ON Semiconductor LM2596 Technical data

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LM2596
3.0 A, Step-Down Switching Regulator
Since LM2596 converter is a switch−mode power supply, its efficiency is significantly higher in comparison with popular threeterminal linear regulators, especially with higher input voltages.
The LM2596 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 5lead TO−220 package with several different lead bend options, and
2
D
PAK surface mount package.
The other features include a guaranteed $4% tolerance on output voltage within specified input voltages and output load conditions, and $15% on the oscillator frequency. External shutdown is included, featuring 80 mA (typical) standby current. Self protection features include switch cycle−by−cycle current limit for the output switch, as well as thermal shutdown for complete protection under fault conditions.
Features
Adjustable Output Voltage Range 1.23 V 37 V
Guaranteed 3.0 A Output Load Current
Wide Input Voltage Range up to 40 V
150 kHz Fixed Frequency Internal Oscillator
TTL Shutdown Capability
Low Power Standby Mode, typ 80 mA
Thermal Shutdown and Current Limit Protection
Internal Loop Compensation
Moisture Sensitivity Level (MSL) Equals 1
PbFree Packages are Available
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1
5
Heatsink surface connected to Pin 3
1
5
Pin 1. V
2. Output
3. Ground
4. Feedback
5. ON
1
5
Heatsink surface (shown as terminal 6 in case outline drawing) is connected to Pin 3
TO−220
TV SUFFIX
CASE 314B
TO−220
T SUFFIX
CASE 314D
in
/OFF
2
D
PAK
D2T SUFFIX
CASE 936A
Applications
Simple HighEfficiency StepDown (Buck) Regulator
Efficient PreRegulator for Linear Regulators
OnCard Switching Regulators
Positive to Negative Converter (BuckBoost)
Negative StepUp Converters
Power Supply for Battery Chargers
© Semiconductor Components Industries, LLC, 2008
November, 2008 Rev. 0
ORDERING INFORMATION
See detailed ordering and shipping information in the package dimensions section on page 23 of this data sheet.
DEVICE MARKING INFORMATION
See general marking information in the device marking section on page 23 of this data sheet.
1 Publication Order Number:
LM2596/D
Unregulated
DC Input
LM2596
Typical Application (Adjustable Output Voltage Version)
C
out
220 mF
R1
1.0k
C
FF
5.0 V Regulated Output 3.0 A Load
ON
/OFF
5
Output
2 GND
3
D1
Regulated
L1
Output
V
out
C
out
Load
Feedback
12 V
Unregulated
DC Input
C
100 mF
/OFF5
4
Output
2
+V
in
LM2596
1
in
GND
3ON
L1
33 mH
D1 1N5822
R2
3.1k
Block Diagram
+V
in
1
C
in
Feedback
C
FF
4
R1
R2
Fixed Gain Error Amplifier
Freq Shift
30 kHz
1.235 V Band-Gap Reference
3.1 V Internal
Comparator
150 kHz
Oscillator
Regulator
Current
Latch
Reset
ON
Limit
/OFF
Driver
3.0 Amp Switch
Thermal
Shutdown
Figure 1. Typical Application and Internal Block Diagram
MAXIMUM RATINGS
Rating Symbol Value Unit
Maximum Supply Voltage V
in
ON/OFF Pin Input Voltage 0.3 V V +V
Output Voltage to Ground (SteadyState) −1.0 V
Power Dissipation
Case 314B and 314D (TO220, 5Lead) P
Thermal Resistance, JunctiontoAmbient
Thermal Resistance, JunctiontoCase
Case 936A (D2PAK) P
Thermal Resistance, JunctiontoAmbient
Thermal Resistance, JunctiontoCase
Storage Temperature Range T
Minimum ESD Rating (Human Body Model: C = 100 pF, R = 1.5 kW)
D
R
q
JA
R
q
JC
D
R
q
JA
R
q
JC
stg
2.0 kV
Lead Temperature (Soldering, 10 seconds) 260 °C
Maximum Junction Temperature T
J
Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect device reliability.
45 V
in
Internally Limited W
65 °C/W
5.0 °C/W
Internally Limited W
70 °C/W
5.0 °C/W
65 to +150 °C
150 °C
V
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LM2596
PIN FUNCTION DESCRIPTION
Pin Symbol Description (Refer to Figure 1)
1 V
2 Output This is the emitter of the internal switch. The saturation voltage V
3 GND Circuit ground pin. See the information about the printed circuit board layout.
4 Feedback This pin is the direct input of the error amplifier and the resistor network R2, R1 is connected externally to allow pro-
5 ON/OFF It allows the switching regulator circuit to be shut down using logic level signals, thus dropping the total input supply
OPERATING RATINGS (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.)
Operating Junction Temperature Range T
Supply Voltage V
This pin is the positive input supply for the LM2596 stepdown switching regulator. In order to minimize voltage transi-
in
ents and to supply the switching currents needed by the regulator, a suitable input bypass capacitor must be present (C
in Figure 1).
in
of this output switch is typically 1.5 V. It should be
kept in mind that the PCB area connected to this pin should be kept to a minimum in order to minimize coupling to
sat
sensitive circuitry.
gramming of the output voltage.
current to approximately 80 mA. The threshold voltage is typically 1.6 V. Applying a voltage above this value (up to
) shuts the regulator off. If the voltage applied to this pin is lower than 1.6 V or if this pin is left open, the regulator
+V
in
will be in the “on” condition.
Rating
Symbol Value Unit
J
in
40 to +125 °C
4.5 to 40 V
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LM2596
SYSTEM PARAMETERS
ELECTRICAL CHARACTERISTICS Specifications with standard type face are for T
over full Operating Temperature Range −40°C to +125°C
Characteristics Symbol Min Typ Max Unit
LM2596 (Note 1, Test Circuit Figure 15)
Feedback Voltage (V
= 12 V, I
in
Feedback Voltage (8.5 V Vin 40 V, 0.5 A I
Efficiency (V
Feedback Bias Current (V
= 12 V, I
in
Load
out
Oscillator Frequency (Note 2) f
Saturation Voltage (I
= 3.0 A, Notes 3 and 4) V
out
Max Duty Cycle “ON” (Note 4) DC 95 %
Current Limit (Peak Current, Notes 2 and 3) I
Output Leakage Current (Notes 5 and 6) Output = 0 V Output = 1.0 V
Quiescent Current (Note 5) I
Standby Quiescent Current (ON/OFF Pin = 5.0 V (“OFF”)) (Note 6)
ON/OFF PIN LOGIC INPUT
Threshold Voltage
V
= 0 V (Regulator OFF) V
out
V
= Nominal Output Voltage (Regulator ON) V
out
ON/OFF Pin Input Current
/OFF Pin = 5.0 V (Regulator OFF) I
ON
ON/OFF Pin = 0 V (regulator ON) I
1. External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. When the LM2596 is used as shown in the Figure 15 test circuit, system performance will be as shown in system parameters section.
2. The oscillator frequency reduces to approximately 30 kHz in the event of an output short or an overload which causes the regulated output voltage to drop approximately 40% from the nominal output voltage. This self protection feature lowers the average dissipation of the IC by lowering the minimum duty cycle from 5% down to approximately 2%.
3. No diode, inductor or capacitor connected to output (Pin 2) sourcing the current.
4. Feedback (Pin 4) removed from output and connected to 0 V.
5. Feedback (Pin 4) removed from output and connected to +12 V to force the output transistor “off”.
= 40 V.
6. V
in
= 0.5 A, V
Load
= 3.0 A, V
out
= 5.0 V, ) V
out
Load
3.0 A, V
= 5.0 V) V
out
FB_nom
= 5.0 V) η 73 %
Characteristics Symbol Min Typ Max Unit
= 5.0 V) I
I
= 25°C, and those with boldface type apply
J
1.23 V
1.193
1.18
135
120
4.2
3.5
25 100
150 165
1.5 1.8
5.6 6.9
0.5
osc
CL
I
FB
b
sat
L
6.0
Q
stby
5.0 10 mA
80 200
1.6 V
IH
IL
IH
IL
2.2
2.4
15 30
0.01 5.0
1.267
1.28
200
180
2.0
7.5
2.0 20
250
1.0
0.8
V
nA
kHz
V
A
mA
mA
V
V
mA
mA
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LM2596
TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15)
1.0
Vin = 20 V
0.8 I
Load
0.6 Normalized at T
0.4
0.2
0
-0.2
-0.4
-0.6
, OUTPUT VOLTAGE CHANGE (%)
out
-0.8
V
-1.0
2.0
1.5
= 500 mA
= 25°C
J
TJ, JUNCTION TEMPERATURE (°C)
Figure 2. Normalized Output Voltage
I
= 3.0 A
Load
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
-0.2
, OUTPUT VOLTAGE CHANGE (%)
out
-0.4
V
1251007550250-25-50 403530252015105.00
-0.6
6.0
5.5
I
Load
T
= 25°C
J
= 500 mA
3.3 V and 5.0 V
, INPUT VOLTAGE (V)
V
in
Figure 3. Line Regulation
12 V and 15 V
Vin = 25 V
INPUT - OUTPUT DIFFERENTIAL (V)
, QUIESCENT CURRENT (mA)
Q
I
1.0
0.5
8.0
6.0
4.0
5.0
I
= 500 mA
Load
, OUTPUT CURRENT (A)
4.5
O
I
L1 = 33 mH
= 0.1 W
R
0
ind
1251007550250-25-50 1251007550250-25-50
TJ, JUNCTION TEMPERATURE (°C)
4.0
TJ, JUNCTION TEMPERATURE (°C)
Figure 4. Dropout Voltage Figure 5. Current Limit
20
V
= 5.0 V
18
16
14
I
= 3.0 A
12
Load
out
Measured at Ground Pin T
= 25°C
J
10
I
= 200 mA
Load
403530252015105.00 1251007550250-25-50
, INPUT VOLTAGE (V)
V
in
μA)
, STANDBY QUIESCENT CURRENT (
I
stby
200
180
160
140
120
100
V
= 5.0 V
ON/OFF
Vin = 40 V
80
60
Vin = 12 V
40
20
0
TJ, JUNCTION TEMPERATURE (°C)
Figure 6. Quiescent Current Figure 7. Standby Quiescent Current
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LM2596
TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15)
200
180
160
TJ = 25°C
35 2.5
Vin, INPUT VOLTAGE (V)
, STANDBY QUIESCENT CURRENT (μA)I
stby
140
120
100
80
60
40
20
0
Figure 8. Standby Quiescent Current
1.0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
NORMALIZED FREQUENCY (%)
8.0
9.0
50 25 0 25 50 75 100 125
TJ, JUNCTION TEMPERATURE (°C)
VIN = 12 V Normalized at 25°C
Figure 10. Switching Frequency
1.6
1.4
1.2
-40°C
1.0
0.8
25°C
0.6 125°C
, SATURATION VOLTAGE (V)
0.4
sat
V
0.2
40302520151050 0 0.5 1.0 1.5 2.0 3.0
0
SWITCH CURRENT (A)
Figure 9. Switch Saturation Voltage
5.0
4.5
4.0
3.5
3.0
2.5
2.0
, INPUT VOLTAGE (V)
1.5
in
V
1.0
0.5
0
-50
V
' 1.23 V
out
I
= 500 mA
Load
TJ, JUNCTION TEMPERATURE (°C)
1251007550250-25
Figure 11. Minimum Supply Operating Voltage
, FEEDBACK PIN CURRENT (nA)
b
I
-100
100
-20
-40
-60
-80
80
60
40
20
0
1251007550250-25-50
, JUNCTION TEMPERATURE (°C)
T
J
Figure 12. Feedback Pin Current
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LM2596
TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15)
10 V
A
0
4.0 A
B
2.0 A
0
4.0 A
C
2.0 A
D
0
Figure 13. Switching Waveforms Figure 14. Load Transient Response
Vout = 5 V A: Output Pin Voltage, 10 V/div B: Switch Current, 2.0 A/div C: Inductor Current, 2.0 A/div, ACCoupled D: Output Ripple Voltage, 50 mV/div, ACCoupled
Horizontal Time Base: 5.0 ms/div
Output
Voltage
Change
- 100 mV
Load
Current
100 mV
0
3.0 A
2.0 A
1.0 A
0
100 ms/div2 ms/div
8.5 V - 40 V Unregulated
DC Input
C
in
100 mF
Adjustable Output Voltage Versions
Feedback
V
in
LM2596
1
4
Output
2
/OFFGND
53ON
+ V
ref
= 1.23 V, R1
ref
V
V
ǒ
1.0 )
out
1.0Ǔ
ref
V
out
R2 + R1ǒ
Where V between 1.0 k and 5.0 k
Figure 15. Typical Test Circuit
L1
33 mH
D1 1N5822
R2
Ǔ
R1
C
out
220 mF
R2
R1
5,000 V
C
FF
V
out
Load
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LM2596
PCB LAYOUT GUIDELINES
As in any switching regulator, the layout of the printed circuit board is very important. Rapidly switching currents associated with wiring inductance, stray capacitance and parasitic inductance of the printed circuit board traces can generate voltage transients which can generate electromagnetic interferences (EMI) and affect the desired operation. As indicated in the Figure 15, to minimize inductance and ground loops, the length of the leads indicated by heavy lines should be kept as short as possible.
For best results, single−point grounding (as indicated) or ground plane construction should be used.
DESIGN PROCEDURE
Buck Converter Basics
The LM2596 is a “Buck” or StepDown Converter which is the most elementary forward−mode converter. Its basic schematic can be seen in Figure 16.
The operation of this regulator topology has two distinct time periods. The first one occurs when the series switch is on, the input voltage is connected to the input of the inductor.
The output of the inductor is the output voltage, and the rectifier (or catch diode) is reverse biased. During this period, since there is a constant voltage source connected across the inductor, the inductor current begins to linearly ramp upwards, as described by the following equation:
I
L(on)
+
ǒ
VIN* V
L
OUT
Ǔ
t
on
During this “on” period, energy is stored within the core material in the form of magnetic flux. If the inductor is properly designed, there is sufficient energy stored to carry the requirements of the load during the “off” period.
Power Switch
L
On the other hand, the PCB area connected to the Pin 2 (emitter of the internal switch) of the LM2596 should be kept to a minimum in order to minimize coupling to sensitive circuitry.
Another sensitive part of the circuit is the feedback. It is important to keep the sensitive feedback wiring short. To assure this, physically locate the programming resistors near to the regulator, when using the adjustable version of the LM2596 regulator.
This period ends when the power switch is once again turned on. Regulation of the converter is accomplished by varying the duty cycle of the power switch. It is possible to describe the duty cycle as follows:
t
on
d +
, where T is the period of switching.
T
For the buck converter with ideal components, the duty cycle can also be described as:
V
out
d +
V
in
Figure 17 shows the buck converter, idealized waveforms of the catch diode voltage and the inductor current.
V
on(SW)
Power Switch
Off
Diode VoltageInductor Current
VD(FWD)
Power
Switch
On
Power Switch
Off
Power
Switch
On
in
Figure 16. Basic Buck Converter
DV
C
out
R
Load
The next period is the “off” period of the power switch. When the power switch turns off, the voltage across the inductor reverses its polarity and is clamped at one diode voltage drop below ground by the catch diode. The current now flows through the catch diode thus maintaining the load current loop. This removes the stored energy from the inductor. The inductor current during this time is:
I
L(off)
+
ǒ
V
OUT
* V
L
Ǔ
t
D
off
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I
pk
I
min
Diode Diode
Figure 17. Buck Converter Idealized Waveforms
8
Power Switch
Power
Switch
I
Load
Time
(AV)
Time
LM2596
PROCEDURE (ADJUSTABLE OUTPUT VERSION: LM2596)
Procedure Example
Given Parameters:
= Regulated Output Voltage
V
out
= Maximum DC Input Voltage
V
in(max)
I
Load(max)
1. Programming Output Voltage
To select the right programming resistor R1 and R2 value (see Figure 1) use the following formula:
Resistor R1 can be between 1.0 k and 5.0 kW. (For best temperature coefficient and stability with time, use 1% metal film resistors).
= Maximum Load Current
ǒ
V
+ V
out
ref
1.0 )
R2 + R1
R2 R1
ǒ
Ǔ
V
out
V
ref
where V
* 1.0
= 1.23 V
ref
Ǔ
Given Parameters:
= 5.0 V
V
out
= 12 V
V
in(max)
I
Load(max)
1. Programming Output Voltage (selecting R1 and R2) Select R1 and R2:
= 3.0 A
R2
V
+ 1.23ǒ1.0 )
out
V
out
R2 + R1
R2 = 3.0 kW, choose a 3.0k metal film resistor.
ǒ
V
ref
Ǔ
R1
* 1.0Ǔ+
Select R1 = 1.0 kW
5V
ǒ
1.23 V
* 1.0
Ǔ
2. Input Capacitor Selection (Cin)
To prevent large voltage transients from appearing at the input and for stable operation of the converter, an aluminium or tantalum electrolytic bypass capacitor is needed between the input pin +V located close to the IC using short leads. This capacitor should have a low ESR (Equivalent Series Resistance) value.
For additional information see input capacitor section in the “Application Information” section of this data sheet.
3. Catch Diode Selection (D1)
A. Since the diode maximum peak current exceeds the
regulator maximum load current the catch diode current rating must be at least 1.2 times greater than the maximum load current. For a robust design, the diode should have a current rating equal to the maximum current limit of the LM2596 to be able to withstand a continuous output short.
B. The reverse voltage rating of the diode should be at least
1.25 times the maximum input voltage.
and ground pin GND This capacitor should be
in
2. Input Capacitor Selection (Cin)
A 100 mF, 50 V aluminium electrolytic capacitor located near
the input and ground pin provides sufficient bypassing.
3. Catch Diode Selection (D1) A. For this example, a 3.0 A current rating is adequate.
B. For robust design use a 30 V 1N5824 Schottky diode or
any suggested fast recovery diode in the Table 2.
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LM2596
PROCEDURE (ADJUSTABLE OUTPUT VERSION: LM2596) (CONTINUED)
Procedure Example
4. Inductor Selection (L1)
A. Use the following formula to calculate the inductor Volt x
microsecond [V x ms] constant:
E T +ǒVIN* V
OUT
* V
SAT
Ǔ
OUT
VIN* V
SAT
) V
D
1000
150 kHz
V
) V
D
B. Match the calculated E x T value with the corresponding
number on the vertical axis of the Inductor Value Selection Guide shown in Figure 18. This E x T constant is a measure of the energy handling capability of an inductor and is dependent upon the type of core, the core area, the number of turns, and the duty cycle.
C. Next step is to identify the inductance region intersected by
the E x T value and the maximum load current value on the horizontal axis shown in Figure 18.
D. Select an appropriate inductor from Table 3.
The inductor chosen must be rated for a switching frequency of 150 kHz and for a current rating of 1.15 x I The inductor current rating can also be determined by calculating the inductor peak current:
where t
ǒ
Vin* V
I
+ I
p(max)
is the “on” time of the power switch and
on
Load(max)
ton+
)
V
out
1.0
x
V
f
osc
in
2L
out
Ǔ
t
on
ǒ
V ms
Load
4. Inductor Selection (L1) A. Calculate E x T [V x ms] constant:
E T +ǒ12 * 5 * 1.5Ǔ
Ǔ
E T +ǒ5.5Ǔ
B. E x T = 27 [V x ms]
C. I
Load(max)
Inductance Region = L40
D. Proper inductor value = 33 mH
.
Choose the inductor from Table 3.
5.5
7.5
= 3.0 A
5 ) 0.5
12 * 5 ) 0.5
6.6ǒV ms
1000
ǒ
150 kHz
V ms
Ǔ
Ǔ
5. Output Capacitor Selection (C
out
)
A. Since the LM2596 is a forwardmode switching regulator
with voltage mode control, its open loop has 2pole−1−zero frequency characteristic. The loop stability is determined by the output capacitor (capacitance, ESR) and inductance values.
For stable operation use recommended values of the output capacitors in Table 1. Low ESR electrolytic capacitors between 220uFand 1500uF provide best results.
B. The capacitors voltage rating should be at least 1.5 times
greater than the output voltage, and often much higher voltage rating is needed to satisfy low ESR requirement
6. Feedforward Capacitor (CFF)
It provides additional stability mainly for higher input voltages. For Cff selection use Table 1. The compensation capacitor between
0.6 nF and 40 nF is wired in parallel with the output voltage setting resistor R2, The capacitor type can be ceramic, plastic, etc..
5. Output Capacitor Selection (C
out
)
A. In this example is recommended Nichicon PM
capacitors: 470 mF/35 V or 220 mF/35 V
6. Feedforward Capacitor (CFF)
In this example is recommended feedforward capacitor 15 nF or 5 nF.
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LM2596
LM2596 Series Buck Regulator Design Procedures (continued)
Table 1. RECOMMENDED VALUES OF THE OUTPUT CAPACITOR AND FEEDFORWARD CAPACITOR
(I
= 3 A)
load
Nichicon PM Capacitors
Vin (V)
40 1500/35/24 1000/35/29 1000/35/29 680/35/36 560/25/55 560/25/55 470/35/46 470/35/46
26 1200/35/26 820/35 680/35/36 560/35/41 470/25/65 470/25/65 330/35/60
22 1000/35/29 680/35/36 560/35/41 330/25/85 330/25/85 220/35/85
20 820/35/32 470/35/46 470/25/65 330/25/85 330/25/85 220/35/85
18 820/35/32 470/35/46 470/25/65 330/25/85 330/25/85 220/35/85
12 820/35/32 470/35/46 220/35/85 220/25/111
10 820/35/32 470/35/46 220/35/85
V
(V) 2 4 6 9 12 15 24 28
out
CFF (nF] 40 15 5 2 1.5 1 0.6 0.6
Capacity/Voltage Range/ESR (mF/V/mW)
70 60
50
220uH
L35L27
L36
L27
L42
L43
L44
L37
40
150uH
L29
L38
30 25
100uH
68uH
L30
L39
20
15
E*T(V*us)
10
9 8
7
6
5
4
Figure 18. Inductor Value Selection Guides (For Continuous Mode Operation)
L21
L31
47uH
L32
L40
L40
33uH
L22
L40
22uH
L23
L34
L24
L15
L25
15uH
0.6 0.8 1.0 1.5 2.0 2.5 3.0
Maximum load current (A)
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Table 2. DIODE SELECTION
3.0 A 4.0 6.0 A 3.0 A 4.0 6.0 A
Through
V
R
20 V 1N5820
Hole
MBR320P
SR302
Surface
Mount
SK32 1N5823
LM2596
Schottky Fast Recovery
Through
Hole
SR502 SB520
Surface
Mount
Through
Hole
Surface
Mount
Through
Hole
Surface
Mount
30 V 1N5821
MBR330
SR303
31DQ03
40 V 1N5822
MBR340
SR304
31DQ04
50 V MBR350
31DQ05
SR305
60 V MBR360
DQ06
SR306
NOTE: Diodes listed in bold are available from ON Semiconductor.
SK33
30WQ03
SK34
30WQ04
MBRS340T3
MBRD340
SK35
30WQ05
MBRS360T3
MBRD360
1N5824
SR503 SB530
1N5825
SR504 SB540
SB550 50WQ05
50SQ080 MBRD660CT
50WQ03
MBRD640CT
50WQ04
MUR320
31DF1
HER302
(all diodes
rated
to at least
100 V)
MURS320T3
MURD320
30WF10
(all diodes
rated
to at least
100 V)
MUR420
HER602
(all diodes
rated
to at least
100 V)
MURD620CT
50WF10
(all diodes
rated
to at least
100 V)
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12
LM2596
Table 3. INDUCTOR MANUFACTURERS PART NUMBERS
Schott Renco Pulse Engineering Coilcraft
Inductance
(mH)
L15 22 0.99 67148350 67148460 RL12842243 RL150022PE53815 PE53815S DO3308223
L21 68 0.99 67144070 67144450 RL54715 RL150068PE53821 PE53821S DO3316683
L22 47 1.17 67144080 67144460 RL54716 PE53822 PE53822S DO3316473
L23 33 1.40 67144090 67144470 RL54717 PE53823 PE53823S DO3316333
L24 22 1.70 67148370 67148480 RL12832243 PE53824 PE53825S DO3316223
L25 15 2.10 67148380 67148490 RL12831543 PE53825 PE53824S DO3316153
L26 330 0.80 67144100 67144480 RL54711 PE53826 PE53826S DO5022P334
L27 220 1.00 67144110 67144490 RL54712 PE53827 PE53827S DO5022P224
L28 150 1.20 67144120 67144500 RL54713 PE53828 PE53828S DO5022P154
L29 100 1.47 67144130 67144510 RL54714 PE53829 PE53829S DO5022P104
L30 68 1.78 67144140 67144520 RL54715 PE53830 PE53830S DO5022P683
L31 47 2.20 67144150 67144530 RL54716 PE53831 PE53831S DO5022P473
L32 33 2.50 67144160 67144540 RL54717 PE53932 PE53932S DO5022P333
L33 22 3.10 67148390 67148500 RL12832243 PE53933 PE53933S DO5022P223
L34 15 3.40 67148400 67148790 RL12831543 PE53934 PE53934S DO5022P153
L35 220 1.70 67144170 RL54731 PE53935 PE53935S
L36 150 2.10 67144180 RL54734 PE54036 PE54036S
L37 100 2.50 67144190 RL54721 PE54037 PE54037S
L38 68 3.10 67144200 RL54722 PE54038 PE54038S DO5040H683ML
L39 47 3.50 67144210 RL54723 PE54039 PE54039S DO5040H473ML
L40 33 3.50 67144220 67148290 RL54724 PE54040 PE54040S DO5040H333ML
L41 22 3.50 67144230 67148300 RL54725 PE54041 PE54041S DO5040H223ML
L42 150 2.70 67148410 RL54734 PE54042 PE54042S
L43 100 3.40 67144240 RL54732 PE54043
L44 68 3.40 67144250 RL54733 PE54044 DO5040H683ML
Current
(A)
Through
Hole
Surface
Mount
Through
Hole
Surface
Mount
Through
Hole
Surface
Mount
Surface Mount
-
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LM2596
APPLICATION INFORMATION
EXTERNAL COMPONENTS
Input Capacitor (Cin)
The Input Capacitor Should Have a Low ESR
For stable operation of the switch mode converter a low ESR (Equivalent Series Resistance) aluminium or solid tantalum bypass capacitor is needed between the input pin and the ground pin, to prevent large voltage transients from appearing at the input. It must be located near the regulator and use short leads. With most electrolytic capacitors, the capacitance value decreases and the ESR increases with lower temperatures. For reliable operation in temperatures below 25°C larger values of the input capacitor may be needed. Also paralleling a ceramic or solid tantalum capacitor will increase the regulator stability at cold temperatures.
RMS Current Rating of C
in
The important parameter of the input capacitor is the RMS current rating. Capacitors that are physically large and have large surface area will typically have higher RMS current ratings. For a given capacitor value, a higher voltage electrolytic capacitor will be physically larger than a lower voltage capacitor, and thus be able to dissipate more heat to the surrounding air, and therefore will have a higher RMS current rating. The consequence of operating an electrolytic capacitor beyond the RMS current rating is a shortened operating life. In order to assure maximum capacitor operating lifetime, the capacitor’s RMS ripple current rating should be:
I
> 1.2 x d x I
rms
Load
where d is the duty cycle, for a buck regulator
V
t
t
and d +
Output Capacitor (C
on
+
T
|V
out
d +
|V
out
| ) V
out
on
|
)
out
+
T
V
in
for a buck*boost regulator.
For low output ripple voltage and good stability, low ESR output capacitors are recommended. An output capacitor has two main functions: it filters the output and provides
regulator loop stability. The ESR of the output capacitor and the peaktopeak value of the inductor ripple current are the main factors contributing to the output ripple voltage value. Standard aluminium electrolytics could be adequate for some applications but for quality design, low ESR types are recommended.
An aluminium electrolytic capacitor’s ESR value is related to many factors such as the capacitance value, the voltage rating, the physical size and the type of construction. In most cases, the higher voltage electrolytic capacitors have lower ESR value. Often capacitors with much higher voltage ratings may be needed to provide low ESR values that, are required for low output ripple voltage.
Feedfoward Capacitor
(Adjustable Output Voltage Version)
This capacitor adds lead compensation to the feedback loop and increases the phase margin for better loop stability. For C
FF selection, see the design procedure section.
The Output Capacitor Requires an ESR Value That Has an Upper and Lower Limit
As mentioned above, a low ESR value is needed for low output ripple voltage, typically 1% to 2% of the output voltage. But if the selected capacitor’s ESR is extremely low (below 0.05 W), there is a possibility of an unstable feedback loop, resulting in oscillation at the output. This situation can occur when a tantalum capacitor, that can have a very low ESR, is used as the only output capacitor.
At Low Temperatures, Put in Parallel Aluminium Electrolytic Capacitors with Tantalum Capacitors
Electrolytic capacitors are not recommended for temperatures below −25°C. The ESR rises dramatically at cold temperatures and typically rises 3 times at −25°C and as much as 10 times at −40°C. Solid tantalum capacitors have much better ESR spec at cold temperatures and are recommended for temperatures below −25°C. They can be also used in parallel with aluminium electrolytics. The value of the tantalum capacitor should be about 10% or 20% of the total capacitance. The output capacitor should have at least 50% higher RMS ripple current rating at 150 kHz than the peaktopeak inductor ripple current.
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LM2596
Catch Diode
Locate the Catch Diode Close to the LM2596
The LM2596 is a stepdown buck converter; it requires a fast diode to provide a return path for the inductor current when the switch turns off. This diode must be located close to the LM2596 using short leads and short printed circuit traces to avoid EMI problems.
Use a Schottky or a Soft Switching UltraFast Recovery Diode
Since the rectifier diodes are very significant sources of losses within switching power supplies, choosing the rectifier that best fits into the converter design is an important process. Schottky diodes provide the best performance because of their fast switching speed and low forward voltage drop.
They provide the best efficiency especially in low output voltage applications (5.0 V and lower). Another choice could be FastRecovery, or UltraFast Recovery diodes. It has to be noted, that some types of these diodes with an abrupt turnoff characteristic may cause instability or EMI troubles.
A fast−recovery diode with soft recovery characteristics can better fulfill some quality, low noise design requirements. Table 2 provides a list of suitable diodes for the LM2596 regulator. Standard 50/60 Hz rectifier diodes, such as the 1N4001 series or 1N5400 series are NOT suitable.
Inductor
The magnetic components are the cornerstone of all switching power supply designs. The style of the core and the winding technique used in the magnetic component’s design has a great influence on the reliability of the overall power supply.
Using an improper or poorly designed inductor can cause high voltage spikes generated by the rate of transitions in current within the switching power supply, and the possibility of core saturation can arise during an abnormal operational mode. Voltage spikes can cause the semiconductors to enter avalanche breakdown and the part can instantly fail if enough energy is applied. It can also cause significant RFI (Radio Frequency Interference) and EMI (Electro−Magnetic Interference) problems.
Continuous and Discontinuous Mode of Operation
The LM2596 stepdown converter can operate in both the continuous and the discontinuous modes of operation. The regulator works in the continuous mode when loads are relatively heavy, the current flows through the inductor continuously and never falls to zero. Under light load conditions, the circuit will be forced to the discontinuous mode when inductor current falls to zero for certain period of time (see Figure 19 and Figure 20). Each mode has distinctively different operating characteristics, which can affect the regulator performance and requirements. In many cases the preferred mode of operation is the continuous mode. It offers greater output power, lower peak currents in the switch, inductor and diode, and can have a lower output
ripple voltage. On the other hand it does require larger inductor values to keep the inductor current flowing continuously, especially at low output load currents and/or high input voltages.
To simplify the inductor selection process, an inductor selection guide for the LM2596 regulator was added to this data sheet (Figure 18). This guide assumes that the regulator is operating in the continuous mode, and selects an inductor that will allow a peaktopeak inductor ripple current to be a certain percentage of the maximum design load current. This percentage is allowed to change as different design load currents are selected. For light loads (less than approximately 300 mA) it may be desirable to operate the regulator in the discontinuous mode, because the inductor value and size can be kept relatively low. Consequently, the percentage of inductor peakto−peak current increases. This discontinuous mode of operation is perfectly acceptable for this type of switching converter. Any buck regulator will be forced to enter discontinuous mode if the load current is light enough.
2.0 A
Inductor
Current
Waveform
Waveform
Selecting the Right Inductor Style
0 A
2.0 A
Power
Switch
Current
0 A
HORIZONTAL TIME BASE: 2.0 ms/DIV
Figure 19. Continuous Mode Switching Current
Waveforms
Some important considerations when selecting a core type are core material, cost, the output power of the power supply, the physical volume the inductor must fit within, and the amount of EMI (ElectroMagnetic Interference) shielding that the core must provide. The inductor selection guide covers different styles of inductors, such as pot core, Ecore, toroid and bobbin core, as well as different core materials such as ferrites and powdered iron from different manufacturers.
For high quality design regulators the toroid core seems to be the best choice. Since the magnetic flux is contained within the core, it generates less EMI, reducing noise problems in sensitive circuits. The least expensive is the bobbin core type, which consists of wire wound on a ferrite rod core. This type of inductor generates more EMI due to the fact that its core is open, and the magnetic flux is not contained within the core.
When multiple switching regulators are located on the same printed circuit board, open core magnetics can cause
VERTRICAL RESOLUTION 1.0 A/DIV
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15
LM2596
interference between two or more of the regulator circuits, especially at high currents due to mutual coupling. A toroid, pot core or E−core (closed magnetic structure) should be used in such applications.
Do Not Operate an Inductor Beyond its Maximum Rated Current
Exceeding an inductor’s maximum current rating may cause the inductor to overheat because of the copper wire losses, or the core may saturate. Core saturation occurs when the flux density is too high and consequently the cross sectional area of the core can no longer support additional lines of magnetic flux.
This causes the permeability of the core to drop, the inductance value decreases rapidly and the inductor begins to look mainly resistive. It has only the DC resistance of the winding. This can cause the switch current to rise very rapidly and force the LM2596 internal switch into cyclebycycle current limit, thus reducing the DC output load current. This can also result in overheating of the
GENERAL RECOMMENDATIONS
Output Voltage Ripple and Transients
Source of the Output Ripple
Since the LM2596 is a switch mode power supply regulator, its output voltage, if left unfiltered, will contain a sawtooth ripple voltage at the switching frequency. The output ripple voltage value ranges from 0.5% to 3% of the output voltage. It is caused mainly by the inductor sawtooth ripple current multiplied by the ESR of the output capacitor.
Short Voltage Spikes and How to Reduce Them
The regulator output voltage may also contain short voltage spikes at the peaks of the sawtooth waveform (see Figure 21). These voltage spikes are present because of the fast switching action of the output switch, and the parasitic inductance of the output filter capacitor. There are some other important factors such as wiring inductance, stray capacitance, as well as the scope probe used to evaluate these transients, all these contribute to the amplitude of these spikes. To minimize these voltage spikes, low inductance capacitors should be used, and their lead lengths must be kept short. The importance of quality printed circuit board layout design should also be highlighted.
Voltage spikes caused by
Filtered
Output
Voltage
Unfiltered
Output
Voltage
HORIZONTAL TIME BASE: 5.0 ms/DIV
Figure 21. Output Ripple Voltage Waveforms
switching action of the output switch and the parasitic inductance of the output capacitor
20 mV/DIV
VERTRICAL
RESOLUTION
inductor and/or the LM2596. Different inductor types have different saturation characteristics, and this should be kept in mind when selecting an inductor.
0.4 A
Inductor
Current
Waveform
0 A
0.4 A
Power
Switch
Current
Waveform
Minimizing the Output Ripple
0 A
HORIZONTAL TIME BASE: 2.0 ms/DIV
Figure 20. Discontinuous Mode Switching Current
Waveforms
In order to minimize the output ripple voltage it is possible to enlarge the inductance value of the inductor L1 and/or to use a larger value output capacitor. There is also another way to smooth the output by means of an additional LC filter (20 mH, 100 mF), that can be added to the output (see Figure 30) to further reduce the amount of output ripple and transients. With such a filter it is possible to reduce the output ripple voltage transients 10 times or more. Figure 21 shows the difference between filtered and unfiltered output waveforms of the regulator shown in Figure 30.
The lower waveform is from the normal unfiltered output of the converter, while the upper waveform shows the output ripple voltage filtered by an additional LC filter.
Heatsinking and Thermal Considerations
The ThroughHole Package TO−220
The LM2596 is available in two packages, a 5−pin
2
TO220(T, TV) and a 5−pin surface mount D
PAK(D2T). Although the TO220(T) package needs a heatsink under most conditions, there are some applications that require no heatsink to keep the LM2596 junction temperature within the allowed operating range. Higher ambient temperatures require some heat sinking, either to the printed circuit (PC) board or an external heatsink.
The Surface Mount Package D2PAK and its Heatsinking
The other type of package, the surface mount D2PAK, is designed to be soldered to the copper on the PC board. The copper and the board are the heatsink for this package and the other heat producing components, such as the catch diode and inductor. The PC board copper area that the package is soldered to should be at least 0.4 in
2
(or 260 mm2) and ideally should have 2 or more square inches (1300 mm of 0.0028 inch copper. Additional increases of copper area beyond approximately 6.0 in
2
(4000 mm2) will not improve
VERTICAL RESOLUTION 200 mA/DIV
2
)
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LM2596
heat dissipation significantly. If further thermal improvements are needed, double sided or multilayer PC boards with large copper areas should be considered. In order to achieve the best thermal performance, it is highly recommended to use wide copper traces as well as large areas of copper in the printed circuit board layout. The only exception to this is the OUTPUT (switch) pin, which should not have large areas of copper (see page 8 ‘PCB Layout Guideline’).
Thermal Analysis and Design
The following procedure must be performed to determine
whether or not a heatsink will be required. First determine:
1. P
maximum regulator power dissipation in the
D(max)
application.
2. T
) maximum ambient temperature in the
A(max
application.
3. T
J(max)
maximum allowed junction temperature (125°C for the LM2596). For a conservative design, the maximum junction temperature should not exceed 110°C to assure safe operation. For every additional +10°C temperature rise that the junction must withstand, the estimated operating lifetime of the component is halved.
4. R
5. R
JC
q
JA
q
package thermal resistance junctioncase. package thermal resistance junction−ambient.
(Refer to Maximum Ratings on page 2 of this data sheet or
and R
R
JC
q
JA
q
values).
The following formula is to calculate the approximate
total power dissipated by the LM2596:
PD = (Vin x IQ) + d x I
Load
x V
sat
where d is the duty cycle and for buck converter
V
t
I
(quiescent current) and V
Q
d +
on
O
+
,
V
T
in
can be found in the
sat
LM2596 data sheet, is minimum input voltage applied,
V
in
V
is the regulator output voltage,
O
is the load current.
I
Load
The dynamic switching losses during turnon and
turnoff can be neglected if proper type catch diode is used.
Packages Not on a Heatsink (Free−Standing)
For a freestanding application when no heatsink is used, the junction temperature can be determined by the following expression:
TJ = (R
where (R
)(PD) represents the junction temperature rise
JA
q
caused by the dissipated power and T
) (PD) + T
q
JA
A
is the maximum
A
ambient temperature.
Packages on a Heatsink
If the actual operating junction temperature is greater than the selected safe operating junction temperature determined in step 3, than a heatsink is required. The junction temperature will be calculated as follows:
where R
TJ = PD (R
is the thermal resistance junctioncase,
JC
q
R
is the thermal resistance caseheatsink,
CS
q
is the thermal resistance heatsinkambient.
R
SA
q
+ R
q
JA
+ R
q
CS
) + T
q
SA
A
If the actual operating temperature is greater than the selected safe operating junction temperature, then a larger heatsink is required.
Some Aspects That can Influence Thermal Design
It should be noted that the package thermal resistance and the junction temperature rise numbers are all approximate, and there are many factors that will affect these numbers, such as PC board size, shape, thickness, physical position, location, board temperature, as well as whether the surrounding air is moving or still.
Other factors are trace width, total printed circuit copper area, copper thickness, single− or double−sided, multilayer board, the amount of solder on the board or even color of the traces.
The size, quantity and spacing of other components on the board can also influence its effectiveness to dissipate the heat.
12 to 40 V
Unregulated
DC Input
C
100 mF/50 V
Feedback
+V
in
LM2596ADJ
in
Figure 22. Inverting Buck−Boost Develops −12 V
ON/OFF
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GND
17
L1
33 mH
D1 1N5822
C
out
220 mF
R4
R3
12 V @ 0.7 A Regulated
Output
LM2596
ADDITIONAL APPLICATIONS
Inverting Regulator
An inverting buck−boost regulator using the LM2596ADJ is shown in Figure 22. This circuit converts a positive input voltage to a negative output voltage with a common ground by bootstrapping the regulators ground to the negative output voltage. By grounding the feedback pin, the regulator senses the inverted output voltage and regulates it.
In this example the LM259612 is used to generate a
12 V output. The maximum input voltage in this case cannot exceed +28 V because the maximum voltage appearing across the regulator is the absolute sum of the input and output voltages and this must be limited to a maximum of 40 V.
This circuit configuration is able to deliver approximately
0.7 A to the output when the input voltage is 12 V or higher. At lighter loads the minimum input voltage required drops to approximately 4.7 V, because the buckboost regulator topology can produce an output voltage that, in its absolute value, is either greater or less than the input voltage.
Since the switch currents in this buckboost configuration are higher than in the standard buck converter topology, the available output current is lower.
This type of buck−boost inverting regulator can also require a larger amount of startup input current, even for light loads. This may overload an input power source with a current limit less than 5.0 A.
Such an amount of input startup current is needed for at least 2.0 ms or more. The actual time depends on the output voltage and size of the output capacitor.
Because of the relatively high startup currents required by this inverting regulator topology, the use of a delayed startup or an undervoltage lockout circuit is recommended.
Using a delayed startup arrangement, the input capacitor can charge up to a higher voltage before the switch−mode regulator begins to operate.
The high input current needed for startup is now partially supplied by the input capacitor C
.
in
It has been already mentioned above, that in some situations, the delayed startup or the undervoltage lockout features could be very useful. A delayed startup circuit applied to a buckboost converter is shown in Figure 27. Figure 29 in the “Undervoltage Lockout” section describes an undervoltage lockout feature for the same converter topology.
Design Recommendations:
The inverting regulator operates in a different manner than the buck converter and so a different design procedure has to be used to select the inductor L1 or the output capacitor C
out
.
The output capacitor values must be larger than what is normally required for buck converter designs. Low input voltages or high output currents require a large value output capacitor (in the range of thousands of mF).
The recommended range of inductor values for the inverting converter design is between 68 mH and 220 mH. To select an inductor with an appropriate current rating, the inductor peak current has to be calculated.
The following formula is used to obtain the peak inductor current:
I
peak
where ton+
I
Load(Vin
[
|VO|
Vin) |VO|
) |VO|)
V
in
x
1.0
f
osc
)
, and f
Vinxt
2L
osc
on
1
+ 52 kHz.
Under normal continuous inductor current operating conditions, the worst case occurs when V
is minimal.
in
12 to 40 V
Unregulated
DC Input
C
100 mF/50 V
Feedback
+V
in
LM2596ADJ
in
C1
0.1 mF
Figure 23. Inverting BuckBoost Develops 12 V
ON/OFF
R2 47k
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GND
18
L1
33 mH
D1 1N5822
C
out
220 mF
R4
R3
12 V @ 0.7 A Regulated
Output
LM2596
t
+V
in
C
in
Shutdown
On
Off
Input
R3
470
5.0 V
0
NOTE: This picture does not show the complete circuit.
100 mF
R1
47 k
MOC8101
+V
in
1
LM2596XX
35GN
ON/OFF
R2 47 k
D
-V
Figure 24. Inverting Buck−Boost Regulator Shutdown
Circuit Using an Optocoupler
With the inverting configuration, the use of the ON/OFF pin requires some level shifting techniques. This is caused by the fact, that the ground pin of the converter IC is no longer at ground. Now, the ON
/OFF pin threshold voltage (1.3 V approximately) has to be related to the negative output voltage level. There are many different possible shut down methods, two of them are shown in Figures 24 and 25.
5.6 k
R2
Shutdown Input
+V
Q1 2N3906
in
1
LM2596XX
ON/OFF
R1 12 k
35GN
D
-V
out
+V
+V
in
ou
NOTE: This picture does not show the complete circuit.
Off
0
On
C
in
100 mF
Figure 25. Inverting Buck−Boost Regulator Shutdown
Circuit Using a PNP Transistor
Negative Boost Regulator
This example is a variation of the buck−boost topology and it is called negative boost regulator. This regulator experiences relatively high switch current, especially at low input voltages. The internal switch current limiting results in lower output load current capability.
The circuit in Figure 26 shows the negative boost configuration. The input voltage in this application ranges from 5.0 V to −12 V and provides a regulated 12 V output. If the input voltage is greater than 12 V, the output will rise above 12 V accordingly, but will not damage the regulator.
+V
in
LM2596ADJ
C
in
100 mF/
50 V
12 V
Unregulated
DC Input
ON/OFF
L1
33 mH
Figure 26. Negative Boost Regulator
Design Recommendations:
The same design rules as for the previous inverting buckboost converter can be applied. The output capacitor C
must be chosen larger than would be required for a what
out
standard buck converter. Low input voltages or high output currents require a large value output capacitor (in the range of thousands of mF). The recommended range of inductor
R4
C
out
GND
Feedback
D1
1N5822
R3
470 mF
12 V @ 0.7 A Regulated
Output
values for the negative boost regulator is the same as for inverting converter design.
Another important point is that these negative boost converters cannot provide current limiting load protection in the event of a short in the output so some other means, such as a fuse, may be necessary to provide the load protection.
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Delayed Startup
There are some applications, like the inverting regulator already mentioned above, which require a higher amount of startup current. In such cases, if the input power source is limited, this delayed startup feature becomes very useful.
To provide a time delay between the time when the input voltage is applied and the time when the output voltage comes up, the circuit in Figure 27 can be used. As the input voltage is applied, the capacitor C1 charges up, and the voltage across the resistor R2 falls down. When the voltage on the ON
/OFF pin falls below the threshold value 1.3 V, the regulator starts up. Resistor R1 is included to limit the maximum voltage applied to the ON
/OFF pin. It reduces the power supply noise sensitivity, and also limits the capacitor C1 discharge current, but its use is not mandatory.
When a high 50 Hz or 60 Hz (100 Hz or 120 Hz respectively) ripple voltage exists, a long delay time can cause some problems by coupling the ripple into the ON
/OFF pin, the regulator could be switched periodically
on and off with the line (or double) frequency.
+V
in
C
in
100 mF
NOTE: This picture does not show the complete circuit.
Figure 27. Delayed Startup Circuitry
Undervoltage Lockout
+V
C1
0.1 mF
R1
47 k
in
1
LM2596XX
35GN
ON/OFF
R2 47 k
D
Some applications require the regulator to remain off until the input voltage reaches a certain threshold level. Figure 28 shows an undervoltage lockout circuit applied to a buck regulator. A version of this circuit for buckboost converter is shown in Figure 29. Resistor R3 pulls the ON
/OFF pin high and keeps the regulator off until the input voltage reaches a predetermined threshold level with respect to the ground Pin 3, which is determined by the following expression:
R2
Ǔ
Vth[ VZ1)ǒ1.0 )
R1
(Q1)
V
BE
LM2596
+V
in
R2
10 k
Z1
1N5242B
R1
10 k
NOTE: This picture does not show the complete circuit.
R3
47 k
Q1 2N3904
Figure 28. Undervoltage Lockout Circuit for
Buck Converter
The following formula is used to obtain the peak inductor
current:
I
[
Load(Vin
I
peak
|VO|
where ton+
Vin) |VO|
Under normal continuous inductor current operating
conditions, the worst case occurs when V
+V
in
R2
15 k
Z1
1N5242B
R1
15 k
NOTE: This picture does not show the complete circuit.
R3
47 k
Q1 2N3904
Figure 29. Undervoltage Lockout Circuit for
BuckBoost Converter
Adjustable Output, Low−Ripple Power Supply
A 3.0 A output current capability power supply that
features an adjustable output voltage is shown in Figure 30.
This regulator delivers 3.0 A into 1.2 V to 35 V output. The input voltage ranges from roughly 3.0 V to 40 V. In order to achieve a 10 or more times reduction of output ripple, an additional L−C filter is included in this circuit.
+V
C 100 mF
) |VO|)
V
in
x
+V
C
in
100 mF
in
f
in
1
in
1
1.0 osc
LM2596XX
ON/OFF
Vth 13 V
)
, and f
in
LM2596XX
ON/OFF
35GN
D
Vinxt
on
2L
1
+ 52 kHz.
osc
is minimal.
35GN
D
Vth 13 V
V
out
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LM2596
40 V Max Unregulated DC Input
C
100 mF
Feedback
/OFFGN
4
Output
2
33 mH
D1 1N5822
L1
R2 50 k
C
out
220 mF
R1
1.21 k
+V
in
LM2596Adj
1
in
53ON
D
Figure 30. 1.2 to 35 V Adjustable 3.0 A Power Supply with Low Output Ripple
L2
20 mH
C1
100 mF
Optional Output
Ripple Filter
Output
Voltage
1.2 to 35 V @ 3.0 A
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LM2596
THE LM2596 STEP−DOWN VOLTAGE REGULATOR WITH 5.0 V @ 3.0 A OUTPUT POWER CAPABILITY.
TYPICAL APPLICATION WITH THROUGHHOLE PC BOARD LAYOUT
4 Feedback
Unregulated DC Input
+Vin = 10 V to 40 V
C1
100 mF
/50 V
C1 100 mF, 50 V, Aluminium Electrolytic C2 220 mF, 25 V, Aluminium Electrolytic D1 3.0 A, 40 V, Schottky Rectifier, 1N5822 L1 33 mH, DO5040H, Coilcraft R1 1.0 kW, 0.25 W R2 3.0 kW, 0.25 W
+V
in
1
LM2596ADJ
53ON
D
ON/OFF
Output
2
/OFFGN
33 mH
D1 1N5822
L1
R2
3.0 k
C2 220 mF /16 V
R1
1.0 k
V
+ V
out
V
= 1.23 V
ref
R1 is between 1.0 k and 5.0 k
C
FF
ref
)ǒ1.0 )
Regulated Output Filtered
V
= 5.0 V @ 3.0 A
out2
R2 R1
Figure 31. Schematic Diagram of the 5.0 V @ 3.0 A Step−Down Converter Using the LM2596−ADJ
Ǔ
NOTE: Not to scale. NOTE: Not to scale.
Figure 32. Printed Circuit Board Layout
Component Side
Figure 33. Printed Circuit Board Layout
Copper Side
References
National Semiconductor LM2596 Data Sheet and Application Note
National Semiconductor LM2595 Data Sheet and Application Note
Marty Brown “Practical Switching Power Supply Design”, Academic Press, Inc., San Diego 1990
Ray Ridley “High Frequency Magnetics Design”, Ridley Engineering, Inc. 1995
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22
LM2596
ORDERING INFORMATION
Device Package Shipping
LM2596TADJG TO220
(PbFree)
LM2596TVADJG TO220 (F)
(PbFree)
LM2596DSADJG D2PAK
(PbFree)
LM2596DSADJR4G D2PAK
(PbFree)
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
50 Units / Rail
50 Units / Rail
50 Units / Rail
800 / Tape & Reel
MARKING DIAGRAMS
TO−220
TV SUFFIX
CASE 314B
LM
2596TADJ
AWLYWWG
1
TO−220
T SUFFIX
CASE 314D
LM
2596TADJ
AWLYWWG
5
15
A = Assembly Location WL = Wafer Lot Y = Year WW = Work Week G = PbFree Package
2
D
PAK
DS SUFFIX
CASE 936A
LM
2596ADJ
AWLYWWG
15
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23
LM2596
PACKAGE DIMENSIONS
TO−220
TV SUFFIX
CASE 314B05
ISSUE L
Q
U
F
K
5X
D
0.10 (0.254) PMT
M
Q
U
K
D
5 PL
0.356 (0.014) T
B
P
B
B1
12345
OPTIONAL CHAMFER
E
A
C
L
S
5X J
G
0.24 (0.610) T
M
H
V
W
N
SEATING
T
PLANE
NOTES:
1. DIMENSIONING AND TOLERANCING PER ANSI Y14.5M, 1982.
2. CONTROLLING DIMENSION: INCH.
3. DIMENSION D DOES NOT INCLUDE INTERCONNECT BAR (DAMBAR) PROTRUSION. DIMENSION D INCLUDING PROTRUSION SHALL NOT EXCEED 0.043 (1.092) MAXIMUM.
DIM MIN MAX MIN MAX
A 0.572 0.613 14.529 15.570 B 0.390 0.415 9.906 10.541 C 0.170 0.180 4.318 4.572 D 0.025 0.038 0.635 0.965 E 0.048 0.055 1.219 1.397 F 0.850 0.935 21.590 23.749 G 0.067 BSC 1.702 BSC H 0.166 BSC 4.216 BSC
J 0.015 0.025 0.381 0.635 K 0.900 1.100 22.860 27.940 L 0.320 0.365 8.128 9.271 N 0.320 BSC 8.128 BSC Q 0.140 0.153 3.556 3.886 S --- 0.620 --- 15.748 U 0.468 0.505 11.888 12.827 V --- 0.735 --- 18.669 W 0.090 0.110 2.286 2.794
MILLIMETERSINCHES
TO−220
T SUFFIX
CASE 314D04
ISSUE F
SEATING
T
PLANE
DETAIL A-A
C
E
A
L
J
G
M
M
Q
H
B
B1
NOTES:
1. DIMENSIONING AND TOLERANCING PER ANSI Y14.5M, 1982.
2. CONTROLLING DIMENSION: INCH.
3. DIMENSION D DOES NOT INCLUDE INTERCONNECT BAR (DAMBAR) PROTRUSION. DIMENSION D INCLUDING PROTRUSION SHALL NOT EXCEED 10.92 (0.043) MAXIMUM.
DIM MIN MAX MIN MAX
A 0.572 0.613 14.529 15.570 B 0.390 0.415 9.906 10.541
B1 0.375 0.415 9.525 10.541
C 0.170 0.180 4.318 4.572 D 0.025 0.038 0.635 0.965
E 0.048 0.055 1.219 1.397 G 0.067 BSC 1.702 BSC H 0.087 0.112 2.210 2.845
J 0.015 0.025 0.381 0.635 K 0.977 1.045 24.810 26.543
L 0.320 0.365 8.128 9.271 Q 0.140 0.153 3.556 3.886 U 0.105 0.117 2.667 2.972
MILLIMETERSINCHES
DETAIL A−A
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24
LM2596
PACKAGE DIMENSIONS
D2PAK
D2T SUFFIX
CASE 936A02
ISSUE C
K
B
D
0.010 (0.254) T
M
C
A
123
45
G
S
H
OPTIONAL CHAMFER
10.66
0.42
T
TERMINAL 6
E
V
M
L
N
P
R
SOLDERING FOOTPRINT*
8.38
0.33
NOTES:
1. DIMENSIONING AND TOLERANCING PER ANSI
U
Y14.5M, 1982.
2. CONTROLLING DIMENSION: INCH.
3. TAB CONTOUR OPTIONAL WITHIN DIMENSIONS A AND K.
4. DIMENSIONS U AND V ESTABLISH A MINIMUM MOUNTING SURFACE FOR TERMINAL 6.
5. DIMENSIONS A AND B DO NOT INCLUDE MOLD FLASH OR GATE PROTRUSIONS. MOLD FLASH AND GATE PROTRUSIONS NOT TO EXCEED 0.025 (0.635) MAXIMUM.
DIMAMIN MAX MIN MAX
INCHES
0.386 0.403 9.804 10.236
B 0.356 0.368 9.042 9.347 C 0.170 0.180 4.318 4.572 D 0.026 0.036 0.660 0.914
E 0.045 0.055 1.143 1.397 G 0.067 BSC 1.702 BSC H 0.539 0.579 13.691 14.707 K 0.050 REF 1.270 REF
L 0.000 0.010 0.000 0.254 M 0.088 0.102 2.235 2.591 N 0.018 0.026 0.457 0.660
P 0.058 0.078 1.473 1.981 R 5 REF
S 0.116 REF 2.946 REF U 0.200 MIN 5.080 MIN
V 0.250 MIN 6.350 MIN
__
MILLIMETERS
5 REF
1.702
0.067
1.016
3.05
0.04
0.12
16.02
0.63
mm
ǒ
SCALE 3:1
inches
Ǔ
*For additional information on our PbFree strategy and soldering
details, please download the ON Semiconductor Soldering and Mounting Techniques Reference Manual, SOLDERRM/D.
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LM2596/D
25
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