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LM2599T-3.3
Datasheet (NSC)
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Datasheet LM2599T-12, LM2599SX-ADJ, LM2599SX-5.0, LM2599SX-3.3, LM2599SX-12 Datasheet (NSC)

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Page 1
LM2599 SIMPLE SWITCHER
®
Power Converter 150 kHz 3A
Step-Down Voltage Regulator, with Features
General Description
The LM2599 series of regulators are monolithic integrated circuits that provide all the active functions for a step-down (buck) switching regulator, capable of driving a 3A load with excellent line and load regulation. These devices are avail­able in fixed output voltages of 3.3V, 5V, 12V, and an adjust­able output version.
This series of switching regulators is similar to the LM2596 series, with additionalsupervisory and performance features added.
†
, improved line and load specifications, fixed-frequency oscillator, Shutdown/Soft-start, error flag de­lay and error flag output.
The LM2599 series operates at a switching frequency of 150 kHz thus allowing smaller sized filter components than what would be needed with lower frequency switching regulators. Available in a standard 7-lead TO-220 package with several different lead bend options, and a 7-lead TO-263 Surface mount package.
A standard series of inductors (both through hole and sur­face mount types) are available from several different manu­facturers optimized for use with the LM2599 series. This fea­ture greatly simplifies the design of switch-mode power supplies.
Other features include a guaranteed
±
4%tolerance on out­put voltage under all conditions of input voltage and output load conditions, and
±
15%on the oscillator frequency. Ex-
ternal shutdown is included, featuring typically 80 µA
Features
n 3.3V, 5V, 12V, and adjustable output versions n Adjustable version output voltage range, 1.2V to 37V
±
4%max over line and load conditions
n Guaranteed 3A output current n Available in 7-pin TO-220 and TO-263 (surface mount)
Package
n Input voltage range up to 40V n 150 kHz fixed frequency internal oscillator n Shutdown/Soft-start n Out of regulation error flag n Error output delay n Low power standby mode, I
Q
typically 80 µA
n High Efficiency n Uses readily available standard inductors n Thermal shutdown and current limit protection
Applications
n Simple high-efficiency step-down (buck) regulator n Efficient pre-regulator for linear regulators n On-card switching regulators n Positive to Negative converter
Note:†Patent Number 5,382,918.
Typical Application (Fixed Output Voltage Versions)
SIMPLE SWITCHER®and
Switchers Made Simple
®
are registered trademarks of National Semiconductor Corporation.
DS012582-1
April 1998
LM2599 SIMPLE SWITCHER Power Converter 150 kHz 3A Step-Down Voltage Regulator, with
Features
© 2000 National Semiconductor Corporation DS012582 www.national.com
Page 2
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications.
Maximum Supply Voltage (V
IN
) 45V
SD /SS Pin Input Voltage (Note 2)
6V Delay Pin Voltage (Note 2) 1.5V Flag Pin Voltage −0.3 ≤ V ≤45V Feedback Pin Voltage −0.3 ≤ V ≤+25V Output Voltage to Ground
(Steady State) −1V Power Dissipation Internally limited Storage Temperature Range −65˚C to +150˚C
ESD Susceptibility
Human Body Model (Note 3) 2 kV
Lead Temperature
S Package
Vapor Phase (60 sec.) +215˚C Infrared (10 sec.) +245˚C
T Package (Soldering, 10 sec.) +260˚C
Maximum Junction Temperature +150˚C
Operating Conditions
Temperature Range −40˚C ≤ TJ≤ +125˚C Supply Voltage 4.5V to 40V
LM2599-3.3 Electrical Characteristics
Specifications with standard type face are for T
J
=
25˚C, and those with boldface type apply over full Operating Tempera-
ture Range.
Symbol Parameter Conditions LM2599-3.3 Units
(Limits)
Typ Limit
(Note 4) (Note 5)
SYSTEM PARAMETERS (Note 6) Test Circuit
Figure 1
V
OUT
Output Voltage 4.75V ≤ VIN≤ 40V, 0.2A ≤ I
LOAD
≤ 3A 3.3 V
3.168/3.135 V(min)
3.432/3.465 V(max)
η Efficiency V
IN
=
12V, I
LOAD
=
3A 73
%
LM2599-5.0 Electrical Characteristics
Specifications with standard type face are for T
J
=
25˚C, and those with boldface type apply over full Operating Tempera-
ture Range.
Symbol Parameter Conditions LM2599-5.0 Units
(Limits)
Typ Limit
(Note 4) (Note 5)
SYSTEM PARAMETERS (Note 6) Test Circuit
Figure 1
V
OUT
Output Voltage 7V ≤ VIN≤ 40V, 0.2A ≤ I
LOAD
≤ 3A 5 V
4.800/4.750 V(min)
5.200/5.250 V(max)
η Efficiency V
IN
=
12V, I
LOAD
=
3A 80
%
LM2599
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Page 3
LM2599-12 Electrical Characteristics
Specifications with standard type face are for T
J
=
25˚C, and those with boldface type apply over full Operating Tempera-
ture Range.
Symbol Parameter Conditions LM2599-12 Units
(Limits)
Typ Limit
(Note 4) (Note 5)
SYSTEM PARAMETERS (Note 6) Test Circuit
Figure 1
V
OUT
Output Voltage 15V ≤ VIN≤ 40V, 0.2A ≤ I
LOAD
≤ 3A 12 V
11.52/11.40 V(min)
12.48/12.60 V(max)
η Efficiency V
IN
=
25V, I
LOAD
=
3A 90
%
LM2599-ADJ Electrical Characteristics
Specifications with standard type face are for T
J
=
25˚C, and those with boldface type apply over full Operating Temperature
Range.
Symbol Parameter Conditions LM2599-ADJ Units
(Limits)
Typ Limit
(Note 4) (Note 5)
SYSTEM PARAMETERS (Note 6) Test Circuit
Figure 1
V
FB
Feedback Voltage 4.5V ≤ VIN≤ 40V, 0.2A ≤ I
LOAD
≤ 3A 1.230 V
V
OUT
programmed for 3V. Circuit of
Figure 1
. 1.193/1.180 V(min)
1.267/1.280 V(max)
η Efficiency V
IN
=
12V, V
OUT
=
3V, I
LOAD
=
3A 73
%
All Output Voltage Versions Electrical Characteristics
Specifications with standard type face are for T
J
=
25˚C, and those with boldface type apply over full Operating Tempera-
ture Range. Unless otherwise specified, V
IN
=
12V for the 3.3V, 5V, and Adjustable version and V
IN
=
24V for the 12V ver-
sion. I
LOAD
=
500 mA
Symbol Parameter Conditions LM2599-XX Units
(Limits)
Typ Limit
(Note4)(Note 5)
DEVICE PARAMETERS
I
b
Feedback Bias Current Adjustable Version Only, V
FB
=
1.3V 10 nA 50/100 nA (max)
f
O
Oscillator Frequency (Note 7) 150 kHz
127/110 kHz(min) 173/173 kHz(max)
V
SAT
Saturation Voltage I
OUT
=
3A (Note 8) (Note 9) 1.16 V
1.4/1.5 V(max)
DC Max Duty Cycle (ON) (Note 9) 100
%
Min Duty Cycle (OFF) (Note 10) 0
I
CL
Current Limit Peak Current, (Note 8) (Note 9) 4.5 A
3.6/3.4 A(min)
6.9/7.5 A(max)
I
L
Output Leakage Current (Note 8) (Note 10) (Note 11) Output=0V 50 µA(max)
Output=−1V 2 mA
30 mA(max)
I
Q
Operating Quiescent SD /SS Pin Open (Note 10) 5mA Current 10 mA(max)
LM2599
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Page 4
All Output Voltage Versions Electrical Characteristics
(Continued)
Specifications with standard type face are for T
J
=
25˚C, and those with boldface type apply over full Operating Tempera-
ture Range. Unless otherwise specified, V
IN
=
12V for the 3.3V, 5V, and Adjustable version and V
IN
=
24V for the 12V ver-
sion. I
LOAD
=
500 mA
Symbol Parameter Conditions LM2599-XX Units
(Limits)
Typ Limit
(Note4)(Note 5)
DEVICE PARAMETERS
I
STBY
Standby Quiescent SD /SS pin=0V (Note 11) 80 µA Current 200/250 µA(max)
θ
JC
Thermal Resistance TO220 or TO263 Package, Junction to Case 2 ˚C/W
θ
JA
TO220 Package, Juncton to Ambient (Note 12) 50 ˚C/W
θ
JA
TO263 Package, Juncton to Ambient (Note 13) 50 ˚C/W
θ
JA
TO263 Package, Juncton to Ambient (Note 14) 30 ˚C/W
θ
JA
TO263 Package, Juncton to Ambient (Note 15) 20 ˚C/W
SHUTDOWN/SOFT-START CONTROL Test Circuit of
Figure 1
V
SD
Shutdown Threshold 1.3 V Voltage Low, (Shutdown Mode) 0.6 V(max)
High, (Soft-start Mode) 2 V(min)
V
SS
Soft-start Voltage V
OUT
=
20%of Nominal Output Voltage 2 V
V
OUT
=
100%of Nominal Output Voltage 3
I
SD
Shutdown Current V
SHUTDOWN
=
0.5V
5µA
10 µA(max)
I
SS
Soft-start Current V
Soft-start
=
2.5V 1.6 µA 5 µA(max)
FLAG/DELAY CONTROL Test Circuit of
Figure 1
Regulator Dropout Detector Low (Flag ON) 96
%
Threshold Voltage 92
%
(min)
98
%
(max)
VF
SAT
Flag Output Saturation I
SINK
=
3 mA 0.3 V
Voltage V
DELAY
=
0.5V 0.7/1.0 V(max)
IF
L
Flag Output Leakage Current V
FLAG
=
40V 0.3 µA Delay Pin Threshold 1.25 V Voltage Low (Flag ON) 1.21 V(min)
High (Flag OFF) and V
OUT
Regulated 1.29 V(max)
Delay Pin Source Current V
DELAY
=
0.5V 3 µA 6 µA(max)
Delay Pin Saturation Low (Flag ON) 55 mV
350/400 mV(max)
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is in­tended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: Voltage internally clamped. If clamp voltage is exceeded, limit current to a maximum of 1 mA. Note 3: The human body model is a 100 pF capacitor discharged through a 1.5k resistor into each pin. Note 4: Typical numbers are at 25˚C and represent the most likely norm. Note 5: All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100%pro-
duction tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to cal­culate Average Outgoing Quality Level (AOQL).
Note 6: External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. When the LM2599 is used as shown in the
Figure 1
test circuit, system performance will be as shown in system parameters section of Electrical Characteristics.
Note 7: The switching frequency is reduced when the second stage current limit is activated. The amount of reduction is determined by the severity of current over­load.
Note 8: No diode, inductor or capacitor connected to output pin. Note 9: Feedback pin removed from output and connected to 0V to force the output transistor switch ON.
LM2599
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Page 5
All Output Voltage Versions Electrical Characteristics
(Continued)
Note 10: Feedback pin removed from output and connected to 12V for the 3.3V, 5V, and the ADJ. version, and 15V for the 12V version, to force the output transistor switch OFF.
Note 11: V
IN
=
40V.
Note 12: Junction to ambient thermal resistance (no external heat sink) for the package mounted TO-220 package mounted vertically, with the leads soldered to a printed circuit board with (1 oz.) copper area of approximately 1 in
2
.
Note 13: Junction to ambient thermal resistance with the TO-263 package tab soldered to a single sided printed circuit board with 0.5 in
2
of (1 oz.) copper area.
Note 14: Junction to ambient thermal resistance with the TO-263 package tab soldered to a single sided printed circuit board with 2.5 in
2
of (1 oz.) copper area.
Note 15: Junction to ambient thermal resistance with the TO-263 package tab soldered to a double sided printed circuit board with 3 in
2
of (1 oz.) copper area on
the LM2599S side of the board, and approximately 16 in
2
of copper on the other side of the p-c board. See application hints in this data sheet and the thermal model
in Switchers Made Simple version 4.2.1 (or later) software.
Typical Performance Characteristics (Circuit of
Figure 1
)
Normalized Output Voltage
DS012582-2
Line Regulation
DS012582-3
Efficiency
DS012582-4
Switch Saturation Voltage
DS012582-5
Switch Current Limit
DS012582-6
Dropout Voltage
DS012582-7
Operating Quiescent Current
DS012582-8
Shutdown Quiescent Current
DS012582-9
Minimum Operating Supply Voltage
DS012582-10
LM2599
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Page 6
Typical Performance Characteristics (Circuit of
Figure 1
) (Continued)
Feedback Pin Bias Current
DS012582-11
Flag Saturation Voltage
DS012582-12
Switching Frequency
DS012582-13
Soft-start
DS012582-14
Shutdown /Soft-start Current
DS012582-15
Daisy Pin Current
DS012582-16
Soft-start Response
DS012582-18
Shutdown/Soft-start Threshold Voltage
DS012582-53
LM2599
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Page 7
Typical Performance Characteristics (Circuit of
Figure 1
) (Continued)
Connection Diagrams and Order Information
Continuous Mode Switching Waveforms V
IN
=
20V, V
OUT
=
5V, I
LOAD
=
2A
L=32 µH, C
OUT
=
220 µF, C
OUT
ESR=50 mΩ
DS012582-20
A: Output Pin Voltage, 10V/div. B: Inductor Current 1A/div. C: Output Ripple Voltage, 50 mV/div.
Horizontal Time Base: 2 µs/div.
Discontinuous Mode Switching Waveforms V
IN
=
20V, V
OUT
=
5V, I
LOAD
=
500 mA
L=10 µH, C
OUT
=
330 µF, C
OUT
ESR=45 mΩ
DS012582-19
A: Output Pin Voltage, 10V/div. B: Inductor Current 0.5A/div. C: Output Ripple Voltage, 100 mV/div.
Horizontal Time Base: 2 µs/div.
Load Transient Response for Continuous Mode V
IN
=
20V, V
OUT
=
5V, I
LOAD
=
500 mA to 2A
L=32 µH, C
OUT
=
220 µF, C
OUT
ESR=50 mΩ
DS012582-21
A: Output Voltage, 100 mV/div. (AC) B: 500 mA to 2A Load Pulse
Horizontal Time Base: 50 µs/div.
Load Transient Response for Discontinuous Mode V
IN
=
20V, V
OUT
=
5V, I
LOAD
=
500 mA to 2A
L=10 µH, C
OUT
=
330 µF, C
OUT
ESR=45 mΩ
DS012582-22
A: Output Voltage, 100 mV/div. (AC) B: 500 mA to 2A Load Pulse
Horizontal Time Base: 200 µs/div.
Bent and Staggered Leads, Through Hole Package
7-Lead TO-220 (T)
DS012582-50
Order Number LM2599T-3.3, LM2599T-5.0,
LM2599T-12 or LM2599T-ADJ
See NS Package Number TA07B
Surface Mount Package
7-Lead TO-263 (S)
DS012582-23
Order Number LM2599S-3.3, LM2599S-5.0,
LM2599S-12 or LM2599S-ADJ
See NS Package Number TS7B
LM2599
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Page 8
Test Circuit and Layout Guidelines
Fixed Output Voltage Versions
DS012582-24
Component Values shown are for V
IN
=
15V,
V
OUT
=
5V, I
LOAD
=
3A.
C
IN
— 470 µF, 50V,Aluminum Electrolytic Nichicon “PL Series”
C
OUT
— 220 µF, 25V Aluminum Electrolytic, Nichicon “PL Series” D1 — 5A, 40V Schottky Rectifier, 1N5825 L1 — 68 µH, L38
Typical Values
CSS— 0.1 µF C
DELAY
— 0.1 µF
R
Pull Up
— 4.7k
LM2599
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Page 9
Test Circuit and Layout Guidelines (Continued)
As in any switching regulator, layout is very important. Rap­idly switching currents associated with wiring inductance can generate voltage transients which can cause problems. For minimal inductance and ground loops, the wires indicated by
heavy lines should be wide printed circuit traces and should be kept as short as possible. For best results, ex-
ternal components should be located as close to the switcher lC as possible using ground plane construction or single point grounding.
If open core inductors are used, special care must be taken as to the location and positioning of this type of induc­tor.Allowing the inductor flux to intersect sensitive feedback, lC groundpath and C
OUT
wiring can cause problems.
When using the adjustable version, special care must be taken as to the location of the feedback resistors and the as­sociated wiring. Physically locate both resistors near the IC, and route the wiring away from the inductor, especially an open core type of inductor. (See application section for more information.)
Adjustable Output Voltage Versions
DS012582-25
where V
REF
=
1.23V
Select R1to be approximately 1 kΩ,usea1%resistor for best stability. Component Values shown are for V
IN
=
20V,
V
OUT
=
10V, I
LOAD
=
3A.
C
IN
: — 470 µF, 35V,Aluminum Electrolytic Nichicon “PL Series”
C
OUT
: — 220 µF, 35V Aluminum Electrolytic, Nichicon “PL Series” D1 — 5A, 30V Schottky Rectifier, 1N5824 L1 — 68 µH, L38 R
1
—1kΩ,1
%
R
2
— 7.15k, 1
%
C
FF
— 3.3 nF, See Application Information Section
R
FF
—3kΩ, See Application Information Section
Typical Values
CSS— 0.1 µF C
DELAY
— 0.1 µF
R
PULL UP
— 4.7k
FIGURE 1. Standard Test Circuits and Layout Guides
LM2599
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Page 10
LM2599 Series Buck Regulator Design Procedure (Fixed Output)
PROCEDURE (Fixed Output Voltage Version) EXAMPLE (Fixed Output Voltage Version)
Given:
V
OUT
=
Regulated Output Voltage (3.3V, 5V or 12V)
V
IN
(max)=Maximum DC Input Voltage
I
LOAD
(max)=Maximum Load Current
Given:
V
OUT
=
5V
V
IN
(max)=12V
I
LOAD
(max)=3A
1. Inductor Selection (L1) A. Select the correct inductor value selection guide from
Fig-
ure 4
,
Figure 5
,or6.(Output voltages of 3.3V, 5V, or 12V re­spectively.) For all other voltages, see the design procedure for the adjustable version.
B. From the inductor value selection guide, identify the induc­tance region intersected by the Maximum Input Voltage line and the Maximum Load Current line. Each region is identified by an inductance value and an inductor code (LXX).
C. Select an appropriate inductor from the four manufactur­er’s part numbers listed in
Figure 8
.
1. Inductor Selection (L1) A. Use the inductor selection guide for the 5V version shown
in
Figure 5
.
B. From the inductor value selection guide shown in
Figure 5
, the inductance region intersected by the 12V horizontal line and the 3A vertical line is 33 µH, and the inductor code is L40.
C. The inductance value required is 33 µH. From the table in
Figure 8
, go to the L40 line and choose an inductor part num­ber from any of the four manufacturers shown. (In most in­stance, both through hole and surface mount inductors are available.)
2. Output Capacitor Selection (C
OUT
)
A. In the majority of applications, low ESR (Equivalent Series
Resistance) electrolytic capacitors between 82 µF and 820 µF and low ESR solid tantalum capacitors between 10 µF and 470 µF provide the best results. This capacitor should be located close to the IC using short capacitor leads and short copper traces. Do not use capacitors larger than 820 µF.
For additional information, see section on output capaci­tors in application information section.
B. To simplify the capacitor selection procedure, refer to the
quick design component selection table shown in
Figure 2
. This table contains different input voltages, output voltages, and load currents, and lists various inductors and output ca­pacitors that will provide the best design solutions.
C. The capacitor voltage rating for electrolytic capacitors should be at least 1.5 times greater than the output voltage, and often much higher voltage ratings are needed to satisfy the low ESR requirements for low output ripple voltage.
D. For computer aided design software, see
Switchers
Made Simple
(version 4.2.1 or later).
2. Output Capacitor Selection (C
OUT
)
A. See section on output capacitors in application infor­mation section.
B. From the quick design component selection table shown
in
Figure 2
, locate the 5V output voltage section. In the load current column, choose the load current line that is closest to the current needed in your application, for this example, use the 3A line. In the maximum input voltage column, select the line that covers the input voltage needed in your application, in this example, use the 15V line. Continuing on this line are recommended inductors and capacitors that will provide the best overall performance.
The capacitor list contains both through hole electrolytic and surface mount tantalum capacitors from four different capaci­tor manufacturers. It is recommended that both the manufac­turers and the manufacturer’s series that are listed in the table be used.
In this example aluminum electrolytic capacitors from several different manufacturers are available with the range of ESR numbers needed.
330 µF 35V Panasonic HFQ Series 330 µF 35V Nichicon PL Series
C. For a 5V output, a capacitor voltage rating at least 7.5V or more is needed. But even a low ESR, switching grade, 220 µF 10V aluminum electrolytic capacitor would exhibit ap­proximately 225 mΩ of ESR (see the curve in
Figure 16
for the ESR vs voltage rating). This amount of ESR would result in relatively high output ripple voltage. To reduce the ripple to 1%of the output voltage, or less, a capacitor with a higher value or with a higher voltage rating (lower ESR) should be selected. A 16V or 25V capacitor will reduce the ripple volt­age by approximately half.
LM2599
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Page 11
LM2599 Series Buck Regulator Design Procedure (Fixed Output) (Continued)
PROCEDURE (Fixed Output Voltage Version) EXAMPLE (Fixed Output Voltage Version)
3. Catch Diode Selection (D1) A. The catch diode current rating must be at least 1.3 times
greater than the maximum load current. Also, if the power supply design must withstand a continuous output short, the diode should have a current rating equal to the maximum current limit of the LM2599. The most stressful condition for this diode is an overload or shorted output condition.
B. The reverse voltage rating of the diode should be at least
1.25 times the maximum input voltage. C. This diode must be fast (short reverse recovery time) and
must be located close to the LM2599 using short leads and short printed circuit traces. Because of their fast switching speed and low forward voltage drop, Schottky diodes provide the best performance and efficiency, and should be the first choice, especially in low output voltage applications. Ultra-fast recovery, or High-Efficiency rectifiers also provide good results. Ultra-fast recovery diodes typically have re­verse recovery times of 50 ns or less. Rectifiers such as the IN5400 series are much too slow and should not be used.
3. Catch Diode Selection (D1) A. Refer to the table shown in
Figure 11
. In this example, a 5A, 20V, 1N5823 Schottky diode will provide the best perfor­mance, and will not be overstressed even for a shorted out­put.
4. Input Capacitor (C
IN
)
Alow ESR aluminum or tantalum bypass capacitor is needed between the input pin and ground to prevent large voltage transients from appearing at the input. In addition, the RMS current rating of the input capacitor should be selected to be at least
1
⁄2the DC load current. The capacitor manufacturers data sheet must be checked to assure that this current rating is not exceeded. The curve shown in
Figure 15
shows typical RMS current ratings for several different aluminum electro­lytic capacitor values.
This capacitor should be located close to the IC using short leads and the voltage rating should be approximately 1.5 times the maximum input voltage.
If solid tantalum input capacitors are used, it is recomended that they be surge current tested by the manufacturer.
Use caution when using ceramic capacitors for input bypass­ing, because it may cause severe ringing at the V
IN
pin.
For additional information, see section on input capaci­tors in Application Information section.
4. Input Capacitor (C
IN
)
The important parameters for the Input capacitor are the in­put voltage rating and the RMS current rating. With a nominal input voltage of 12V, an aluminum electrolytic capacitor with a voltage rating greater than 18V (1.5 x V
IN
) would be
needed. The next higher capacitor voltage rating is 25V. The RMS current rating requirement for the input capacitor in
a buck regulator is approximately
1
⁄2the DC load current. In this example, with a 3A load, a capacitor with a RMS current rating of at least 1.5Ais needed. The curves shown in
Figure
15
can be used to select an appropriate input capacitor. From the curves, locate the 35V line and note which capaci­tor values have RMS current ratings greater than 1.5A. A 680 µF, 35V capacitor could be used.
For a through hole design, a 680 µF/35V electrolytic capaci­tor (Panasonic HFQ series or Nichicon PL series or equiva­lent) would be adequate. other types or other manufacturers capacitors can be used provided the RMS ripple current rat­ings are adequate.
For surface mount designs, solid tantalum capacitors are recommended. The TPS series available from AVX, and the 593D series from Sprague are both surge current tested.
LM2599
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Page 12
LM2599 Series Buck Regulator Design Procedure (Fixed Output) (Continued)
LM2599 Series Buck Regulator Design Procedure (Adjustable Output)
PROCEDURE (Adjustable Output Voltage Version) EXAMPLE (Adjustable Output Voltage Version)
Given:
V
OUT
=
Regulated Output Voltage
V
IN
(max)=Maximum Input Voltage
I
LOAD
(max)=Maximum Load Current
F=Switching Frequency
(Fixed at a nominal 150 kHz).
Given:
V
OUT
=
20V
V
IN
(max)=28V
I
LOAD
(max)=3A
F=Switching Frequency
(Fixed at a nominal 150 kHz).
1. Programming Output Voltage (Selecting R1and R2,as shown in
Figure 1
)
Use the following formula to select the appropriate resistor values.
Select a value for R1between 240Ω and 1.5 kΩ. The lower resistor values minimize noise pickup in the sensitive feed­back pin. (For the lowest temperature coefficient and the best stability with time, use 1%metal film resistors.)
1. Programming Output Voltage (Selecting R1and R2,as shown in
Figure 1
)
Select R
1
to be 1 kΩ,1%. Solve for R2.
R
2
=
1k (16.26 − 1)=15.26k, closest 1%value is 15.4 kΩ.
R
2
=
15.4 kΩ.
Conditions Inductor Output Capacitor
Through Hole Electrolytic Surface Mount Tantalum
Output Load Max Input Inductance Inductor Panasonic Nichicon AVX TPS Sprague
Voltage Current Voltage (µH) (
#
) HFQ Series PL Series Series 595D Series
(V) (A) (V) (µF/V) (µF/V) (µF/V) (µF/V)
3.3
3
5 22 L41 470/25 560/16 330/6.3 390/6.3
7 22 L41 560/35 560/35 330/6.3 390/6.3 10 22 L41 680/35 680/35 330/6.3 390/6.3 40 33 L40 560/35 470/35 330/6.3 390/6.3
6 22 L33 470/25 470/35 330/6.3 390/6.3
2 10 33 L32 330/35 330/35 330/6.3 390/6.3
40 47 L39 330/35 270/50 220/10 330/10
5
3
8 22 L41 470/25 560/16 220/10 330/10 10 22 L41 560/25 560/25 220/10 330/10 15 33 L40 330/35 330/35 220/10 330/10 40 47 L39 330/35 270/35 220/10 330/10
9 22 L33 470/25 560/16 220/10 330/10
2 20 68 L38 180/35 180/35 100/10 270/10
40 68 L38 180/35 180/35 100/10 270/10
12
3
15 22 L41 470/25 470/25 100/16 180/16 18 33 L40 330/25 330/25 100/16 180/16 30 68 L44 180/25 180/25 100/16 120/20 40 68 L44 180/35 180/35 100/16 120/20 15 33 L32 330/25 330/25 100/16 180/16
2 20 68 L38 180/25 180/25 100/16 120/20
40 150 L42 82/25 82/25 68/20 68/25
FIGURE 2. LM2599 Fixed Voltage Quick Design Component Selection Table
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LM2599 Series Buck Regulator Design Procedure (Adjustable Output)
(Continued)
PROCEDURE (Adjustable Output Voltage Version) EXAMPLE (Adjustable Output Voltage Version)
2. Inductor Selection (L1) A. Calculate the inductor Volt
•
microsecond constant E•T
(V
•
µs), from the following formula:
where V
SAT
=
internal switch saturation voltage=1.16V and
V
D
=
diode forward voltage drop=0.5V
B. Use the E
•
T value from the previous formula and match
it with the E
•
T number on the vertical axis of the Inductor
Value Selection Guide shown in
Figure 7
.
C. on the horizontal axis, select the maximum load current. D. Identify the inductance region intersected by the E
•
T value and the Maximum Load Current value. Each region is identified by an inductance value and an inductor code (LXX).
E. Select an appropriate inductor from the four manufactur­er’s part numbers listed in
Figure 8
.
2. Inductor Selection (L1) A. Calculate the inductor Volt
•
microsecond constant (E
•
T),
B. E•T=34.2 (V•µs) C. I
LOAD
(max)=3A
D. From the inductor value selection guide shown in
Figure 7
,
the inductance region intersected by the 34 (V
•
µs) horizon­tal line and the 3A vertical line is 47 µH, and the inductor code is L39.
E. From the table in
Figure 8
, locate line L39, and select an inductor part number from the list of manufacturers part num­bers.
3. Output Capacitor Selection (C
OUT
)
A. In the majority of applications, low ESR electrolytic or solid
tantalum capacitors between 82 µF and 820 µF provide the best results. This capacitor should be located close to the IC using short capacitor leads and short copper traces. Do not use capacitors larger than 820 µF. For additional informa-
tion, see section on output capacitors in application in­formation section.
B. To simplify the capacitor selection procedure, refer to the
quick design table shown in
Figure 3
. This table contains dif­ferent output voltages, and lists various output capacitors that will provide the best design solutions.
C. The capacitor voltage rating should be at least 1.5 times greater than the output voltage, and often much higher volt­age ratings are needed to satisfy the low ESR requirements needed for low output ripple voltage.
3. Output Capacitor SeIection (C
OUT
)
A. See section on C
OUT
in Application Information section.
B. From the quick design table shown in
Figure 3
, locate the output voltage column. From that column, locate the output voltage closest to the output voltage in your application. In this example, select the 24V line. Under the output capacitor section, select a capacitor from the list of through hole elec­trolytic or surface mount tantalum types from four different capacitor manufacturers. It is recommended that both the manufacturers and the manufacturers series that are listed in the table be used.
In this example, through hole aluminum electrolytic capaci­tors from several different manufacturers are available.
220/35 Panasonic HFQ Series 150/35 Nichicon PL Series
C. For a 20V output, a capacitor rating of at least 30V or more is needed. In this example, either a 35V or 50V capaci­tor would work. A 50V rating was chosen because it has a lower ESR which provides a lower output ripple voltage.
Other manufacturers or other types of capacitors may also be used, provided the capacitor specifications (especially the 100 kHz ESR) closely match the types listed in the table. Re­fer to the capacitor manufacturers data sheet for this informa­tion.
4. Feedforward Capacitor (C
FF
) (See
Figure 1
)
For output voltages greater than approximately 10V, an addi­tional capacitor is required. The compensation capacitor is typically between 100 pF and 33 nF, and is wired in parallel with the output voltage setting resistor, R
2
. It provides addi­tional stability for high output voltages, low input-output volt­ages, and/or very low ESR output capacitors, such as solid tantalum capacitors.
This capacitor type can be ceramic, plastic, silver mica, etc. (Because of the unstable characteristics of ceramic capaci­tors made with Z5U material, they are not recommended.)
4. Feedforward Capacitor (C
FF
)
The table shown in
Figure 3
contains feed forward capacitor values for various output voltages. In this example, a 560 pF capacitor is needed.
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LM2599 Series Buck Regulator Design Procedure (Adjustable Output)
(Continued)
PROCEDURE (Adjustable Output Voltage Version) EXAMPLE (Adjustable Output Voltage Version)
5. Catch Diode Selection (D1) A. The catch diode current rating must be at least 1.3 times
greater than the maximum load current. Also, if the power supply design must withstand a continuous output short, the diode should have a current rating equal to the maximum current limit of the LM2599. The most stressful condition for this diode is an overload or shorted output condition.
B. The reverse voltage rating of the diode should be at least
1.25 times the maximum input voltage. C. This diode must be fast (short reverse recovery time) and
must be located close to the LM2599 using short leads and short printed circuit traces. Because of their fast switching speed and low forward voltage drop, Schottky diodes provide the best performance and efficiency, and should be the first choice, especially in low output voltage applications. Ultra-fast recovery, or High-Efficiency rectifiers are also a good choice, but some types with an abrupt turn-off charac­teristic may cause instability or EMl problems. Ultra-fast re­covery diodes typically have reverse recovery times of 50 ns or less. Rectifiers such as the 1N4001 series are much too slow and should not be used.
5. Catch Diode Selection (D1) A. Refer to the table shown in
Figure 11
. Schottky diodes provide the best performance, and in this example a 3A, 40V, 1N5825 Schottky diode would be a good choice. The 3A di­ode rating is more than adequate and will not be over­stressed even for a shorted output.
6. Input Capacitor (C
IN
)
Alow ESR aluminum or tantalum bypass capacitor is needed between the input pin and ground to prevent large voltage transients from appearing at the input. In addition, the RMS current rating of the input capacitor should be selected to be at least
1
⁄2the DC load current. The capacitor manufacturers data sheet must be checked to assure that this current rating is not exceeded. The curve shown in
Figure 15
shows typical RMS current ratings for several different aluminum electro­lytic capacitor values.
This capacitor should be located close to the IC using short leads and the voltage rating should be approximately 1.5 times the maximum input voltage.
If solid tantalum input capacitors are used, it is recomended that they be surge current tested by the manufacturer.
Use caution when using a high dielectric constant ceramic capacitor for input bypassing, because it may cause severe ringing at the V
IN
pin.
For additional information, see section on input capaci­tor in application information section.
6. Input Capacitor (C
IN
)
The important parameters for the Input capacitor are the in­put voltage rating and the RMS current rating. With a nominal input voltage of 28V, an aluminum electrolytic aluminum elec­trolytic capacitor with a voltage rating greater than 42V (1.5 x V
IN
) would be needed. Since the the next higher capacitor voltage rating is 50V, a 50V capacitor should be used. The capacitor voltage rating of (1.5 x V
IN
) is a conservative guide-
line, and can be modified somewhat if desired. The RMS current rating requirement for the input capacitor of
a buck regulator is approximately
1
⁄2the DC load current. In this example, with a 3A load, a capacitor with a RMS current rating of at least 1.5A is needed.
The curves shown in
Figure 15
can be used to select an ap­propriate input capacitor. From the curves, locate the 50V line and note which capacitor values have RMS current rat­ings greater than 1.5A. Either a 470 µF or 680 µF, 50V ca­pacitor could be used.
For a through hole design, a 680 µF/50V electrolytic capaci­tor (Panasonic HFQ series or Nichicon PL series or equiva­lent) would be adequate. Other types or other manufacturers capacitors can be used provided the RMS ripple current rat­ings are adequate.
For surface mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to the ca­pacitor sure current rating (see Application Information or in­put capacitors in this data sheet). The TPS series available from AVX, and the 593D series from Sprague are both surge current tested.
To further simplify the buck regulator design procedure, Na­tional Semiconductor is making available computer design software to be used with the Simple Switcher line ot switch­ing regulators. Switchers Made Simple (version 4.2.1 or later) is available on a 3
1
⁄2" diskette for IBM compatible
computers.
LM2599
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LM2599 Series Buck Regulator Design Procedure (Adjustable Output)
(Continued)
LM2599 Series Buck Regulator Design Procedure
INDUCTOR VALUE SELECTION GUIDES (For Continuous Mode Operation)
Output
Voltage
(V)
Through Hole Output Capacitor Surface Mount Output Capacitor
Panasonic Nichicon PL Feedforward AVX TPS Sprague Feedforward
HFQ Series Series Capacitor Series 595D Series Capacitor
(µF/V) (µF/V) (µF/V) (µF/V)
2 820/35 820/35 33 nF 330/6.3 470/4 33 nF 4 560/35 470/35 10 nF 330/6.3 390/6.3 10 nF 6 470/25 470/25 3.3 nF 220/10 330/10 3.3 nF
9 330/25 330/25 1.5 nF 100/16 180/16 1.5 nF 12 330/25 330/25 1 nF 100/16 180/16 1 nF 15 220/35 220/35 680 pF 68/20 120/20 680 pF 24 220/35 150/35 560 pF 33/25 33/25 220 pF 28 100/50 100/50 390 pF 10/35 15/50 220 pF
FIGURE 3. Output Capacitor and Feedforward Capacitor Selection Table
DS012582-26
FIGURE 4. LM2599-3.3
DS012582-27
FIGURE 5. LM2599-5.0
DS012582-28
FIGURE 6. LM2599-12
DS012582-29
FIGURE 7. LM2599-ADJ
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LM2599 Series Buck Regulator Design Procedure (Continued)
Inductance
(µH)
Current
(A)
Schott Renco Pulse Engineering Coilcraft
Through Surface Through Surface Through Surface Surface
Hole Mount Hole Mount Hole Mount Mount
L15 22 0.99 67148350 67148460 RL-1284-22-43 RL1500-22 PE-53815 PE-53815-S DO3308-223 L21 68 0.99 67144070 67144450 RL-5471-5 RL1500-68 PE-53821 PE-53821-S DO3316-683 L22 47 1.17 67144080 67144460 RL-5471-6 — PE-53822 PE-53822-S DO3316-473 L23 33 1.40 67144090 67144470 RL-5471-7 — PE-53823 PE-53823-S DO3316-333 L24 22 1.70 67148370 67148480 RL-1283-22-43 — PE-53824 PE-53825-S DO3316-223 L25 15 2.1 67148380 67148490 RL-1283-15-43 — PE-53825 PE-53824-S DO3316-153 L26 330 0.80 67144100 67144480 RL-5471-1 — PE-53826 PE-53826-S DOS022P-334 L27 220 1.00 67144110 67144490 RL-5471-2 — PE-53827 PE-53827-S DOS022P-224 L28 150 1.20 67144120 67144500 RL-5471-3 — PE-53828 PE-53828-S DOS022P-154 L29 100 1.47 67144130 67144510 RL-5471-4 — PE-53829 PE-53829-S DOS022P-104 L30 68 1.78 67144140 67144520 RL-5471-5 — PE-53830 PE-53830-S DOS022P-683 L31 47 2.2 67144150 67144530 RL-5471-6 — PE-53831 PE-53831-S DOS022P-473 L32 33 2.5 67144160 67144540 RL-5471-7 — PE-53932 PE-53932-S DOS022P-333 L33 22 3.1 67148390 67148500 RL-1283-22-43 — PE-53933 PE-53933-S DOS022P-223 L34 15 3.4 67148400 67148790 RL-1283-15-43 — PE-53934 PE-53934-S DOS022P-153 L35 220 1.70 67144170 — RL-5473-1 — PE-53935 PE-53935-S — L36 150 2.1 67144180 — RL-5473-4 — PE-54036 PE-54036-S — L37 100 2.5 67144190 — RL-5472-1 — PE-54037 PE-54037-S — L38 68 3.1 67144200 — RL-5472-2 — PE-54038 PE-54038-S — L39 47 3.5 67144210 — RL-5472-3 — PE-54039 PE-54039-S — L40 33 3.5 67144220 67148290 RL-5472-4 — PE-54040 PE-54040-S — L41 22 3.5 67144230 67148300 RL-5472-5 — PE-54041 PE-54041-S — L42 150 2.7 67148410 — RL-5473-4 — PE-54042 PE-54042-S — L43 100 3.4 67144240 — RL-5473-2 — PE-54043 — — L44 68 3.4 67144250 — RL-5473-3 — PE-54044 — —
FIGURE 8. Inductor Manufacturers Part Numbers
Coilcraft Inc. Phone (800) 322-2645
FAX (708) 639-1469
Coilcraft Inc., Europe Phone +11 1236 730 595
FAX +44 1236 730 627
Pulse Engineering Inc. Phone (619) 674-8100
FAX (619) 674-8262
Pulse Engineering Inc., Phone +353 93 24 107 Europe FAX +353 93 24 459 Renco Electronics Inc. Phone (800) 645-5828
FAX (516) 586-5562
Schott Corp. Phone (612) 475-1173
FAX (612) 475-1786
FIGURE 9. Inductor Manufacturers Phone Numbers
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Page 17
LM2599 Series Buck Regulator Design Procedure (Continued)
Nichicon Corp. Phone (708) 843-7500
FAX (708) 843-2798
Panasonic Phone (714) 373-7857
FAX (714) 373-7102
AVX Corp. Phone (803) 448-9411
FAX (803) 448-1943
Sprague/Vishay Phone (207) 324-4140
FAX (207) 324-7223
FIGURE 10. Capacitor Manufacturers Phone Numbers
VR
3 Amp Diodes 4 to 6 Amp Diodes
Surface Mount Through Hole Surface Mount Through Hole
Schottky
Ultra Fast Schot-
tky
Ultra Fast Schot-
tky
Ultra Fast Schot-
tky
Ultra Fast
Recovery Recovery Recovery Recovery
20V
All of 1N5820 All of All of SR502 All of
SK32 these SR302 these these 1N5823 these
diodes MBR320 diodes diodes SB520 diodes
30V
30WQ03 are rated 1N5821 are rated are rated are rated
SK33 to at MBR330 to at 50WQ03 to at SR503 to at
least 31DQ03 least least 1N5824 least
40V
50V. 1N5822 50V. 50V. SB530 50V.
SK34 SR304 50WQ04 SR504
MBRS340 MBR340 1N5825
30WQ04 MURS320 31DQ04 MUR320 MURS620 SB540 MUR620
50V
or
more
SK35 30WF10 SR305 50WF10 HER601
MBRS360 MBR350 50WQ05 SB550
30WQ05 31DQ05 50SQ080
FIGURE 11. Diode Selection Table
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Page 18
Block Diagram
Application Information
PIN FUNCTIONS +V
IN
(Pin 1)—This is the positive input supply for the IC switching regulator. A suitable input bypass capacitor must be present at this pin to minimize voltage transients and to supply the switching currents needed by the regulator.
Ground (Pin 4) — Circuit ground. Output (Pin 2)—Internal switch. The voltage at this pin
switches between approximately (+V
IN−VSAT
) and approxi-
mately −0.5V, with a duty cycle of V
OUT/VIN
. To minimize coupling to sensitive circuitry,the PC board copper area con­nected to this pin should be kept to a minimum.
Feedback (Pin 6)—Senses the regulated output voltage to complete the feedback loop.
Shutdown /Soft-start (Pin 7)—This dual function pin pro­vides the following features: (a) Allows the switching regula­tor circuit to be shut down using logic level signals thus drop­ping the total input supply current to approximately 80 µA. (b)Adding a capacitor to this pin provides a soft-start feature which minimizes startup current and provides a controlled ramp up of the output voltage.
Error Flag (Pin 3)—Open collector output that provides a low signal (flag transistor ON) when the regulated output voltage drops more than 5%from the nominal output volt­age. On start up, Error Flag is low until V
OUT
reaches 95%of the nominal output voltage and a delay time determined by the Delay pin capacitor. This signal can be used as a reset to a microprocessor on power-up.
Delay (Pin 5)—At power-up, this pin can be used to provide a time delay between the time the regulated output voltage reaches 95%of the nominal output voltage, and the time the error flag output goes high.
Special Note If any of the above three features (Shutdown /Soft-start, Error Flag, or Delay) are not used, the respective pins should be left open.
EXTERNAL COMPONENTS
SOFT-START CAPACITOR C
SS
—A capacitor on this pin provides the regulator with a Soft-start feature (slow start-up). When the DC input voltage is first applied to the regulator, or when the Shutdown /Soft-start pin is allowed to go high, a constant current (ap­proximately 5 µA begins charging this capacitor). As the ca­pacitor voltage rises, the regulator goes through four operat­ing regions (See the bottom curve in
Figure 13
).
1. Regulator in Shutdown.
When the SD /SS pin voltage is between 0V and 1.3V, the regulator is in shutdown, the out­put voltage is zero, and the IC quiescent current is approxi­mately 85 µA.
2. Regulator ON, but the output voltage is zero.
With the SD /SS pin voltage between approximately 1.3V and 1.8V, the internal regulator circuitry is operating, the quiescent cur­rent rises to approximately 5 mA, but the output voltage is still zero. Also, as the 1.3V threshold is exceeded, the Soft-start capacitor charging current decreases from 5 µA down to approximately 1.6 µA. This decreases the slope of capacitor voltage ramp.
3. Soft-start Region.
When the SD /SS pin voltage is be­tween 1.8V and 2.8V (@25˚C), the regulator is in a Soft-start condition. The switch (Pin 2) duty cycle initially starts out very low, with narrow pulses and gradually get wider as the capacitor SD /SS pin ramps up towards 2.8V. As the duty cycle increases, the output voltage also increases at a con­trolled ramp up. See the center curve in
Figure 13
. The input
supply current requirement also starts out at a low level for
DS012582-30
FIGURE 12.
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Page 19
Application Information (Continued)
the narrow pulses and ramp up in a controlled manner. This is a very useful feature in some switcher topologies that re­quire large startup currents (such as the inverting configura­tion) which can load down the input power supply.
Note: The lower curve shown in
Figure 13
shows the Soft-start region from 0%to 100%. This is not the duty cycle percentage, but the output volt­age percentage. Also, the Soft-start voltage range has a negative tem­perature coefficient associated with it. See the Soft-start curve in the electrical characteristics section.
4. Normal operation.
Above 2.8V, the circuit operates as a standard Pulse Width Modulated switching regulator. The capacitor will continue to charge up until it reaches the inter­nal clamp voltage of approximately 7V. If this pin is driven from a voltage source, the current must be limited to about 1 mA.
DS012582-31
FIGURE 13. Soft-start, Delay, Error, Output
DS012582-32
FIGURE 14. Timing Diagram for 5V Output
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Page 20
Application Information (Continued)
DELAY CAPACITOR C
DELAY
—Provides delay for the error flag output. See the
upper curve in
Figure 13
, and also refer to timing diagrams in
Figure 14
. A capacitor on this pin provides a time delay be­tween the time the regulated output voltage (when it is in­creasing in value) reaches 95%of the nominal output volt­age, and the time the error flag output goes high. A 3 µA constant current from the delay pin charges the delay ca­pacitor resulting in a voltage ramp. When this voltage reaches a threshold of approximately 1.3V, the open collec­tor error flag output (or power OK) goes high. This signal can be used to indicate that the regulated output has reached the correct voltage and has stabilized.
If, for any reason, the regulated output voltage drops by 5
% or more, the error output flag (Pin 3) immediately goes low (internal transistor turns on). The delay capacitor provides very little delay if the regulated output is dropping out of regulation. The delay time for an output that is decreasing is approximately a 1000 times less than the delay for the rising output. For a 0.1 µF delay capacitor, the delay time would be approximately 50 ms when the output is rising and passes through the 95%threshold, but the delay for the output drop­ping would only be approximately 50 µs.
R
Pull Up
—The error flag output, (or power OK) is the collec­tor of a NPN transistor, with the emitter internally grounded. To use the error flag, a pullup resistor to a positive voltage is needed. The error flag transistor is rated up to a maximum of 45V and can sink approximately 3 mA. If the error flag is not used, it can be left open.
FEEDFORWARD CAPACITOR
(Adjustable Output Voltage Version)
C
FF
-AFeedforward Capacitor CFF, shown across R2 in
Fig-
ure 1
is used when the output voltage is greater than 10V or
when C
OUT
has a very low ESR. This capacitor adds lead compensation to the feedback loop and increases the phase margin for better loop stability.For C
FF
selection, see the de-
sign procedure section. If the output ripple is large (
>
5%of the nominal output volt­age), this ripple can be coupled to the feedback pin through the feedforward capacitor and cause the error comparator to trigger the error flag. In this situation, adding a resistor, R
FF
, in series with the feedforward capacitor, approximately 3 times R1, will attenuate the ripple voltage at the feedback pin.
INPUT CAPACITOR C
IN
—A low ESR aluminum or tantalum bypass capacitor is needed between the input pin and ground pin. It must be lo­cated near the regulator using short leads. This capacitor prevents large voltage transients from appearing at the in­put, and provides the instantaneous current needed each time the switch turns on.
The important parameters for the Input capacitor are the voltage rating and the RMS current rating. Because of the relatively high RMS currents flowing in a buck regulator’s in­put capacitor, this capacitor should be chosen for its RMS current rating rather than its capacitance or voltage ratings, although the capacitance value and voltage rating are di­rectly related to the RMS current rating.
The RMS current rating of a capacitor could be viewed as a capacitor’s power rating. The RMS current flowing through the capacitors internal ESR produces power which causes
the internal temperature of the capacitor to rise. The RMS current rating of a capacitor is determined by the amount of current required to raise the internal temperature approxi­mately 10˚C above an ambient temperature of 105˚C. The ability of the capacitor to dissipate this heat to the surround­ing air will determine the amount of current the capacitor can safely sustain. Capacitors that are physically large and have a 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 consequences of operating an electrolytic capacitor above the RMS current rating is a shortened operating life. The higher temperature speeds up the evaporation of the ca­pacitor’s electrolyte, resulting in eventual failure.
Selecting an input capacitor requires consulting the manu­facturers data sheet for maximum allowable RMS ripple cur­rent. For a maximum ambient temperature of 40˚C, a gen­eral guideline would be to select a capacitor with a ripple current rating of approximately 50%of the DC load current. For ambient temperatures up to 70˚C, a current rating of 75%of the DC load current would be a good choice for a conservative design. The capacitor voltage rating must be at least 1.25 times greater than the maximum input voltage, and often a much higher voltage capacitor is needed to sat­isfy the RMS current requirements.
DS012582-33
FIGURE 15. RMS Current Ratings for Low
ESR Electrolytic Capacitors (Typical)
DS012582-34
FIGURE 16. Capacitor ESR vs Capacitor Voltage Rating
(Typical Low ESR Electrolytic Capacitor)
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Application Information (Continued)
A graph shown in
Figure 15
shows the relationship between an electrolytic capacitor value, its voltage rating, and the RMS current it is rated for. These curves were obtained from the Nichicon “PL” series of low ESR, high reliability electro­lytic capacitors designed for switching regulator applications. Other capacitor manufacturers offer similar types of capaci­tors, but always check the capacitor data sheet.
“Standard” electrolytic capacitors typically have much higher ESR numbers, lower RMS current ratings and typically have a shorter operating lifetime.
Because of their small size and excellent performance, sur­face mount solid tantalum capacitors are often used for input bypassing, but several precautions must be observed. A small percentage of solid tantalum capacitors can short if the inrush current rating is exceeded. This can happen at turn on when the input voltage is suddenly applied, and of course, higher input voltages produce higher inrush currents. Sev­eral capacitor manufacturers do a 100%surge current test­ing on their products to minimize this potential problem. If high turn on currents are expected, it may be necessary to limit this current by adding either some resistance or induc­tance before the tantalum capacitor, or select a higher volt­age capacitor. As with aluminum electrolytic capacitors, the RMS ripple current rating must be sized to the load current.
OUTPUT CAPACITOR C
OUT
—An output capacitor is required to filter the output and provide regulator loop stability. Low impedance or low ESR Electrolytic or solid tantalum capacitors designed for switching regulator applications must be used. When select­ing an output capacitor, the important capacitor parameters are; the 100 kHz Equivalent Series Resistance (ESR), the RMS ripple current rating, voltage rating, and capacitance value. For the output capacitor, the ESR value is the most important parameter.
The output capacitor requires an ESR value that has an up­per and lower limit. For low output ripple voltage, a low ESR value is needed. This value is determined by the maximum allowable output ripple voltage, typically 1%to 2%of the out­put voltage. But if the selected capacitor’s ESR is extremely low, there is a possibility of an unstable feedback loop, re­sulting in an oscillation at the output. Using the capacitors listed in the tables, or similar types, will provide design solu­tions under all conditions.
If very low output ripple voltage (less than 15 mV) is re­quired, refer to the section on Output Voltage Ripple and Transients for a post ripple filter.
An aluminum electrolytic capacitor’s ESR value is related to the capacitance value and its voltage rating. In most cases, higher voltage electrolytic capacitors have lower ESR values (see
Figure 16
). Often, capacitors with much higher voltage ratings may be needed to provide the low ESR values re­quired for low output ripple voltage.
The output capacitor for many different switcher designs of­ten can be satisfied with only three or four different capacitor values and several different voltage ratings. See the quick design component selection tables in
Figure 2
and3for typi­cal capacitor values, voltage ratings, and manufacturers ca­pacitor types.
Electrolytic capacitors are not recommended for tempera­tures below −25˚C. The ESR rises dramatically at cold tem­peratures and typically rises 3X
@
−25˚C and as much as
10X at −40˚C. See curve shown in
Figure 17
.
Solid tantalum capacitors have a much better ESR spec for cold temperatures and are recommended for temperatures below −25˚C.
CATCH DIODE
Buck regulators require a diode to provide a return path for the inductor current when the switch turns off. This must be a fast diode and must be located close to the LM2599 using short leads and short printed circuit traces.
Because of their very fast switching speed and low forward voltage drop, Schottky diodes provide the best performance, especially in low output voltage applications (5V and lower). Ultra-fast recovery, or High-Efficiency rectifiers are also a good choice, but some types with an abrupt turnoff charac­teristic may cause instability or EMI problems. Ultra-fast re­covery diodes typically have reverse recovery times of 50 ns or less. Rectifiers such as the IN5400 series are much too slow and should not be used.
INDUCTOR SELECTION
The LM2599 (or any of the Simple Switcher family) can be used for both continuous or discontinuous modes of opera­tion.
In many cases the preferred mode of operation is the con­tinuous mode. It offers greater output power, lower peak switch, inductor and diode currents, and can have lower out­put ripple voltage. But 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 (nomograph) was designed (see
Figure 4
through
7
). 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 peak-to-peak inductor ripple current percentage is not fixed, but is allowed to change as different design load currents are selected. (See
Figure 18
).
DS012582-35
FIGURE 17. Capacitor ESR Change vs Temperature
LM2599
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Page 22
Application Information (Continued)
By allowing the percentage of inductor ripple current to in­crease for low load currents, the inductor value and size can be kept relatively low.
When operating in the continuous mode, the inductor current waveform ranges from a triangular to a sawtooth type of waveform (depending on the input voltage), with the average value of this current waveform equal to the DC output load current.
Inductors are available in different styles such as pot core, toroid, E-core, bobbin core, etc., as well as different core ma­terials, such as ferrites and powdered iron. The least expen­sive, the bobbin, rod or stick core, consists of wire wound on a ferrite bobbin. This type of construction makes for an inex­pensive inductor, but since the magnetic flux is not com­pletely contained within the core, it generates more Electro-Magnetic Interference (EMl). This magnetic flux can induce voltages into nearby printed circuit traces, thus caus­ing problems with both the switching regulator operation and nearby sensitive circuitry,and can give incorrect scope read­ings because of induced voltages in the scope probe. Also see section on Open Core Inductors.
When multiple switching regulators are located on the same PC board, open core magnetics can cause interference be­tween two or more of the regulator circuits, especially at high currents.A torroid or E-core inductor (closed magnetic struc­ture) should be used in these situations.
The inductors listed in the selection chart include ferrite E-core construction for Schott, ferrite bobbin core for Renco and Coilcraft, and powdered iron toroid for Pulse Engineer­ing.
The inductor manufacturer’s data sheets include current and energy limits to avoid inductor saturation.
DISCONTINUOUS MODE OPERATION
The selection guide chooses inductor values suitable for continuous mode operation, but for low current applications and/or high input voltages, a discontinuous mode design may be a better choice. It would use an inductor that would be physically smaller, and would need only one half to one third the inductance value needed for a continuous mode de­sign. The peak switch and inductor currents will be higher in a discontinuous design, but at these low load currents (1A and below), the maximum switch current will still be less than the switch current limit.
Discontinuous operation can have voltage waveforms that are considerable different than a continuous design. The out­put pin (switch) waveform can have some damped sinusoi­dal ringing present. (See Typical Performance Characteris­tics photo titled Discontinuous Mode Switching Waveforms) This ringing is normal for discontinuous operation, and is not caused by feedback loop instabilities. In discontinuous op­eration, there is a period of time where neither the switch or the diode are conducting, and the inductor current has dropped to zero. During this time, a small amount of energy can circulate between the inductor and the switch/diode parasitic capacitance causing this characteristic ringing. Nor­mally this ringing is not a problem, unless the amplitude be­comes great enough to exceed the input voltage, and even then, there is very little energy present to cause damage.
Switchers Made Simple
(ver­sion 4.3) will provide all component values for continuous and discontinuous modes of operation.
OUTPUT VOLTAGE RIPPLE AND TRANSIENTS
The output voltage of a switching power supply operating in the continuous mode will contain a sawtooth ripple voltage at the switcher frequency, and may also contain short voltage spikes at the peaks of the sawtooth waveform.
The output ripple voltage is a function of the inductor saw­tooth ripple current and the ESR of the output capacitor. A typical output ripple voltage can range from approximately
0.5%to 3%of the output voltage. To obtain low ripple volt­age, the ESR of the output capacitor must be low, however, caution must be exercised when using extremely low ESR capacitors because they can affect the loop stability, result­ing in oscillation problems. If very low output ripple voltage is needed (less than 20 mV), a post ripple filter is recom-
DS012582-36
FIGURE 18. (∆I
IND
) Peak-to-Peak Inductor Ripple
Current (as a Percentage of the
Load Current) vs Load Current
DS012582-37
FIGURE 19. Post Ripple Filter Waveform
LM2599
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Page 23
Application Information (Continued)
mended (See
Figure 1
). The inductance required is typically between 1 µH and 5 µH, with low DC resistance, to maintain good load regulation. A low ESR output filter capacitor is also required to assure good dynamic load response and ripple reduction. The ESR of this capacitor may be as low as de­sired, because it is out of the regulator feedback loop. The photo shown in
Figure 19
shows a typical output ripple volt-
age, with and without a post ripple filter. When observing output ripple with a scope, it is essential
that a short, low inductance scope probe ground connection be used. Most scope probe manufacturers provide a special probe terminator which is soldered onto the regulator board, preferable at the output capacitor. This provides a very short scope ground thus eliminating the problems associated with the 3 inch ground lead normally provided with the probe, and provides a much cleaner and more accurate picture of the ripple voltage waveform.
The voltage spikes are caused by the fast switching action of the output switch, the diode, and the parasitic inductance of the output filter capacitor, and its associated wiring. To mini­mize these voltage spikes, the output capacitor should be designed for switching regulator applications, and the lead lengths must be kept very short. Wiring inductance, stray ca­pacitance, as well as the scope probe used to evaluate these transients, all contribute to the amplitude of these spikes.
If the load current drops to a low enough level, the bottom of the sawtooth current waveform will reach zero, and the switcher will smoothly change from a continuous to a discon­tinuous mode of operation. Most switcher designs (irregard­less how large the inductor value is) will be forced to run dis­continuous if the output is lightly loaded. This is a perfectly acceptable mode of operation.
In a switching regulator design, knowing the value of the peak-to-peak inductor ripple current (∆I
IND
) can be useful for determining a number of other circuit parameters. Param­eters such as, peak inductor or peak switch current, mini­mum load current before the circuit becomes discontinuous,
output ripple voltage and output capacitor ESR can all be calculated from the peak-to-peak ∆I
IND
. When the inductor
nomographs shown in
Figure 4
through7are used to select an inductor value, the peak-to-peak inductor ripple current can immediately be determined. The curve shown in
Figure
20
shows the range of (∆I
IND
) that can be expected for differ­ent load currents. The curve also shows how the peak-to-peak inductor ripple current (∆I
IND
) changes as you go from the lower border to the upper border (for a given load current) within an inductance region. The upper border rep­resents a higher input voltage, while the lower border repre­sents a lower input voltage (see Inductor Selection Guides).
These curves are only correct for continuous mode opera­tion, and only if the inductor selection guides are used to se­lect the inductor value
Consider the following example:
V
OUT
=
5V, maximum load current of 2.5A
V
IN
=
12V, nominal, varying between 10V and 16V.
The selection guide in
Figure 5
shows that the vertical line for a 2.5A load current, and the horizontal line for the 12V in­put voltage intersect approximately midway between the up­per and lower borders of the 33 µH inductance region. A 33 µH inductor will allow a peak-to-peak inductor current (∆I
IND
) to flow that will be a percentage of the maximum load cur­rent. Referring to
Figure 20
, follow the 2.5A line approxi­mately midway into the inductance region, and read the peak-to-peak inductor ripple current (∆I
IND
) on the left hand
axis (approximately 620 mA p-p). As the input voltage increases to 16V, it approaches the up-
per border of the inductance region, and the inductor ripple current increases. Referring to the curve in
Figure 20
,itcan be seen that for a load current of 2.5A, the peak-to-peak in­ductor ripple current (∆I
IND
) is 620 mA with 12V in, and can range from 740 mA at the upper border (16V in) to 500 mA at the lower border (10V in).
Once the ∆I
IND
value is known, the following formulas can be used to calculate additional information about the switching regulator circuit.
1. Peak Inductor or peak switch current
2. Minimum load current before the circuit becomes dis-
continuous
3. Output Ripple Voltage=(∆I
IND
)x(ESR of C
OUT
)
=
0.62Ax0.1Ω=62 mV p-p
4.
OPEN CORE INDUCTORS
Another possible source of increased output ripple voltage or unstable operation is from an open core inductor. Ferrite bobbin or stick inductors have magnetic lines of flux flowing through the air from one end of the bobbin to the other end.
DS012582-49
FIGURE 20. Peak-to-Peak Inductor
Ripple Current vs Load Current
LM2599
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Page 24
Application Information (Continued)
These magnetic lines of flux will induce a voltage into any wire or PC board copper trace that comes within the induc­tor’s magnetic field. The strength of the magnetic field, the orientation and location of the PC copper trace to the mag­netic field, and the distance between the copper trace and the inductor, determine the amount of voltage generated in the copper trace. Another way of looking at this inductive coupling is to consider the PC board copper trace as one turn of a transformer (secondary) with the inductor winding as the primary. Many millivolts can be generated in a copper trace located near an open core inductor which can cause stability problems or high output ripple voltage problems.
If unstable operation is seen, and an open core inductor is used, it’s possible that the location of the inductor with re­spect to other PC traces may be the problem. To determine if this is the problem, temporarily raise the inductor away from the board by several inches and then check circuit op­eration. If the circuit now operates correctly, then the mag­netic flux from the open core inductor is causing the problem. Substituting a closed core inductor such as a torroid or E-core will correct the problem, or re-arranging the PC layout may be necessary. Magnetic flux cutting the IC device ground trace, feedback trace, or the positive or negative traces of the output capacitor should be minimized.
Sometimes, locating a trace directly beneath a bobbin in­ductor will provide good results, provided it is exactly in the center of the inductor (because the induced voltages cancel themselves out), but if it is off center one direction or the other, then problems could arise. If flux problems are present, even the direction of the inductor winding can make a difference in some circuits.
This discussion on open core inductors is not to frighten the user, but to alert the user on what kind of problems to watch out for when using them. Open core bobbin or “stick” induc­tors are an inexpensive, simple way of making a compact ef­ficient inductor, and they are used by the millions in many dif­ferent applications.
THERMAL CONSIDERATIONS
The LM2599 is available in two packages, a 7-pin TO-220 (T) and a 7-pin surface mount TO-263 (S).
The TO-220 package needs a heat sink under most condi­tions. The size of the heat sink depends on the input voltage, the output voltage, the load current and the ambient tem­perature. The curves in
Figure 21
show the LM2599T junc­tion temperature rises above ambient temperature for a 3A load and different input and output voltages. The data for these curves was taken with the LM2599T (TO-220 pack­age) operating as a buck switching regulator in an ambient temperature of 25˚C (still air). These temperature rise num­bers are all approximate and there are many factors that can affect these temperatures. Higher ambient temperatures re­quire more heat sinking.
The TO-263 surface mount package tab is designed to be soldered to the copper on a printed circuit board. The copper and the board are the heat sink 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
, and ideally should have 2 or more square inches of 2 oz. (0.0028 in) copper. Additional copper area improves the thermal characteristics, but with copper areas greater than approximately 6 in
2
, only
small improvements in heat dissipation are realized. If fur-
ther thermal improvements are needed, double sided, multi­layer pc-board with large copper areas and/or airflow are recommended.
The curves shown in
Figure 22
show the LM2599S (TO-263 package) junction temperature rise above ambient tempera­ture with a 2Aload for various input and output voltages. This data was taken with the circuit operating as a buck switching regulator with all components mounted on a pc board to simulate the junction temperature under actual operating conditions. This curve can be used for a quick check for the approximate junction temperature for various conditions, but be aware that there are many factors that can affect the junc­tion temperature. When load currents higher than 2A are used, double sided or multilayer pc-boards with large copper areas and/or airflow might be needed, especially for high ambient temperatures and high output voltages.
DS012582-38
Circuit Data for Temperature Rise Curve TO-220
Package (T) Capacitors Through hole electrolytic Inductor Through hole Renco Diode Through hole, 5A 40V, Schottky PC board 3 square inches single sided 2 oz. copper
(0.0028")
FIGURE 21. Junction Temperature Rise, TO-220
DS012582-39
LM2599
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Page 25
Application Information (Continued)
For the best thermal performance, wide copper traces and generous amounts of printed circuit board copper should be used in the board layout. (One exception to this is the output (switch) pin, which should not have large areas of copper.) Large areas of copper provide the best transfer of heat (lower thermal resistance) to the surrounding air, and moving air lowers the thermal resistance even further.
Package thermal resistance and junction temperature rise numbers are all approximate, and there are many factors that will affect these numbers. Some of these factors include board size, shape, thickness, position, location, and even board temperature. Other factors are, trace width, total printed circuit copper area, copper thickness, single- or double-sided, multilayer board and the amount of solder on the board. The effectiveness of the pc board to dissipate heat also depends on the size, quantity and spacing of other components on the board, as well as whether the surround­ing air is still or moving. Furthermore, some of these compo­nents such as the catch diode will add heat to the pc board and the heat can vary as the input voltage changes. For the inductor, depending on the physical size, type of core mate­rial and the DC resistance, it could either act as a heat sink taking heat away from the board, or it could add heat to the board.
SHUTDOWN /SOFT-START
The circuit shown in
Figure 25
is a standard buck regulator with 20V in, 12V out, 1A load, and using a 0.068 µF Soft-start capacitor.The photo in
Figure 23 Figure 24
show the effects of Soft-start on the output voltage, the input current, with, and without a Soft-start capacitor. The reduced input current required at startup is very evident when comparing the two
photos. The Soft-start feature reduces the startup current from 2.6A down to 650 mA, and delays and slows down the output voltage rise time.
This reduction in start up current is useful in situations where the input power source is limited in the amount of current it can deliver. In some applications Soft-start can be used to replace undervoltage lockout or delayed startup functions.
If a very slow output voltage ramp is desired, the Soft-start capacitor can be made much larger. Many seconds or even minutes are possible.
If only the shutdown feature is needed, the Soft-start capaci­tor can be eliminated.
Circuit Data for Temperature Rise Curve TO-263
Package (S) Capacitors Surface mount tantalum, molded “D” size Inductor Surface mount, Pulse engineering, 68 µH Diode Surface mount, 5A 40V, Schottky PC board 9 square inches single sided 2 oz. copper
(0.0028")
FIGURE 22. Junction Temperature Rise, TO-263
DS012582-40
FIGURE 23. Output Voltage, Input Current,
at Start-Up, WITH Soft-start
DS012582-41
FIGURE 24. Output Voltage, Input Current,
at Start-Up, WITHOUT Soft-start
LM2599
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Page 26
Application Information (Continued)
lNVERTING REGULATOR
The circuit in
Figure 26
converts a positive input voltage to a negative output voltage with a common ground. The circuit operates by bootstrapping the regulator’s ground pin to the negative output voltage, then grounding the feedback pin, the regulator senses the inverted output voltage and regu­lates it.
This example uses the LM2599-5 to generate a −5V output, but other output voltages are possible by selecting other out­put voltage versions, including the adjustable version. Since this regulator topology can produce an output voltage that is either greater than or less than the input voltage, the maxi­mum output current greatly depends on both the input and output voltage. The curve shown in
Figure 27
provides a guide as to the amount of output load current possible for the different input and output voltage conditions.
The maximum voltage appearing across the regulator is the absolute sum of the input and output voltage, and this must be limited to a maximum of 40V. In this example, when con-
verting +20V to −5V, the regulator would see 25V between the input pin and ground pin. The LM2599 has a maximum input voltage rating of 40V.
DS012582-42
FIGURE 25. Typical Circuit Using Shutdown /Soft-start and Error Flag Features
DS012582-43
FIGURE 26. Inverting −5V Regulator With Shutdown and Soft-start
LM2599
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Page 27
Application Information (Continued)
An additional diode is required in this regulator configuration. Diode D1 is used to isolate input voltage ripple or noise from coupling through the C
IN
capacitor to the output, under light or no load conditions. Also, this diode isolation changes the topology to closely resemble a buck configuration thus pro­viding good closed loop stability. A Schottky diode is recom­mended for low input voltages, (because of its lower voltage drop) but for higher input voltages, a IN5400 diode could be used.
Figure 26
will provide good results in the majority of invert-
ing designs. This type of inverting regulator can require relatively large
amounts of input current when starting up, even with light loads. Input currents as high as the LM2599 current limit (ap­proximately 4.5A) are needed for 2 ms or more, until the out­put reaches its nominal output voltage. The actual time de­pends on the output voltage and the size of the output capacitor. Input power sources that are current limited or sources that can not deliver these currents without getting loaded down, may not work correctly. Because of the rela­tively high startup currents required by the inverting topology, the Soft-start feature shown in
Figure 26
is recommended.
Also shown in
Figure 26
are several shutdown methods for the inverting configuration. With the inverting configuration, some level shifting is required, because the ground pin of the regulator is no longer at ground, but is now at the negative output voltage. The shutdown methods shown accept ground referenced shutdown signals.
UNDERVOLTAGE LOCKOUT
Some applications require the regulator to remain off until the input voltage reaches a predetermined voltage.
Figure
28
contains a undervoltage lockout circuit for a buck configu-
ration, while
Figure 29
and30are for the inverting types (only the circuitry pertaining to the undervoltage lockout is shown).
Figure 28
uses a zener diode to establish the threshold voltage when the switcher begins operating. When the input voltage is less than the zener voltage, resistors R1 and R2 hold the Shutdown /Soft-start pin low, keeping the regulator in the shutdown mode. As the input voltage ex-
ceeds the zener voltage, the zener conducts, pulling the Shutdown /Soft-start pin high, allowing the regulator to begin switching. The threshold voltage for the undervoltage lockout feature is approximately 1.5V greater than the zener voltage.
Figure 29
and30apply the same feature to an inverting cir-
cuit.
Figure 29
features a constant threshold voltage for turn on and turn off (zener voltage plus approximately one volt). If hysteresis is needed, the circuit in
Figure 30
has a turn ON voltage which is different than the turn OFF voltage. The amount of hysteresis is approximately equal to the value of the output voltage. Since the SD /SS pin has an internal 7V zener clamp, R2 is needed to limit the current into this pin to approximately 1 mA when Q1 is on.
NEGATIVE VOLTAGE CHARGE PUMP
Occasionally a low current negative voltage is needed for bi­asing parts of a circuit. A simple method of generating a negative voltage using a charge pump technique and the switching waveform present at the OUT pin, is shown in
Fig-
ure 31
. This unregulated negative voltage is approximately equal to the positive input voltage (minus a few volts), and can supply up to a 600 mA of output current. There is a re-
Inverting Regulator
DS012582-44
FIGURE 27. Maximum Load Current for
Inverting Regulator Circuit
DS012582-45
FIGURE 28. Undervoltage Lockout for a Buck
Regulator
DS012582-47
FIGURE 29. Undervoltage Lockout Without
Hysteresis for an Inverting Regulator
DS012582-46
FIGURE 30. Undervoltage Lockout With
Hysteresis for an Inverting Regulator
LM2599
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Page 28
Application Information (Continued)
quirement however, that there be a minimum load of 1.2A on the regulated positive output for the charge pump to work correctly. Also, resistor R1 is required to limit the charging current of C1 to some value less than the LM2599 current limit (typically 4.5A).
This method of generating a negative output voltage without an additional inductor can be used with other members of the Simple Switcher Family, using either the buck or boost topology.
TYPICAL THROUGH HOLE PC BOARD LAYOUT, FIXED OUTPUT (1X SIZE), DOUBLE SIDED
DS012582-48
FIGURE 31. Charge Pump for Generating a
Low Current, Negative Output Voltage
DS012582-51
CIN: — 470 µF, 50V, Aluminum Electrolytic Panasonic, “HFQ Series” C
OUT
: — 330 µF, 35V,Aluminum Electrolytic Panasonic, “HFQ Series” D1: — 5A, 40V Schottky Rectifier, 1N5825 L1: — 47 µH, L39, Renco, Through Hole R
PULL UP
: — 10k
C
DELAY
: — 0.1 µF
C
SD/SS
: — 0.1 µF
Thermalloy Heat Sink
#
7020
LM2599
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Page 29
Application Information (Continued)
TYPICAL THROUGH HOLE PC BOARD LAYOUT, ADJUSTABLE OUTPUT (1X SIZE), DOUBLE SIDED
DS012582-52
CIN: — 470 µF, 50V, Aluminum Electrolytic Panasonic, “HFQ Series” C
OUT
: — 220 µF, 35V Aluminum Electrolytic Panasonic, “HFQ Series” D1: — 5A, 40V Schottky Rectifier, 1N5825 L1: — 47 µH, L39, Renco, Through Hole R
1
:—1kΩ,1
%
R
2
: — Use formula in Design Procedure
C
FF
: — See
Figure 4
.
R
FF
: — See Application Information Section (CFFSection)
R
PULL UP
: — 10k
C
DELAY
: — 0.1 µF
C
SD/SS
: — 0.1 µF
Thermalloy Heat Sink
#
7020
FIGURE 32. PC Board Layout
LM2599
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Page 30
Physical Dimensions inches (millimeters) unless otherwise noted
7-Lead TO-220 Bent and Staggered Package
Order Number LM2599T-3.3, LM2599T-5.0,
LM2599T-12 or LM2599T-ADJ
NS Package Number TA07B
LM2599
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Page 31
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user.
2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness.
National Semiconductor Corporation
Americas Tel: 1-800-272-9959 Fax: 1-800-737-7018 Email: support@nsc.com
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Fax: +49 (0) 180-530 85 86
Email: europe.support@nsc.com Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Français Tel: +33 (0) 1 41 91 8790
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Tel: 65-2544466 Fax: 65-2504466 Email: ap.support@nsc.com
National Semiconductor Japan Ltd.
Tel: 81-3-5639-7560 Fax: 81-3-5639-7507
www.national.com
7-Lead TO-263 Bent and Formed Package
Order Number LM2599S-3.3, LM2599S-5.0, LM2599S-12 or LM2599S-ADJ
NS Package Number TS7B
LM2599 SIMPLE SWITCHER Power Converter 150 kHz 3A Step-Down Voltage Regulator, with
Features
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
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