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FEATURES APPLICATIONS
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
NC
NC
OUTPUT
NC
GND
NC
FEEDBACK
NC
VIN
NC
NC
GND
GND
NC
NC
ON/OFF
N (PDIP) PACKAGE
(TOP VIEW)
NC − No internal connection
DESCRIPTION/ORDERING INFORMATION
LM25751-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATOR
SLVS569E – JANUARY 2005 – REVISED JANUARY 2006
•Simple High-Efficiency Step-Down (Buck)•Adjustable With a Range of 1.23 V to 37 V and
Regulator±4% Regulation (Max) Over Line, Load, and
•Pre-Regulator for Linear RegulatorsTemperature Conditions
•On-Card Switching Regulators•Specified 1-A Output Current
•Positive-to-Negative Converter (Buck-Boost)•Wide Input Voltage Range …4.75 V to 40 V•Uses Readily Available Standard Inductors•52-kHz (Typ) Fixed-Frequency InternalOscillator
•TTL Shutdown Capability With 50- µA (Typ)Standby Current•High Efficiency …as High as 88% (Typ)•Thermal Shutdown and Current-LimitProtection With Cycle-by-Cycle CurrentLimiting
•For the Full Offering of Voltages (IncludingFixed-Output Options) and Packages(Including TO-263), see TL2575 Datasheet
The LM2575 greatly simplifies the design of switching power supplies by conveniently providing all the activefunctions needed for a step-down (buck) switching regulator in an integrated circuit. Accepting a wide inputvoltage range and available in an adjustable output version, the LM2575 has an integrated switch capable ofdelivering 1 A of load current, with excellent line and load regulation. The device also offers internal frequencycompensation, a fixed-frequency oscillator, cycle-by-cycle current limiting, and thermal shutdown. In addition, amanual shutdown is available via an external ON/OFF pin.
The LM2575 represents a superior alternative to popular three-terminal linear regulators. Due to its highefficiency, it significantly reduces the size of the heat sink and, in many cases, no heat sink is required.Optimized for use with standard series of inductors available from several different manufacturers, the LM2575greatly simplifies the design of switch-mode power supplies by requiring a minimal addition of only four to sixexternal components for operation.
The LM2575 is characterized for operation over the virtual junction temperature range of –40 °C to 125 °C.
ORDERING INFORMATION
V
OT
J
PACKAGE
(1)
ORDERABLE PART NUMBER TOP-SIDE MARKING(NOM)
–40 °C to 125 °C ADJ PDIP – N Tube of 25 LM2575IN LM2575IN
(1) Package drawings, standard packing quantities, thermal data, symbolization, and PCB design guidelines are available atwww.ti.com/sc/package.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of TexasInstruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date.
Copyright © 2005–2006, Texas Instruments IncorporatedProducts conform to specifications per the terms of the TexasInstruments standard warranty. Production processing does notnecessarily include testing of all parameters.
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Internal
Regulator ON/OFF
_
+
_
+
1.23-V
Band-Gap
Reference 52-kHz
Oscillator Reset Thermal
Shutdown Current
Limit
FEEDBACK
7
CIN
+
VIN
6
Unregulated
DC Input
GND
5, 12, 13
OUTPUT
3
ON/OFF
9
COUT
+
D1 L
O
A
D
VOUT
1-A
Switch
Driver
Fixed-Gain
Error Amp Comparator
R2
R1
R1 = Open, R2 = 0 Ω
L1
Absolute Maximum Ratings
(1)
Package Thermal Data
(1)
Recommended Operating Conditions
LM2575
1-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATOR
SLVS569E – JANUARY 2005 – REVISED JANUARY 2006
FUNCTIONAL BLOCK DIAGRAM
over operating free-air temperature range (unless otherwise noted)
MIN MAX UNIT
V
IN
Supply voltage 42 VON/OFF pin input voltage –0.3 V
IN
VOutput voltage to GND (steady state) –1 VT
J
Maximum junction temperature 150 °CT
stg
Storage temperature range –65 150 °C
(1) Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratingsonly, and functional operation of the device at these or any other conditions beyond those indicated under “recommended operatingconditions” is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
PACKAGE BOARD θ
JC
θ
JA
PDIP (N) High K, JESD 51-7 51 °C/W 67 °C/W
(1) Maximum power dissipation is a function of T
J
(max), θ
JA
, and T
A
. The maximum allowable power dissipation at any allowable ambienttemperature is P
D
= (T
J
(max) – T
A
)/ θ
JA
. Operating at the absolute maximum T
J
of 150 °C can affect reliability.
over operating free-air temperature range (unless otherwise noted)
MIN MAX UNIT
V
IN
Supply voltage 4.75 40 VT
J
Operating virtual junction temperature –40 125 °C
2
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Electrical Characteristics
LM25751-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATOR
SLVS569E – JANUARY 2005 – REVISED JANUARY 2006
I
LOAD
= 200 mA, V
IN
= 12 V (unless otherwise noted) (see Figure 1 )
PARAMETER TEST CONDITIONS T
J
MIN TYP MAX UNIT
V
OUT
= 5 V, I
LOAD
= 0.2 A 25 °C 1.217 1.23 1.243V
OUT
Feedback voltage 25 °C 1.193 1.23 1.267 V8 V ≤V
IN
≤40 V, V
OUT
= 5 V,0.2 A ≤I
LOAD
≤1 A
Full range 1.18 1.28ηEfficiency V
IN
= 12 V, V
OUT
= 5 V, I
LOAD
= 1 A 25 °C 77 %25 °C 50 100I
IB
Feedback bias current V
OUT
= 5 V nAFull range 50025 °C 47 52 58f
o
Oscillator frequency
(1)
kHzFull range 42 6325 °C 0.9 1.2V
SAT
Saturation voltage I
OUT
= 1 A
(2)
VFull range 1.4Maximum duty cycle
(3)
25 °C 93 98 %25 °C 1.7 2.8 3.6I
CL
Peak current
(1) (2)
AFull range 1.3 4V
IN
= 40
(4)
, Output = 0 V 2I
L
Output leakage current 25 °C mAV
IN
= 40
(4)
, Output = –1 V 7.5 30I
Q
Quiescent current
(4)
25 °C 5 10 mAI
STBY
Standby quiescent current OFF ( ON/OFF pin = 5 V) 25 °C 50 200 µA25 °C 2.2 1.4V
IH
OFF (V
OUT
= 0 V)
Full range 2.4ON/OFF logic input level V25 °C 1.2 1V
IL
ON (V
OUT
= nominal voltage)
Full range 0.8I
IH
OFF ( ON/OFF pin = 5 V) 12 30ON/OFF input current 25 °CµAI
IL
ON ( ON/OFF pin = 0 V) 0 10
(1) In the event of an output short or an overload condition, self-protection features lower the oscillator frequency to ∼18 kHz and theminimum duty cycle from 5% to ∼2%. The resulting output voltage drops to ∼40% of its nominal value, causing the average powerdissipated by the IC to lower.(2) Output is not connected to diode, inductor, or capacitor. Output is sourcing current.(3) Feedback is disconnected from output and connected to 0 V.(4) To force the output transistor off, FEEDBACK is disconnected from output and connected to 12 V.
3
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TYPICAL OPERATING CHARACTERISTICS
LM2575
1-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATOR
SLVS569E – JANUARY 2005 – REVISED JANUARY 2006
T
A
= 25 °C (unless otherwise noted)
GRAPH PREVIEWS
Normalized Output Voltage
Line Regulation
Dropout Voltage
Current Limit
Quiescent Current
Standby Quiescent Current
Quiescent Current vs Duty Cycle
Oscillator Frequency
Switch Saturation Voltage
Efficiency
Minimum Operating Voltage (Adjustable Version)
Feedback Voltage vs Duty Cycle
Feedback Pin Current (Adjustable Version)
Switching Waveforms
Load Transient Response
4
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APPLICATION INFORMATION
Layout Guidelines
LM2575
(ADJ)
CIN
100 µF
+
+VIN
16
5, 12, 13 GND 9 ON/OFF D1
11DQ06
OUTPUT
3
L1
330 µH
COUT
330 µF
+
FEEDBACK
7
L
O
A
D
VOUT
7-V to 60-V
Unregulated
DC Input
Adjustable Output Voltage Versions
VOUT = VREF(1 + R2/R1) = 5 V
Where
VREF = 1.23 V
R1 = 2 k
R2 = 6.12 k
R2
R1
Input Capacitor (C
IN
)
IC,RMS 1.2(ton
T) ILOAD, where:
ton
TVOUT
VIN {buck regulator}, and
ton
T|VOUT|
(|VOUT|VIN){buck−boost regulator}
Output Capacitor (C
OUT
)
LM25751-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATOR
SLVS569E – JANUARY 2005 – REVISED JANUARY 2006
With any switching regulator, circuit layout plays an important role in circuit performance. Wiring and parasiticinductances, as well as stray capacitances, are subjected to rapidly switching currents, which can result inunwanted voltage transients. To minimize inductance and ground loops, the length of the leads indicated byheavy lines (see Figure 1 ) should be minimized. Optimal results can be achieved by single-point grounding or byground-plane construction. For the same reasons, the two programming resistors used in the adjustable versionshould be located as close as possible to the regulator to keep the sensitive feedback wiring short.
Figure 1. Test Circuit and Layout Guidelines
For stability concerns, an input bypass capacitor (electrolytic, C
IN
≥47 µF) needs to be located as close aspossible to the regulator. For operating temperatures below –25 °C, C
IN
may need to be larger in value. Inaddition, since most electrolytic capacitors have decreasing capacitances and increasing ESR as temperaturedrops, adding a ceramic or solid tantalum capacitor in parallel increases the stability in cold temperatures.
To extend the capacitor operating lifetime, the capacitor RMS ripple current rating should be:
For both loop stability and filtering of ripple voltage, an output capacitor also is required, again in close proximityto the regulator. For best performance, low-ESR aluminum electrolytics are recommended, although standardaluminum electrolytics may be adequate for some applications. Based on the following equation:
Output Ripple Voltage = (ESR of C
OUT
)×(inductor ripple current)
5
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Catch Diode
Inductor
LM2575
1-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATOR
SLVS569E – JANUARY 2005 – REVISED JANUARY 2006
APPLICATION INFORMATION (continued)Output ripple of 50 mV to 150 mV typically can be achieved with capacitor values of 220 µF to 680 µF. LargerC
OUT
can reduce the ripple 20 mV to 50 mV peak-to-peak. To improve further on output ripple, paralleling ofstandard electrolytic capacitors may be used. Alternatively, higher-grade capacitors such as “high frequency”,“low inductance”, or “low ESR” can be used.
The following should be taken into account when selecting C
OUT
:•At cold temperatures, the ESR of the electrolytic capacitors can rise dramatically (typically 3 ×nominal valueat –25 °C). Because solid tantalum capacitors have significantly better ESR specifications at coldtemperatures, they should be used at operating temperature lower than –25 °C. As an alternative, tantalumsalso can be paralleled to aluminum electrolytics and should contribute 10% to 20% to the total capacitance.•Low ESR for C
OUT
is desirable for low output ripple. However, the ESR should be greater than 0.05 Ωtoavoid the possibility of regulator instability. Hence, a sole tantalum capacitor used for C
OUT
is mostsusceptible to this occurrence.•The capacitor’s ripple current rating of 52 kHz should be at least 50% higher than the peak-to-peak inductorripple current.
As with other external components, the catch diode should be placed close to the output to minimize unwantednoise. Schottky diodes have fast switching speeds and low forward voltage drops and, thus, offer the bestperformance, especially for switching regulators with low output voltages (V
OUT
< 5 V). If a high-efficiency,fast-recovery, or ultra-fast-recovery diode is used in place of a Schottky, it should have a soft recovery (versusabrupt turn-off characteristics) to avoid the chance of causing instability and EMI. Standard 50-/60-Hz diodes,such as the 1N4001 or 1N5400 series, are NOT suitable.
Proper inductor selection is key to the performance-switching power-supply designs. One important factor toconsider is whether the regulator will be used in continuous (inductor current flows continuously and never dropsto zero) or in discontinuous mode (inductor current goes to zero during the normal switching cycle). Each modehas distinctively different operating characteristics and, therefore, can affect the regulator performance andrequirements. In many applications, the continuous mode is the preferred mode of operation, since it offersgreater output power with lower peak currents, and also can result in lower output ripple voltage. The advantagesof continuous mode of operation come at the expense of a larger inductor required to keep inductor currentcontinuous, especially at low output currents and/or high input voltages.
The LM2575 can operate in either continuous or discontinuous mode. With heavy load currents, the inductorcurrent flows continuously and the regulator operates in continuous mode. Under light load, the inductor fullydischarges and the regulator is forced into the discontinuous mode of operation. For light loads (approximately200 mA or less), this discontinuous mode of operation is perfectly acceptable and may be desirable solely tokeep the inductor value and size small. Any buck regulator eventually operates in discontinuous mode when theload current is light enough.
The type of inductor chosen can have advantages and disadvantages. If high performance/quality is a concern,then more-expensive toroid core inductors are the best choice, as the magnetic flux is contained completelywithin the core, resulting in less EMI and noise in nearby sensitive circuits. Inexpensive bobbin core inductors,however, generate more EMI as the open core does confine the flux within the core. Multiple switching regulatorslocated in proximity to each other are particularly susceptible to mutual coupling of magnetic fluxes from eachother’s open cores. In these situations, closed magnetic structures (such as a toroid, pot core, or E-core) aremore appropriate.
Regardless of the type and value of inductor used, the inductor never should carry more than its rated current.Doing so may cause the inductor to saturate, in which case the inductance quickly drops, and the inductor lookslike a low-value resistor (from the dc resistance of the windings). As a result, switching current rises dramatically(until limited by the current-by-current limiting feature of the LM2575) and can result in overheating of theinductor and the IC itself. Note that different types of inductors have different saturation characteristics.
6
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Output Voltage Ripple and Transients
Feedback Connection
ON/OFF Input
Grounding
LM25751-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATOR
SLVS569E – JANUARY 2005 – REVISED JANUARY 2006
APPLICATION INFORMATION (continued)
As with any switching power supply, the output of the LM2575 has a sawtooth-ripple voltage at the switchingfrequency. Typically about 1% of the output voltage, this ripple is due mainly to the inductor sawtooth-ripplecurrent and the ESR of the output capacitor (see note on C
OUT
). Furthermore, the output also may contain smallvoltage spikes at the peaks of the sawtooth waveform. This is due to the fast switching of the output switch andthe parasitic inductance of C
OUT
. These voltage spikes can be minimized through the use of low-inductancecapacitors.
There are several ways to reduce the output ripple voltage: a larger inductor, a larger C
OUT
, or both. Anothermethod is to use a small LC filter (20 µH and 100 µF) at the output. This filter can reduce the output ripplevoltage by a factor of 10 (see Figure 1 ).
FEEDBACK must be connected between the two programming resistors. Again, both of these resistors should bein close proximity to the regulator, and each should be less than 100 k Ωto minimize noise pickup.
ON/OFF should be grounded or be a low-level TTL voltage (typically <1.6 V) for normal operation. To shut downthe LM2575 and put it in standby mode, a high-level TTL or CMOS voltage should be supplied to this pin.ON/OFF should not be left open and safely can be pulled up to V
IN
with or without a pullup resistor.
The power and ground connections of the LM2575 must be low impedance to help maintain output stability. Withthe 16-pin package, all the ground pins (including signal and power grounds) should be soldered directly to widePCB copper traces to ensure low-inductance connections and good thermal dissipation.
7
PACKAGING INFORMATION
Orderable Device Status (1) Package
Type Package
Drawing Pins Package
Qty Eco Plan (2) Lead/Ball Finish MSL Peak Temp (3)
LM2575IN ACTIVE PDIP N 16 25 Pb-Free
(RoHS) CU NIPD N / A for Pkg Type
LM2575INE4 ACTIVE PDIP N 16 25 Pb-Free
(RoHS) CU NIPD N / A for Pkg Type
(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) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check
http://www.ti.com/productcontent for the latest availability information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements
for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered
at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and
package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS
compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame
retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material)
(3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder
temperature.
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.
PACKAGE OPTION ADDENDUM
www.ti.com 18-Jul-2006
Addendum-Page 1
IMPORTANT NOTICE
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