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LM2596
GENERAL DESCRIPTION
The LM2596 series of regulators are monolithic integrated circuits that provide all the active functions for a step-down (buck) switching regulator, capable of driving a 3A load with excellent line and load regulation. These devices are available in fixed output voltages of 3.3V, 5V, 12V, and an adjustable output version. Requiring a minimum number of external components, these regulators are simple to use and include internal frequency compensation, and a fixed-frequency oscillator. The LM2596 series operates at a switching frequency of 150 kHz thus allowing smaller sized filter components than what would be needed with lower frequency switching regulators. Available in a standard 5-lead TO-220 package with several different lead bend options, and a 5-lead TO-263 surface mount package. A standard series of inductors are available from several different manufacturers optimized for use with the LM2596 series. This feature greatly simplifies the design of switch-mode power supplies. Other features include a guaranteed 4% tolerance on output voltage under specified input voltage and output load conditions, and 15% on the oscillator frequency. External shutdown is included, featuring typically 80 standby A current. Self protection features include a two stage frequency reducing current limit for the output switch and an over temperature shutdown for complete protection under fault conditions.
FEATURES
3.3V, 5V, 12V, and adjustable output versions Adjustable version output voltage range, 1.2V to 37V 4% max over line and load conditions Available in TO-220 and TO-263 packages Guaranteed 3A output load current Input voltage range up to 40V Requires only 4 external components Excellent line and load regulation specifications 150 kHz fixed frequency internal oscillator TTL shutdown capability Low power standby mode, IQ typically 80 A High efficiency Uses readily available standard inductors Thermal shutdown and current limit protection
APPLICATIONS
Simple high-efficiency step-down (buck) regulator On-card switching regulators Positive to negative converter
TYPICAL APPLICATION (Fixed Output Voltage Versions)
12V
+ VIN + CIN 680F 1 5.0 5 3
4 L1 2 +C
OUT
5.0V 220 F
ON/ OFF
BLOCK DIAGRAM
VIN + START UP 2.5V + COM COM + R2 GM + AMP Active capacitor + OUTPUT 150kHz OSC GND +
FEEDBACK
LATCH + DRIVER
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LM2596
PIN FUNCTIONS
+VIN - This 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. Ground - Circuit ground. Output - Internal switch. The voltage at this pin switches between (+VIN - VSAT ) and approximately -0.5V, with a duty cycle of approximately VOUT /VIN. To minimize coupling to sensitive circuitry, the PC board copper area connected to this pin should be kept to a minimum. Feedback -- Senses the regulated output voltage to complete the feedback loop. ON/OFF - Allows the switching regulator circuit to be shut down using logic level signals thus dropping the total input supply current to approximately 80 Pulling this pin below a A. threshold voltage of approximately 1.3V turns the regulator on, and pulling this pin above 1.3V (up to a maximum of 25V) 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 will be in the ON condition.
ABSOLUTE MAXIMUM RATINGS (Note 1)
Maximum Supply Voltage 45V ON /OFF Pin Input Voltage -0.3 V +25V Feedback Pin Voltage -0.3 V +25V Output Voltage to Ground (Steady State) -1V Power Dissipation Internally limited 0C to +1500Ctorage Temperature Range S -65 ESD Susceptibility Human Body Model (Note 2) 2 kV Lead Temperature S Package Vapor Phase (60 sec.) +2150C Infrared (10 sec.) +2450C T Package (Soldering, 10 sec.) +2600C Maximum Junction Temperature +1500C
OPERATING CONDITIONS
Temperature Range -400CTJ+1250C
LM2596-3.3 ELECTRICAL CHARACTERISTICS
Specifications with standard type face are for TJ = 250C, and those with boldface type apply over full Operating Temperature Range LM2596-3.3 Units Symbol Parameter Conditions Typ Limit (Limits) (Note 3) (Note 4) SYSTEM PARAMETERS (Note 5)Test Circuit Figure 1 V VOUT Output Voltage 4.7V5VIN40V, 0.2AILOAD3A 3.3 3.168/3.135 V(min) 3.432/3.465 V(max) Efficiency VIN=12V, ILOAD=3A 73 %
LM2596-5.0 ELECTRICAL CHARACTERISTICS
Specifications with standard type face are for TJ = 250C, and those with boldface type apply over full Operating Temperature Range LM2596-5.0 Units Symbol Parameter Conditions Typ Limit (Limits) (Note 3) (Note 4) SYSTEM PARAMETERS (Note 5)Test Circuit Figure 1 V VOUT Output Voltage 7VVIN40V, 0.2AILOAD3A 5.0 4.800/4.750 V(min) 5.200/5.250 V(max) Efficiency VIN=12V, ILOAD=3A 80 %
LM2596-12 ELECTRICAL CHARACTERISTICS
Specifications with standard type face are for TJ = 250C, and those with boldface type apply over full Operating Temperature Range LM2596-12 Units Symbol Parameter Conditions Typ Limit (Limits) (Note 3) (Note 4) SYSTEM PARAMETERS (Note 5)Test Circuit Figure 1 V VOUT Output Voltage 15VVIN40V, 0.2AILOAD3A 12.0 11.52/11.40 V(min) 12.48/12.60 V(max) Efficiency VIN=12V, ILOAD=3A 90 %
LM2596-ADJ ELECTRICAL CHARACTERISTICS
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LM2596
Specifications with standard type face are for TJ = 250C, and those with boldface type apply over full Operating Temperature Range LM2596-ADJ Symbol Parameter Conditions Typ Limit (Note 4) (Note 3) SYSTEM PARAMETERS (Note 5)Test Circuit Figure 1 1.230 VOUT Output Voltage 4.5VVIN40V, 0.2AILOAD3A 1.193/1.180 VOUT programmed for 3V. Circuit of 1.267/1.280 Figure 1. Efficiency VIN=12V, VOUT=3V, ILOAD=3A Units (Limits) V V(min) V(max)
ALL OUTPUT VOLTAGE VERSIONS ELECTRICAL CHARACTERISTICS
Specifications with standard type face are for TJ = 250C, and those with boldface type apply over full Operating Temperature Range. Unless otherwise specified, VIN = 12V for the 3.3V, 5V, and Adjustable version and VIN = 24V for the 12V version. ILOAD = 500 mA LM2596-XX Units Symbol Parameter Conditions Typ Limit (Limits) (Note 3) (Note 4) DEVICE PARAMETERS nA Feedback Bias Current Adjustable Version Only, VFB=1.3V 10 Ib nA (max) 50/100 kHz fO Oscillator Frequency (Note 6) 150 kHz (min) 127/110 kHz (max) 173/173 V VSAT Saturation Voltage IOUT=3A (Notes 7, 8) 1.16 V (max) 1.4/1.5 (Note 8) 100 DC Max Duty Cycle (ON) % (Note 9) 0 Min Duty Cycle (OFF) A ICL Current Limit Peak Current (Notes 7, 8) 4.5 A (min) 3.6/3.4 A (max) 6.9/7.5 IL Output Leakage Current Output=0V (Notes 7, 9) 50 A (max) Output=-0.9V (Note 10) 10 mA mA (max) 30 mA IQ Quiescent Current (Note 9) 5 mA (max) 10 ON/OFF pin=5V (OFF) (Note 10) 80 ISTBY Standby A Quiescent 200/250 A (max) 0C/W JC Thermal Resistance TO-220 or TO-263 Package, Junction to Case 2 0C/W JA TO-220 Package, Junction to Ambient (Note 11) 50 0C/W JA TO-263 Package, Junction to Ambient (Note 12) 50 0C/W JA TO-263 Package, Junction to Ambient (Note 13) 30 0C/W JA TO-263 Package, Junction to Ambient (Note 14) 20 ON/OFF CONTROL Test Circuit Figure 1 ON/OFF Pin Logic Input 1.3 V Threshold Voltage Low (Regulator ON) V (max) VIH 0.6 High (Regulator OFF) V (min) VIL 2.0 IH 5 A LOGIC=2.5V (Regulator OFF) 15 O VN/OFF Pin Input Current A (max) VLOGIC=0.5V (Regulator ON) 0.02 A 5 A (max) Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. Note 2: The human body model is a 100 pF capacitor discharged through a 1.5k resistor into each pin. Note 3: Typical numbers are at 250C and represent the most likely norm. Note 4: All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100% production tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL). Note 5: External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect switching regulator system performance. When the LM2596 is used as shown in the Figure 1 test circuit, system performance will be as shown in system parameters section of Electrical Characteristics.
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LM2596
Note 6: The switching frequency is reduced when the second stage current limit is activated. The amount of reduction is determined by the severity of current over-load. Note 7: No diode, inductor or capacitor connected to output pin. Note 8: Feedback pin removed from output and connected to 0V to force the output transistor switch ON. Note 9: Feedback pin removed from output and connected to 12V for the 3.3V, 5V, and the ADJ. version, and 15V for the 12V version, to force the output transistor switch OFF. Note 10: VIN = 40V. Note 11: Junction to ambient thermal resistance (no external heat sink) for the TO-220 package mounted vertically, with the leads soldered to a printed circuit board with (1 oz.) copper area of approximately 1 in2 Note 12: Junction to ambient thermal resistance with the TO-263 package tab soldered to a single printed circuit board with 0.5 in2 of (1 oz.) copper area. Note 13: Junction to ambient thermal resistance with the TO-263 package tab soldered to a single sided printed circuit board with 2.5 in2 of (1 oz.) copper area. Note 14: Junction to ambient thermal resistance with the TO-263 package tab soldered to a double sided printed circuit board with 3 in2 of (1 oz.) copper area on the LM2596S side of the board, and approximately 16 in2 of copper on the other side of the p-c board.
TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 1)
Normalized Output Voltage
1.5 1.0 0.5 0 -0.5 -1.0 -0.4 -50 -25 0 25 50 75 0.4 0.3 0.2 0.1 0 -0.1 -0.2 -0.3 0 5 10 35 40 15 20 25 30
Line Regulation
95 90 85 80 5V 75 70 65
INPUT VOLTAGE (V)
Efficiency
20V 12V
0 5 10 35 40
15
20 25
30
Switch Saturation
1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 25 C 0.6 0
0 0 0 T = -40 C
Voltage
VIN= 12V
Switch Current Limit
5.5 5.0 V = 12V IN VOUT =5V 1.6 1.4
Dropout Voltage
4.5 4.0 125 C 1 23 4
SWITCH CURRENT (A)
1.2 1.0 0.8 0.6 -50 -25 75 I = 1A 0
I = LOAD
3A
3.5 - 50 -25 75
0
25
50
25
50
4
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LM2596
TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 1) (Continued)
Operating Quiescent Current
24 20 16 12 8 4 0 -50 -25 75 0 25 50 I = 0 120 100 80 60 2 40 20 0 0 10 20 30 40 SUPPLY VOLTAGE (V) 1 0 -50 -25 75
0 T = 25 C
Shutdown Quiescent Current
_ V 5 5V 4 3
Minimum Operating Supply Voltage
0
25
50
ON/OFF Threshold Voltage
2.5 2.0 OFF 1.5 1.0 0.5 ON 8 7 6 5 4 3 2 1 -50 -25 75 0 25 50 0 0
ON/OFF Pin Current (Sinking) Switching Frequency
160 155 150 145 140 135 130 -50 -25 75 0 25 50
10
15
20
25
ON/ OF PIN VOLTAGE (V)
Feedback Pin Bias Current
10 7.5 5.0 2.5 0 -2.5 -5.0 -50 -25 75
ADJUSTABLE VERSION ONLY
0
25
50
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LM2596
TYPICAL PERFORMANCE CHARACTERISTICS
Continuous Mode Switching Waveforms VIN=20V, VOUT=5V, ILOAD=2A L=32H, COUT=220F, COUTESR=50m
20V
Discontinuous Mode Switching Waveforms VIN=20V, VOUT=5V, ILOAD=500mA L=10H, COUT=330F, COUTESR=45m
20V
A
10V 0V 2A
A
10V 0V 1A
B
1A 0A
B
0A
C
AC/ div A: Output Pin Voltage,10V/ div B: Inductor Current 1A/ div C: Output Ri pple Voltage,50mV/ div
C
AC/ div A: Output Pin Voltage,10V/ div B: Inductor Current 1A/ div C: Output Ri pple Voltage,100mV/ div
Horizontal Time Base: 2s/ div
Load Transient Response for Continuous Mode VIN=20V, VOUT=5V, ILOAD=500mA to 2A L=32H, COUT=220F, COUTESR=50m
Horizontal Time Base: 2s/ div
Load Transient Response for Discontinuous Mode VIN=20V, VOUT=5V, ILOAD=500mA to 2A L=10H, COUT=330F, COUTESR=45m
A
AC div
A
AC div
B
1A 0A A: Output Voltage, 100mV/ div.(AC) B: 500mA to 2A Load Pulse
B
1A 0A A: Output Voltage,100mV/ div. (AC) B: 500mA to 2A Load Pulse
Horizontal Time Base: 100 s
/ div
Horizontal Time Base: 200s/ div
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LM2596
TEST CIRCUIT AND LAYOUT GUIDELINES
Fixed Output Voltage Versions
4 + + VIN + 3 CIN 5 2 L1 + COUT L1 +
CIN - 470 F ,50V,Aluminum Electrolytic Nichicon " PL COUT Series" F ,25V,Aluminum Electrolytic Nichicon " - 220 PL Series"D1 - 5A,40V Schottky Rectifer,1N5825 ,L38 L1 68 H
Adjustable Output Voltage Versions
CFF R2
R1 4 + + VIN + 3 CIN
5
2
L1
+ COUT
R2 V 1+ ) ( V REF R1 = where VREF=1.23V VOUT -1) R =R ( 2 Select R1 to be approximately 1k , use a1% resistor for best CIN - 470 F ,50V,Aluminum Electrolytic Nichicon " stability. PL COUT Series"F ,35V,Aluminum Electrolytic Nichicon " - 220 PL Series"D1 - 5A,40V Schottky Rectifer,1N5825 ,L38 L1 68 H R1 1k see Application Information Section , 1% C
Figure 1. Standard Test Circuits and Layout Guides 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 should be wide printed circuit traces and should be kept as short as possible. For best results, external components should be located 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, special care must be taken as to the location of the feedback resistors and the associated wiring. Physically locate both resistors near the IC, and route the wiring away from the inductor, especially an open core type of inductor.
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LM2596
LM2596 SERIES BUCK REGULATOR DESIGN PROCEDURE (FIXED OUTPUT)
PROCEDURE (Fixed Output Voltage Version) Given: Given: VOUT = Regulated Output Voltage (3.3V, 5V or 12V) VIN (max) = Maximum DC Input Voltage I (max) = Maximum Load Current 1. Inductor Selection (L1) A. Select the correct inductor value selection guide from Figures Figure 4, Figure 5,or Figure 6. (Output voltages of 3.3V, 5V, or 12V respectively.) For all other voltages, see the design procedure for the adjustable version. B. 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). C. Select an appropriate inductor from the four manufacturer' part s numbers listed in Figure 8. EXAMPLE (Fixed Output Voltage Version)
VOUT =5V VIN (max) = 12V I (max) = 3A 1. Inductor Selection (L1) A. Use the inductor selection guide for the 5V version shown in Figure 5.
B. From the inductor value selection guide shown in Figure 5, the inductance region intersected by the 12V horizontal line and the 3A vertical line is 33 and the inductor code is L40. H, C. The inductance value required is 33 From the table in Figure 8, go to the H. L40 line and choose an inductor part number from any of the four manufacturers shown. (In most in-stance, both through hole and surface mount inductors are available.) 2. Output Capacitor Selection (COUT) A. See section on output capacitors in application information section.
2. Output Capacitor Selection (COUT) A. In the majority of applications, low ESR (Equivalent Series Resistance) electrolytic capacitors between 82 and 820 and F F low ESR solid tantalum capacitors between 10 and 470 F F provide the best results. This capacitor should be located close to the IC using short capacitor leads and short copper traces. Do not use capacitors larger than 820 F. B. To simplify the capacitor selection procedure, refer to the quick design component selection table shown in Figure 2. This table contains different input voltages, output voltages, and load currents, and lists various inductors and output capacitors that will provide the best design solutions.
B. From the quick design component selection table shown in Figure 2, locate the 5V output voltage section. In the load current column, choose the load current line that is closest to the current needed in your application, for this example, use the 3A line. In the maximum input voltage column, select the line that covers the input voltage needed in your application, in this example, use the 15V line. Continuing on this line are recommended inductors and capacitors that will provide the best overall performance. The capacitor list contains both through hole electrolytic and surface mount tantalum capacitors from four different capacitor manufacturers. It is recommended that both the manufacturers and the manufacturer' series that are listed in the table be used. s In this example aluminum electrolytic capacitors from several different manufacturers are available with the range of ESR numbers needed. 330 35V Panasonic HFQ Series F 330 35V Nichicon PL Series F C. For a 5V output, a capacitor voltage rating at least 7.5V or more is needed. But even a low ESR, switching grade, 220 10V aluminum electrolytic capacitor F would exhibit approximately 225 mW of ESR (see the curve in Figure 14 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 value or with a higher voltage rating (lower ESR) should be selected. A 16V or 25V capacitor will reduce the ripple volt-age by approximately half. 3. Catch Diode Selection (D1) A. Refer to the table shown in Figure 11. In this example, a 5A, 20V, 1N5823 Schottky diode will provide the best performance, and will not be overstressed even for a shorted output.
C. The capacitor voltage rating for electrolytic capacitors should 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 for low output ripple voltage.
3. Catch Diode Selection (D1) A. 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 should have a current rating equal to the maximum current limit of the LM2596. The most stressful condition for this diode is an overload or shorted output condition. B. The reverse voltage rating of the diode should be at least 1.25 times the maximum input voltage. C. This diode must be fast (short reverse recovery time) and must be located close to the LM2596 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 should 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 1N5400 series are much too slow and should not be used.
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LM2596
PROCEDURE (Fixed Output Voltage Version) EXAMPLE (Fixed Output Voltage Version) 4. Input Capacitor (CIN) 4. Input Capacitor (CIN) A low ESR aluminum or tantalum bypass capacitor is needed between the The important parameters for the Input capacitor are the input voltage rating and the input pin and ground pin to prevent large volt-age transients from appearing RMS current rating. With a nominal input voltage of 12V, an aluminum electrolytic capacitor with a voltage rating at the input. This capacitor should be located close to the IC using short leads. In addition, the RMS current rating of the input capacitor greater than 18V (1.5 x VIN ) would be needed. The next higher capacitor voltage rating is 25V. should be selected to be at least 1/2 the DC load current. The capacitor manufacturers data sheet must be checked to assure that this current rating The RMS current rating requirement for the input capacitor in is not exceeded. The curve shown in Figure 9 shows typical RMS current a buck regulator is approximately 1 /2 the DC load current. In this example, with a 3A load, a capacitor with a RMS current rating of at least 1.5A is needed. The ratings for several different aluminum electrolytic capacitor values. curves shown in Figure 9 can be used to select an appropriate input capacitor. For an aluminum electrolytic, the capacitor voltage rating should be From the curves, locate the 35V line and note which capacitor values have RMS approximately 1.5 times the maximum input voltage. current ratings greater than 1.5A. A 680 F/35V capacitor could be used. The tantalum capacitor voltage rating should be 2 times the maximum For a through hole design, a 680 F/35V electrolytic capacitor (Panasonic HFQ input voltage and it is recommended that they be surge current tested by series or Nichicon PL series or equivalent) would be adequate. other types or other the manufacturer. Use caution when using ceramic capacitors for input bypassing, because it manufacturers capacitors can be used provided the RMS ripple current ratings are adequate. may cause severe ringing at the VIN pin. For surface mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to the capacitor surge current rating. The TPS series available from AVX, and the 593D series from Sprague are both surge current tested.
LM2596 SERIES BUCK REGULATOR DESIGN PROCEDURE (FIXED OUTPUT) (Continued)
Output Voltage (V) 3.3 Conditions Inductor Load Current (A) 3 Output Capacitor Through Hole Electrolytic Surface Mount Tantalum Panasonic AVX TPS Sprague 595D Series Nichicon PL HFQ Series Series (F/V) Series (F/V) (F/V) (F/V) L41 470/25 560/16 330/6.3 L41 L41 L40 L33 L32 L39 L41 L41 L40 L39 L33 560/35 680/35 560/35 470/25 330/35 330/35 470/25 560/25 330/35 330/35 470/25 560/35 680/35 470/35 470/35 330/35 270/50 560/16 560/25 330/35 270/35 560/16 330/6.3 330/6.3 330/6.3 330/6.3 330/6.3 220/10 220/10 220/10 220/10 220/10 220/10
Max Input Voltage (V) 5 7
Inductance (H)
Inductor (#) 22 390/6.3 22 390/6.3 22 390/6.3 33 390/6.3 22 390/6.3 33 390/6.3 47 330/10 22 330/10 22 330/10 33 330/10 47 330/10 22 330/10
2
10 40
5
3
6 10
2
40 8
12
3 10 15 2 40 9
LM2596 SERIES BUCK REGULATOR DESIGN PROCEDURE (ADJUSTABLE OUTPUT)
PROCEDURE (Adjustable Output Voltage Version) Given: Given: VOUT = Regulated Output Voltage VIN(max) = Maximum Input Voltage ILOAD(max) = Maximum Load Current F=Switching Frequency (Fixed at a(Selecting150 and R2, as shown in 1. Programming Output Voltage nominal R1 kHz). Figure 1) Use the following formula to select the appropriate resistor values. EXAMPLE (Adjustable Output Voltage Version)
VOUT = 20V VIN(max) = 28V ILOAD(max) = 3A F=Switching Frequency (Fixed at a(Selecting R1 and R2, as shown 1. Programming Output Voltage nominal 150 kHz). in Figure 1) Select R1 to be 1 k, 1%. Solve for R2.
VOUT VREF (1
R2 ) R 1 where
VREF 1.23 V
Select a value for R1 between 240 and 1.5k. 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.)
VOUT 20 V R 2 R 1( 1) 1k( VREF 1.23 V
R2=1k (16.26-1)=15.26k, closest 1% value is 15.4k R2 = 15.4 k.
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LM2596
PROCEDURE (Adjustable Output Voltage Version) EXAMPLE (Adjustable Output Voltage Version)
R 2 R 1(
1) VREF
1000 200 . 5 1 0 150 (V s) 1 ) 28 .. 1 6 5 . 84) 6 2 . 05 3 .
VOUT
2. Inductor Selection (L1) 2. Inductor Selection (L1) A. Calculate the inductor Volt * microsecond constant ET (V from A. Calculate the inductor Volt microsecond constant s), the following formula: (ET),
VD ET (V VOUTVSAT) V IN 1000 s) VINVSAT VD kHz 150
where VSAT = internal switch saturation voltage = 1.16V and VD = diode forward voltage drop = 0.5V B. Use the ET value from the previous formula and match it with the ET number on the vertical axis of the Inductor Value Selection Guide shown in Figure 7. C. on the horizontal axis, select the maximum load current. D. Identify the inductance region intersected by the ET value and the Maximum Load Current value. Each region is identified by an inductance value and an inductor code (LXX). E. Select an appropriate inductor from the four manufacturer' part s numbers listed in Figure 8. 3. Output Capacitor Selection (COUT) A. In the majority of applications, low ESR electrolytic or solid tantalum capacitors between 82 and 820 provide the best results. This capacitor F F should be located close to the IC using short capacitor leads and short copper traces. Do not use capacitors larger than 820 F. B. To simplify the capacitor selection procedure, refer to the quick design table shown in Figure 3. This table contains different output voltages, and lists various output capacitors that will provide the best design solutions.
ET 28 ( E T (
20 . 1
C. D. From the inductor value selection guide shown in Figure 7, the inductance region intersected by the 34 (V horizontal line and s) the 3A vertical line is 47 and the inductor code is L39. H, E. From the table in Figure 8, locate line L39, and select an inductor part number from the list of manufacturers part numbers. 3. Output Capacitor SeIection (COUT)
B. From the quick design table shown in Figure 3, 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 24V line. Under the output capacitor section, select a capacitor from the list of through hole electrolytic or surface mount tantalum types from four different capacitor manufacturers. It is recommended that both the manufacturers and the manufacturers series that are listed in the table be used. In this example, through hole aluminum electrolytic capacitors from several different manufacturers are available. 220 F/35V Panasonic HFQ Series 150 F/35V Nichicon PL Series
C. The capacitor voltage rating should be at least 1.5 times greater than C. For a 20V output, a capacitor rating of at least 30V or more is the output voltage, and often much higher voltage ratings are needed to needed. In this example, either a 35V or 50V capacitor would satisfy the low ESR requirements needed for low output ripple voltage. work. A 35V rating was chosen, although a 50V rating could also be used if a lower output ripple voltage is needed. 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 the table. Refer to the capacitor manufacturers data sheet for this information. 4. Feedforward Capacitor (CFF ) (See Figure 1) For output voltages greater than approximately 10V, an additional capacitor is required. The compensation capacitor is typically between 100 pF and 33 nF, and is wired in parallel with the output voltage setting resistor, R2. It provides additional stability for high output voltages, low input-output voltages, and/or very low ESR output capacitors, such as solid tantalum capacitors. 4. Feedforward Capacitor (CFF ) The table shown in Figure 3 contains feed forward capacitor values for various output voltages. In this example, a 560 pF capacitor is needed.
CFF
This capacitor type can be ceramic, plastic, silver mica, etc. (Because of the unstable characteristics of ceramic capacitors made with Z5U material, they are not recommended.)
1 3110 R
2
3
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LM2596
LM2596 SERIES BUCK REGULATOR DESING PROCEDURE (ADJUSTABLE OUTPUT)
Output Voltage (V) 2 4 6 9 12 15 24 28 Through Hole Output Capacitor Surface Mount Output Capacitor AVX TPS Series Panasonic HFQ Nichicon PL Series Sprague 595D Feedforward Feedforward Series (F/V) Series (F/V) Capacitor (F/V) (F/V) capacitor 820/35 820/35 33 nF 330/6.3 470/4 33 nF 560/35 470/35 10 nF 330/6.3 390/6.3 10 nF 470/25 470/25 3.3 nF 220/10 330/10 3.3 nF 330/25 330/25 1.5 nF 100/16 180/16 1.5 nF 330/25 330/25 1 nF 100/16 180/16 1 nF 220/35 220/35 680 pF 68/20 120/20 680 pF 220/35 150/35 560 pF 33/25 33/25 220 pF 100/50 100/50 390 pF 10/35 15/50 220 pF Figure 3. Output Capacitor and Feedforward Capacitor Selection Table
LM2596 SERIES BUCK REGULATOR DESIGN PROCEDURE Inductor Value Selection Guides (For Continuous Mode Operation)
40V
L29 L30 L31 L21 L22 L32 L33 L40
20V 10V 8V 7V 6V
40V L27 30V 25V 20V L28 19V L29 18V 17V 16V L21 15V
L22 L23
L36 L37 L38 L30 L31 L32
L43
L39 L40
L23 L24
L34
L33
L15
L25 L16
5V 0.6 3.0
0.8
1.0
1.5
2.0
2.5
Figure 4. LM2596-3.3
L34 14V 0.6 0.8 1.0 1.5 2.0 2.5 3.0 MAXIMUM LOAD CURRENT (A) Figure 6. LM2596-12
L24
BEIJING ESTEK ELECTRONICS CO.,LTD
11
LM2596
40V 20V 15V 12V 10V 9V 8V
L21 L22 L23 L24 L29 L38 L30 L31 L32 L33 L34 L39 L40 70 60 L27 50 40 30 25 20 15 10 9 8 7 6 5 4 L21 L22 L23 L24 L15 L25 L35 L28
Figure 7. LM2596-ADJ
L43 L36 L37 L38 L30 L31 L32 L39 L40 L33 L34
L44
L29
7V 0.6 3.0
L25
0.8
1.0
1.5
2.0
2.5
MAXIMUM LOAD CURRENT (A)
0.6 0.8 1.0 1.5 2.0 2.5 3.0 MAXIMUM LOAD CURRENT (A)
LM2596 SERIES BUCK REGULATOR DESIGN PROCEDURE (Continued)
Inductance (H) L15 22 DO3308-223 L21 68 DO3316-683 L22 47 DO3316-473 L23 33 DO3316-333 L24 22 DO3316-223 L25 15 DO3316-153 L26 330 DO5022P-334 L27 220 DO5022P-224 L28 150 DO5022P-154 L29 100 DO5022P-104 L30 68 DO5022P-683 L31 47 DO5022P-473 L32 33 DO5022P-333 L33 22 DO5022P-223 L34 15 Current (A) 0.99 0.99 1.17 1.40 1.70 2.10 0.80 1.00 1.20 1.47 1.78 2.20 2.50 3.10 3.40 Schott Engineering Through Surface Hole Mount 67148350 67148460 67144070 67144080 67144090 67148370 67148380 67144100 67144110 67144120 67144130 67144140 67144150 67144160 67148390 67148400 67144450 67144460 67144470 67148480 67148490 67144480 67144490 67144500 67144510 67144520 67144530 67144540 67148500 67148790 Through Hole RL-1284-22-43 RL-5471-5 RL-5471-6 RL-5471-7 RL-1283-22-43 RL-1283-15-43 RL-5471-1 RL-5471-2 RL-5471-3 RL-5471-4 RL-5471-5 RL-5471-6 RL-5471-7 RL-1283-22-43 RL-1283-15-43 Renco Pulse Coilcraft Surface Surface Through Surface Mount Mount Hole Mount RL1500-22 PE-53815 PE-53815-S RL1500-68 PE-53821 PE-53822 PE-53823 PE-53821-S PE-53822-S PE-53823-S PE-53825-S PE-53824-S
PE-53824 PE-53825 PE-53826-S PE-53827-S PE-53828-S PE-53829-S PE-53830-S PE-53831-S PE-53932-S
PE-53826 PE-53827 PE-53828 PE-53829 PE-53830 PE-53831 PE-53932 -
PE-53933 PE-53934
PE-53933-S PE-53934-S
2200 2000 1800 1600 1400 1200 1000 800 600 400 200 0 10 20 30 40 50 60 70 CAPACITOR VOLTAGE RATING (V)
Figure 9. RMS Current Ratings for Low ESR Electrolytic Capacitors (typical)
BEIJING ESTEK ELECTRONICS CO.,LTD
12
LM2596
Address :
Postalcode:100039 Tel: 86-010-58895780 / 81 / 82 / 83 / 84 Http://www.estek.com.cn Email:sales@estek.com.cn
6A06--6A07 Rm 6A07,Changyin Office Building ,No.88,Yong Ding Road,Hai Dian District ,Beijing
Fax : 010-58895793
REV No:01-060814
BEIJING ESTEK ELECTRONICS CO.,LTD
13

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