LM2575
1-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATOR
www.ti.com
SLVS569E – JANUARY 2005 – REVISED JANUARY 2006
FEATURES
APPLICATIONS
•
•
•
•
•
•
•
•
•
•
Adjustable With a Range of 1.23 V to 37 V and
±4% Regulation (Max) Over Line, Load, and
Temperature Conditions
Specified 1-A Output Current
Wide Input Voltage Range…4.75 V to 40 V
Uses Readily Available Standard Inductors
52-kHz (Typ) Fixed-Frequency Internal
Oscillator
TTL Shutdown Capability With 50-µA (Typ)
Standby Current
High Efficiency…as High as 88% (Typ)
Thermal Shutdown and Current-Limit
Protection With Cycle-by-Cycle Current
Limiting
For the Full Offering of Voltages (Including
Fixed-Output Options) and Packages
(Including TO-263), see TL2575 Datasheet
•
•
•
Simple High-Efficiency Step-Down (Buck)
Regulator
Pre-Regulator for Linear Regulators
On-Card Switching Regulators
Positive-to-Negative Converter (Buck-Boost)
N (PDIP) PACKAGE
(TOP VIEW)
NC
NC
OUTPUT
NC
GND
NC
FEEDBACK
NC
1
16
2
15
3
14
4
13
5
12
6
11
7
10
8
9
VIN
NC
NC
GND
GND
NC
NC
ON/OFF
NC − No internal connection
DESCRIPTION/ORDERING INFORMATION
The LM2575 greatly simplifies the design of switching power supplies by conveniently providing all the active
functions needed for a step-down (buck) switching regulator in an integrated circuit. Accepting a wide input
voltage range and available in an adjustable output version, the LM2575 has an integrated switch capable of
delivering 1 A of load current, with excellent line and load regulation. The device also offers internal frequency
compensation, a fixed-frequency oscillator, cycle-by-cycle current limiting, and thermal shutdown. In addition, a
manual shutdown is available via an external ON/OFF pin.
The LM2575 represents a superior alternative to popular three-terminal linear regulators. Due to its high
efficiency, 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 LM2575
greatly simplifies the design of switch-mode power supplies by requiring a minimal addition of only four to six
external components for operation.
The LM2575 is characterized for operation over the virtual junction temperature range of –40°C to 125°C.
ORDERING INFORMATION
TJ
–40°C to 125°C
(1)
VO
(NOM)
ADJ
PACKAGE (1)
PDIP – N
Tube of 25
ORDERABLE PART NUMBER
LM2575IN
TOP-SIDE MARKING
LM2575IN
Package drawings, standard packing quantities, thermal data, symbolization, and PCB design guidelines are available at
www.ti.com/sc/package.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2005–2006, Texas Instruments Incorporated
LM2575
1-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATOR
www.ti.com
SLVS569E – JANUARY 2005 – REVISED JANUARY 2006
FUNCTIONAL BLOCK DIAGRAM
Unregulated
DC Input
VIN
Internal
Regulator
6
+
ON/OFF
ON/OFF
9
CIN
FEEDBACK
7
R2
Fixed-Gain
Error Amp
+
_
R1
Comparator
+
_
Driver
1-A
Switch
OUTPUT
L1
3
+
D1
1.23-V
Band-Gap
Reference
VOUT
COUT
L
O
A
D
GND
52-kHz
Oscillator
Reset
Thermal
Shutdown
Current
Limit
5, 12, 13
R1 = Open, R2 = 0 Ω
Absolute Maximum Ratings (1)
over operating free-air temperature range (unless otherwise noted)
MIN
VIN
Supply voltage
ON/OFF pin input voltage
–0.3
Output voltage to GND (steady state)
TJ
Maximum junction temperature
Tstg
Storage temperature range
(1)
–65
MAX
UNIT
42
V
VIN
V
–1
V
150
°C
150
°C
Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratings
only, and functional operation of the device at these or any other conditions beyond those indicated under “recommended operating
conditions” is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
Package Thermal Data (1)
(1)
PACKAGE
BOARD
θJC
θJA
PDIP (N)
High K, JESD 51-7
51°C/W
67°C/W
Maximum power dissipation is a function of TJ(max), θJA, and TA. The maximum allowable power dissipation at any allowable ambient
temperature is PD = (TJ(max) – TA)/θJA. Operating at the absolute maximum TJ of 150°C can affect reliability.
Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
MIN
MAX
VIN
Supply voltage
4.75
40
V
TJ
Operating virtual junction temperature
–40
125
°C
2
UNIT
www.ti.com
LM2575
1-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATOR
SLVS569E – JANUARY 2005 – REVISED JANUARY 2006
Electrical Characteristics
ILOAD = 200 mA, VIN = 12 V (unless otherwise noted) (see Figure 1)
PARAMETER
MIN
TYP
MAX
VOUT = 5 V, ILOAD = 0.2 A
TEST CONDITIONS
25°C
1.217
1.23
1.243
25°C
1.193
1.23
1.267
Full range
1.18
VOUT
Feedback voltage
8 V ≤ VIN ≤ 40 V, VOUT = 5 V,
0.2 A ≤ ILOAD ≤ 1 A
η
Efficiency
VIN = 12 V, VOUT = 5 V, ILOAD = 1 A
IIB
Feedback bias current
fo
Oscillator frequency (1)
VSAT
Saturation voltage
VOUT = 5 V
IOUT = 1 A (2)
Maximum duty cycle (3)
ICL
Peak current (1) (2)
IL
Output leakage current
IQ
Quiescent current (4)
ISTBY
Standby quiescent current
VIH
VIN = 40 (4), Output = 0 V
VIN = 40 (4), Output = –1 V
OFF (ON/OFF pin = 5 V)
OFF (VOUT = 0 V)
ON/OFF logic input level
VIL
ON (VOUT = nominal voltage)
IIH
OFF (ON/OFF pin = 5 V)
IIL
(1)
(2)
(3)
(4)
ON/OFF input current
ON (ON/OFF pin = 0 V)
TJ
UNIT
V
1.28
25°C
77
25°C
50
Full range
%
100
nA
500
25°C
47
Full range
42
25°C
52
58
63
0.9
Full range
kHz
1.2
V
1.4
25°C
93
98
25°C
1.7
2.8
Full range
1.3
%
3.6
2
25°C
A
4
7.5
30
mA
25°C
5
10
mA
25°C
50
200
µA
25°C
2.2
Full range
2.4
25°C
1.4
1.2
Full range
25°C
V
1
0.8
12
30
0
10
µA
In the event of an output short or an overload condition, self-protection features lower the oscillator frequency to ∼18 kHz and the
minimum duty cycle from 5% to ∼2%. The resulting output voltage drops to ∼40% of its nominal value, causing the average power
dissipated by the IC to lower.
Output is not connected to diode, inductor, or capacitor. Output is sourcing current.
Feedback is disconnected from output and connected to 0 V.
To force the output transistor off, FEEDBACK is disconnected from output and connected to 12 V.
3
LM2575
1-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATOR
SLVS569E – JANUARY 2005 – REVISED JANUARY 2006
TYPICAL OPERATING CHARACTERISTICS
TA = 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
www.ti.com
LM2575
1-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATOR
www.ti.com
SLVS569E – JANUARY 2005 – REVISED JANUARY 2006
APPLICATION INFORMATION
Layout Guidelines
With any switching regulator, circuit layout plays an important role in circuit performance. Wiring and parasitic
inductances, as well as stray capacitances, are subjected to rapidly switching currents, which can result in
unwanted voltage transients. To minimize inductance and ground loops, the length of the leads indicated by
heavy lines (see Figure 1) should be minimized. Optimal results can be achieved by single-point grounding or by
ground-plane construction. For the same reasons, the two programming resistors used in the adjustable version
should be located as close as possible to the regulator to keep the sensitive feedback wiring short.
Adjustable Output Voltage Versions
+VIN
16
FEEDBACK
7
LM2575
(ADJ)
OUTPUT
3
7-V to 60-V
Unregulated
DC Input
+
5, 12, 13 GND
9 ON/OFF
CIN
100 µF
L1
VOUT
330 µH
R2
D1
11DQ06
+
L
O
A
D
COUT
330 µF
R1
VOUT = VREF(1 + R2/R1) = 5 V
Where
VREF = 1.23 V
R1 = 2 k
R2 = 6.12 k
Figure 1. Test Circuit and Layout Guidelines
Input Capacitor (CIN)
For stability concerns, an input bypass capacitor (electrolytic, CIN ≥ 47 µF) needs to be located as close as
possible to the regulator. For operating temperatures below –25°C, CIN may need to be larger in value. In
addition, since most electrolytic capacitors have decreasing capacitances and increasing ESR as temperature
drops, 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:
I C,RMS 1.2(
t on
)I
, where:
T LOAD
V
ton
OUT {buck regulator}, and
T
VIN
|VOUT|
ton
{buck−boost regulator}
(|V OUT| V IN)
T
Output Capacitor (COUT)
For both loop stability and filtering of ripple voltage, an output capacitor also is required, again in close proximity
to the regulator. For best performance, low-ESR aluminum electrolytics are recommended, although standard
aluminum electrolytics may be adequate for some applications. Based on the following equation:
Output Ripple Voltage = (ESR of COUT) × (inductor ripple current)
5
LM2575
1-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATOR
www.ti.com
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. Larger
COUT can reduce the ripple 20 mV to 50 mV peak-to-peak. To improve further on output ripple, paralleling of
standard 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 COUT:
• At cold temperatures, the ESR of the electrolytic capacitors can rise dramatically (typically 3× nominal value
at –25°C). Because solid tantalum capacitors have significantly better ESR specifications at cold
temperatures, they should be used at operating temperature lower than –25°C. As an alternative, tantalums
also can be paralleled to aluminum electrolytics and should contribute 10% to 20% to the total capacitance.
• Low ESR for COUT is desirable for low output ripple. However, the ESR should be greater than 0.05 Ω to
avoid the possibility of regulator instability. Hence, a sole tantalum capacitor used for COUT is most
susceptible to this occurrence.
• The capacitor’s ripple current rating of 52 kHz should be at least 50% higher than the peak-to-peak inductor
ripple current.
Catch Diode
As with other external components, the catch diode should be placed close to the output to minimize unwanted
noise. Schottky diodes have fast switching speeds and low forward voltage drops and, thus, offer the best
performance, especially for switching regulators with low output voltages (VOUT < 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 (versus
abrupt 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.
Inductor
Proper inductor selection is key to the performance-switching power-supply designs. One important factor to
consider is whether the regulator will be used in continuous (inductor current flows continuously and never drops
to zero) or in discontinuous mode (inductor current goes to zero during the normal switching cycle). Each mode
has distinctively different operating characteristics and, therefore, can affect the regulator performance and
requirements. In many applications, the continuous mode is the preferred mode of operation, since it offers
greater output power with lower peak currents, and also can result in lower output ripple voltage. The advantages
of continuous mode of operation come at the expense of a larger inductor required to keep inductor current
continuous, 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 inductor
current flows continuously and the regulator operates in continuous mode. Under light load, the inductor fully
discharges and the regulator is forced into the discontinuous mode of operation. For light loads (approximately
200 mA or less), this discontinuous mode of operation is perfectly acceptable and may be desirable solely to
keep the inductor value and size small. Any buck regulator eventually operates in discontinuous mode when the
load 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 completely
within 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 regulators
located in proximity to each other are particularly susceptible to mutual coupling of magnetic fluxes from each
other’s open cores. In these situations, closed magnetic structures (such as a toroid, pot core, or E-core) are
more 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 looks
like 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 the
inductor and the IC itself. Note that different types of inductors have different saturation characteristics.
6
www.ti.com
LM2575
1-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATOR
SLVS569E – JANUARY 2005 – REVISED JANUARY 2006
APPLICATION INFORMATION (continued)
Output Voltage Ripple and Transients
As with any switching power supply, the output of the LM2575 has a sawtooth-ripple voltage at the switching
frequency. Typically about 1% of the output voltage, this ripple is due mainly to the inductor sawtooth-ripple
current and the ESR of the output capacitor (see note on COUT). Furthermore, the output also may contain small
voltage spikes at the peaks of the sawtooth waveform. This is due to the fast switching of the output switch and
the parasitic inductance of COUT. These voltage spikes can be minimized through the use of low-inductance
capacitors.
There are several ways to reduce the output ripple voltage: a larger inductor, a larger COUT, or both. Another
method is to use a small LC filter (20 µH and 100 µF) at the output. This filter can reduce the output ripple
voltage by a factor of 10 (see Figure 1).
Feedback Connection
FEEDBACK must be connected between the two programming resistors. Again, both of these resistors should be
in close proximity to the regulator, and each should be less than 100 kΩ to minimize noise pickup.
ON/OFF Input
ON/OFF should be grounded or be a low-level TTL voltage (typically <1.6 V) for normal operation. To shut down
the 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 VIN with or without a pullup resistor.
Grounding
The power and ground connections of the LM2575 must be low impedance to help maintain output stability. With
the 16-pin package, all the ground pins (including signal and power grounds) should be soldered directly to wide
PCB copper traces to ensure low-inductance connections and good thermal dissipation.
7
PACKAGE OPTION ADDENDUM
www.ti.com
18-Jul-2006
PACKAGING INFORMATION
Orderable Device
Status (1)
Package
Type
Package
Drawing
Pins Package Eco Plan (2)
Qty
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
Lead/Ball Finish
MSL Peak Temp (3)
(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.
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to Customer on an annual basis.
Addendum-Page 1
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