LM2594
0.5 A, Step-Down Switching
Regulator
The LM2594 regulator is monolithic integrated circuit ideally suited
for easy and convenient design of a step−down switching regulator
(buck converter). It is capable of driving a 0.5 A load with excellent
line and load regulation. This device is available in adjustable output
version. It is internally compensated to minimize the number of
external components to simplify the power supply design.
Since LM2594 converter is a switch−mode power supply, its
efficiency is significantly higher in comparison with popular
three−terminal linear regulators, especially with higher input voltages.
The LM2594 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
8−Lead PDIP and 8−Lead Surface Mount packages.
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 50 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.
MARKING
DIAGRAMS
8
8
1
SOIC−8
D SUFFIX
CASE 751
1
Adjustable Output Voltage Range 1.23 V − 37 V
Guaranteed 0.5 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 50 mA
Thermal Shutdown and Current Limit Protection
Internal Loop Compensation
Moisture Sensitivity Level (MSL) Equals 1
These are Pb−Free Devices
PDIP−8
N SUFFIX
CASE 626
= Assembly Location
= Wafer Lot
= Year
= Work Week
= Pb−Free Package
PIN CONNECTIONS
SOIC−8
NC
1
8 OUTPUT
NC
2
7 VIN
NC
3
6 GND
FB
4
5 ON/OFF
(Top View)
Applications
•
•
•
•
•
•
LM2594
AYWW
G
2594−ADJ
AWL
YYWW
A
WL
YY
WW
G or G
Features
•
•
•
•
•
•
•
•
•
•
http://onsemi.com
PDIP−8
Simple High−Efficiency Step−Down (Buck) Regulator
Efficient Pre−Regulator for Linear Regulators
On−Card Switching Regulators
Positive to Negative Converter (Buck−Boost)
Negative Step−Up Converters
Power Supply for Battery Chargers
NC
1
8
OUTPUT
NC
2
7
VIN
NC
3
6
GND
FB
4
5
ON/OFF
(Top View)
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 23 of this data sheet.
© Semiconductor Components Industries, LLC, 2009
January, 2009 − Rev. 0
1
Publication Order Number:
LM2594/D
LM2594
12 V
Unregulated
Feedback
+VIN
DC Input
4
L1
100 mH
LM2594
7
Output
R1 = 1 kW
R2 = 3k
CFF
8
CIN = 68 mF
5
ON/OFF
6
VOUT = 5 V; Iload = 0.5 A
COUT
GND
220 mF
D1
1N5817
Figure 1. Typical Application
0.5
Figure 2. Representative Block Diagram
PIN FUNCTION DESCRIPTION
Pin No.
Symbol
Description (Refer to Figure 1)
1−3
NC
Not Connected
4
FB
This pin is the direct input of the error amplifier and the resistor network R2, R1 is connected externally to
allow programming of the output voltage.
5
ON/OFF
6
GND
Circuit ground pin. See the information about the printed circuit board layout.
7
+VIN
Positive input supply for LM2594 step−down switching regulator. In order to minimize voltage transients and
to supply the switching currents needed by the regulator, a suitable input bypass capacitor must be present
(CIN in Figure 1)
8
OUTPUT
Emitter of the internal switch. The saturation voltage Vsat of the output switch is typically 1 V. It should be
kept in mind that PCB area connected to this pin should be kept to a minimum in order to minimize coupling
to sensitive circuitry
Allows the switching regulator circuit to be shut down using logic levels, thus dropping the total input supply
current to approximately 50 mA. The threshold voltage is typical. 1.6 V. Applying a voltage above this value
(up to VIN) 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 will be in the “on” condition.
http://onsemi.com
2
LM2594
MAXIMUM RATINGS
Symbol
Value
Unit
Vin
Maximum Supply Voltage
Rating
45
V
ON/OFF
ON/OFF Pin Input Voltage
−0.3 V ≤ V ≤ +Vin
V
−1.0
V
Internally Limited
W
Vout
Output Voltage to Ground (Steady−State)
PD
Power Dissipation
8−Lead DIP
RqJA
Thermal Resistance, Junction−to−Ambient
100
°C/W
RqJC
Thermal Resistance, Junction−to−Case
5.0
°C/W
Internally Limited
W
175
°C/W
−65 to +150
°C
PD
Power Dissipation
8−Lead Surface Mount
RqJA
Thermal Resistance, Junction−to−Ambient
Tstg
Storage Temperature Range
−
Minimum ESD Rating (Human Body Model: C = 100 pF, R = 1.5 kW)
2.0
kV
−
Lead Temperature (Soldering, 10 seconds)
260
°C
TJ
Maximum Junction Temperature
150
°C
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.
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 table)
Rating
Symbol
Value
Unit
TJ
Operating Temperature Range
−40 to +125
°C
VIN
Supply Voltage
4.5 V to 40 V
V
http://onsemi.com
3
LM2594
SYSTEM PARAMETERS
ELECTRICAL CHARACTERISTICS Specifications with standard type face are for TJ = 25°C, and those with boldface type apply
over full Operating Temperature Range −40°C to +125°C
Characteristics
Symbol
Min
Typ
Max
Unit
LM2594 (Note 1, Test Circuit Figure 16)
Feedback Voltage (Vin = 12 V, ILoad = 0.1 A, Vout = 5.0 V, )
VFB_nom
Feedback Voltage (8.0 V ≤ Vin ≤ 40 V, 0.1 A ≤ ILoad ≤ 0.5 A, Vout = 5.0 V)
V
VFB
1.193
1.18
η
−
80
Symbol
Min
Typ
Max
Unit
25
100
200
nA
150
165
180
kHz
1.0
1.2
1.4
V
Efficiency (Vin = 12 V, ILoad = 0.5 A, Vout = 5.0 V)
Characteristics
1.23
Feedback Bias Current (Vout = 5.0 V)
Ib
Oscillator Frequency (Note 2)
fosc
Saturation Voltage (Iout = 0.5 A, Notes 3 and 4)
Vsat
Max Duty Cycle “ON” (Note 4)
DC
Current Limit (Peak Current, Notes 3 and 4)
ICL
Output Leakage Current (Notes 5 and 6)
Output = 0 V
Output = −1.0 V
IL
Quiescent Current (Note 5)
Standby Quiescent Current (ON/OFF Pin = 5.0 V (“OFF”))
(Note 6)
135
120
1.267
1.28
%
95
0.7
0.65
V
%
1.0
1.6
1.8
A
0.5
13
2.0
30
IQ
5.0
10
mA
Istby
50
200
250
mA
mA
ON/OFF PIN LOGIC INPUT
Threshold Voltage
1.6
Vout = 0 V (Regulator OFF)
VIH
Vout = Nominal Output Voltage (Regulator ON)
VIL
V
2.2
2.4
V
1.0
0.8
V
ON/OFF Pin Input Current
ON/OFF Pin = 5.0 V (Regulator OFF)
IIH
−
15
30
mA
ON/OFF Pin = 0 V (regulator ON)
IIL
−
0.01
5.0
mA
1. External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance.
When the LM2594 is used as shown in the Figure 16 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 8) 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”.
6. Vin = 40 V.
http://onsemi.com
4
LM2594
TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 16)
0.8
0.6
Vout, OUTPUT VOLTAGE CHANGE (%)
Vout , OUTPUT VOLTAGE CHANGE (%)
1.0
Vin = 20 V
ILoad = 100 mA
Normalized at TJ = 25°C
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1.0
−50
−25
0
25
50
75
100
125
0.6
Vout = 5 V
0.4
0.2
0
−0.2
−0.4
−0.6
0
5.0
10
15
20
25
30
Figure 4. Line Regulation
1.3
I O, OUTPUT CURRENT (A)
ILoad = 500 mA
1.0
ILoad = 100 mA
0.5
L = 100 mH
R_ind = 30 mW
−25
0
25
60
75
100
1.1
1.0
0.9
0.8
0.6
−50
125
−25
0
25
60
75
Figure 5. Dropout Voltage
Figure 6. Current Limit
160
Vout = 5 V
Measured at GND Pin
TJ = 25°C
9
ILoad = 500 mA
8
7
ILoad = 100 mA
6
5
5
Vin = 12 V
TJ, JUNCTION TEMPERATURE (°C)
10
10
15
20
25
30
35
40
1.2
TJ, JUNCTION TEMPERATURE (°C)
11
35
0.7
I stby , STANDBY QUIESCENT CURRENT ( μA)
INPUT - OUTPUT DIFFERENTIAL (V)
0.8
Figure 3. Normalized Output Voltage
12
I Q, QUIESCENT CURRENT (mA)
1.0
Vin, INPUT VOLTAGE (V)
1.5
4
0
ILoad = 100 mA
TJ = 25°C
1.2
TJ, JUNCTION TEMPERATURE (°C)
2.0
0
−50
1.4
40
140
100
125
100
125
VON/OFF = 5.0 V
120
100
80
Vin = 40 V
60
40
Vin = 12 V
20
0
−50
−25
0
25
60
75
Vin, INPUT VOLTAGE (V)
TJ, JUNCTION TEMPERATURE (°C)
Figure 7. Quiescent Current
Figure 8. Standby Quiescent Current
http://onsemi.com
5
LM2594
TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 16)
1.0
1.2
NORMALIZED FREQUENCY (%)
Vsat , SATURATION VOLTAGE (V)
1.3
1.1
1.0
0.9
−40°C
0.8
25°C
0.7
125°C
0.6
0.5
0
0.1
0.2
0.3
−3.0
−4.0
−5.0
−6.0
−7.0
0.4
−9.0
−50
0.5
0
25
50
75
100
TJ, JUNCTION TEMPERATURE (°C)
Figure 9. Switch Saturation Voltage
Figure 10. Switching Frequency
100
4.5
80
Ib , FEEDBACK PIN CURRENT (nA)
5.0
4.0
3.5
3.0
2.5
2.0
Vout ' 1.23 V
ILoad = 100 mA
1.5
1.0
0.5
0
-50
−25
SWITCH CURRENT (A)
-25
0
25
50
75
100
40
20
0
-20
-40
-60
-80
-100
-50
125
-25
0
25
12 V, 500 mA
85
5 V, 500 mA
80
75
3.3 V, 500 mA
0
5
10
75
100
Figure 12. Feedback Pin Current
95
70
50
TJ, JUNCTION TEMPERATURE (°C)
TJ, JUNCTION TEMPERATURE (°C)
90
15
20
25
30
VIN, INPUT VOLTAGE (V)
Figure 13. Efficiency
http://onsemi.com
6
125
60
Figure 11. Minimum Supply Operating Voltage
EFFICIENCY (%)
V in , INPUT VOLTAGE (V)
−2.0
−8.0
0.4
0.3
0.0
−1.0
35
40
45
125
LM2594
TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 16)
A
10 V
0
100 mV
Output
0
Voltage
Change
- 100 mV
0.8 A
B
0.4 A
0
0.5 A
0.8 A
C
D
Load
Current
0.4 A
0.1 A
0
0
2 ms/div
100 ms/div
Figure 14. Switching Waveforms
Figure 15. Load Transient Response
Vout = 5 V
A: Output Pin Voltage, 10 V/div
B: Switch Current, 0.4 A/div
C: Inductor Current, 0.4 A/div, AC−Coupled
D: Output Ripple Voltage, 50 mV/div, AC−Coupled
Horizontal Time Base: 2.0 ms/div
Adjustable Output Voltage Versions
Feedback
Vin
LM2594
7
L1
100 mH
Output
6
8.5 V - 40 V
Unregulated
DC Input
4
GND
5
Vout
5.0 V/0.5 A
8
ON/OFF
CFF
Cin
100 mF
D1
1N5822
Cout
220 mF
R2
Load
R1
V out + V
ǒ
R2 + R1
ǒ1.0 ) R2
Ǔ
R1
ref
Ǔ
V out
1.0
V ref
Where Vref = 1.23 V, R1
between 1.0 k and 5.0 k
Figure 16. Typical Test Circuit
http://onsemi.com
7
LM2594
PCB LAYOUT GUIDELINES
As in any switching regulator, the layout of the printed
On the other hand, the PCB area connected to the Pin 2
circuit board is very important. Rapidly switching currents
(emitter of the internal switch) of the LM2594 should be
associated with wiring inductance, stray capacitance and
kept to a minimum in order to minimize coupling to sensitive
parasitic inductance of the printed circuit board traces can
circuitry.
generate voltage transients which can generate
Another sensitive part of the circuit is the feedback. It is
electromagnetic interferences (EMI) and affect the desired
important to keep the sensitive feedback wiring short. To
operation. As indicated in the Figure 16, to minimize
assure this, physically locate the programming resistors near
inductance and ground loops, the length of the leads
to the regulator, when using the adjustable version of the
indicated by heavy lines should be kept as short as possible.
LM2594 regulator.
For best results, single−point grounding (as indicated) or
ground plane construction should be used.
DESIGN PROCEDURE
Buck Converter Basics
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:
The LM2594 is a “Buck” or Step−Down Converter which
is the most elementary forward−mode converter. Its basic
schematic can be seen in Figure 17.
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) +
t
d + on , where T is the period of switching.
T
For the buck converter with ideal components, the duty
cycle can also be described as:
V
d + out
V in
Figure 18 shows the buck converter, idealized waveforms
of the catch diode voltage and the inductor current.
ǒVIN * VOUTǓton
Von(SW)
L
Power
Switch
Diode Voltage
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.
L
Vin
Cout
D
Power
Switch
Off
VD(FWD)
Power
Switch
On
Power
Switch
On
RLoad
Time
Figure 17. Basic Buck Converter
Inductor Current
Ipk
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) +
Power
Switch
Off
ILoad(AV)
Imin
Diode
Power
Switch
Diode
Power
Switch
Time
Figure 18. Buck Converter Idealized Waveforms
ǒVOUT * VDǓtoff
L
http://onsemi.com
8
LM2594
PROCEDURE (ADJUSTABLE OUTPUT VERSION: LM2594)
Procedure
Example
Given Parameters:
Vout = Regulated Output Voltage
Vin(max) = Maximum DC Input Voltage
ILoad(max) = Maximum Load Current
Given Parameters:
Vout = 5.0 V
Vin(max) = 12 V
ILoad(max) = 0.5 A
1. Programming Output Voltage
To select the right programming resistor R1 and R2 value (see
Figure 1) use the following formula:
1. Programming Output Voltage (selecting R1 and R2)
Select R1 and R2:
ǒ
Ǔ
R2
V out + V
1.0 )
ref
R1
ǒ
V out + 1.23 1.0 )
ǒ
where Vref = 1.23 V
R2 + R1
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).
V
R2 + R1ǒ
V
out
ref
V out
V
ref
Ǔ
R2
R1
Select R1 = 1.0 kW
Ǔ ǒ
* 1.0
+
Ǔ
5V
* 1.0
1.23 V
R2 = 3.0 kW, choose a 3.0k metal film resistor.
* 1.0Ǔ
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 +Vin and ground pin GND This capacitor should be
located close to the IC using short leads. This capacitor should
have a low ESR (Equivalent Series Resistance) value.
2. Input Capacitor Selection (Cin)
A 68 mF, 50 V aluminium electrolytic capacitor located near
the input and ground pin provides sufficient bypassing.
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
LM2594 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.
3. Catch Diode Selection (D1)
A. For this example, a 1.0 A current rating is adequate.
B. For Vin = 12 V use a 20 V 1N5817 Schottky diode or
any suggested fast recovery diode in the Table 2.
http://onsemi.com
9
LM2594
PROCEDURE (ADJUSTABLE OUTPUT VERSION: LM2594) (CONTINUED)
Procedure
Example
4. Inductor Selection (L1)
A. Calculate E x T [V x ms] constant:
4. Inductor Selection (L1)
A. Use the following formula to calculate the inductor Volt x
microsecond [V x ms] constant:
E
ǒ
T+ V
IN
*V
OUT
*V
Ǔ
SAT
V
V
IN
OUT
*V
)V
SAT
D
)V
1000
D
150 kHz
ǒV
+I
)
T + ǒ12 * 5 * 1.0Ǔ
E
T + ǒ6Ǔ
msǓ
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 19. 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 19.
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 ILoad.
The inductor current rating can also be determined by
calculating the inductor peak current:
I
E
5.5
11.5
5 ) 0.5
1000
12 * 1 ) 0.5
150 kHz
6.7ǒV
ǒV
msǓ
B. E x T = 19.2 [V x ms]
C. ILoad(max) = 0.5 A
Inductance Region = L20
D. Proper inductor value = 100 mH
Choose the inductor from Table 3.
ǒVin * VoutǓ ton
p(max) Load(max)
2L
where ton is the “on” time of the power switch and
V
t on + out x 1.0
V
f osc
in
5. Output Capacitor Selection (Cout)
A. Since the LM2594 is a forward−mode switching regulator
with voltage mode control, its open loop has 2−pole−1−zero
frequency characteristic. The loop stability is determined by
the output capacitor (capacitance, ESR) and inductance
values.
5. Output Capacitor Selection (Cout)
A. In this example is recommended Nichicon PM
capacitors: 220 mF/25 V
For stable operation use recommended values of the output
capacitors in Table 1.
Low ESR electrolytic capacitors between 180 mF and
1000 mF 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 15 nF is wired in parallel with the output voltage setting
resistor R2, The capacitor type can be ceramic, plastic, etc..
6. Feedforward Capacitor (CFF)
In this example is recommended feedforward capacitor
1.5 nF.
http://onsemi.com
10
msǓ
LM2594
LM2594 Series Buck Regulator Design Procedures (continued)
Table 1. RECOMMENDED VALUES OF THE OUTPUT CAPACITOR AND FEEDFORWARD CAPACITOR
(Iload = 0.5 A)
Nichicon Pm Capacitors
Vin (V)
Capacity/Voltage Range / ESR[mF/V/mW]
1000/10/
60
680/250
470/10/
140
470/10/
140
330/10/
160
220/25/
110
220/110
180/25/
140
180/35/
100
35
1000/10/
60
680/150
470/10/
140
330/10/
160
180/25/
140
180/25/
140
180/25/
140
180/25/
140
180/35/
100
26
1000/10/
60
470/10/
140
330/10/
160
220/25/
110
180/25/
140
180/25/
140
100/25/
240
180/25/
140
20
1000/10/
60
470/10/
140
220/25/
110
220/25/
110
100/25/
240
100/25/
240
100/25/
240
18
1000/10/
60
470/10/
140
220/25/
110
220/25/
110
100/25/
240
100/25/
240
100/25/
240
12
470/10/
140
470/10/
140
220/25/
110
180/25/
140
100/25/
240
10
470/10/
140
470/10/
140
220/25/
110
180/25/
140
Vout (V)
2
3
4
6
9
12
15
24
28
CFF (nF)
15
4.7
1.5
1.5
1.5
1.5
1
0.6
0.6
0.3
0.4
E*T(V*us)
40
0.1
0.2
Maximum load current (A)
Figure 19. Inductor Value Selection Guides (For Continuous Mode Operation)
http://onsemi.com
11
0.5
LM2594
Table 2. DIODE SELECTION
1A Diodes
Surface Mouns
VR
Schottky
20 V
MBRS140
Through Hole
Ultra Fast
Recovery
Schottky
All of these diodes are rated
to at least 60 V. MURS120
10BF10
1N5817
30 V
10BQ040
40 V
10MQ040
1N5818
SR102
50 V or more
MBRS160
SR103
10BQ050
11DQ03
10MQ060
1N5819
MBRS1100
SR104
10MQ090
11DQ04
SGL41-60
SR105
SS16
MBR150
MBRS140
11DQ05
10BQ040
MBR160
http://onsemi.com
12
Ultra Fast
Recovery
All of these diodes are rated to at least 60 V.
MUR120 HER101 11DF1
LM2594
Table 3. INDUCTOR MANUFACTURERS PART NUMBERS
Schott
Renco
Pulse Engineering
Coilcraft
Inductance
(mH)
Current
(A)
Through
Hole
Surface
Mount
Through
Hole
Surface
Mount
Through
Hole
Surface
Mount
Surface
Mount
L1
220
0.18
67143910
67144280
RL−5470−3
PE−53801
PE−53801−S
−
DO1608−224
L2
150
0.21
67143920
67144290
RL−5470−4
PE−53802
PE−53802−S
−
DO1608−154
L3
100
0.26
67143930
67144300
RL−5470−5
PE−53803
PE−53803−S
−
DO1608−104
L4
68
0.32
67143940
67144310
RL−1284−68
PE−53804
PE−53804−S
−
DO1608−68
L5
47
0.37
67148310
67148420
RL−1284−47
PE−53805
PE−53805−S
−
DO1608−473
L6
33
0.44
67148320
67148430
RL−1284−33
PE−53806
PE−53806−S
−
DO1608−333
L7
22
0.60
67148330
67148440
RL−1284−22
PE−53807
PE−53807−S
−
DO1608−223
L8
330
0.26
67143950
67144320
RL−5470−2
PE−53808
PE−53808−S
−
DO3308−334
L9
220
0.32
67143960
67144330
RL−5470−3
PE−53809
PE−53809−S
−
DO3308−224
L10
150
0.39
67143970
67144340
RL−5470−4
PE−53810
PE−53810−S
−
DO3308−154
L11
100
0.48
67143980
67144350
RL−5470−5
PE−53811
PE−53811−S
−
DO3308−104
L12
68
0.58
67143990
67144360
RL−5470−6
PE−53812
PE−53812−S
−
DO1608−683
L13
47
0.70
67144000
67144380
RL−5470−7
PE−53813
PE−53813−S
−
DO3308−473
L14
33
0.83
67148340
67148450
RL−1284−33
PE−53814
PE−53814−S
−
DO1608−333
L15
22
0.99
67148350
67148460
RL−1284−22
PE−53815
PE−53815−S
−
DO1608−223
L16
15
1.24
67148360
67148470
RL−1284−15
PE−53816
PE−53816−S
−
DO1608−153
L17
330
0.42
67144030
67144410
RL−5471−1
PE−53817
PE−53817−S
−
DO3316−334
L18
220
0.55
67144040
67144420
RL−5471−2
PE−53818
PE−53818−S
−
DO3316−224
L19
150
0.66
67144050
67144430
RL−5471−3
PE−53819
PE−53819−S
RFB0810−151L
DO3316−154
L20
100
0.82
67144060
67144440
RL−5471−4
PE−53820
PE−53820−S
RFB0810−101L
DO3340P−104
L21
68
0.99
67144070
67144450
RL−5471−5
PE−53821
PE−53821−S
RFB0810−680L
DDO3316−683
L26
330
0.80
67144100
67144480
RL−5471−1
PE−53826
PE−53826−S
−
−
L27
220
1.00
67144110
67144490
RL−5471−2
PE−53827
PE−53827−S
−
−
http://onsemi.com
13
LM2594
APPLICATION INFORMATION
EXTERNAL COMPONENTS
regulator loop stability. The ESR of the output capacitor and
the peak−to−peak 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.
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.
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 CFF selection, see the design procedure section.
RMS Current Rating of Cin
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:
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
Irms > 1.2 x d x ILoad
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
peak−to−peak inductor ripple current.
where d is the duty cycle, for a buck regulator
V
t
d + on + out
T
V in
|V out|
t on
and d +
+
for a buck*boost regulator.
T
|V out| ) V
in
Output Capacitor (Cout)
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
http://onsemi.com
14
LM2594
Catch Diode
Locate the Catch Diode Close to the LM2594
The LM2594 is a step−down 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 LM2594 using short leads and short printed circuit
traces to avoid EMI problems.
Use a Schottky or a Soft Switching
Ultra−Fast 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 Fast−Recovery, or Ultra−Fast 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 LM2594
regulator. Standard 50/60 Hz rectifier diodes, such as the
1N4001 series or 1N5400 series are NOT suitable.
VERTRICAL RESOLUTION 1.0 A/DIV
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 LM2594 regulator was added to this
data sheet (Figure 19). This guide assumes that the regulator
is operating in the continuous mode, and selects an inductor
that will allow a peak−to−peak 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 peak−to−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.
0.4 A
Inductor
Current
Waveform 0 A
Inductor
0.8 A
Power
Switch
Current
Waveform 0 A
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.
HORIZONTAL TIME BASE: 2.0 ms/DIV
Figure 20. Continuous Mode Switching Current
Waveforms
Selecting the Right Inductor Style
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 (Electro−Magnetic Interference) shielding
that the core must provide. The inductor selection guide
covers different styles of inductors, such as pot core, E−core,
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
Continuous and Discontinuous Mode of Operation
The LM2594 step−down 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 20 and Figure 21). 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
http://onsemi.com
15
LM2594
inductor and/or the LM2594. Different inductor types have
different saturation characteristics, and this should be kept
in mind when selecting an inductor.
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.
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 LM2594 internal switch into
cycle−by−cycle current limit, thus reducing the DC output
load current. This can also result in overheating of the
VERTICAL RESOLUTION 200 mA/DIV
Do Not Operate an Inductor Beyond its
Maximum Rated Current
0.05 A
Inductor
Current
Waveform
0A
0.05 A
Power
Switch
Current
Waveform
0A
HORIZONTAL TIME BASE: 2.0 ms/DIV
Figure 21. Discontinuous Mode Switching Current
Waveforms
GENERAL RECOMMENDATIONS
Output Voltage Ripple and Transients
Source of the Output Ripple
Minimizing the Output Ripple
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 (3 mH,
100 mF), that can be added to the output (see Figure 31) 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 22 shows the
difference between filtered and unfiltered output waveforms
of the regulator shown in Figure 31.
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.
Since the LM2594 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 22). 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.
Heatsinking and Thermal Considerations
The LM2574 is available in both 8−pin DIP and SOIC−8
packages. When used in the typical application the copper
lead frame conducts the majority of the heat from the die,
through the leads, to the printed circuit copper. The copper
and the board are the heatsink for this package and the other
heat producing components, such as the catch diode and
inductor. For the best thermal performance, wide copper
traces should be used and all ground and unused pins should
be soldered to generous amounts of printed circuit board
copper, such as a ground plane. Large areas of copper
provide the best transfer of heat to the surrounding air. One
exception to this is the output (switch) pin, which should not
have large areas of copper in order to minimize coupling to
sensitive circuitry.
Additional improvement in heat dissipation can be
achieved even by using of double sided or multilayer boards
which can provide even better heat path to the ambient.
Using a socket for the 8−pin DIP package is not
recommended because socket represents an additional
thermal resistance, and as a result the junction temperature
will be higher.
Voltage spikes
caused by
switching action
of the output
switch and the
parasitic
inductance of the
output capacitor
VERTRICAL
RESOLUTION
20 mV/DIV
Filtered
Output
Voltage
Unfiltered
Output
Voltage
HORIZONTAL TIME BASE: 5.0 ms/DIV
Figure 22. Output Ripple Voltage Waveforms
http://onsemi.com
16
LM2594
The following formula is to calculate the approximate
total power dissipated by the LM2594:
Since the current rating of the LM2594 is only 0.5 A, the
total package power dissipation for this switcher is quite
low, ranging from approximately 0.1 W up to 0.75 W under
varying conditions. In a carefully engineered printed circuit
board, the through−hole DIP package can easily dissipate up
to 0.75 W, even at ambient temperatures of 60°C, and still
keep the maximum junction temperature below 125°C.
PD = (Vin x IQ) + d x ILoad x Vsat
where d is the duty cycle and for buck converter
V
t
d + on + O ,
T
V in
Thermal Analysis and Design
IQ
(quiescent current) and Vsat can be found in the
LM2594 data sheet,
Vin is minimum input voltage applied,
VO is the regulator output voltage,
ILoad is the load current.
The dynamic switching losses during turn−on and
turn−off can be neglected if proper type catch diode is used.
The junction temperature can be determined by the
following expression:
The following procedure must be performed to determine
the operating junction temperature. First determine:
1. PD(max) maximum regulator power dissipation in the
application.
2. TA(max) maximum ambient temperature in the
application.
3. TJ(max)
maximum allowed junction temperature
(125°C for the LM2594). 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. RqJC
package thermal resistance junction−case.
5. RqJA
package thermal resistance
junction−ambient.
(Refer to Maximum Ratings on page 3 of this data sheet or
RqJC and RqJA values).
12 to 25 V
Unregulated
DC Input
Cin
100 mF/50 V
TJ = (RqJA) (PD) + TA
where (RqJA)(PD) represents the junction temperature rise
caused by the dissipated power and TA is the maximum
ambient temperature.
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.
R4
Feedback
+Vin
L1
100 mH
LM2594
CFF
ON/OFF
GND
R3
D1
1N5819
Cout
220 mF
−12 V @ 0.7 A
Regulated
Output
Figure 23. Inverting Buck−Boost Develops −12 V
ADDITIONAL APPLICATIONS
the negative output voltage. By grounding the feedback pin,
the regulator senses the inverted output voltage and
regulates it.
In this example the LM2594 is used to generate a −12 V
output. The maximum input voltage in this case cannot
exceed +28 V because the maximum voltage appearing
Inverting Regulator
An inverting buck−boost regulator using the
LM2594−ADJ is shown in Figure 23. This circuit converts
a positive input voltage to a negative output voltage with a
common ground by bootstrapping the regulators ground to
http://onsemi.com
17
LM2594
features could be very useful. A delayed startup circuit
applied to a buck−boost converter is shown in Figure 28.
Figure 30 in the “Undervoltage Lockout” section describes
an undervoltage lockout feature for the same converter
topology.
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
0.25 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 buck−boost 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 buck−boost 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 1.0 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 Cin.
It has been already mentioned above, that in some
situations, the delayed startup or the undervoltage lockout
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 Cout.
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
(V ) |V |)
O ) V in x t on
[ Load in
2L 1
V
in
|V |
O
where t on +
x 1.0 , and f osc + 52 kHz.
V ) |V | fosc
in
O
I
peak
Under normal continuous inductor current operating
conditions, the worst case occurs when Vin is minimal.
R4
Feedback
12 to 40 V
Unregulated
DC Input
Cin
100 mF/50 V
Design Recommendations:
+Vin
C1
0.1 mF
L1
100 mH
LM2594
CFF
ON/OFF
GND
R3
D1
1N5819
R2
47k
Cout
220 mF
−12 V @ 0.25 A
Regulated
Output
Figure 24. Inverting Buck−Boost Develops with Delayed Startup
http://onsemi.com
18
LM2594
+V
+Vin
+Vin
Shutdown
Input
5.0 V
0
Cin
R1
100 mF 47 k
0
LM2594
7
Shutdown
Input
On
R2
5.6 k
5
ON/OFF 6
+Vin
GN
D
+Vin
7
LM2594
Cin
100 mF
Off
On
Off
R3
470
Q1
2N3906
R2
47 k
5
ON/OFF 6
-Vout
R1
12 k
MOC8101
NOTE: This picture does not show the complete circuit.
GN
D
-Vout
NOTE: This picture does not show the complete circuit.
Figure 25. Inverting Buck−Boost Regulator Shutdown
Circuit Using an Optocoupler
Figure 26. Inverting Buck−Boost Regulator Shutdown
Circuit Using a PNP Transistor
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 25 and 26.
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 27 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.
R4
Cout
470 mF
Feedback
+Vin
Cin
100 mF/
50 V
−12 V
Unregulated
DC Input
LM2594
ON/OFF
GND
D1
1N5822
R3
−12 V @ 0.25 A
Regulated
Output
L1
100 mH
Figure 27. Negative Boost Regulator
Design Recommendations:
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.
The same design rules as for the previous inverting
buck−boost converter can be applied. The output capacitor
Cout must be chosen larger than would be required for a what
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
http://onsemi.com
19
LM2594
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 28 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.
+Vin
+Vin
Cin
100 mF
R1
47 k
5
ON/OFF 6
+Vin
R2
10 k
Cin
100 mF 5
R3
47 k
ON/OFF 6
GN
D
Z1
1N5242B
Q1
2N3904
R1
10 k
Vth ≈ 13 V
NOTE: This picture does not show the complete circuit.
Figure 29. Undervoltage Lockout Circuit for
Buck Converter
The following formula is used to obtain the peak inductor
current:
I
(V ) |V |)
O ) V in x t on
[ Load in
peak
2L 1
V
in
|V |
O
where t on +
x 1.0 , and f osc + 52 kHz.
V ) |V | fosc
in
O
I
GN
D
Under normal continuous inductor current operating
conditions, the worst case occurs when Vin is minimal.
R2
47 k
+Vin
+Vin
LM2594
7
NOTE: This picture does not show the complete circuit.
R2
15 k
Figure 28. Delayed Startup Circuitry
Undervoltage Lockout
Cin
100 mF 5
R3
47 k
Z1
1N5242B
Some applications require the regulator to remain off until
the input voltage reaches a certain threshold level. Figure 29
shows an undervoltage lockout circuit applied to a buck
regulator. A version of this circuit for buck−boost converter
is shown in Figure 30. 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:
ǒ
LM2594
7
LM2594
7
C1
0.1 mF
+Vin
Q1
2N3904
ON/OFF 6
GN
D
Vth ≈ 13 V
R1
15 k
Vout
NOTE: This picture does not show the complete circuit.
Figure 30. Undervoltage Lockout Circuit for
Buck−Boost Converter
Ǔ
(Q1)
V [ V ) 1.0 ) R2 V
th
Z1
R1 BE
Adjustable Output, Low−Ripple Power Supply
A 0.5 A output current capability power supply that
features an adjustable output voltage is shown in Figure 31.
This regulator delivers 0.5 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.
http://onsemi.com
20
LM2594
40 V Max
Unregulated
DC Input
Feedback
4
+Vin
LM2594
7
Cin
100 mF
Output
6
GND
5
L1
100 mH
L2
3 mH
8
ON/OFF
CFF
Cout
220 mF
D1
1N5822
2 to 35 V @ 0.5 A
R2
50 k
R1
1.21 k
C1
100 mF
Optional Output
Ripple Filter
Figure 31. 2 to 35 V Adjustable 0.5 A Power Supply with Low Output Ripple
http://onsemi.com
21
Output
Voltage
LM2594
THE LM2594 STEP−DOWN VOLTAGE REGULATOR WITH 5.0 V @ 0.5 A OUTPUT POWER CAPABILITY.
TYPICAL APPLICATION WITH THROUGH−HOLE PC BOARD LAYOUT
4
Unregulated
DC Input
+Vin
+Vin = 10 V to 40 V
Feedback
LM2594
7
Output
6
GND
5
L1
100 mH
Regulated
Output Filtered
8
ON/OFF
C1
100 mF
/50 V
R2
3.0 k
D1
1N5819
ON/OFF
C2
220 mF
/25 V
−
−
−
−
−
−
100 mF, 50 V, Aluminium Electrolytic
220 mF, 25 V, Aluminium Electrolytic
1.0 A, 40 V, Schottky Rectifier, 1N5819
100 mH, DO3340P, Coilcraft
1.0 kW, 0.25 W
3.0 kW, 0.25 W
Vout2 = 5.0 V @ 0.5 A
R1
1.0 k
V
C1
C2
D1
L1
R1
R2
CFF
ǒ
Ǔ
R2
out + V ref ) 1.0 ) R1
Vref = 1.23 V
R1 is between 1.0 k and 5.0 k
Figure 32. Schematic Diagram of the 5.0 V @ 0.5 A Step−Down Converter Using the LM2594−ADJ
NOTE: Not to scale.
NOTE: Not to scale.
Figure 33. Printed Circuit Board Layout With
Component
Figure 34. Printed Circuit Board Layout
Copper Side
References
•
•
•
•
National Semiconductor LM2594 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
http://onsemi.com
22
LM2594
ORDERING INFORMATION
Device Marking
Package
Shipping†
LM2594DADJG
LM2594
SOIC-8
(Pb Free)
98 Units / Rail
LM2594DADJR2G
LM2594
SOIC-8
(Pb Free)
2500 / Tape & Reel
2594-ADJ
PDIP-8
(Pb Free)
50 Units / Rail
Device
LM2594PADJG
†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.
http://onsemi.com
23
MECHANICAL CASE OUTLINE
PACKAGE DIMENSIONS
PDIP−8
CASE 626−05
ISSUE P
DATE 22 APR 2015
SCALE 1:1
D
A
E
H
8
5
E1
1
4
NOTE 8
b2
c
B
END VIEW
TOP VIEW
WITH LEADS CONSTRAINED
NOTE 5
A2
A
e/2
NOTE 3
L
SEATING
PLANE
A1
C
D1
M
e
8X
SIDE VIEW
b
0.010
eB
END VIEW
M
C A
M
B
M
NOTES:
1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M, 1994.
2. CONTROLLING DIMENSION: INCHES.
3. DIMENSIONS A, A1 AND L ARE MEASURED WITH THE PACKAGE SEATED IN JEDEC SEATING PLANE GAUGE GS−3.
4. DIMENSIONS D, D1 AND E1 DO NOT INCLUDE MOLD FLASH
OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS ARE
NOT TO EXCEED 0.10 INCH.
5. DIMENSION E IS MEASURED AT A POINT 0.015 BELOW DATUM
PLANE H WITH THE LEADS CONSTRAINED PERPENDICULAR
TO DATUM C.
6. DIMENSION eB IS MEASURED AT THE LEAD TIPS WITH THE
LEADS UNCONSTRAINED.
7. DATUM PLANE H IS COINCIDENT WITH THE BOTTOM OF THE
LEADS, WHERE THE LEADS EXIT THE BODY.
8. PACKAGE CONTOUR IS OPTIONAL (ROUNDED OR SQUARE
CORNERS).
DIM
A
A1
A2
b
b2
C
D
D1
E
E1
e
eB
L
M
INCHES
MIN
MAX
−−−−
0.210
0.015
−−−−
0.115 0.195
0.014 0.022
0.060 TYP
0.008 0.014
0.355 0.400
0.005
−−−−
0.300 0.325
0.240 0.280
0.100 BSC
−−−−
0.430
0.115 0.150
−−−−
10 °
MILLIMETERS
MIN
MAX
−−−
5.33
0.38
−−−
2.92
4.95
0.35
0.56
1.52 TYP
0.20
0.36
9.02
10.16
0.13
−−−
7.62
8.26
6.10
7.11
2.54 BSC
−−−
10.92
2.92
3.81
−−−
10 °
NOTE 6
GENERIC
MARKING DIAGRAM*
STYLE 1:
PIN 1. AC IN
2. DC + IN
3. DC − IN
4. AC IN
5. GROUND
6. OUTPUT
7. AUXILIARY
8. VCC
XXXXXXXXX
AWL
YYWWG
XXXX
A
WL
YY
WW
G
= Specific Device Code
= Assembly Location
= Wafer Lot
= Year
= Work Week
= Pb−Free Package
*This information is generic. Please refer to
device data sheet for actual part marking.
Pb−Free indicator, “G” or microdot “ G”,
may or may not be present.
DOCUMENT NUMBER:
DESCRIPTION:
98ASB42420B
PDIP−8
Electronic versions are uncontrolled except when accessed directly from the Document Repository.
Printed versions are uncontrolled except when stamped “CONTROLLED COPY” in red.
PAGE 1 OF 1
ON Semiconductor and
are trademarks of Semiconductor Components Industries, LLC dba ON Semiconductor or its subsidiaries in the United States and/or other countries.
ON Semiconductor reserves the right to make changes without further notice to any products herein. ON Semiconductor makes no warranty, representation or guarantee regarding
the suitability of its products for any particular purpose, nor does ON Semiconductor assume any liability arising out of the application or use of any product or circuit, and specifically
disclaims any and all liability, including without limitation special, consequential or incidental damages. ON Semiconductor does not convey any license under its patent rights nor the
rights of others.
© Semiconductor Components Industries, LLC, 2019
www.onsemi.com
MECHANICAL CASE OUTLINE
PACKAGE DIMENSIONS
SOIC−8 NB
CASE 751−07
ISSUE AK
8
1
SCALE 1:1
−X−
DATE 16 FEB 2011
NOTES:
1. DIMENSIONING AND TOLERANCING PER
ANSI Y14.5M, 1982.
2. CONTROLLING DIMENSION: MILLIMETER.
3. DIMENSION A AND B DO NOT INCLUDE
MOLD PROTRUSION.
4. MAXIMUM MOLD PROTRUSION 0.15 (0.006)
PER SIDE.
5. DIMENSION D DOES NOT INCLUDE DAMBAR
PROTRUSION. ALLOWABLE DAMBAR
PROTRUSION SHALL BE 0.127 (0.005) TOTAL
IN EXCESS OF THE D DIMENSION AT
MAXIMUM MATERIAL CONDITION.
6. 751−01 THRU 751−06 ARE OBSOLETE. NEW
STANDARD IS 751−07.
A
8
5
S
B
0.25 (0.010)
M
Y
M
1
4
−Y−
K
G
C
N
X 45 _
SEATING
PLANE
−Z−
0.10 (0.004)
H
M
D
0.25 (0.010)
M
Z Y
S
X
J
S
8
8
1
1
IC
4.0
0.155
XXXXX
A
L
Y
W
G
IC
(Pb−Free)
= Specific Device Code
= Assembly Location
= Wafer Lot
= Year
= Work Week
= Pb−Free Package
XXXXXX
AYWW
1
1
Discrete
XXXXXX
AYWW
G
Discrete
(Pb−Free)
XXXXXX = Specific Device Code
A
= Assembly Location
Y
= Year
WW
= Work Week
G
= Pb−Free Package
*This information is generic. Please refer to
device data sheet for actual part marking.
Pb−Free indicator, “G” or microdot “G”, may
or may not be present. Some products may
not follow the Generic Marking.
1.270
0.050
SCALE 6:1
INCHES
MIN
MAX
0.189
0.197
0.150
0.157
0.053
0.069
0.013
0.020
0.050 BSC
0.004
0.010
0.007
0.010
0.016
0.050
0 _
8 _
0.010
0.020
0.228
0.244
8
8
XXXXX
ALYWX
G
XXXXX
ALYWX
1.52
0.060
0.6
0.024
MILLIMETERS
MIN
MAX
4.80
5.00
3.80
4.00
1.35
1.75
0.33
0.51
1.27 BSC
0.10
0.25
0.19
0.25
0.40
1.27
0_
8_
0.25
0.50
5.80
6.20
GENERIC
MARKING DIAGRAM*
SOLDERING FOOTPRINT*
7.0
0.275
DIM
A
B
C
D
G
H
J
K
M
N
S
mm Ǔ
ǒinches
*For additional information on our Pb−Free strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
STYLES ON PAGE 2
DOCUMENT NUMBER:
DESCRIPTION:
98ASB42564B
SOIC−8 NB
Electronic versions are uncontrolled except when accessed directly from the Document Repository.
Printed versions are uncontrolled except when stamped “CONTROLLED COPY” in red.
PAGE 1 OF 2
onsemi and
are trademarks of Semiconductor Components Industries, LLC dba onsemi or its subsidiaries in the United States and/or other countries. onsemi reserves
the right to make changes without further notice to any products herein. onsemi makes no warranty, representation or guarantee regarding the suitability of its products for any particular
purpose, nor does onsemi assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation
special, consequential or incidental damages. onsemi does not convey any license under its patent rights nor the rights of others.
© Semiconductor Components Industries, LLC, 2019
www.onsemi.com
SOIC−8 NB
CASE 751−07
ISSUE AK
DATE 16 FEB 2011
STYLE 1:
PIN 1. EMITTER
2. COLLECTOR
3. COLLECTOR
4. EMITTER
5. EMITTER
6. BASE
7. BASE
8. EMITTER
STYLE 2:
PIN 1. COLLECTOR, DIE, #1
2. COLLECTOR, #1
3. COLLECTOR, #2
4. COLLECTOR, #2
5. BASE, #2
6. EMITTER, #2
7. BASE, #1
8. EMITTER, #1
STYLE 3:
PIN 1. DRAIN, DIE #1
2. DRAIN, #1
3. DRAIN, #2
4. DRAIN, #2
5. GATE, #2
6. SOURCE, #2
7. GATE, #1
8. SOURCE, #1
STYLE 4:
PIN 1. ANODE
2. ANODE
3. ANODE
4. ANODE
5. ANODE
6. ANODE
7. ANODE
8. COMMON CATHODE
STYLE 5:
PIN 1. DRAIN
2. DRAIN
3. DRAIN
4. DRAIN
5. GATE
6. GATE
7. SOURCE
8. SOURCE
STYLE 6:
PIN 1. SOURCE
2. DRAIN
3. DRAIN
4. SOURCE
5. SOURCE
6. GATE
7. GATE
8. SOURCE
STYLE 7:
PIN 1. INPUT
2. EXTERNAL BYPASS
3. THIRD STAGE SOURCE
4. GROUND
5. DRAIN
6. GATE 3
7. SECOND STAGE Vd
8. FIRST STAGE Vd
STYLE 8:
PIN 1. COLLECTOR, DIE #1
2. BASE, #1
3. BASE, #2
4. COLLECTOR, #2
5. COLLECTOR, #2
6. EMITTER, #2
7. EMITTER, #1
8. COLLECTOR, #1
STYLE 9:
PIN 1. EMITTER, COMMON
2. COLLECTOR, DIE #1
3. COLLECTOR, DIE #2
4. EMITTER, COMMON
5. EMITTER, COMMON
6. BASE, DIE #2
7. BASE, DIE #1
8. EMITTER, COMMON
STYLE 10:
PIN 1. GROUND
2. BIAS 1
3. OUTPUT
4. GROUND
5. GROUND
6. BIAS 2
7. INPUT
8. GROUND
STYLE 11:
PIN 1. SOURCE 1
2. GATE 1
3. SOURCE 2
4. GATE 2
5. DRAIN 2
6. DRAIN 2
7. DRAIN 1
8. DRAIN 1
STYLE 12:
PIN 1. SOURCE
2. SOURCE
3. SOURCE
4. GATE
5. DRAIN
6. DRAIN
7. DRAIN
8. DRAIN
STYLE 13:
PIN 1. N.C.
2. SOURCE
3. SOURCE
4. GATE
5. DRAIN
6. DRAIN
7. DRAIN
8. DRAIN
STYLE 14:
PIN 1. N−SOURCE
2. N−GATE
3. P−SOURCE
4. P−GATE
5. P−DRAIN
6. P−DRAIN
7. N−DRAIN
8. N−DRAIN
STYLE 15:
PIN 1. ANODE 1
2. ANODE 1
3. ANODE 1
4. ANODE 1
5. CATHODE, COMMON
6. CATHODE, COMMON
7. CATHODE, COMMON
8. CATHODE, COMMON
STYLE 16:
PIN 1. EMITTER, DIE #1
2. BASE, DIE #1
3. EMITTER, DIE #2
4. BASE, DIE #2
5. COLLECTOR, DIE #2
6. COLLECTOR, DIE #2
7. COLLECTOR, DIE #1
8. COLLECTOR, DIE #1
STYLE 17:
PIN 1. VCC
2. V2OUT
3. V1OUT
4. TXE
5. RXE
6. VEE
7. GND
8. ACC
STYLE 18:
PIN 1. ANODE
2. ANODE
3. SOURCE
4. GATE
5. DRAIN
6. DRAIN
7. CATHODE
8. CATHODE
STYLE 19:
PIN 1. SOURCE 1
2. GATE 1
3. SOURCE 2
4. GATE 2
5. DRAIN 2
6. MIRROR 2
7. DRAIN 1
8. MIRROR 1
STYLE 20:
PIN 1. SOURCE (N)
2. GATE (N)
3. SOURCE (P)
4. GATE (P)
5. DRAIN
6. DRAIN
7. DRAIN
8. DRAIN
STYLE 21:
PIN 1. CATHODE 1
2. CATHODE 2
3. CATHODE 3
4. CATHODE 4
5. CATHODE 5
6. COMMON ANODE
7. COMMON ANODE
8. CATHODE 6
STYLE 22:
PIN 1. I/O LINE 1
2. COMMON CATHODE/VCC
3. COMMON CATHODE/VCC
4. I/O LINE 3
5. COMMON ANODE/GND
6. I/O LINE 4
7. I/O LINE 5
8. COMMON ANODE/GND
STYLE 23:
PIN 1. LINE 1 IN
2. COMMON ANODE/GND
3. COMMON ANODE/GND
4. LINE 2 IN
5. LINE 2 OUT
6. COMMON ANODE/GND
7. COMMON ANODE/GND
8. LINE 1 OUT
STYLE 24:
PIN 1. BASE
2. EMITTER
3. COLLECTOR/ANODE
4. COLLECTOR/ANODE
5. CATHODE
6. CATHODE
7. COLLECTOR/ANODE
8. COLLECTOR/ANODE
STYLE 25:
PIN 1. VIN
2. N/C
3. REXT
4. GND
5. IOUT
6. IOUT
7. IOUT
8. IOUT
STYLE 26:
PIN 1. GND
2. dv/dt
3. ENABLE
4. ILIMIT
5. SOURCE
6. SOURCE
7. SOURCE
8. VCC
STYLE 29:
PIN 1. BASE, DIE #1
2. EMITTER, #1
3. BASE, #2
4. EMITTER, #2
5. COLLECTOR, #2
6. COLLECTOR, #2
7. COLLECTOR, #1
8. COLLECTOR, #1
STYLE 30:
PIN 1. DRAIN 1
2. DRAIN 1
3. GATE 2
4. SOURCE 2
5. SOURCE 1/DRAIN 2
6. SOURCE 1/DRAIN 2
7. SOURCE 1/DRAIN 2
8. GATE 1
DOCUMENT NUMBER:
DESCRIPTION:
98ASB42564B
SOIC−8 NB
STYLE 27:
PIN 1. ILIMIT
2. OVLO
3. UVLO
4. INPUT+
5. SOURCE
6. SOURCE
7. SOURCE
8. DRAIN
STYLE 28:
PIN 1. SW_TO_GND
2. DASIC_OFF
3. DASIC_SW_DET
4. GND
5. V_MON
6. VBULK
7. VBULK
8. VIN
Electronic versions are uncontrolled except when accessed directly from the Document Repository.
Printed versions are uncontrolled except when stamped “CONTROLLED COPY” in red.
PAGE 2 OF 2
onsemi and
are trademarks of Semiconductor Components Industries, LLC dba onsemi or its subsidiaries in the United States and/or other countries. onsemi reserves
the right to make changes without further notice to any products herein. onsemi makes no warranty, representation or guarantee regarding the suitability of its products for any particular
purpose, nor does onsemi assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation
special, consequential or incidental damages. onsemi does not convey any license under its patent rights nor the rights of others.
© Semiconductor Components Industries, LLC, 2019
www.onsemi.com
onsemi,
, and other names, marks, and brands are registered and/or common law trademarks of Semiconductor Components Industries, LLC dba “onsemi” or its affiliates
and/or subsidiaries in the United States and/or other countries. onsemi owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property.
A listing of onsemi’s product/patent coverage may be accessed at www.onsemi.com/site/pdf/Patent−Marking.pdf. onsemi reserves the right to make changes at any time to any
products or information herein, without notice. The information herein is provided “as−is” and onsemi makes no warranty, representation or guarantee regarding the accuracy of the
information, product features, availability, functionality, or suitability of its products for any particular purpose, nor does onsemi assume any liability arising out of the application or use
of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. Buyer is responsible for its products
and applications using onsemi products, including compliance with all laws, regulations and safety requirements or standards, regardless of any support or applications information
provided by onsemi. “Typical” parameters which may be provided in onsemi data sheets and/or specifications can and do vary in different applications and actual performance may
vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. onsemi does not convey any license
under any of its intellectual property rights nor the rights of others. onsemi products are not designed, intended, or authorized for use as a critical component in life support systems
or any FDA Class 3 medical devices or medical devices with a same or similar classification in a foreign jurisdiction or any devices intended for implantation in the human body. Should
Buyer purchase or use onsemi products for any such unintended or unauthorized application, Buyer shall indemnify and hold onsemi and its officers, employees, subsidiaries, affiliates,
and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death
associated with such unintended or unauthorized use, even if such claim alleges that onsemi was negligent regarding the design or manufacture of the part. onsemi is an Equal
Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.
PUBLICATION ORDERING INFORMATION
LITERATURE FULFILLMENT:
Email Requests to: orderlit@onsemi.com
onsemi Website: www.onsemi.com
◊
TECHNICAL SUPPORT
North American Technical Support:
Voice Mail: 1 800−282−9855 Toll Free USA/Canada
Phone: 011 421 33 790 2910
Europe, Middle East and Africa Technical Support:
Phone: 00421 33 790 2910
For additional information, please contact your local Sales Representative
工商网监
湘ICP备2023018690号
