LM2590HV - Texas Instruments

LM2590HV - Texas Instruments
LM2590HV
LM2590HV SIMPLE SWITCHERPower Converter 150 kHz 1A Step-Down Voltage
Regulator, with Features
Literature Number: SNVS084B
LM2590HV
SIMPLE SWITCHER ® Power Converter 150 kHz 1A
Step-Down Voltage Regulator, with Features
General Description
Features
The LM2590HV series of regulators are monolithic integrated circuits that provide all the active functions for a
step-down (buck) switching regulator, capable of driving a
1A load with excellent line and load regulation. These devices are available in fixed output voltages of 3.3V, 5V, and
an adjustable output version.
This series of switching regulators is similar to the
LM2591HV with additional supervisory and performance features.
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 LM2590HV 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 output voltage under all conditions of input voltage and output
load conditions, and ± 15% on the oscillator frequency. External 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.
n 3.3V, 5V, and adjustable output versions
n Adjustable version output voltage range, 1.2V to 57V
± 4% max over line and load conditions
n Guaranteed 1A output load current
n Available in 7-pin TO-220 and TO-263 (surface mount)
Package
n Input voltage range up to 60V
n 150 kHz fixed frequency internal oscillator
n Shutdown/Soft-start
n Out of regulation error flag
n Error flag delay
n Low power standby mode, IQ typically 90 µA
n High Efficiency
n Thermal shutdown and current limit protection
Typical Application
Applications
n
n
n
n
Simple high-efficiency step-down (buck) regulator
Efficient pre-regulator for linear regulators
On-card switching regulators
Positive to Negative converter
Note: † Patent Number 5,382,918.
(Fixed Output Voltage Versions)
10134701
SIMPLE SWITCHER ® and Switchers Made Simple ® are registered trademarks of National Semiconductor Corporation.
© 2001 National Semiconductor Corporation
DS101347
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LM2590HV SIMPLE SWITCHER Power Converter 150 kHz 1A Step-Down Voltage Regulator, with
Features
December 2001
LM2590HV
Absolute Maximum Ratings
ESD Susceptibility
(Note 1)
Human Body Model (Note 3)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Maximum Supply Voltage (VIN)
S Package
63V
SD /SS Pin Input Voltage (Note 2)
6V
Delay Pin Voltage (Note 2)
1.5V
+215˚C
Infrared (10 sec.)
+245˚C
+260˚C
Maximum Junction Temperature
+150˚C
−0.3 ≤ V ≤+25V
Feedback Pin Voltage
Output Voltage to Ground
(Steady State)
Operating Conditions
−1V
Internally limited
Temperature Range
−65˚C to +150˚C
Supply Voltage
Power Dissipation
Storage Temperature Range
Vapor Phase (60 sec.)
T Package (Soldering, 10 sec.)
−0.3 ≤ V ≤45V
Flag Pin Voltage
2 kV
Lead Temperature
−40˚C ≤ TJ ≤ +125˚C
4.5V to 60V
LM2590HV-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
LM2590HV-3.3
Typ
Limit
(Note 4)
(Note 5)
Units
(Limits)
SYSTEM PARAMETERS (Note 6) Test Circuit Figure 1
VOUT
η
Output Voltage
Efficiency
4.75V ≤ VIN ≤ 60V, 0.2A ≤ ILOAD ≤ 1A
VIN = 12V, ILOAD = 1A
3.3
V
3.168/3.135
V(min)
3.432/3.465
V(max)
77
LM2590HV-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
LM2590HV-5.0
Typ
Limit
(Note 4)
(Note 5)
Units
(Limits)
SYSTEM PARAMETERS (Note 6) Test Circuit Figure 1
VOUT
η
Output Voltage
Efficiency
7V ≤ VIN ≤ 60V, 0.2A ≤ ILOAD ≤ 1A
VIN = 12V, ILOAD = 1A
5
V
4.800/4.750
V(min)
5.200/5.250
V(max)
82
%
LM2590HV-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
LM2590HV-ADJ
Typ
Limit
(Note 4)
(Note 5)
Units
(Limits)
SYSTEM PARAMETERS (Note 6) Test Circuit Figure 1
VFB
Feedback Voltage
4.5V ≤ VIN ≤ 60V, 0.2A ≤ ILOAD ≤ 1A
VOUT programmed for 3V. Circuit of Figure 1.
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2
1.230
V
1.193/1.180
V(min)
1.267/1.280
V(max)
(Continued)
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Temperature Range.
Symbol
η
Parameter
Efficiency
Conditions
LM2590HV-ADJ
Units
(Limits)
Typ
Limit
(Note 4)
(Note 5)
VIN = 12V, VOUT = 3V, ILOAD = 1A
76
%
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, VIN = 12V for the 3.3V, 5V, and Adjustable version. ILOAD = 500 mA
Symbol
Parameter
Conditions
LM2590HV-XX
Typ
Limit
(Note 4)
(Note 5)
Units
(Limits)
DEVICE PARAMETERS
Ib
Feedback Bias Current
Adjustable Version Only, VFB = 1.3V
10
nA
50/100
fO
Oscillator Frequency
(Note 7)
150
VSAT
Saturation Voltage
IOUT = 1A (Note 8) (Note 9)
0.95
DC
Max Duty Cycle (ON)
(Note 9)
100
Min Duty Cycle (OFF)
(Note 10)
0
Switch current Limit
Peak Current, (Note 8) (Note 9)
kHz
127/110
kHz(min)
173/173
kHz(max)
V
1.2/1.3
ICLIM
IL
Output Leakage Current
(Note 8) (Note 10) (Note 11)
Output = −1V
IQ
Operating Quiescent
ISTBY
Standby Quiescent
5
SD /SS pin = 0V
90
Current
(Note 11)
Current
θJC
Thermal Resistance
A
1.3/1.2
A(min)
2.8/3.0
A(max)
50
µA(max)
30
mA(max)
5
SD /SS Pin Open (Note 10)
V(max)
%
1.9
Output = 0V
nA (max)
mA
mA
10
mA(max)
200/250
µA(max)
µA
TO220 or TO263 Package, Junction to Case
2
˚C/W
θJA
TO220 Package, Juncton to Ambient (Note 12)
50
˚C/W
θJA
TO263 Package, Juncton to Ambient (Note 13)
50
˚C/W
θJA
TO263 Package, Juncton to Ambient (Note 14)
30
˚C/W
θJA
TO263 Package, Juncton to Ambient (Note 15)
20
˚C/W
SHUTDOWN/SOFT-START CONTROL Test Circuit of Figure 1
VSD
Shutdown Threshold
Voltage
1.3
Low, (Shutdown Mode)
High, (Soft-start Mode)
VSS
ISD
Soft-start Voltage
Shutdown Current
VOUT = 20% of Nominal Output Voltage
2
VOUT = 100% of Nominal Output Voltage
3
VSHUTDOWN = 0.5V
5
V
0.6
V(max)
2
V(min)
V
µA
10
ISS
Soft-start Current
VSoft-start = 2.5V
1.5
µA
5
3
µA(max)
µA(max)
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LM2590HV
LM2590HV-ADJ
Electrical Characteristics
LM2590HV
All Output Voltage Versions
Electrical Characteristics (Continued)
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Temperature Range. Unless otherwise specified, VIN = 12V for the 3.3V, 5V, and Adjustable version. ILOAD = 500 mA
Symbol
Parameter
Conditions
LM2590HV-XX
Typ
Limit
(Note 4)
(Note 5)
Units
(Limits)
FLAG/DELAY CONTROL Test Circuit of Figure 1
Regulator Dropout Detector
Low (Flag ON)
96
Threshold Voltage
VFSAT
IFL
Flag Output Saturation
ISINK = 3 mA
Voltage
VDELAY = 0.5V
Flag Output Leakage Current
VFLAG = 60V
Delay Pin Source Current
Delay Pin Saturation
%(min)
98
%(max)
0.7/1.0
V(max)
0.3
V
0.3
Delay Pin Threshold
Voltage
%
92
µA
1.25
V
Low (Flag ON)
1.21
V(min)
High (Flag OFF) and VOUT Regulated
1.29
V(max)
6
µA(max)
VDELAY = 0.5V
3
Low (Flag ON)
µA
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
LM2590HV 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 in2 of (1 oz.) copper area.
Note 14: Junction to ambient thermal resistance with the TO-263 package tab soldered to a single sided printed circuit board with 2.5 in2 of (1 oz.) copper area.
Note 15: Junction to ambient thermal resistance with the TO-263 package tab soldered to a double sided printed circuit board with 3 in2 of (1 oz.) copper area on
the LM2590HVS side of the board, and approximately 16 in2 of copper on the other side of the p-c board. See application hints in this data sheet and the thermal
model in Switchers Made Simple available at http://power.national.com.
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4
NormalizedOutput Voltage
(Circuit of Figure 1)
Line Regulation
Efficiency
10134702
Switch SaturationVoltage
10134703
Switch Current Limit
10134704
Dropout Voltage
10134706
10134705
Operating
Quiescent Current
LM2590HV
Typical Performance Characteristics
Shutdown Quiescent Current
10134708
10134709
5
10134707
Minimum Operating
Supply Voltage
10134710
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LM2590HV
Typical Performance Characteristics
Feedback Pin Bias Current
(Circuit of Figure 1) (Continued)
Flag Saturation Voltage
10134711
10134714
Soft-start Response
10134713
10134712
Shutdown /Soft-start
Current
Soft-start
Switching Frequency
10134715
Shutdown/Soft-start
Threshold Voltage
10134718
Delay Pin Current
10134716
Internal Gain-Phase Characteristics
10134753
10134778
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6
(Circuit of Figure 1) (Continued)
Discontinuous Mode Switching Waveforms
VIN = 20V, VOUT = 5V, ILOAD = 250 mA
L = 15 µH, COUT = 150 µF, COUT ESR = 90 mΩ
Continuous Mode Switching Waveforms
VIN = 20V, VOUT = 5V, ILOAD = 1A
L = 52 µH, COUT = 100 µF, COUT ESR = 100 mΩ
10134720
10134719
Horizontal Time Base: 2 µs/div.
Horizontal Time Base: 2 µs/div.
A: Output Pin Voltage, 10V/div.
A: Output Pin Voltage, 10V/div.
B: Inductor Current 0.5A/div.
B: Inductor Current 0.25A/div.
C: Output Ripple Voltage, 50 mV/div.
C: Output Ripple Voltage, 100 mV/div.
Load Transient Response for Discontinuous Mode
VIN = 20V, VOUT = 5V, ILOAD = 250 mA to 1A
L = 15 µH, COUT = 150 µF, COUT ESR = 90 mΩ
Load Transient Response for Continuous Mode
VIN = 20V, VOUT = 5V, ILOAD = 250 mA to 1A
L = 52 µH, COUT = 100 µF, COUT ESR = 100 mΩ
10134722
Horizontal Time Base: 200 µs/div.
10134721
A: Output Voltage, 100 mV/div. (AC)
Horizontal Time Base: 50 µs/div.
B: 250 mA to 1A Load Pulse
A: Output Voltage, 100 mV/div. (AC)
B: 250 mA to 1A 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)
10134750
10134723
Order Number LM2590HVT-3.3, LM2590HVT-5.0,
or LM2590HVT-ADJ
See NS Package Number TA07B
Order Number LM2590HVS-3.3, LM2590HVS-5.0,
or LM2590HVS-ADJ
See NS Package Number TS7B
7
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LM2590HV
Typical Performance Characteristics
LM2590HV
Test Circuit and Layout Guidelines
Fixed Output Voltage Versions
10134724
Component Values shown are for VIN = 15V,
VOUT = 5V, ILOAD = 1A.
— 470 µF, 50V, Aluminum Electrolytic Nichicon “PM Series”
CIN
COUT
—
220 µF, 25V Aluminum Electrolytic, Nichicon “PM Series”
D1
—
2A, 60V Schottky Rectifier, 21DQ06 (International Rectifier)
L1
—
68 µH, See Inductor Selection Procedure
Adjustable Output Voltage Versions
10134725
Select R1 to be approximately 1 kΩ, use a 1% resistor for best stability.
Component Values shown are for VIN = 20V,
VOUT = 10V, ILOAD = 1A.
— 470 µF, 35V, Aluminum Electrolytic Nichicon “PM Series”
CIN:
COUT:
— 220 µF, 35V Aluminum Electrolytic, Nichicon “PM Series”
D1 — 2A, 60V Schottky Rectifier, 21DQ06 (International Rectifier)
L1 — 100 µH, See Inductor Selection Procedure
R1 — 1 kΩ, 1%
R2 — 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
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8
LM2590HV
Block Diagram
10134730
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 (Adjustable 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 Schottky 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 shutdown 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-pullup) 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.
PIN FUNCTIONS
+VIN (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 (+VIN − VSAT) and approximately −0.5V, with a duty cycle of VOUT/VIN.
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 programmed 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 1/1000th of the set power-up delay time.
9
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LM2590HV
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.
10134731
FIGURE 2. Soft-Start, Delay, Error Output
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10
LM2590HV
10134732
FIGURE 3. Timing Diagram for 5V Output
INDUCTOR VALUE SELECTION GUIDES
(For Continuous Mode Operation)
10134726
FIGURE 4. LM2590HV-3.3
11
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LM2590HV
INDUCTOR VALUE SELECTION GUIDES
(For Continuous Mode Operation) (Continued)
10134727
FIGURE 5. LM2590HV-5.0
10134729
FIGURE 6. LM2590HV-ADJ
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12
(For Continuous Mode Operation) (Continued)
10134765
FIGURE 7. Current Ripple Ratio
Coilcraft Inc.
Coilcraft Inc., Europe
Pulse Engineering Inc.
Phone
(USA): 1-800-322-2645
Web Address
http://www.coilcraft.com
Phone
(UK): 1-236-730595
Web Address
http://www.coilcraft-europe.com
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
Phone
(USA): 1-952-475-1173
Web Address
http://www.shottcorp.com
Schott Corp.
Cooper Electronic Tech.
(Coiltronics)
Phone
(USA): 1-888-414-2645
Web Address
http://www.cooperet.com
FIGURE 8. Contact Information for Suggested Inductor Manufacturers
13
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LM2590HV
INDUCTOR VALUE SELECTION GUIDES
LM2590HV
Application Information
INDUCTOR SELECTION PROCEDURE
Application Note AN-1197 titled ’Selecting Inductors for Buck
Converters’ provides detailed information on this topic. For a
quick-start the designer may refer to the nomographs provided 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 ICLIM of the device, and this current
could be much higher than the rated load, ILOAD. 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 ICLIM. 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 current 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 ICLIM without saturating,
irrespective of the type of core structure/material.
2. The Energy under steady operation is
consider the rather wide tolerance on the nominal inductance 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 (VIN-VSAT-VOUT) multiplied by the time for
which the switch is on in µsecs. See Example 3 below.
Example 1: (VIN ≤ 40V) LM2590HV-5.0, VIN = 24V, Output
5V @ 0.8A
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 100µH/0.8 A 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: (VIN > 40V) LM2590HV-5.0, VIN = 48V, Output
5V @ 1A
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 ICLIM. We therefore quick-select a
100µH/3A inductor (designed for 150 kHz operation) for this
application.
2. We should confirm that it is rated to handle eCLIM by the
procedure shown in AN-1197 and that the losses are acceptable. Here eCLIM is:
Example 3: (VIN ≤ 40V) LM2590HV-ADJ, VIN = 20V, Output
10V @ 1A
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 L is in µH and IPEAK is the peak of the inductor current
waveform with the regulator delivering ILOAD. These are the
energy values shown in the nomographs. See Example 1
below.
3. The Energy under overload is
If VIN > 40V, the inductor should be sized to handle eCLIM
instead of the steady energy values. The worst case ICLIM for
the LM2590HV is 3A. 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 approximate the exact calculated inductance to standard available values. It is a good idea to refer to AN-1197 for
detailed calculations if a certain maximum inductor current ripple is required for various possible reasons. Also
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where VD is the drop across the Catch Diode () 0.5V for a
Schottky) and VSAT the drop across the switch ()1.5V). So
And the switch ON time is
where f is the switching frequency in Hz. So
14
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 voltage rating of
the capacitor and its RMS ripple current capability must
never be exceeded.
(Continued)
Therefore, looking at Figure 4 we quick-select a 100µH/1A
inductor (designed for 150 kHz operation) for this application.
2. We should confirm that it is rated to handle 100 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 eCLIM as in
Example 2 above).
Note that we have taken VSAT as 1.5V which includes an
estimated resistive drop across the inductor.
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 requirements are known.
OUTPUT CAPACITOR
COUT — An output capacitor is required to filter the output
and provide regulator loop stability. Low impedance or low
ESR Electrolytic or solid tantalum capacitors designed for
switching regulator applications must be used. When selecting an output capacitor, the important capacitor parameters
are; the 100 kHz Equivalent Series Resistance (ESR), the
RMS ripple current rating, voltage rating, and capacitance
value. For the output capacitor, the ESR value is the most
important parameter. The ESR should generally not be less
than 100 mΩ or 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 LM2590HV
using short leads and short printed circuit traces.
Because of their very fast switching speed and low forward
voltage drop, Schottky diodes provide the best performance,
especially in low output voltage applications (5V and lower).
Ultra-fast recovery, or High-Efficiency rectifiers are also a
good choice, but some types with an abrupt turnoff characteristic may cause instability or EMI problems. Ultra-fast
recovery diodes typically have reverse recovery times of 50
ns or less. 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).
FEEDFORWARD CAPACITOR
(Adjustable Output Voltage Version)
CFF - A Feedforward Capacitor CFF, shown across R2 in
Figure 1 is used when the output voltage is greater than 10V
or when COUT 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, RFF, in series with the feedforward capacitor, approximately 3 times R1, will attenuate the ripple voltage at
the feedback pin.
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 capacitor can be eliminated.
INPUT CAPACITOR
CIN — A low ESR aluminum or tantalum bypass capacitor is
needed between the input pin and ground pin. It must be
located near the regulator using short leads. This capacitor
prevents large voltage transients from appearing at the input, and provides the instantaneous current needed each
time the switch turns on.
The important parameters for the Input capacitor are the
voltage rating and the RMS current rating. Because of the
15
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LM2590HV
Application Information
LM2590HV
Application Information
(Continued)
10134742
FIGURE 9. Typical Circuit Using Shutdown /Soft-start and Error Flag Features
10134743
FIGURE 10. Inverting −5V Regulator With Shutdown and Soft-start
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 regulates it.
This example uses the LM2590HV-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.
To determine how much load current is possible before the
internal device current limit is reached (and power limiting
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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 ILOAD is limited by the requirement that IPEAK ≤ ICLIM.
While checking for this, take ICLIM to be the lowest possible
current limit value (min across tolerance and temperature is
1.2A for the LM2590HV). Also to account for inductor tolerances, 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 as16
LM2590HV
Application Information
(Continued)
suming 100% efficiency, which is never so. Therefore expect
IPEAK 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 between the input pin and ground pin. The LM2590HV 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 CIN capacitor to the output, under light
or no load conditions. Also, this diode isolation changes the
topology to closely resemble a buck configuration thus providing good closed loop stability. A Schottky diode is recommended for low input voltages, (because of its lower voltage
drop) but for higher input voltages, a IN5400 diode could be
used.
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,
3A 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 LM2590HV current limit
(approximately 3.0A) 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 relatively 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.
10134745
FIGURE 11. Undervoltage Lockout for a Buck
Regulator
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 approximately 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.
10134747
FIGURE 12. Undervoltage Lockout Without
Hysteresis for an Inverting Regulator
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 configuration, 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 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.
10134746
FIGURE 13. Undervoltage Lockout With
Hysteresis for an Inverting Regulator
Layout Suggestions
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, with reference to
Figure 1, the wires indicated by heavy lines should be wide
printed circuit traces and should be kept as short as
17
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LM2590HV
Application Information
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.
(Continued)
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 inductor. Allowing the inductor flux to intersect sensitive feedback,
lC groundpath and COUT wiring can cause problems.
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18
LM2590HV
Physical Dimensions
inches (millimeters)
unless otherwise noted
7-Lead TO-220 Bent and Staggered Package
Order Number LM2590HVT-3.3, LM2590HVT-5.0 or LM2590HVT-ADJ
NS Package Number TA07B
19
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LM2590HV SIMPLE SWITCHER Power Converter 150 kHz 1A Step-Down Voltage Regulator, with
Features
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
7-Lead TO-263 Bent and Formed Package
Order Number LM2590HVS-3.3, LM2590HVS-5.0 or LM2590HVS-ADJ
NS Package Number TS7B
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