How it Works
Datasheet
Loading...
LM2599

Datasheet LM2599 Datasheet (National Semiconductor)

Download
Page 1
现货库存、技术资料、百科信息、热点资讯，精彩尽在鼎好!
LM2599 SIMPLE SWITCHER
®
Power Converter 150 kHz 3A
Step-Down Voltage Regulator, with Features
December 2000
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.
Requiring a minimum number of external components, these regulators are simple to use and include internal frequency compensation fixed-frequency oscillator, Shutdown/Soft-start, error flag de­lay and error flag output.
Other features include a guaranteed put voltage under all conditions of input voltage and output load conditions, and ternal shutdown is included, featuring typically 80 µA
†
, improved line and load specifications,
±
4% tolerance on out-
±
15% on the oscillator frequency. Ex-
standby current. Self protection features include a two stage current limit for the output switch and an over temperature shutdown for complete protection under fault conditions.
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 n High Efficiency n Uses readily available standard inductors n Thermal shutdown and current limit protection
typically 80 µA
Q
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)
DS012582-1
SIMPLE SWITCHER®and
© 2001 National Semiconductor Corporation DS012582 www.national.com
Switchers Made Simple
®
are registered trademarks of National Semiconductor Corporation.
Page 2
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
LM2599
please contact the National Semiconductor Sales Office/ Distributors for availability and specifications.
Maximum Supply Voltage (V SD /SS Pin Input Voltage (Note 2) 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
) 45V
IN
6V
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 TJ= 25˚C, and those with boldface type apply over full Operating Tempera­ture Range.
Symbol Parameter Conditions LM2599-3.3 Units
Typ Limit
(Note 4) (Note 5) SYSTEM PARAMETERS (Note 6) Test Circuit V
OUT
η Efficiency V
Output Voltage 4.75V ≤ VIN≤ 40V, 0.2A ≤ I
IN
= 12V, I
Figure 1
≤ 3A 3.3 V
LOAD
3.168/3.135 V(min)
3.432/3.465 V(max)
=3A 73 %
LOAD
(Limits)
LM2599-5.0 Electrical Characteristics
Specifications with standard type face are for TJ= 25˚C, and those with boldface type apply over full Operating Tempera­ture Range.
Symbol Parameter Conditions LM2599-5.0 Units
Typ Limit
(Note 4) (Note 5) SYSTEM PARAMETERS (Note 6) Test Circuit V
OUT
η Efficiency V
Output Voltage 7V ≤ VIN≤ 40V, 0.2A ≤ I
IN
= 12V, I
Figure 1
≤ 3A 5 V
LOAD
4.800/4.750 V(min)
5.200/5.250 V(max)
=3A 80 %
LOAD
(Limits)
www.national.com 2
Page 3
LM2599-12 Electrical Characteristics
Specifications with standard type face are for TJ= 25˚C, and those with boldface type apply over full Operating Tempera­ture Range.
Symbol Parameter Conditions LM2599-12 Units
Typ Limit
(Limits)
(Note 4) (Note 5) SYSTEM PARAMETERS (Note 6) Test Circuit V
OUT
Output Voltage 15V ≤ VIN≤ 40V, 0.2A ≤ I
Figure 1
≤ 3A 12 V
LOAD
11.52/11.40 V(min)
12.48/12.60 V(max)
η Efficiency V
= 25V, I
IN
=3A 90 %
LOAD
LM2599-ADJ Electrical Characteristics
Specifications with standard type face are for TJ= 25˚C, and those with boldface type apply over full Operating Tempera­ture Range.
Symbol Parameter Conditions LM2599-ADJ Units
Typ Limit
(Note 4) (Note 5) SYSTEM PARAMETERS (Note 6) Test Circuit V
FB
Feedback Voltage 4.5V ≤ VIN≤ 40V, 0.2A ≤ I
V
programmed for 3V. Circuit of
OUT
Figure 1
≤ 3A 1.230 V
LOAD
Figure 1
. 1.193/1.180 V(min)
1.267/1.280 V(max)
η Efficiency V
= 12V, V
IN
OUT
= 3V, I
=3A 73 %
LOAD
(Limits)
LM2599
All Output Voltage Versions Electrical Characteristics
Specifications with standard type face are for TJ= 25˚C, and those with boldface type apply over full Operating Tempera­ture Range. Unless otherwise specified, V
sion. I
LOAD
= 500 mA
Symbol Parameter Conditions LM2599-XX Units
DEVICE PARAMETERS
I
b
f
O
V
SAT
Feedback Bias Current Adjustable Version Only, VFB= 1.3V 10 nA
Oscillator Frequency (Note 7) 150 kHz
Saturation Voltage I
DC Max Duty Cycle (ON) (Note 9) 100 %
Min Duty Cycle (OFF) (Note 10) 0
I
CL
I
L
Current Limit Peak Current, (Note 8) (Note 9) 4.5 A
Output Leakage Current (Note 8) (Note 10) (Note 11) Output = 0V 50 µA(max)
= 12V for the 3.3V, 5V, and Adjustable version and VIN= 24V for the 12V ver-
IN
Typ Limit
(Note4)(Note 5)
50/100 nA (max)
127/110 kHz(min) 173/173 kHz(max)
= 3A (Note 8) (Note 9) 1.16 V
OUT
1.4/1.5 V(max)
3.6/3.4 A(min)
6.9/7.5 A(max)
Output = −1V 2 mA
30 mA(max)
(Limits)
www.national.com3
Page 4
All Output Voltage Versions Electrical Characteristics
LM2599
Specifications with standard type face are for TJ= 25˚C, and those with boldface type apply over full Operating Tempera­ture Range. Unless otherwise specified, V
sion. I
LOAD
= 500 mA
Symbol Parameter Conditions LM2599-XX Units
DEVICE PARAMETERS
I
Q
Operating Quiescent SD /SS Pin Open (Note 10) 5mA Current 10 mA(max)
I
STBY
Standby Quiescent SD /SS pin = 0V (Note 11) 80 µA Current 200/250 µA(max)
θ
JC
θ
JA
θ
JA
θ
JA
θ
JA
Thermal Resistance TO220 or TO263 Package, Junction to Case 2 ˚C/W
SHUTDOWN/SOFT-START CONTROL Test Circuit of V
SD
Shutdown Threshold 1.3 V Voltage Low, (Shutdown Mode) 0.6 V(max)
V
SS
I
SD
I
SS
Soft-start Voltage V
Shutdown Current V
Soft-start Current V
FLAG/DELAY CONTROL Test Circuit of
Regulator Dropout Detector Low (Flag ON) 96 % Threshold Voltage 92 %(min)
VF
SAT
Flag Output Saturation I Voltage V
IF
L
Flag Output Leakage Current V Delay Pin Threshold 1.25 V Voltage Low (Flag ON) 1.21 V(min)
Delay Pin Source Current V
Delay Pin Saturation Low (Flag ON) 55 mV
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%
production tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).
Note 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
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.
Figure 1
test circuit, system performance will be as shown in system parameters section of Electrical Characteristics.
(Continued)
= 12V for the 3.3V, 5V, and Adjustable version and VIN= 24V for the 12V ver-
IN
Typ Limit
(Note4)(Note 5)
TO220 Package, Juncton to Ambient (Note 12) 50 ˚C/W TO263 Package, Juncton to Ambient (Note 13) 50 ˚C/W TO263 Package, Juncton to Ambient (Note 14) 30 ˚C/W TO263 Package, Juncton to Ambient (Note 15) 20 ˚C/W
Figure 1
High, (Soft-start Mode) 2 V(min)
= 20% of Nominal Output Voltage 2 V
OUT
V
= 100% of Nominal Output Voltage 3
OUT SHUTDOWN
= 0.5V 5µA
10 µA(max)
Soft-start
= 2.5V 1.6 µA
5 µA(max)
Figure 1
98 %(max)
= 3 mA 0.3 V
SINK
= 0.5V 0.7/1.0 V(max)
DELAY
= 40V 0.3 µA
FLAG
High (Flag OFF) and V
= 0.5V 3 µA
DELAY
Regulated 1.29 V(max)
OUT
6 µA(max)
350/400 mV(max)
(Limits)
www.national.com 4
Page 5
All Output Voltage Versions Electrical Characteristics
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. Note 10: Feedback pin removed from output and connected to12Vfor the 3.3V, 5V, and the ADJ. version,and 15V for the 12V version, to force the output transistor
switch OFF.
Note 11: V 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
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 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 Note 15: Junction to ambient thermal resistance with the TO-263 package tab soldered to a double sided printed circuit board with 3 in
the LM2599S side of the board, and approximately 16 in in Switchers Made Simple version 4.2.1 (or later) software.
IN
= 40V.
(Continued)
2
.
2
of copper on the other side of the p-c board. See application hints in this data sheetandthe thermal model
2
of (1 oz.) copper area.
2
of (1 oz.) copper area.
2
of (1 oz.) copper area on
LM2599
Typical Performance Characteristics (Circuit of
Normalized Output Voltage
DS012582-2
Switch Saturation Voltage
Line Regulation
Switch Current Limit
Figure 1
DS012582-3
)
Efficiency
DS012582-4
Dropout Voltage
Operating Quiescent Current
DS012582-5
DS012582-8
Shutdown Quiescent Current
DS012582-6
DS012582-9
DS012582-7
Minimum Operating Supply Voltage
DS012582-10
www.national.com5
Page 6
Typical Performance Characteristics (Circuit of
LM2599
Feedback Pin Bias Current
Flag Saturation Voltage
Figure 1
) (Continued)
Switching Frequency
Soft-start
Soft-start Response
DS012582-11
DS012582-14
Shutdown /Soft-start Current
Shutdown/Soft-start Threshold Voltage
DS012582-12
DS012582-13
Daisy Pin Current
DS012582-16
DS012582-15
DS012582-18
www.national.com 6
DS012582-53
Page 7
LM2599
Typical Performance Characteristics (Circuit of
Continuous Mode Switching Waveforms V
= 20V, V
IN
L = 32 µH, C
A: Output Pin Voltage, 10V/div. B: Inductor Current 1A/div. C: Output Ripple Voltage, 50 mV/div.
OUT
OUT
=5V,I
LOAD
= 220 µF, C
=2A
ESR=50mΩ
OUT
Horizontal Time Base: 2 µs/div.
Load Transient Response for Continuous Mode V
= 20V, V
IN
L = 32 µH, C
OUT
OUT
=5V,I
LOAD
= 220 µF, C
= 500 mA to 2A
ESR=50mΩ
OUT
DS012582-20
Discontinuous Mode Switching Waveforms
= 20V, V
V
IN
L = 10 µH, C
A: Output Pin Voltage, 10V/div. B: Inductor Current 0.5A/div. C: Output Ripple Voltage, 100 mV/div.
Load Transient Response for Discontinuous Mode
= 20V, V
V
IN
L = 10 µH, C
Figure 1
OUT
OUT
=5V,I
) (Continued)
LOAD
= 330 µF, C
= 500 mA
ESR=45mΩ
OUT
Horizontal Time Base: 2 µs/div.
OUT
OUT
=5V,I
= 330 µF, C
= 500 mA to 2A
LOAD
OUT
ESR=45mΩ
DS012582-19
DS012582-21
A: Output Voltage, 100 mV/div. (AC) B: 500 mA to 2A Load Pulse
A: Output Voltage, 100 mV/div. (AC) B: 500 mA to 2A Load Pulse
Horizontal Time Base: 50 µs/div.
Connection Diagrams and Order Information
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
Order Number LM2599S-3.3, LM2599S-5.0,
DS012582-22
Horizontal Time Base: 200 µs/div.
Surface Mount Package
7-Lead TO-263 (S)
DS012582-23
LM2599S-12 or LM2599S-ADJ
See NS Package Number TS7B
www.national.com7
Page 8
Test Circuit and Layout Guidelines
LM2599
Component Values shown are for VIN= 15V,
=5V,I
V
OUT
— 470 µF, 50V, Aluminum Electrolytic Nichicon “PL Series”
C
IN
— 220 µF, 25V Aluminum Electrolytic, Nichicon “PL Series”
C
OUT
D1 — 5A, 40V Schottky Rectifier, 1N5825 L1 — 68 µH, L38
Typical Values
CSS— 0.1 µF C
DELAY
R
Pull Up
= 3A.
LOAD
— 0.1 µF — 4.7k
Fixed Output Voltage Versions
DS012582-24
www.national.com 8
Page 9
Test Circuit and Layout Guidelines (Continued)
Adjustable Output Voltage Versions
LM2599
DS012582-25
where V
Select R1to be approximately 1 kΩ, use a 1% resistor for best stability. Component Values shown are for V V
OUT
C
IN
C
OUT
D1 — 5A, 30V Schottky Rectifier, 1N5824 L1 — 68 µH, L38 R
1
R
2
C
FF
R
FF
Typical Values
CSS—0.1 µF C
DELAY
R
PULL UP
= 1.23V
REF
= 20V,
= 10V, I
: — 470 µF, 35V, Aluminum Electrolytic Nichicon “PL Series”
: — 220 µF, 35V Aluminum Electrolytic, Nichicon “PL Series”
—1kΩ,1% — 7.15k, 1%
— 3.3 nF, See Application Information Section —3kΩ, See Application Information Section
—0.1 µF
—4.7k
LOAD
= 3A.
IN
FIGURE 1. Standard Test Circuits and Layout Guides
As in any switching regulator, layout is very important. Rap­idly switching currents associated with wiring inductance can generate voltage transients which can cause problems. For minimal inductance and ground loops, the wires indicated by
external components should be located as close to the switcher lC as possible using ground plane construction or single point grounding.
If open core inductors are used, special care must be taken as to the location and positioning of this type of induc­tor.Allowing the inductor flux to intersect sensitive feedback, lC groundpath and C
wiring can cause problems.
OUT
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.)
www.national.com9
Page 10
LM2599 Series Buck Regulator Design Procedure (Fixed Output)
LM2599
PROCEDURE (Fixed Output Voltage Version) EXAMPLE (Fixed Output Voltage Version)
Given:
V
= Regulated Output Voltage (3.3V, 5V or 12V)
OUT
V
(max) = Maximum DC Input Voltage
IN
I
(max) = Maximum Load Current
LOAD
1. Inductor Selection (L1) A. Select the correct inductor value selection guide from
Figure 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
2. Output Capacitor Selection (C
Figure 8
.
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
Made Simple
(version 4.2.1 or later).
Switchers
Given:
=5V
V
OUT
V
(max) = 12V
IN
I
(max) = 3A
LOAD
1. Inductor Selection (L1) A. Use the inductor selection guide for the 5V version shown
Figure 5
in
.
B. From the inductor value selection guide shown in 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 A. See section on output capacitors in application infor-
mation 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 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.
OUT
Figure 5
,
)
Figure 17
for
www.national.com 10
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.
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
1
at least
⁄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 16
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
pin.
IN
For additional information, see section on input capaci­tors in Application Information section.
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
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 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
16
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.
IN
Figure
LM2599
)
www.national.com11
Page 12
LM2599 Series Buck Regulator Design Procedure (Fixed Output) (Continued)
LM2599
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) (
(V) (A) (V) (µF/V) (µF/V) (µF/V) (µF/V)
5 22 L41 470/25 560/16 330/6.3 390/6.3
3
3.3
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
8 22 L41 470/25 560/16 220/10 330/10
3
5
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 15 22 L41 470/25 470/25 100/16 180/16
3
12
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
#
) HFQ Series PL Series Series 595D Series
FIGURE 2. LM2599 Fixed Voltage Quick Design Component Selection Table
LM2599 Series Buck Regulator Design Procedure (Adjustable Output)
PROCEDURE (Adjustable Output Voltage Version) EXAMPLE (Adjustable Output Voltage Version)
Given:
V
= Regulated Output Voltage
OUT
V
(max) = Maximum Input Voltage
IN
I
(max) = Maximum Load Current
LOAD
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.)
Given:
V
= 20V
OUT
V
(max) = 28V
IN
I
(max) = 3A
LOAD
F = Switching Frequency
(Fixed at a nominal 150 kHz).
1. Programming Output Voltage (Selecting R1and R2,as shown in
Select R
Figure 1
1
)
to be 1 kΩ, 1%. Solve for R2.
R2= 1k (16.26 − 1) = 15.26k, closest 1% value is 15.4 kΩ. R
= 15.4 kΩ.
2
www.national.com 12
Page 13
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
(V
µs), from the following formula:
•
microsecond constant E•T
•
2. Inductor Selection (L1) A. Calculate the inductor Volt
T),
microsecond constant (E
•
LM2599
•
where V V
= diode forward voltage drop = 0.5V
D
B. Use the E it with the E Value Selection Guide shown in
= internal switch saturation voltage = 1.16V and
SAT
T value from the previous formula and match
•
T number on the vertical axis of the Inductor
•
Figure 7
.
C. on the horizontal axis, select the maximum load current. D. Identify the inductance region intersected by the E
•
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
3. Output Capacitor Selection (C
Figure 8
.
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.
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
. It provides addi-
2
tional stability for high output voltages, low input-output volt­ages, and/or very low ESR output capacitors, such as solid tantalum capacitors.
B. E•T = 34.2 (V•µs) C. I D. From the inductor value selection guide shown in
T
the inductance region intersected by the 34 (V tal line and the 3A vertical line is 47 µH, and the inductor
LOAD
(max) = 3A
Figure 7
µs) horizon-
•
,
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 SeIection (C A. See section on C
in Application Information section.
OUT
B. From the quick design table shown in
OUT
)
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
The table shown in
Figure 3
)
FF
contains feed forward capacitor values for various output voltages. In this example, a 560 pF capacitor is needed.
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.)
www.national.com13
Page 14
LM2599 Series Buck Regulator Design Procedure (Adjustable Output)
(Continued)
LM2599
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.
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
1
at least
⁄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 16
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
pin.
IN
For additional information, see section on input capaci­tor in application information section.
5. Catch Diode Selection (D1) A. Refer to the table shown in
Figure 11
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
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
) would be needed. Since the the next higher
IN
capacitor voltage rating is 50V, a 50V capacitor should be used. The capacitor voltage rating of (1.5 x V vative guideline, 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 16
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.
. Schottky diodes
) is a conser-
IN
www.national.com 14
Page 15
LM2599 Series Buck Regulator Design Procedure (Adjustable Output)
(Continued)
LM2599
Output
Voltage
(V)
Panasonic Nichicon PL Feedforward AVX TPS Sprague Feedforward
HFQ Series Series Capacitor Series 595D Series Capacitor
Through Hole Output Capacitor Surface Mount Output 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
LM2599 Series Buck Regulator Design Procedure
INDUCTOR VALUE SELECTION GUIDES (For Continuous Mode Operation)
FIGURE 4. LM2599-3.3
FIGURE 5. LM2599-5.0
DS012582-26
DS012582-27
DS012582-28
FIGURE 6. LM2599-12
DS012582-29
FIGURE 7. LM2599-ADJ
www.national.com15
Page 16
LM2599 Series Buck Regulator Design Procedure (Continued)
LM2599
Inductance
(µH)
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 — —
Current
(A)
Schott Renco Pulse Engineering Coilcraft
Through Surface Through Surface Through Surface Surface
Hole Mount Hole Mount Hole Mount Mount
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
www.national.com 16
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
3 Amp Diodes 4 to 6 Amp Diodes
Surface Mount Through Hole Surface Mount Through Hole
VR
Schottky
20V
30V
40V
50V
or
more
SK32 these SR302 these these 1N5823 these
30WQ03 are rated 1N5821 are rated are rated are rated
SK33 to at MBR330 to at 50WQ03 to at SR503 to at
SK34 SR304 50WQ04 SR504
MBRS340 MBR340 1N5825
30WQ04 MURS320 31DQ04 MUR320 MURS620 SB540 MUR620
SK35 30WF10 SR305 50WF10 HER601
MBRS360 MBR350 50WQ05 SB550
30WQ05 31DQ05 50SQ080
Ultra Fast Schot-
tky
Recovery Recovery Recovery Recovery
All of 1N5820 All of All of SR502 All of
diodes MBR320 diodes diodes SB520 diodes
least 31DQ03 least least 1N5824 least 50V. 1N5822 50V. 50V. SB530 50V.
Ultra Fast Schot-
tky
Ultra Fast Schot-
LM2599
Ultra Fast
tky
FIGURE 11. Diode Selection Table
www.national.com17
Page 18
Block Diagram
LM2599
FIGURE 12.
Application Information
PIN FUNCTIONS +V
(Pin 1)—This is the positive input supply for the IC
IN
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
mately −0.5V, with a duty cycle of V 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 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.
OUT/VIN
reaches 95% of
OUT
) and approxi­. To minimize
DS012582-30
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
—A capacitor on this pin provides the regulator with a
SS
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
1. Regulator in Shutdown.
When the SD /SS pin voltage is
Figure 13
).
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
www.national.com 18
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
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.
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.
If the part is operated with an input voltage at or below the internal soft-start clamp voltage of approximately 7V, the voltage on the SD/SS pin tracks the input voltage and can be disturbed by a step in the voltage. To maintain proper func­tion under these conditions, it is strongly recommended that the SD/SS pin be clamped externally between the 3V maxi­mum soft-start threshold and the 4.5V minimum input volt­age.
Figure 15
is an example of an external 3.7V (approx.) clamp that prevents a line-step related glitch but does not interfere with the soft-start behavior of the device.
Figure 13
shows the Soft-start region from
Above 2.8V, the circuit operates as a
LM2599
FIGURE 13. Soft-start, Delay, Error, Output
FIGURE 14. Timing Diagram for 5V Output
DS012582-31
DS012582-32
www.national.com19
Page 20
Application Information (Continued)
LM2599
FIGURE 15. External 3.7V Soft-Start Clamp
DELAY CAPACITOR C
upper curve in
Figure 14
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
lector 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
Figure 1
or when C compensation to the feedback loop and increases the phase margin for better loop stability. For C design procedure section.
If the output ripple is large ( 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 proximately 3 times R1, will attenuate the ripple voltage at the feedback pin.
—Provides delay for the error flag output. See the
DELAY
Figure 13
, and also refer to timing diagrams in
. A capacitor on this pin provides a time delay
—The error flag output, (or power OK) is the col-
Pull Up
- A Feedforward Capacitor CFF, shown across R2 in
FF
is used when the output voltage is greater than 10V
has a very low ESR. This capacitor adds lead
OUT
selection, see the
FF
>
5% of the nominal output
, in series with the feedforward capacitor, ap-
FF
DS012582-65
INPUT CAPACITOR
—A low ESR aluminum or tantalum bypass capacitor is
C
IN
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.
www.national.com 20
Page 21
Application Information (Continued)
DS012582-33
FIGURE 16. RMS Current Ratings for Low
ESR Electrolytic Capacitors (Typical)
DS012582-34
FIGURE 17. Capacitor ESR vs Capacitor Voltage Rating
(Typical Low ESR Electrolytic Capacitor)
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.
A graph shown in 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.
Figure 16
shows the relationship between
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
—An output capacitor is required to filter the output
OUT
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 17
). 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
and for 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 10X at −40˚C. See curve shown in
@
−25˚C and as much as
Figure 18
.
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 charac-
LM2599
3
www.national.com21
Page 22
Application Information (Continued)
LM2599
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.
FIGURE 19. (∆I
Current (as a Percentage of the
Load Current) vs Load Current
DS012582-36
) Peak-to-Peak Inductor Ripple
IND
DS012582-35
FIGURE 18. Capacitor ESR Change vs Temperature
INDUCTOR SELECTION
All switching regulators have two basic modes of operation; continuous and discontinuous. The difference between the two types relates to the inductor current, whether it is flowing continuously, or if it drops to zero for a period of time in the normal switching cycle. Each mode has distinctively different operating characteristics, which can affect the regulators performance and requirements. Most switcher designs will operate in the discontinuous mode when the load current is low.
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
7
). This guide assumes that the regulator is operating in the
Figure 4
through
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 19
).
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.
Exceeding an inductor’s maximum current rating may cause the inductor to overheat because of the copper wire losses, or the core may saturate. If the inductor begins to saturate, the inductance decreases rapidly and the inductor begins to look mainly resistive (the DC resistance of the winding). This can cause the switch current to rise very rapidly and force the switch into a cycle-by-cycle current limit, thus reducing the DC output load current. This can also result in overheat­ing of the inductor and/or the LM2599. Different inductor types have different saturation characteristics, and this should be kept in mind when selecting an inductor.
The inductor manufacturer’s data sheets include current and energy limits to avoid inductor saturation.
www.national.com 22
Page 23
Application Information (Continued)
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.
Different inductor types and/or core materials produce differ­ent amounts of this characteristic ringing. Ferrite core induc­tors have very little core loss and therefore produce the most ringing. The higher core loss of powdered iron inductors produce less ringing. If desired, a series RC could be placed in parallel with the inductor to dampen the ringing. The computer aided design software (version 4.3) will provide all component values for continu­ous and discontinuous modes of operation.
Switchers Made Simple
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 recommended (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 20
shows a typical output ripple voltage, 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.
LM2599
DS012582-37
FIGURE 20. Post Ripple Filter Waveform
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.
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
DS012582-49
FIGURE 21. Peak-to-Peak Inductor
Ripple Current vs Load Current
When a switching regulator is operating in the continuous mode, the inductor current waveform ranges from a triangu­lar to a sawtooth type of waveform (depending on the input voltage). For a given input and output voltage, the peak-to-peak amplitude of this inductor current waveform remains constant. As the load current increases or de­creases, the entire sawtooth current waveform also rises and falls. The average value (or the center) of this current waveform is equal to the DC load current.
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
) can be useful for
IND
www.national.com23
Page 24
Application Information (Continued)
LM2599
eters 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 nomographs shown in
Figure 4
an inductor value, the peak-to-peak inductor ripple current can immediately be determined. The curve shown in
21
shows the range of (∆I
IND
different load currents. The curve also shows how the peak-to-peak inductor ripple current (∆I 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
= 5V, maximum load current of 2.5A
OUT
V
= 12V, nominal, varying between 10V and 16V.
IN
The selection guide in
Figure 5
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
) to flow that will be a percentage of the maximum load
IND
current. Referring to
Figure 21
, follow the 2.5A line approxi­mately midway into the inductance region, and read the peak-to-peak inductor ripple current (∆I axis (approximately 620 mA p-p).
As the input voltage increases to 16V, it approaches the upper border of the inductance region, and the inductor ripple current increases. Referring to the curve in it can be seen that for a load current of 2.5A, the peak-to-peak inductor ripple current (∆I 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
value is known, the following formulas can be
IND
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
= 0.62Ax0.1Ω=62mVp-p
4.
. When the inductor
IND
through7are used to select
) that can be expected for
) changes as you
IND
shows that the vertical line
) on the left hand
IND
) is 620 mA with
IND
)x(ESR of C
IND
Figure 21
)
OUT
Figure
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. 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
Figure 22
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,
www.national.com 24
Page 25
Application Information (Continued)
but with copper areas greater than approximately 6 in small improvements in heat dissipation are realized. If fur­ther thermal improvements are needed, double sided, mul­tilayer pc-board with large copper areas and/or airflow are recommended.
The curves shown in
Figure 23
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.
2
, only
LM2599
DS012582-39
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")
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 22. Junction Temperature Rise, TO-220
FIGURE 23. Junction Temperature Rise, TO-263
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 26
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 24 Figure 25
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.
www.national.com25
Page 26
Application Information (Continued)
LM2599
FIGURE 24. Output Voltage, Input Current,
at Start-Up, WITH Soft-start
DS012582-40
DS012582-41
FIGURE 25. Output Voltage, Input Current,
at Start-Up, WITHOUT Soft-start
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.
FIGURE 26. Typical Circuit Using Shutdown /Soft-start and Error Flag Features
www.national.com 26
DS012582-42
Page 27
Application Information (Continued)
FIGURE 27. Inverting −5V Regulator With Shutdown and Soft-start
lNVERTING REGULATOR
The circuit in 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 guide as to the amount of output load current possible for the different input and output voltage conditions.
Figure 27
converts a positive input voltage to a
Inverting Regulator
Figure 28
provides a
DS012582-43
capacitor to the output, under light
IN
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.
Because of differences in the operation of the inverting regulator, the standard design procedure is not used to select the inductor value. In the majority of designs, a 33 µH,
3.5Ainductor is the best choice. Capacitor selection can also be narrowed down to just a few values. Using the values shown in
Figure 27
will provide good results in the majority of
inverting 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
Also shown in
Figure 27
Figure 27
is recommended.
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.
LM2599
DS012582-44
FIGURE 28. Maximum Load Current for
Inverting Regulator Circuit
UNDERVOLTAGE LOCKOUT
Some applications require the regulator to remain off until the input voltage reaches a predetermined voltage.
29
contains a undervoltage lockout circuit for a buck configu-
ration, while
Figure 30
and30are for the inverting types
Figure
(only the circuitry pertaining to the undervoltage lockout is
www.national.com27
Page 28
Application Information (Continued)
shown).
LM2599
Figure 29
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 ex­ceeds 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.
DS012582-45
FIGURE 29. Undervoltage Lockout for a Buck
Regulator
Figure 30
circuit.
and30apply the same feature to an inverting
Figure 30
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 31
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.
has a
DS012582-47
FIGURE 30. Undervoltage Lockout Without
Hysteresis for an Inverting Regulator
DS012582-46
FIGURE 31. Undervoltage Lockout With
Hysteresis for an Inverting Regulator
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
Figure 32
. 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 requirement 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.
www.national.com 28
DS012582-48
FIGURE 32. Charge Pump for Generating a
Low Current, Negative Output Voltage
Page 29
Application Information (Continued)
TYPICAL THROUGH HOLE PC BOARD LAYOUT, FIXED OUTPUT (1X SIZE), DOUBLE SIDED
LM2599
CIN: — 470 µF, 50V, Aluminum Electrolytic Panasonic, “HFQ Series”
: — 330 µF, 35V, Aluminum Electrolytic Panasonic, “HFQ Series”
C
OUT
D1: — 5A, 40V Schottky Rectifier, 1N5825 L1: — 47 µH, L39, Renco, Through Hole
: — 10k
R
PULL UP
: — 0.1 µF
C
DELAY
: — 0.1 µF
C
SD/SS
Thermalloy Heat Sink
#
7020
DS012582-51
www.national.com29
Page 30
Application Information (Continued)
TYPICAL THROUGH HOLE PC BOARD LAYOUT, ADJUSTABLE OUTPUT (1X SIZE), DOUBLE SIDED
LM2599
CIN: — 470 µF, 50V, Aluminum Electrolytic Panasonic, “HFQ Series”
: — 220 µF, 35V Aluminum Electrolytic Panasonic, “HFQ Series”
C
OUT
D1: — 5A, 40V Schottky Rectifier, 1N5825 L1: — 47 µH, L39, Renco, Through Hole
:—1kΩ,1%
R
1
: — Use formula in Design Procedure
R
2
: — See
C
FF
: — See Application Information Section (CFFSection)
R
FF
R
PULL UP
C
DELAY
C
SD/SS
Thermalloy Heat Sink
Figure 4
: — 10k
: — 0.1 µF
: — 0.1 µF
.
#
7020
FIGURE 33. PC Board Layout
DS012582-52
www.national.com 30
Page 31
Physical Dimensions inches (millimeters) unless otherwise noted
LM2599
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
www.national.com31
Page 32
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
Features
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
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
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.
labeling, can be reasonably expected to result in a significant injury to the user.
National Semiconductor Corporation
Americas
LM2599 SIMPLE SWITCHER Power Converter 150 kHz 3A Step-Down Voltage Regulator, with
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.
Tel: 1-800-272-9959 Fax: 1-800-737-7018 Email: support@nsc.com
www.national.com
National Semiconductor Europe
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
National Semiconductor Asia Pacific Customer Response Group
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
Loading...
Buy Points How it Works FAQ Contact Us Questions and Suggestions Privacy Policy Cookie Policy Terms of Use