-53811 PE-53811-S DO3308-104
L12 68 0.58 67143990 67144360 RL-5470-6 RL1500-68 PE-53812 PE-53812-S DO1608-683
L13 47 0.70 67144000 67144380 RL-5470-7 RL1500-47 PE-53813 PE-53813-S DO3308-473
L14 33 0.83 67148340 67148450 RL-1284-33 RL1500-33 PE-53814 PE-53814-S DO1608-333
L15 22 0.99 67148350 67148460 RL-1284-22 RL1500-22 PE-53815 PE-53815-S DO1608-223
L16 15 1.24 67148360 67148470 RL-1284-15 RL1500-15 PE-53816 PE-53816-S DO1608-153
L17 330 0.42 67144030 67144410 RL-5471-1 RL1500-330 PE-53817 PE-53817-S DO3316-334
L18 220 0.55 67144040 67144420 RL-5471-2 RL1500-220 PE-53818 PE-53818-S DO3316-224
L19 150 0.66 67144050 67144430 RL-5471-3 RL1500-150 PE-53819 PE-53819-S DO3316-154
L20 100 0.82 67144060 67144440 RL-5471-4 RL1500-100 PE-53820 PE-53820-S DO3316-104
L21 68 0.99 67144070 67144450 RL-5471-5 RL1500-68 PE-53821 PE-53821-S DDO3316-683
L26 330 0.80 67144100 67144480 RL-5471-1 PE-53826 PE-53826-S
L27 220 1.00 67144110 67144490 RL-5471-2 PE-53827 PE-53827-S
9.1.5 Output Voltage Ripple and Transients
The output voltage of a switching power supply operating in the continuous mode contains a sawtooth ripple
voltage at the switcher frequency, and can also contain short voltage spikes at the peaks of the sawtooth
waveform.
The output ripple voltage is a function of the inductor sawtooth ripple current and the ESR of the output
capacitor. A typical output ripple voltage can range from approximately 0.5% to 3% of the output voltage. To
obtain low ripple voltage, the ESR of the output capacitor must be low; however, caution must be exercised when
using extremely low ESR capacitors because they can affect the loop stability, resulting in oscillation problems. If
very low output ripple voltage is needed (less than 15 mV), TI recommends a post ripple filter (see Figure 35).
The inductance required is typically between 1 μH and 5 μH, with low DC resistance, to maintain good load
regulation. A low ESR output filter capacitor is also required to assure good dynamic load response and ripple
reduction. The ESR of this capacitor can be as low as desired, because it is out of the regulator feedback loop.
Figure 22 shows a typical output ripple voltage, with and without a post ripple filter.
When observing output ripple with a scope, it is essential that a short, low inductance scope probe ground
connection be used. Most scope probe manufacturers provide a special probe terminator which is soldered onto
the regulator board, preferably at the output capacitor. This provides a very short scope ground, thus eliminating
the problems associated with the three-inch ground lead normally provided with the probe, and provides a much
cleaner and more accurate picture of the ripple voltage waveform.
The voltage spikes are caused by the fast switching action of the output switch and the diode, the parasitic
inductance of the output filter capacitor, and its associated wiring. To minimize these voltage spikes, the output
capacitor must be designed for switching regulator applications, and the lead lengths must be kept very short.
Wiring inductance, stray capacitance, as well as the scope probe used to evaluate these transients, all contribute
to the amplitude of these spikes.
When a switching regulator is operating in the continuous mode, the inductor current waveform ranges from a
triangular to a sawtooth type of waveform (depending on the input voltage). For a given input and output voltage,
the peak-to-peak amplitude of this inductor current waveform remains constant. As the load current increases or
decreases, the entire sawtooth current waveform also rises and falls. The average value (or the center) of this
current waveform is equal to the DC load current.
If the load current drops to a low enough level, the bottom of the sawtooth current waveform reaches zero, and
the switcher smoothly changes from a continuous to a discontinuous mode of operation. Most switcher designs
(regardless how large the inductor value is) is forced to run discontinuous if the output is lightly loaded. This is a
perfectly acceptable mode of operation.
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Figure 31. Peak-to-Peak Inductor
Ripple Current vs Load Current
In a switching regulator design, knowing the value of the peak-to-peak inductor ripple current (ΔIIND) can be
useful for determining a number of other circuit parameters. Parameters such as, peak inductor or peak switch
current, minimum load current before the circuit becomes discontinuous, output ripple voltage and output
capacitor ESR can all be calculated from the peak-to-peak ΔIIND. When the inductor nomographs shown in
Figure 27 through Figure 30 are used to select an inductor value, the peak-to-peak inductor ripple current can
immediately be determined. Figure 31 shows the range of (ΔIIND) that can be expected for different load currents.
Figure 31 also shows how the peak-to-peak inductor ripple current (ΔIIND) changes as the designer goes from the
lower border to the upper border (for a given load current) within an inductance region. The upper border
represents a higher input voltage, while the lower border represents a lower input voltage (see Inductor
Selection).
These curves are only correct for continuous mode operation, and only if the inductor selection guides are used
to select the inductor value.
Consider the following example:
VOUT = 5 V, maximum load current of 300 mA
VIN = 15 V, nominal, varying between 11 V and 20 V
The selection guide in Figure 28 shows that the vertical line for a 0.3-A load current and the horizontal line for the
15-V input voltage intersect approximately midway between the upper and lower borders of the 150-μH
inductance region. A 150-μH inductor allows a peak-to-peak inductor current (ΔIIND) to flow a percentage of the
maximum load current. Referring to Figure 31, follow the 0.3-A line approximately midway into the inductance
region, and read the peak-to-peak inductor ripple current (ΔIIND) on the left hand axis (approximately 150 mAp-p).
As the input voltage increases to 20 V, it approaches the upper border of the inductance region, and the inductor
ripple current increases. Figure 31 shows that for a load current of 0.3 A, the peak-to-peak inductor ripple current
(ΔIIND) is 150 mA with 15V in, and can range from 175 mA at the upper border (20 V in) to 120 mA at the lower
border (11 V in).
Once the ΔIIND value is known, the following formulas can be used to calculate additional information about the
switching regulator circuit.
1. Peak Inductor or peak switch current
2. Minimum load current before the circuit becomes discontinuous
3. Output Ripple Voltage
= (ΔIIND) × (ESR of COUT)
= 0.150 A × 0.240 Ω= 36 mVp-p
or
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4. ESR of COUT
9.1.6 Open Core Inductors
Another possible source of increased output ripple voltage or unstable operation is from an open core inductor.
Ferrite bobbin or stick inductors have magnetic lines of flux flowing through the air from one end of the bobbin to
the other end. These magnetic lines of flux induces a voltage into any wire or PCB copper trace that comes
within the inductor's magnetic field. The strength of the magnetic field, the orientation and location of the PC
copper trace to the magnetic field, and the distance between the copper trace and the inductor, determine the
amount of voltage generated in the copper trace. Another way of looking at this inductive coupling is to consider
the PCB copper trace as one turn of a transformer (secondary) with the inductor winding as the primary. Many
millivolts can be generated in a copper trace located near an open core inductor which can cause stability
problems or high output ripple voltage problems.
If unstable operation is seen, and an open core inductor is used, it is possible that the location of the inductor
with respect to other PC traces may be the problem. To determine if this is the problem, temporarily raise the
inductor away from the board by several inches and then check circuit operation. If the circuit now operates
correctly, then the magnetic flux from the open core inductor is causing the problem. Substituting a closed core
inductor such as a torroid or E-core corrects the problem, or re-arranging the PC layout may be necessary.
Magnetic flux cutting the IC device ground trace, feedback trace, or the positive or negative traces of the output
capacitor must be minimized.
Sometimes, locating a trace directly beneath a bobbin inductor provides good results, provided it is exactly in the
center of the inductor (because the induced voltages cancel themselves out), but if it is off center one direction or
the other, then problems could arise. If flux problems are present, even the direction of the inductor winding can
make a difference in some circuits.
This discussion on open core inductors is not to frighten the user, but to alert the user on what kind of problems
to watch out for when using them. Open core bobbin or stick inductors are an inexpensive, simple way of making
a compact efficient inductor, and they are used by the millions in many different applications.
9.2 Typical Applications
9.2.1 Series Buck Regulator (Fixed Output)
Select components with higher voltage ratings for designs using the LM2594HV with an input voltage between 40
V and 60 V.
CIN 68-μF, 35-V, Aluminum Electrolytic Nichicon “PL Series”
COUT 120-μF, 25-V Aluminum Electrolytic, Nichicon “PL Series”
D1 1-A, 40-V Schottky Rectifier, 1N5819
L1 100-μH, L20
Figure 32. Fixed Output Voltage Versions
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Typical Applications (continued)
9.2.1.1 Design Requirements
Table 4 lists the design parameters of this example.
Table 4. Design Parameters
PARAMETER EXAMPLE VALUE
Regulated output voltage (3.3-V, 5-V or 12-V), VOUT 5 V
Maximum DC input voltage, VIN(max) 12 V
Maximum load current, ILOAD(max) 0.4 A
9.2.1.2 Detailed Design Procedure
9.2.1.2.1 Inductor Selection (L1)
1. Select the correct inductor value selection guide from Figure 27,Figure 28,orFigure 29 (output voltages of
3.3 V, 5 V, or 12 V, respectively). For all other voltages, see Detailed Design Procedure for the adjustable
version.
Use the inductor selection guide for the 5-V version shown in Figure 28.
2. From the inductor value selection guide, identify the inductance region intersected by the maximum input
voltage line and the maximum load current line. Each region is identified by an inductance value and an
inductor code (LXX).
From the inductor value selection guide shown in Figure 28, the inductance region intersected by the 12-V
horizontal line and the 0.4-A vertical line is 100 μH, and the inductor code is L20.
3. Select an appropriate inductor from the four manufacturer's part numbers listed in Table 3.
The inductance value required is 100 μH. See row L20 of Table 3 and choose an inductor part number from
any of the four manufacturers shown. (In most instance, both through-hole and surface-mount inductors are
available.)
9.2.1.2.2 Output Capacitor Selection (COUT)
1. In the majority of applications, low ESR (Equivalent Series Resistance) electrolytic capacitors between 82 μF
and 220 μF and low-ESR, solid tantalum capacitors between 15 μF and 100 μF provide the best results. This
capacitor must be located close to the IC using short capacitor leads and short copper traces. Do not use
capacitors larger than 220 μF. For additional information, see Output Capacitor (COUT).
2. To simplify the capacitor selection procedure, see Figure 30 for quick design component selection. This table
contains different input voltages, output voltages, and load currents, and lists various inductors and output
capacitors that provides the best design solutions.
From Figure 30, locate the 5-V output voltage section. In the load current column, choose the load current
line that is closest to the current required for the application; for this example, use the 0.5-A line. In the
maximum input voltage column, select the line that covers the input voltage required for the application; in
this example, use the 15-V line. The rest of this line shows the recommended inductors and capacitors that
provides the best overall performance.
The capacitor list contains both through hole electrolytic and surface mount tantalum capacitors from four
different capacitor manufacturers. TI recommends using both the manufacturers and the manufacturer's
series that are listed in Table 5.
In this example, aluminum electrolytic capacitors from several different manufacturers are available with the
range of ESR numbers needed:
120-μF, 2-5V Panasonic HFQ Series
120-μF, 2-5V Nichicon PL Series
3. The capacitor voltage rating for electrolytic capacitors must be at least 1.5 times greater than the output
voltage, and often require much higher voltage ratings to satisfy the low ESR requirements for low output
ripple voltage.
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For a 5-V output, a capacitor voltage rating at least 7.5 V or more is required. But, in this example, even a
low ESR, switching grade, 120-μF, 10-V aluminum electrolytic capacitor would exhibit approximately 400 mΩ
of ESR (see Figure 24 for the ESR vs voltage rating). This amount of ESR would result in relatively high
output ripple voltage. To reduce the ripple to 1% of the output voltage, or less, a capacitor with a higher
voltage rating (lower ESR) must be selected. A 16-V or 25-V capacitor reduces the ripple voltage by
approximately half.
9.2.1.2.3 Catch Diode Selection (D1)
1. The catch diode current rating must be at least 1.3 times greater than the maximum load current. Also, if the
power supply design must withstand a continuous output short, the diode must have a current rating equal to
the maximum current limit of the LM2594. The most stressful condition for this diode is an overload or
shorted output condition.
See Table 2. In this example, a 1-A, 20-V, 1N5817 Schottky diode provides the best performance, and will
not be overstressed even for a shorted output.
2. The reverse voltage rating of the diode must be at least 1.25 times the maximum input voltage.
3. This diode must be fast (short reverse recovery time) and must be located close to the LM2594 using short
leads and short printed circuit traces. Because of their fast switching speed and low forward voltage drop,
Schottky diodes provide the best performance and efficiency, and must be the first choice, especially in low
output voltage applications. Ultra-fast recovery, or high-efficiency rectifiers also provide good results. Ultra-
fast recovery diodes typically have reverse recovery times of 50 ns or less. Rectifiers such as the 1N4001
must not be used because they are too slow.
9.2.1.2.4 Input Capacitor (CIN)
A low ESR aluminum or tantalum bypass capacitor is needed between the input pin and ground to prevent large
voltage transients from appearing at the input. In addition, the RMS current rating of the input capacitor must be
selected to be at least ½ the DC load current. The capacitor manufacturers data sheet must be checked to
assure that this current rating is not exceeded. Figure 23 shows typical RMS current ratings for several different
aluminum electrolytic capacitor values.
This capacitor must be located close to the IC using short leads and the voltage rating must be approximately 1.5
times the maximum input voltage.
If solid tantalum input capacitors are used, TI recommends that they be surge current tested by the
manufacturer.
Use caution when using ceramic capacitors for input bypassing, because it may cause severe ringing at the VIN
pin.
The important parameters for the Input capacitor are the input voltage rating and the RMS current rating. With a
nominal input voltage of 12 V, an aluminum electrolytic capacitor with a voltage rating greater than 18 V
(1.5 × VIN) is necessary. The next higher capacitor voltage rating is 25 V.
The RMS current rating requirement for the input capacitor in a buck regulator is approximately ½ the DC load
current. In this example, with a 400-mA load, a capacitor with a RMS current rating of at least 200 mA is needed.
Figure 23 can be used to select an appropriate input capacitor. From the curves, locate the 25-V line and note
which capacitor values have RMS current ratings greater than 200 mA. Either a 47-μF or 68-μF, 25-V capacitor
can be used.
For a through hole design, a 68-μF, 25-V electrolytic capacitor (Panasonic HFQ series or Nichicon PL series or
equivalent) would be adequate. Other types or other manufacturers' capacitors can be used provided the RMS
ripple current ratings are adequate.
For surface-mount designs, solid tantalum capacitors are recommended. The TPS series available from AVX,
and the 593D series from Sprague are both surge current tested.
For additional information, see Input Capacitor (CIN).
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Table 5. LM2594xx Fixed Voltage Quick Design Component Selection Table
CONDITIONS INDUCTOR OUTPUT CAPACITOR
THROUGH HOLE SURFACE MOUNT
OUTPUT
VOLTAGE
(V)
LOAD
CURRENT
(A)
MAX INPUT
VOLTAGE
(V)
INDUCTANCE
(μH) INDUCTOR
(#)
PANASONIC
HFQ SERIES
(μF/V)
NICHICON
PL SERIES
(μF/V)
AVX TPS
SERIES
(μF/V)
SPRAGUE
595D SERIES
(μF/V)
3.3
0.5
5 33 L14 220/16 220/16 100/16 100/6.3
7 47 L13 120/25 120/25 100/16 100/6.3
10 68 L21 120/25 120/25 100/16 100/6.3
40 100 L20 120/35 120/35 100/16 100/6.3
6 68 L4 120/25 120/25 100/16 100/6.3
0.2 10 150 L10 120/16 120/16 100/16 100/6.3
40 220 L9 120/16 120/16 100/16 100/6.3
5
0.5
8 47 L13 180/16 180/16 100/16 33/25
10 68 L21 180/16 180/16 100/16 33/25
15 100 L20 120/25 120/25 100/16 33/25
40 150 L19 120/25 120/25 100/16 33/25
9 150 L10 82/16 82/16 100/16 33/25
0.2 20 220 L9 120/16 120/16 100/16 33/25
40 330 L8 120/16 120/16 100/16 33/25
12
0.5
15 68 L21 82/25 82/25 100/16 15/25
18 150 L19 82/25 82/25 100/16 15/25
30 220 L27 82/25 82/25 100/16 15/25
40 330 L26 82/25 82/25 100/16 15/25
15 100 L11 82/25 82/25 100/16 15/25
0.2 20 220 L9 82/25 82/25 100/16 15/25
40 330 L17 82/25 82/25 100/16 15/25
9.2.1.3 Application Curves
Discontinuous mode switching waveforms
VIN = 20 V, VOUT = 5 V, ILOAD = 200 mA
L = 33 μH, COUT = 220 μF, COUT ESR = 60 mΩ
A: Output pin voltage, 10 V/div.
B: Inductor current, 0.2 A/div.
C: Output ripple voltage, 20 mV/div.
Figure 33. Horizontal Time Base: 2 μs/div
Load transient response for discontinuous mode
VIN = 20 V, VOUT = 5 V, ILOAD = 100 mA to 200 mA
L = 33 μH, COUT = 220 μF, COUT ESR = 60 mΩ
A: Output voltage, 50 mV/div. (AC)
B: 100-mA to 200-mA load pulse
Figure 34. Horizontal Time Base: 200 μs/div
Copyright © 2016, Texas Instruments Incorporated
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9.2.2 Series Buck Regulator (Adjustable Output)
CIN 68-μF, 35-V, Aluminum Electrolytic Nichicon “PL Series”
COUT 120-μF, 25-V Aluminum Electrolytic, Nichicon “PL Series”
D1 1-A, 40-V Schottky Rectifier, 1N5819
L1 100-μH, L20
R1 1 kΩ, 1%
CFF See Feedforward Capacitor (CFF)
Figure 35. Adjustable Output Voltage Version
9.2.2.1 Design Requirements
Table 6 lists the design parameters of this example.
Table 6. Design Parameter
PARAMETER EXAMPLE VALUE
Regulated output voltage, VOUT 20 V
Maximum input voltage, VIN(max) 28 V
Maximum load current, ILOAD(max) 0.5 A
Switching frequency, F Fixed at a nominal 150 kHz
9.2.2.2 Detailed Design Procedure
9.2.2.2.1 Programming Output Voltage
Selecting R1and R2, as shown in Figure 35.
Use Equation 1 to select the appropriate resistor values.
(1)
Select R1to be 1 kΩ, 1%. Solve for R2using Equation 2.
(2)
Select a value for R1between 240 Ωand 1.5 kΩusing Equation 3. The lower resistor values minimize noise
pickup in the sensitive feedback pin. (For the lowest temperature coefficient and the best stability with time, use
1% metal film resistors.)
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(3)
R2= 1 k (16.26 1) = 15.26 k, closest 1% value is 15.4 kΩ
R2= 15.4 kΩ
9.2.2.2.2 Inductor Selection (L1)
1. Calculate the inductor Volt microsecond constant E × T (V × μs) with Equation 4.
where
VSAT = internal switch saturation voltage = 0.9 V
VD= diode forward voltage drop = 0.5 V (4)
2. Calculate the inductor Volt microsecond constant (E × T) with Equation 5.
(5)
3. Use the E × T value from the previous formula and match it with the E × T number on the vertical axis of the
Inductor Value Selection Guide shown in Figure 30.
E × T = 35.2 (V × μs) (6)
4. On the horizontal axis, select the maximum load current: ILOAD(max) = 0.5 A
5. Identify the inductance region intersected by the E × T value and the maximum load current value. Each
region is identified by an inductance value and an inductor code (LXX).
From the inductor value selection guide shown in Figure 30, the inductance region intersected by the 35 (V ×
μs) horizontal line and the 0.5-A vertical line is 150 μH, and the inductor code is L19.
6. Select an appropriate inductor from the four manufacturer's part numbers listed in Table 3.
From Table 3, locate line L19, and select an inductor part number from the list of manufacturers' part
numbers.
9.2.2.2.3 Output Capacitor Selection (COUT)
1. In the majority of applications, low ESR electrolytic or solid tantalum capacitors between 82 μF and 220 μF
provide the best results. This capacitor must be located close to the IC using short capacitor leads and short
copper traces. Do not use capacitors larger than 220 μF. For additional information, see Output Capacitor
(COUT).
2. To simplify the capacitor selection procedure, see Table 7 for a quick design guide. This table contains
different output voltages, and lists various output capacitors that provides the best design solutions.
From Table 7, locate the output voltage column. From that column, locate the output voltage closest to the
output voltage in your application. In this example, select the 24-V line. Under Output Capacitor (COUT),
select a capacitor from the list of through hole electrolytic or surface mount tantalum types from four different
capacitor manufacturers. TI recommends that both the manufacturers and the manufacturers series that are
listed in Table 7.
In this example, through hole aluminum electrolytic capacitors from several different manufacturers are
available.
82-µF, 50-V Panasonic HFQ Series
120-µF, 50-V Nichicon PL Series
3. The capacitor voltage rating must be at least 1.5 times greater than the output voltage, and often much
higher voltage ratings are needed to satisfy the low ESR requirements needed for low output ripple voltage.
For a 20-V output, a capacitor rating of at least 30-V or more is required. In this example, either a 35-V or
50-V capacitor would work. A 50-V rating was chosen because it has a lower ESR which provides a lower
output ripple voltage.
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Other manufacturers or other types of capacitors may also be used, provided the capacitor specifications
(especially the 100-kHz ESR) closely match the types listed in Table 7. Refer to the capacitor manufacturers
data sheet for this information.
9.2.2.2.4 Feedforward Capacitor (CFF)
For output voltages greater than approximately 10 V, an additional capacitor is required. The compensation
capacitor is typically between 50 pF and 10 nF, and is wired in parallel with the output voltage setting resistor,
R2. It provides additional stability for high output voltages, low input or output voltages, and very low ESR output
capacitors, such as solid tantalum capacitors calculated with Equation 7.
(7)
This capacitor type can be ceramic, plastic, silver mica, and so forth (because of the unstable characteristics of
ceramic capacitors made with Z5U material, they are not recommended).
Table 7 contains feedforward capacitor values for various output voltages. In this example, a 1-nF capacitor is
needed.
9.2.2.2.5 Catch Diode Selection (D1)
1. The catch diode current rating must be at least 1.3 times greater than the maximum load current. Also, if the
power supply design must withstand a continuous output short, the diode must have a current rating equal to
the maximum current limit of the LM2594. The most stressful condition for this diode is an overload or
shorted output condition.
See Table 2. Schottky diodes provide the best performance, and in this example a 1-A, 40-V, 1N5819
Schottky diode is a good choice. The 1-A diode rating is more than adequate and will not be overstressed
even for a shorted output.
2. The reverse voltage rating of the diode must be at least 1.25 times the maximum input voltage.
3. This diode must be fast (short reverse recovery time) and must be placed close to the LM2594 using short
leads and short printed circuit traces. Because of their fast switching speed and low forward voltage drop,
Schottky diodes provide the best performance and efficiency, and must be the first choice, especially in low
output voltage applications. Ultra-fast recovery or high-efficiency rectifiers are also good choices, but some
types with an abrupt turnoff characteristic may cause instability or EMl problems. Ultra-fast recovery diodes
typically have reverse recovery times of 50 ns or less. Rectifiers such as the 1N4001 series must not be
used because they are too slow.
9.2.2.2.6 Input Capacitor (CIN)
A low ESR aluminum or tantalum bypass capacitor is required between the input pin and ground to prevent large
voltage transients from appearing at the input. In addition, the RMS current rating of the input capacitor must be
selected to be at least ½ the DC load current. The capacitor manufacturers data sheet must be checked to
assure that this current rating is not exceeded. Figure 23 shows typical RMS current ratings for several different
aluminum electrolytic capacitor values.
This capacitor must be located close to the IC using short leads and the voltage rating must be approximately 1.5
times the maximum input voltage.
If solid tantalum input capacitors are used, TI recommends that they be surge current tested by the
manufacturer.
Use caution when using ceramic capacitors for input bypassing, because it may cause severe ringing at the VIN
pin.
The important parameters for the Input capacitor are the input voltage rating and the RMS current rating. With a
nominal input voltage of 28 V, an aluminum electrolytic aluminum electrolytic capacitor with a voltage rating
greater than 42 V (1.5 × VIN) is required. Because the next higher capacitor voltage rating is 50 V, a 50-V
capacitor must be used. The capacitor voltage rating of (1.5 × VIN) is a conservative guideline, and can be
modified somewhat if desired.
The RMS current rating requirement for the input capacitor of a buck regulator is approximately ½ the DC load
current. In this example, with a 400 mA load, a capacitor with a RMS current rating of at least 200 mA is needed.
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Figure 23 shows curves that can be used to select an appropriate input capacitor. From the curves, locate the
50-V line and note which capacitor values have RMS current ratings greater than 200 mA. A 47-μF, 50-V low
ESR electrolytic capacitor is needed.
For a through-hole design, a 47-μF, 50-V electrolytic capacitor (Panasonic HFQ series or Nichicon PL series or
equivalent) would be adequate. Other types or other manufacturers' capacitors can be used provided the RMS
ripple current ratings are adequate.
For surface mount designs, solid tantalum capacitors are recommended. The TPS series available from AVX,
and the 593D series from Sprague are both surge current tested.
For additional information, see Input Capacitor (CIN).
Table 7. Output Capacitor and Feedforward Capacitor Selection Table
OUTPUT
VOLTAGE
(V)
THROUGH-HOLE OUTPUT CAPACITOR SURFACE-MOUNT OUTPUT CAPACITOR
PANASONIC HFQ
SERIES (μF/V) NICHICON PL SERIES
(μF/V) FEEDFORWARD
CAPACITOR AVX TPS
SERIES (μF/V) SPRAGUE 595D
SERIES (μF/V) FEEDFORWARD
CAPACITOR
1.2 220/25 220/25 0 220/10 220/10 0
4 180/25 180/25 4.7 nF 100/10 120/10 4.7 nF
6 82/25 82/25 4.7 nF 100/10 120/10 4.7 nF
9 82/25 82/25 3.3 nF 100/16 100/16 3.3 nF
12 82/25 82/25 2.2 nF 100/16 100/16 2.2 nF
15 82/25 82/25 1.5 nF 68/20 100/20 1.5 nF
24 82/50 120/50 1 nF 10/35 15/35 220 pF
28 82/50 120/50 820 pF 10/35 15/35 220 pF
9.2.2.3 Application Curves
Continuous mode switching waveforms
VIN = 20 V, VOUT = 5 V, ILOAD = 400 mA
L = 100 μH, COUT = 120 μF, COUT ESR = 140 mΩ
A: Output pin voltage, 10 V/div.
B: Inductor current, 0.2 A/div.
C: Output ripple voltage, 20 mV/div.
Figure 36. Horizontal Time Base: 2 μs/div
Load transient response for continuous mode
VIN = 20 V, VOUT = 5 V, ILOAD = 200 mA to 500 mA
L = 100 μH, COUT = 120 μF, COUT ESR = 140 mΩ
A: Output voltage, 50 mV/div. (AC)
B: 200-mA to 500-mA load pulse
Figure 37. Horizontal Time Base: 50 μs/div
10 Power Supply Recommendations
The LM2594 is designed to operate from an input voltage supply up to 45 V and 60 V (HV version). This input
supply must be well regulated and able to withstand maximum input current and maintain a stable voltage.
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11 Layout
11.1 Layout Guidelines
As in any switching regulator, layout is very important. Rapidly switching currents associated with wiring
inductance can generate voltage transients which can cause problems. For minimal inductance and ground
loops, the wires indicated by heavy lines must be wide printed circuit traces and must be kept as short as
possible. For best results, external components must be placed as close to the switcher lC as possible using
ground plane construction or single point grounding.
If open core inductors are used, special care must be taken as to the location and positioning of this type of
inductor. Allowing the inductor flux to intersect sensitive feedback, lC groundpath and COUT wiring can cause
problems.
When using the adjustable version, take special care regarding as to the location of the feedback resistors and
the associated wiring. Physically place both resistors near the IC, and route the wiring away from the inductor,
especially an open core type of inductor.
11.2 Layout Example
CIN = 10-μF, 35-V, Solid Tantalum AVX, TPS series
COUT = 00-μF, 10-V Solid Tantalum AVX, TPS series
D1 = 1-A, 40-V Schottky Rectifier, surface mount
L1 = 100-μH, L20, Coilcraft DO33
Figure 38. Typical Surface-Mount PCB Layout, Fixed Output (2X Size)
CIN = 10-μF, 35-V, Solid Tantalum AVX, TPS series
COUT = 100-μF, 10-V Solid Tantalum AVX, TPS series
D1 = 1-A, 40-V Schottky Rectifier, surface mount
L1 = 100-μH, L20, Coilcraft DO33
R1 = 1 kΩ, 1%
R2= Use formula in Design Procedure
CFF = See Table 7
Figure 39. Typical Surface-Mount PCB Layout, Adjustable Output (2X Size)
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11.3 Thermal Considerations
The LM2594xx is available in two packages: an 8-pin through-hole PDIP and an 8-pin surface-mount SOIC. Both
packages are molded plastic with a copper lead frame. When the package is soldered to the printed-circuit board
(PCB), the copper and the board are the heat sink for the LM2594 and the other heat producing components.
For best thermal performance, wide copper traces must be used and all ground and unused pins must be
soldered to generous amounts of PCB copper, such as a ground plane (one exception to this is the output
(switch pin, which must not have large areas of copper). Large areas of copper provide the best transfer of heat
(lower thermal resistance) to the surrounding air, and even double-sided or multilayer boards provide a better
heat path to the surrounding air. Unless power levels are small, sockets are not recommended because of the
added thermal resistance it adds and the resultant higher junction temperatures.
Package thermal resistance and junction temperature rise numbers are all approximate, and there are many
factors that affects the junction temperature. Some of these factors include board size, shape, thickness,
position, location, and even board temperature. Other factors are trace width, printed-circuit copper area, copper
thickness, single- or double-sided multilayer board, and the amount of solder on the board. The effectiveness of
the PCB to dissipate heat also depends on the size, quantity, and spacing of other components on the board.
Furthermore, some of these components such as the catch diode adds heat to the PCB and the heat can vary as
the input voltage changes. For the inductor, depending on the physical size, type of core material, and the DC
resistance, it could either act as a heat sink taking heat away from the board, or it could add heat to the board.
Circuit Data for Temperature Rise Curve (8-Pin PDIP)
Capacitors Through hole electrolytic
Inductor Through hole, Schott, 100 μH
Diode Through hole, 1-A, 40-V, Schottky
PCB 4 square inches single sided 2 oz. copper (0.0028)
Figure 40. Junction Temperature Rise, 8-Pin PDIP
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Thermal Considerations (continued)
Circuit Data for Temperature Rise Curve
(Surface Mount)
Capacitors Surface mount tantalum, molded Dsize
Inductor Surface mount, Coilcraft DO33, 100 μH
Diode Surface mount, 1-A, 40-V, Schottky
PCB 4 square inches single sided 2 oz. copper (0.0028)
Figure 41. Junction Temperature Rise, 8-Pin SOIC
Figure 40 and Figure 41 show the LM2594 junction temperature rise above ambient temperature with a 500-mA
load for various input and output voltages. This data was taken with the circuit operating as a buck switcher with
all components mounted on a PCB to simulate the junction temperature under actual operating conditions. This
curve is typical, and can be used for a quick check on the maximum junction temperature for various conditions,
but keep in mind that there are many factors that can affect the junction temperature.
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12 Device and Documentation Support
12.1 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 8. Related Links
PARTS PRODUCT FOLDER SAMPLE & BUY TECHNICAL
DOCUMENTS TOOLS &
SOFTWARE SUPPORT &
COMMUNITY
LM2594 Click here Click here Click here Click here Click here
LM2594HV Click here Click here Click here Click here Click here
12.2 Support Resources
TI E2E™ support forums are an engineer's go-to source for fast, verified answers and design help straight
from the experts. Search existing answers or ask your own question to get the quick design help you need.
Linked content is provided "AS IS" by the respective contributors. They do not constitute TI specifications and do
not necessarily reflect TI's views; see TI's Terms of Use.
12.3 Trademarks
E2E is a trademark of Texas Instruments.
SIMPLE SWITCHER is a registered trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
12.4 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.
12.5 Glossary
SLYZ022 TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
13 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.
PACKAGE OPTION ADDENDUM
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Addendum-Page 1
PACKAGING INFORMATION
Orderable Device Status
(1)
Package Type Package
Drawing Pins Package
Qty Eco Plan
(2)
Lead/Ball Finish
(6)
MSL Peak Temp
(3)
Op Temp (°C) Device Marking
(4/5)
Samples
LM2594HVM-12/NOPB ACTIVE SOIC D 8 95 Green (RoHS
& no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 2594H
M-12
LM2594HVM-3.3/NOPB ACTIVE SOIC D 8 95 Green (RoHS
& no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 2594H
M-3.3
LM2594HVM-5.0 NRND SOIC D 8 95 TBD Call TI Call TI -40 to 125 2594H
M-5.0
LM2594HVM-5.0/NOPB ACTIVE SOIC D 8 95 Green (RoHS
& no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 2594H
M-5.0
LM2594HVM-ADJ NRND SOIC D 8 95 TBD Call TI Call TI -40 to 125 2594H
M-ADJ
LM2594HVM-ADJ/NOPB ACTIVE SOIC D 8 95 Green (RoHS
& no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 2594H
M-ADJ
LM2594HVMX-12/NOPB ACTIVE SOIC D 8 2500 Green (RoHS
& no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 2594H
M-12
LM2594HVMX-3.3/NOPB ACTIVE SOIC D 8 2500 Green (RoHS
& no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 2594H
M-3.3
LM2594HVMX-5.0/NOPB ACTIVE SOIC D 8 2500 Green (RoHS
& no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 2594H
M-5.0
LM2594HVMX-ADJ/NOPB ACTIVE SOIC D 8 2500 Green (RoHS
& no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 2594H
M-ADJ
LM2594HVN-12/NOPB ACTIVE PDIP P 8 40 Green (RoHS
& no Sb/Br) SN Level-1-NA-UNLIM -40 to 125 LM2594HV
N-12 P+
LM2594HVN-3.3/NOPB ACTIVE PDIP P 8 40 Green (RoHS
& no Sb/Br) Call TI | SN Level-1-NA-UNLIM -40 to 125 LM2594HV
N-3.3 P+
LM2594HVN-5.0/NOPB ACTIVE PDIP P 8 40 Green (RoHS
& no Sb/Br) Call TI | SN Level-1-NA-UNLIM -40 to 125 LM2594HV
N-5.0 P+
LM2594HVN-ADJ/NOPB ACTIVE PDIP P 8 40 Green (RoHS
& no Sb/Br) Call TI | SN Level-1-NA-UNLIM -40 to 125 LM2594HV
N-ADJ P+
LM2594M-12/NOPB ACTIVE SOIC D 8 95 Green (RoHS
& no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 2594
M-12
LM2594M-3.3 NRND SOIC D 8 95 TBD Call TI Call TI -40 to 125 2594
M-3.3
LM2594M-3.3/NOPB ACTIVE SOIC D 8 95 Green (RoHS
& no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 2594
M-3.3
PACKAGE OPTION ADDENDUM
www.ti.com 7-May-2020
Addendum-Page 2
Orderable Device Status
(1)
Package Type Package
Drawing Pins Package
Qty Eco Plan
(2)
Lead/Ball Finish
(6)
MSL Peak Temp
(3)
Op Temp (°C) Device Marking
(4/5)
Samples
LM2594M-5.0 NRND SOIC D 8 95 TBD Call TI Call TI -40 to 125 2594
M-5.0
LM2594M-5.0/NOPB ACTIVE SOIC D 8 95 Green (RoHS
& no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 2594
M-5.0
LM2594M-ADJ/NOPB ACTIVE SOIC D 8 95 Green (RoHS
& no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 2594
M-ADJ
LM2594MX-12/NOPB ACTIVE SOIC D 8 2500 Green (RoHS
& no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 2594
M-12
LM2594MX-3.3/NOPB ACTIVE SOIC D 8 2500 Green (RoHS
& no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 2594
M-3.3
LM2594MX-5.0/NOPB ACTIVE SOIC D 8 2500 Green (RoHS
& no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 2594
M-5.0
LM2594MX-ADJ/NOPB ACTIVE SOIC D 8 2500 Green (RoHS
& no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 2594
M-ADJ
LM2594N-12/NOPB ACTIVE PDIP P 8 40 Green (RoHS
& no Sb/Br) Call TI | SN Level-1-NA-UNLIM -40 to 125 LM2594N
-12 P+
LM2594N-3.3/NOPB ACTIVE PDIP P 8 40 Green (RoHS
& no Sb/Br) Call TI | SN Level-1-NA-UNLIM -40 to 125 LM2594N
-3.3 P+
LM2594N-5.0/NOPB ACTIVE PDIP P 8 40 Green (RoHS
& no Sb/Br) Call TI | SN Level-1-NA-UNLIM -40 to 125 LM2594N
-5.0 P+
LM2594N-ADJ/NOPB ACTIVE PDIP P 8 40 Green (RoHS
& no Sb/Br) Call TI | SN Level-1-NA-UNLIM -40 to 125 LM2594N
-ADJ P+
(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 <=1000ppm threshold. Antimony trioxide based
flame retardants must also meet the <=1000ppm threshold requirement.
(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
PACKAGE OPTION ADDENDUM
www.ti.com 7-May-2020
Addendum-Page 3
(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device Package
Type Package
Drawing Pins SPQ Reel
Diameter
(mm)
Reel
Width
W1 (mm)
A0
(mm) B0
(mm) K0
(mm) P1
(mm) W
(mm) Pin1
Quadrant
LM2594HVMX-12/NOPB SOIC D 8 2500 330.0 12.4 6.5 5.4 2.0 8.0 12.0 Q1
LM2594HVMX-3.3/NOPB SOIC D 8 2500 330.0 12.4 6.5 5.4 2.0 8.0 12.0 Q1
LM2594HVMX-5.0/NOPB SOIC D 8 2500 330.0 12.4 6.5 5.4 2.0 8.0 12.0 Q1
LM2594HVMX-ADJ/NOPB SOIC D 8 2500 330.0 12.4 6.5 5.4 2.0 8.0 12.0 Q1
LM2594MX-12/NOPB SOIC D 8 2500 330.0 12.4 6.5 5.4 2.0 8.0 12.0 Q1
LM2594MX-3.3/NOPB SOIC D 8 2500 330.0 12.4 6.5 5.4 2.0 8.0 12.0 Q1
LM2594MX-5.0/NOPB SOIC D 8 2500 330.0 12.4 6.5 5.4 2.0 8.0 12.0 Q1
LM2594MX-ADJ/NOPB SOIC D 8 2500 330.0 12.4 6.5 5.4 2.0 8.0 12.0 Q1
PACKAGE MATERIALS INFORMATION
www.ti.com 7-May-2020
Pack Materials-Page 1
*All dimensions are nominal
Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)
LM2594HVMX-12/NOPB SOIC D 8 2500 367.0 367.0 35.0
LM2594HVMX-3.3/NOPB SOIC D 8 2500 367.0 367.0 35.0
LM2594HVMX-5.0/NOPB SOIC D 8 2500 367.0 367.0 35.0
LM2594HVMX-ADJ/NOPB SOIC D 8 2500 367.0 367.0 35.0
LM2594MX-12/NOPB SOIC D 8 2500 367.0 367.0 35.0
LM2594MX-3.3/NOPB SOIC D 8 2500 367.0 367.0 35.0
LM2594MX-5.0/NOPB SOIC D 8 2500 367.0 367.0 35.0
LM2594MX-ADJ/NOPB SOIC D 8 2500 367.0 367.0 35.0
PACKAGE MATERIALS INFORMATION
www.ti.com 7-May-2020
Pack Materials-Page 2
www.ti.com
PACKAGE OUTLINE
C
.228-.244 TYP
[5.80-6.19]
.069 MAX
[1.75]
6X .050
[1.27]
8X .012-.020
[0.31-0.51]
2X
.150
[3.81]
.005-.010 TYP
[0.13-0.25]
0 - 8 .004-.010
[0.11-0.25]
.010
[0.25]
.016-.050
[0.41-1.27]
4X (0 -15 )
A
.189-.197
[4.81-5.00]
NOTE 3
B .150-.157
[3.81-3.98]
NOTE 4
4X (0 -15 )
(.041)
[1.04]
SOIC - 1.75 mm max heightD0008A
SMALL OUTLINE INTEGRATED CIRCUIT
4214825/C 02/2019
NOTES:
1. Linear dimensions are in inches [millimeters]. Dimensions in parenthesis are for reference only. Controlling dimensions are in inches.
Dimensioning and tolerancing per ASME Y14.5M.
2. This drawing is subject to change without notice.
3. This dimension does not include mold flash, protrusions, or gate burrs. Mold flash, protrusions, or gate burrs shall not
exceed .006 [0.15] per side.
4. This dimension does not include interlead flash.
5. Reference JEDEC registration MS-012, variation AA.
18
.010 [0.25] C A B
5
4
PIN 1 ID AREA
SEATING PLANE
.004 [0.1] C
SEE DETAIL A
DETAIL A
TYPICAL
SCALE 2.800
www.ti.com
EXAMPLE BOARD LAYOUT
.0028 MAX
[0.07]
ALL AROUND
.0028 MIN
[0.07]
ALL AROUND
(.213)
[5.4]
6X (.050 )
[1.27]
8X (.061 )
[1.55]
8X (.024)
[0.6]
(R.002 ) TYP
[0.05]
SOIC - 1.75 mm max heightD0008A
SMALL OUTLINE INTEGRATED CIRCUIT
4214825/C 02/2019
NOTES: (continued)
6. Publication IPC-7351 may have alternate designs.
7. Solder mask tolerances between and around signal pads can vary based on board fabrication site.
METAL SOLDER MASK
OPENING
NON SOLDER MASK
DEFINED
SOLDER MASK DETAILS
EXPOSED
METAL
OPENING
SOLDER MASK METAL UNDER
SOLDER MASK
SOLDER MASK
DEFINED
EXPOSED
METAL
LAND PATTERN EXAMPLE
EXPOSED METAL SHOWN
SCALE:8X
SYMM
1
45
8
SEE
DETAILS
SYMM
www.ti.com
EXAMPLE STENCIL DESIGN
8X (.061 )
[1.55]
8X (.024)
[0.6]
6X (.050 )
[1.27] (.213)
[5.4]
(R.002 ) TYP
[0.05]
SOIC - 1.75 mm max heightD0008A
SMALL OUTLINE INTEGRATED CIRCUIT
4214825/C 02/2019
NOTES: (continued)
8. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate
design recommendations.
9. Board assembly site may have different recommendations for stencil design.
SOLDER PASTE EXAMPLE
BASED ON .005 INCH [0.125 MM] THICK STENCIL
SCALE:8X
SYMM
SYMM
1
45
8
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