LM2593HV
LM2593HV SIMPLE SWITCHERPower Converter 150 kHz 2A Step-Down Voltage
Regulator, with Features
Literature Number: SNVS082D
LM2593HV
SIMPLE SWITCHER®Power Converter 150 kHz 2A
Step-Down Voltage Regulator, with Features
General Description
The LM2593HV series of regulators are monolithic inte-
grated circuits that provide all the active functions for a
step-down (buck) switching regulator, capable of driving a
2A load with excellent line and load regulation. These de-
vices are available in fixed output voltages of 3.3V, 5V, and
an adjustable output version.
This series of switching regulators is similar to the
LM2592HV with additional supervisory and performance fea-
tures.
Requiring a minimum number of external components, these
regulators are simple to use and include internal frequency
compensation†, improved line and load specifications,
fixed-frequency oscillator, Shutdown/Soft-start, output error
flag and flag delay.
The LM2593HV 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.
Other features include a guaranteed ±4% tolerance on out-
put voltage under all conditions of input voltage and output
load conditions, and ±15% on the oscillator frequency. Ex-
ternal shutdown is included, featuring typically 90 µA
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
n3.3V, 5V, and adjustable output versions
nAdjustable version output voltage range, 1.2V to 57V
±4% max over line and load conditions
nGuaranteed 2A output load current
nAvailable in 7-pin TO-220 and TO-263 (surface mount)
Package
nInput voltage range up to 60V
n150 kHz fixed frequency internal oscillator
nShutdown/Soft-start
nOut of regulation error flag
nError flag delay
nLow power standby mode, I
Q
typically 90 µA
nHigh Efficiency
nThermal shutdown and current limit protection
Applications
nSimple high-efficiency step-down (buck) regulator
nEfficient pre-regulator for linear regulators
nOn-card switching regulators
nPositive to Negative converter
Note: †Patent Number 5,382,918.
Typical Application (Fixed Output Voltage Versions)
10133301
SIMPLE SWITCHER®and
Switchers Made Simple
®are registered trademarks of National Semiconductor Corporation.
December 2001
LM2593HV SIMPLE SWITCHER Power Converter 150 kHz 2A Step-Down Voltage Regulator, with
Features
© 2001 National Semiconductor Corporation DS101333 www.national.com
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
) 63V
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 ≤T
J
≤+125˚C
Supply Voltage 4.5V to 60V
LM2593HV-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 LM2593HV-3.3 Units
(Limits)
Typ Limit
(Note 4) (Note 5)
SYSTEM PARAMETERS (Note 6) Test Circuit
Figure 1
V
OUT
Output Voltage 4.75V ≤V
IN
≤60V, 0.2A ≤I
LOAD
≤2A 3.3 V
3.168/3.135 V(min)
3.432/3.465 V(max)
ηEfficiency V
IN
= 12V, I
LOAD
=2A 76
LM2593HV-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 LM2593HV-5.0 Units
(Limits)
Typ Limit
(Note 4) (Note 5)
SYSTEM PARAMETERS (Note 6) Test Circuit
Figure 1
V
OUT
Output Voltage 7V ≤V
IN
≤60V, 0.2A ≤I
LOAD
≤2A 5 V
4.800/4.750 V(min)
5.200/5.250 V(max)
ηEfficiency V
IN
= 12V, I
LOAD
=2A 81 %
LM2593HV-ADJ
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 LM2593HV-ADJ Units
(Limits)
Typ Limit
(Note 4) (Note 5)
SYSTEM PARAMETERS (Note 6) Test Circuit
Figure 1
V
FB
Feedback Voltage 4.5V ≤V
IN
≤60V, 0.2A ≤I
LOAD
≤2A 1.230 V
V
OUT
programmed for 3V. Circuit of
Figure 1
. 1.193/1.180 V(min)
1.267/1.280 V(max)
LM2593HV
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LM2593HV-ADJ
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.
Symbol Parameter Conditions LM2593HV-ADJ Units
(Limits)
Typ Limit
(Note 4) (Note 5)
ηEfficiency V
IN
= 12V, V
OUT
= 3V, I
LOAD
=2A 75 %
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. I
LOAD
= 500 mA
Symbol Parameter Conditions LM2593HV-XX Units
(Limits)
Typ Limit
(Note 4) (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
= 2A (Note 8) (Note 9) 1.10 V
1.3/1.4 V(max)
DC Max Duty Cycle (ON) (Note 9) 100 %
Min Duty Cycle (OFF) (Note 10) 0
I
CLIM
Switch current Limit Peak Current, (Note 8) (Note 9) 3.0 A
2.4/2.3 A(min)
3.7/4.0 A(max)
I
L
Output Leakage Current (Note 8) (Note 10) (Note 11) Output = 0V 50 µA(max)
Output = −1V 5 mA
30 mA(max)
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) 90 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) 2V(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 1.5 µA
5 µA(max)
LM2593HV
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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. I
LOAD
= 500 mA
Symbol Parameter Conditions LM2593HV-XX Units
(Limits)
Typ Limit
(Note 4) (Note 5)
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
= 60V 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) 70 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%
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
LM2593HV 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.
Note 10: Feedback pin removed from output and connected to 12V for the 3.3V, 5V, and the ADJ. version to force the output transistor switch OFF.
Note 11: VIN = 60V.
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 in2.
Note 13: Junction to ambient thermal resistance with the TO-263 package tab soldered to a single sided printed circuit board with 0.5 in2of (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 in2of (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 in2of (1 oz.) copper area on
the LM2593HVS side of the board, and approximately 16 in2of 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 available at http://power.national.com.
LM2593HV
www.national.com 4
Typical Performance Characteristics (Circuit of
Figure 1
)
Normalized
Output Voltage Line Regulation Efficiency
10133302 10133303 10133304
Switch Saturation
Voltage Switch Current Limit Dropout Voltage
10133305 10133306 10133307
Operating
Quiescent Current Shutdown
Quiescent Current Minimum Operating
Supply Voltage
10133308 10133309 10133310
LM2593HV
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Typical Performance Characteristics (Circuit of
Figure 1
) (Continued)
Feedback Pin
Bias Current Flag Saturation
Voltage Switching Frequency
10133311 10133312 10133313
Soft-start Shutdown /Soft-start
Current Delay Pin Current
10133314 10133315 10133316
Soft-start Response Shutdown/Soft-start
Threshold Voltage Internal Gain-Phase Characteristics
10133318 10133353
10133378
LM2593HV
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Typical Performance Characteristics (Circuit of
Figure 1
) (Continued)
Continuous Mode Switching Waveforms
V
IN
= 20V, V
OUT
= 5V, I
LOAD
=2A
L = 32 µH, C
OUT
= 220 µF, C
OUT
ESR=50mΩ
Discontinuous Mode Switching Waveforms
V
IN
= 20V, V
OUT
= 5V, I
LOAD
= 500 mA
L = 10 µH, C
OUT
= 330 µF, C
OUT
ESR=45mΩ
10133320
Horizontal Time Base: 2 µs/div.
A: Output Pin Voltage, 10V/div.
B: Inductor Current 1A/div.
C: Output Ripple Voltage, 50 mV/div.
10133319
Horizontal Time Base: 2 µs/div.
A: Output Pin Voltage, 10V/div.
B: Inductor Current 0.5A/div.
C: Output Ripple Voltage, 100 mV/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=50mΩ
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=45mΩ
10133321
Horizontal Time Base: 50 µs/div.
A: Output Voltage, 100 mV/div. (AC)
B: 500 mA to 2A Load Pulse
10133322
Horizontal Time Base: 200 µs/div.
A: Output Voltage, 100 mV/div. (AC)
B: 500 mA to 2A Load Pulse
Connection Diagrams and Order Information
Bent and Staggered Leads, Through Hole Package
7-Lead TO-220 (T) Surface Mount Package
7-Lead TO-263 (S)
10133350
Order Number LM2593HVT-3.3, LM2593HVT-5.0,
or LM2593HVT-ADJ
See NS Package Number TA07B
10133323
Order Number LM2593HVS-3.3, LM2593HVS-5.0,
or LM2593HVS-ADJ
See NS Package Number TS7B
LM2593HV
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Test Circuit and Layout Guidelines
Fixed Output Voltage Versions
10133324
Component Values shown are for VIN = 15V,
VOUT = 5V, ILOAD = 2A.
CIN — 470 µF, 50V, Aluminum Electrolytic Nichicon “PM Series”
COUT — 220 µF, 25V Aluminum Electrolytic, Nichicon “PM Series”
D1 — 3.3A, 60V Schottky Rectifier, 31DQ06 (International Rectifier)
L1 — 33 µH, See Inductor Selection Procedure
Adjustable Output Voltage Versions
10133325
Select R1to be approximately 1 kΩ, use a 1% resistor for best stability.
Component Values shown are for VIN = 20V,
VOUT = 10V, ILOAD = 2A.
CIN: — 470 µF, 35V, Aluminum Electrolytic Nichicon “PM Series”
COUT: — 220 µF, 35V Aluminum Electrolytic, Nichicon “PM Series”
D1 — 3.3A, 60V Schottky Rectifier, 31DQ06 (International Rectifier)
L1 — 47 µH, See Inductor Selection Procedure
R1—1kΩ,1%
R
2— 7.15k, 1%
CFF — 3.3 nF
Typical Values
CSS —0.1 µF
CDELAY —0.1 µF
RPULL UP — 4.7k (use 22k if VOUT is ≥45V)
†Resistive divider is required to aviod exceeding maximum rating of 45V/3mA on/into flag pin.
†† Small signal Schottky diode to prevent damage to feedback pin by negative spike when output is shorted (CFF not being able to discharge immediately will
drag feedback pin below ground). Required if VIN >40V
FIGURE 1. Standard Test Circuits and Layout Guides
LM2593HV
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Block Diagram
10133330
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.
Output (Pin 2)—Internal switch. The voltage at this pin
switches between approximately (+V
IN
−V
SAT
) and approxi-
mately −0.5V, with a duty cycle of V
OUT
/V
IN
.
Error Flag (Pin 3)—Open collector output that goes active
low (≤1.0V) when the output of the switching regulator is out
of regulation (less than 95% of its nominal value). In this
state it can sink maximum 3mA. When not low, it can be
pulled high to signal that the output of the regulator is in
regulation (power good). During power-up, it can be pro-
grammed to go high after a certain delay as set by the Delay
pin (Pin 5). The maximum rating of this pin should not be
exceeded, so if the rail to which it will be pulled-up to is
higher than 45V, a resistive divider must be used instead of
a single pull-up resistor, as indicated in
Figure 1
.
Ground (Pin 4)—Circuit ground.
Delay (Pin 5)—This sets a programmable power-up delay
from the moment that the output reaches regulation, to the
high signal output (power good) on Pin 3. A capacitor on this
pin starts charging up by means on an internal ()3 µA)
current source when the regulated output rises to within 5%
of its nominal value. Pin 3 goes high (with an external
pull-up) when the voltage on the capacitor on Pin 5 exceeds
1.3V. The voltage on this pin is clamped internally to about
1.7V. If the regulated output drops out of regulation (less
than 95% of its nominal value), the capacitor on Pin 5 is
rapidly discharged internally and Pin 3 will be forced low in
about 1/1000
th
of the set power-up delay time.
Feedback (Pin 6)—Senses the regulated output voltage to
complete the feedback loop. This pin is directly connected to
the Output for the fixed voltage versions, but is set to 1.23V
by means of a resistive divider from the output for the
Adjustable version. If a feedforward capacitor is used (Ad-
justable version), then a negative voltage spike is generated
on this pin whenever the output is shorted. This happens
because the feedforward capacitor cannot discharge fast
enough, and since one end of it is dragged to Ground, the
other end goes momentarily negative. To prevent the energy
rating of this pin from being exceeded, a small-signal Schot-
tky diode to Ground is recommended for DC input voltages
above 40V whenever a feedforward capacitor is present
(See
Figure 1
). Feedforward capacitor values larger than 0.1
µF are not recommended for the same reason, whatever be
the DC input voltage.
Shutdown /Soft-start (Pin 7)—The regulator is in shut-
down mode, drawing about 90 µA, when this pin is driven to
a low level (≤0.6V), and is in normal operation when this Pin
is left floating (internal pull-up) or driven to a high level (≥
2.0V). The typical value of the threshold is 1.3V and the pin
is internally clamped to a maximum of about 7V. If it is driven
higher than the clamp voltage, it must be ensured by means
of an external resistor that the current into the pin does not
exceed 1mA. The duty cycle is minimum (0%) if this Pin is
below 1.8V, and increases as the voltage on the pin is
increased. The maximum duty cycle (100%) occurs when
this pin is at 2.8V or higher. So adding a capacitor to this pin
produces a softstart feature. An internal current source will
charge the capacitor from zero to its internally clamped
value. The charging current is about 5 µA when the pin is
below 1.3V but is reduced to only 1.6 µA above 1.3V, so as
to allow the use of smaller softstart capacitors.
LM2593HV
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PIN FUNCTIONS (Continued)
Note If any of the above three features (Shutdown
/Soft-start, Error Flag, or Delay) are not used, the respective
pins can be left open.
10133331
FIGURE 2. Soft-Start, Delay, Error Output
LM2593HV
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INDUCTOR VALUE SELECTION GUIDES
(For Continuous Mode Operation)
10133332
FIGURE 3. Timing Diagram for 5V Output
10133365
FIGURE 4. LM2593HV-3.3
LM2593HV
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INDUCTOR VALUE SELECTION GUIDES (For Continuous Mode Operation) (Continued)
10133366
FIGURE 5. LM2593HV-5.0
10133367
FIGURE 6. LM2593HV-ADJ
LM2593HV
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INDUCTOR VALUE SELECTION GUIDES (For Continuous Mode Operation) (Continued)
10133368
FIGURE 7. Current Ripple Ratio
Coilcraft Inc. Phone (USA): 1-800-322-2645
Web Address http://www.coilcraft.com
Coilcraft Inc., Europe Phone (UK): 1-236-730595
Web Address http://www.coilcraft-europe.com
Pulse Engineering Inc. Phone (USA): 1-858-674-8100
Web Address http://www.pulseeng.com
Pulse Engineering Inc., Phone (UK): 1-483-401700
Europe Web Address http://www.pulseeng.com
Renco Electronics Inc. Phone (USA): 1-321-637-1000
Web Address http://www.rencousa.com
Schott Corp. Phone (USA): 1-952-475-1173
Web Address http://www.shottcorp.com
Cooper Electronic Tech.
(Coiltronics) Phone (USA): 1-888-414-2645
Web Address http://www.cooperet.com
FIGURE 8. Contact Information for Suggested Inductor Manufacturers
LM2593HV
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Application Information
INDUCTOR SELECTION PROCEDURE
Application NoteAN-1197 titled ’Selecting Inductors for Buck
Converters’ provides detailed information on this topic. For a
quick-start the designer may refer to the nomographs pro-
vided in
Figure 4
to
Figure 6
. To widen the choice of the
Designer to a more general selection of available inductors,
the nomographs provide the required inductance and also
the energy in the core expressed in microjoules (µJ), as an
alternative to just prescribing custom parts. The following
points need to be highlighted:
1. The Energy values shown on the nomographs apply to
steady operation at the corresponding x-coordinate
(rated maximum load current). However under start-up,
without soft-start, or a short-circuit on the output, the
current in the inductor will momentarily/repetitively hit
the current limit I
CLIM
of the device, and this current
could be much higher than the rated load, I
LOAD
. This
represents an overload situation, and can cause the
Inductor to saturate (if it has been designed only to
handle the energy of steady operation). However most
types of core structures used for such applications have
a large inherent air gap (for example powdered iron
types or ferrite rod inductors), and so the inductance
does not fall off too sharply under an overload. The
device is usually able to protect itself by not allowing the
current to ever exceed I
CLIM
. But if the DC input voltage
to the regulator is over 40V, the current can slew up so
fast under core saturation, that the device may not be
able to act fast enough to restrict the current. The cur-
rent can then rise without limit till destruction of the
device takes place.
Therefore to ensure reliability, it is
recommended, that if the DC Input Voltage exceeds
40V, the inductor must ALWAYS be sized to handle an
instantaneous current equal to I
CLIM
without saturating,
irrespective of the type of core structure/material
.
2. The Energy under steady operation is
where L is in µH and I
PEAK
is the peak of the inductor current
waveform with the regulator delivering I
LOAD
. These are the
energy values shown in the nomographs. See
Example 1
below.
3. The Energy under overload is
If V
IN
>40V, the inductor should be sized to handle e
CLIM
instead of the steady energy values. The worst case I
CLIM
for
the LM2593HV is 4A. The Energy rating depends on the
Inductance. See
Example 2
below.
4. The nomographs were generated by allowing a greater
amount of percentage current ripple in the Inductor as
the maximum rated load decreases (see
Figure 7
). This
was done to permit the use of smaller inductors at light
loads.
Figure 7
however shows only the ’median’ value
of the current ripple. In reality there may be a great
spread around this because the nomographs approxi-
mate the exact calculated inductance to standard avail-
able values. It is a good idea to refer to AN-1197 for
detailed calculations if a certain maximum inductor cur-
rent ripple is required for various possible reasons. Also
consider the rather wide tolerance on the nominal induc-
tance of commercial inductors.
5.
Figure 6
shows the inductor selection curves for the
Adjustable version. The y-axis is ’Et’, in Vµsecs. It is the
applied volts across the inductor during the ON time of
the switch (V
IN
-V
SAT
-V
OUT
) multiplied by the time for
which the switch is on in µsecs. See Example 3 below.
Example 1: (V
IN
≤40V) LM2593HV-5.0, V
IN
= 24V, Output
5V @1A
1. A first pass inductor selection is based upon
Inductance
and rated max load current
. We choose an inductor with the
Inductance value indicated by the nomograph (
Figure 5
) and
a current rating equal to the maximum load current. We
therefore quick-select a 68µH/1A inductor (designed for 150
kHz operation) for this application.
2. We should confirm that it is rated to handle 50 µJ (see
Figure 5
) by either estimating the peak current or by a
detailed calculation as shown in AN-1197, and also that the
losses are acceptable.
Example 2: (V
IN
>40V) LM2593HV-5.0, V
IN
= 48V, Output
5V @1.5A
1. A first pass inductor selection is based upon
Inductance
and the switch currrent limit
. We choose an inductor with the
Inductance value indicated by the nomograph (
Figure 5
) and
a current rating equal to I
CLIM
. We therefore quick-select a
68µH/4A inductor (designed for 150 kHz operation) for this
application.
2. We should confirm that it is rated to handle e
CLIM
by the
procedure shown inAN-1197 and that the losses are accept-
able. Here e
CLIM
is:
Example 3: (V
IN
≤40V) LM2593HV-ADJ, V
IN
= 20V, Output
10V @2A
1. Since input voltage is less than 40V, a first pass inductor
selection is based upon Inductance and rated max load
current. We choose an inductor with the Inductance value
indicated by the nomograph
Figure 6
and a current rating
equal to the maximum load. But we first need to calculate Et
for the given application. The Duty cycle is
where V
D
is the drop across the Catch Diode ()0.5V for a
Schottky) and V
SAT
the drop across the switch ()1.5V). So
And the switch ON time is
where f is the switching frequency in Hz. So
LM2593HV
www.national.com 14
Application Information (Continued)
Therefore, looking at
Figure 4
we quick-select a 47µH/2A
inductor (designed for 150 kHz operation) for this applica-
tion.
2. We should confirm that it is rated to handle 200 µJ (see
Figure 6
) by the procedure shown in AN-1197 and that the
losses are acceptable. (If the DC Input voltage had been
greater than 40V we would need to consider e
CLIM
as in
Example 2 above).
This completes the simplified inductor selection procedure.
For more general applications and better optimization, the
designer should refer to AN-1197.
Figure 8
provides helpful
contact information on suggested Inductor manufacturers
who may be able to recommend suitable parts, if the require-
ments are known.
FEEDFORWARD CAPACITOR
(Adjustable Output Voltage Version)
C
FF
- A Feedforward Capacitor C
FF
, shown across R2 in
Figure 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.
If the output voltage 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, ap-
proximately 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 in-
put, 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 di-
rectly related to the RMS current rating. The voltage rating of
the capacitor and its RMS ripple current capability must
never be exceeded.
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 select-
ing 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 ESR should generally not be less
than 100 mΩor there will be loop instability. If the ESR is too
large, efficiency and output voltage ripple are effected. So
ESR must be chosen carefully.
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 LM2593HV
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-
teristic may cause instability or EMI problems. Ultra-fast
recovery diodes typically have reverse recovery times of 50
ns or less. The diode must be chosen for its average/RMS
current rating and maximum voltage rating. The voltage
rating of the diode must be greater than the DC input voltage
(not the output voltage).
SHUTDOWN /SOFT-START
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 capaci-
tor can be eliminated.
LM2593HV
www.national.com15
Application Information (Continued)
lNVERTING REGULATOR
The circuit in
Figure 10
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 regu-
lates it.
This example uses the LM2593HV-5 to generate a −5V
output, but other output voltages are possible by selecting
other output voltage versions, including the adjustable ver-
sion. 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.
To determine how much load current is possible before the
internal device current limit is reached (and power limiting
occurs), the system must be evaluated as a buck-boost
configuration rather than as a buck. The peak switch current
in Amperes, for such a configuration is given as:
where L is in µH and f is in Hz. The maximum possible load
current I
LOAD
is limited by the requirement that I
PEAK
≤I
CLIM
.
While checking for this, take I
CLIM
to be the lowest possible
current limit value (min across tolerance and temperature is
2.3A for the LM2593HV). Also to account for inductor toler-
ances, we should take the min value of Inductance for L in
the equation above (typically 20% less than the nominal
value). Further, the above equation disregards the drop
across the Switch and the diode. This is equivalent to as-
10133342
FIGURE 9. Typical Circuit Using Shutdown /Soft-start and Error Flag Features
10133343
FIGURE 10. Inverting −5V Regulator With Shutdown and Soft-start
LM2593HV
www.national.com 16
Application Information (Continued)
suming 100% efficiency, which is never so. Therefore expect
I
PEAK
to be an additional 10-20% higher than calculated from
the above equation.
The reader is also referred to Application Note AN-1157 for
examples based on positive to negative configuration.
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 60V. In this example, when
converting +20V to −5V, the regulator would see 25V be-
tween the input pin and ground pin. The LM2593HV has a
maximum input voltage rating of 60V.
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 pro-
viding good closed loop stability. A Schottky diode is recom-
mended 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,
4A inductor is the best choice. Capacitor selection can also
be narrowed down to just a few values.
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 LM2593HV current limit
(approximately 4.0A) 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 rela-
tively high startup currents required by the inverting topology,
the Soft-Start feature shown in
Figure 10
is recommended.
Also shown in
Figure 10
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 11
contains a undervoltage lockout circuit for a buck configura-
tion, while
Figure 12
and
Figure 13
are for the inverting types
(only the circuitry pertaining to the undervoltage lockout is
shown).
Figure 11
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 12
and
Figure 13
apply the same feature to an
inverting circuit.
Figure 12
features a constant threshold
voltage for turn on and turn off (zener voltage plus approxi-
mately one volt). If hysteresis is needed, the circuit in
Figure
13
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 is shown in
Figure 14
. This unregulated negative voltage is approxi-
mately 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
10133345
FIGURE 11. Undervoltage Lockout for a Buck
Regulator
10133347
FIGURE 12. Undervoltage Lockout Without
Hysteresis for an Inverting Regulator
10133346
FIGURE 13. Undervoltage Lockout With
Hysteresis for an Inverting Regulator
LM2593HV
www.national.com17
Application Information (Continued)
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 LM2593HV current
limit.
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.
THERMAL CONSIDERATIONS
The LM2593HV is available in two packages, a 5-pin TO-220
(T) and a 5-pin surface mount TO-263 (S).
The TO-220 package needs a heat sink under most condi-
tions. The size of the heatsink depends on the input voltage,
the output voltage, the load current and the ambient tem-
perature. 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, mul-
tilayer PC board with large copper areas and/or airflow are
recommended.
The curves shown in
Figure 15
show the LM2593HVS
(TO-263 package) junction temperature rise above ambient
temperature with a 2A load 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, espe-
cially for high ambient temperatures and high output volt-
ages.
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 surround-
ing air is still or moving. Furthermore, some of these com-
ponents 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.
10133348
FIGURE 14. Charge Pump for Generating aLow Current, Negative Output Voltage
LM2593HV
www.national.com 18
Application Information (Continued)
Layout Suggestions
As in any switching regulator, layout is very important. Rap-
idly switching currents associated with wiring inductance can
generate voltage transients which can cause problems. For
minimal inductance and ground loops, with reference to
Figure 1
, the wires indicated by heavy lines should be wide
printed circuit traces and should be kept as short as
possible. For best results, external components should be
located as close to the switcher lC as possible using ground
plane construction or single point grounding.
If open core inductors are used, special care must be
taken as to the location and positioning of this type of induc-
tor. 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.
10133338
FIGURE 15. Junction Temperature Rise, TO-263
LM2593HV
www.national.com19
Physical Dimensions inches (millimeters)
unless otherwise noted
7-Lead TO-220 Bent and Staggered Package
Order Number LM2593HVT-3.3, LM2593HVT-5.0 or LM2593HVT-ADJ
NS Package Number TA07B
LM2593HV
www.national.com 20
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
7-Lead TO-263 Bent and Formed Package
Order Number LM2593HVS-3.3, LM2593HVS-5.0 or LM2593HVS-ADJ
NS Package Number TS7B
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COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
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www.national.com
LM2593HV SIMPLE SWITCHER Power Converter 150 kHz 2A 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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