LM2591HV
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SNVS074D –MAY 2001–REVISED APRIL 2013
LM2591HV SIMPLE SWITCHER
®
Power Converter 150 kHz 1A Step-Down Voltage
Regulator
Check for Samples: LM2591HV
1FEATURES DESCRIPTION
The LM2591HV series of regulators are monolithic
23• 3.3V, 5V, and Adjustable Output Versions integrated circuits that provide all the active functions
• Adjustable Version Output Voltage Range, for a step-down (buck) switching regulator, capable of
1.2V to 57V ±4% Max Over Line and Load driving a 1A load with excellent line and load
Conditions regulation. These devices are available in fixed output
voltages of 3.3V, 5V, and an adjustable output
• Specified 1A Output Load Current version.
• Available in 5-Pin Package This series of switching regulators is similar to the
• Input Voltage Range Up to 60V LM2590HV, but without some of the supervisory and
• 150 kHz Fixed Frequency Internal Oscillator performance features of the latter.
• On/Off Control Requiring a minimum number of external
• Low Power Standby Mode, IQTypically 90 μAcomponents, these regulators are simple to use and
• High Efficiency include internal frequency compensation†, improved
line and load specifications and a fixed-frequency
• Thermal Shutdown and Current Limit oscillator.
Protection The LM2591HV operates at a switching frequency of
APPLICATIONS 150 kHz thus allowing smaller sized filter components
than what would be needed with lower frequency
• Simple High-Efficiency Step-Down (Buck) switching regulators. Available in a standard 5-lead
Regulator package with several different lead bend options, and
• Efficient Pre-Regulator for Linear Regulators a 5-lead Surface mount package.
• On-Card Switching Regulators Other features include a specified ±4% tolerance on
• Positive to Negative Converter 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.
† Patent Number 5,382,918.
Typical Application
(Fixed Output Voltage Versions)
Figure 1.
1Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
2SIMPLE SWITCHER is a registered trademark of Texas Instruments.
3All other trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date. Copyright © 2001–2013, Texas Instruments Incorporated
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
LM2591HV
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These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
ABSOLUTE MAXIMUM RATINGS (1)(2)
Maximum Supply Voltage (VIN) 63V
ON/OFF Pin Voltage −0.3 ≤V≤+25V
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 (3) 2 kV
Lead Temperature KTT Package Vapor Phase (60 sec.) +215°C
Infrared (10 sec.) +245°C
NDH Package (Soldering, 10 sec.) +260°C
Maximum Junction Temperature +150°C
(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 ensure specific performance limits. For ensured specifications and test
conditions, see Electrical Characteristics.
(2) If Military/Aerospace specified devices are required, please contact the TI Sales Office/ Distributors for availability and specifications.
(3) The human body model is a 100 pF capacitor discharged through a 1.5k resistor into each pin.
OPERATING CONDITIONS
Temperature Range −40°C ≤TJ≤+125°C
Supply Voltage 4.5V to 60V
ELECTRICAL CHARACTERISTICS LM2591HV-3.3
Specifications with standard type face are for TJ= 25°C, and those with boldface type apply over full Operating
Temperature Range.
Symbol Parameter Conditions LM2591HV-3.3 Units
(Limits)
Typ (1) Limit (2)
SYSTEM PARAMETERS Test Circuit Test Circuit and Layout Guidelines(3)
VOUT Output Voltage 4.75V ≤VIN ≤60V, 0.2A ≤ILOAD ≤1A 3.3 V
3.168/3.135 V(min)
3.432/3.465 V(max)
ηEfficiency VIN = 12V, ILOAD = 1A 77
(1) Typical numbers are at 25°C and represent the most likely norm.
(2) All limits ensured 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 ensured via correlation using standard Statistical Quality Control
(SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).
(3) External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance.
When the LM2591HV is used as shown in Test Circuit and Layout Guidelines test circuit, system performance will be as shown in
Electrical Characteristics.
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ELECTRICAL CHARACTERISTICS LM2591HV-5.0
Specifications with standard type face are for TJ= 25°C, and those with boldface type apply over full Operating
Temperature Range.
Symbol Parameter Conditions LM2591HV-5.0 Units
(Limits)
Typ (1) Limit (2)
SYSTEM PARAMETERS Test Circuit Test Circuit and Layout Guidelines(3)
VOUT Output Voltage 7V ≤VIN ≤60V, 0.2A ≤ILOAD ≤1A 5 V
4.800/4.750 V(min)
5.200/5.250 V(max)
ηEfficiency VIN = 12V, ILOAD = 1A 82 %
(1) Typical numbers are at 25°C and represent the most likely norm.
(2) All limits ensured 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 ensured via correlation using standard Statistical Quality Control
(SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).
(3) External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance.
When the LM2591HV is used as shown in Test Circuit and Layout Guidelines test circuit, system performance will be as shown in
Electrical Characteristics.
ELECTRICAL CHARACTERISTICS LM2591HV-ADJ
Specifications with standard type face are for TJ= 25°C, and those with boldface type apply over full Operating
Temperature Range.
Symbol Parameter Conditions LM2591HV-ADJ Units
(Limits)
Typ (1) Limit (2)
SYSTEM PARAMETERS Test Circuit Test Circuit and Layout Guidelines(3)
VFB Feedback Voltage 4.5V ≤VIN ≤60V, 0.2A ≤ILOAD ≤1A 1.230 V
VOUT programmed for 3V. Circuit of Test Circuit and 1.193/1.180 V(min)
Layout Guidelines. 1.267/1.280 V(max)
ηEfficiency VIN = 12V, VOUT = 3V, ILOAD = 1A 76 %
(1) Typical numbers are at 25°C and represent the most likely norm.
(2) All limits ensured 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 ensured via correlation using standard Statistical Quality Control
(SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).
(3) External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance.
When the LM2591HV is used as shown in Test Circuit and Layout Guidelines test circuit, system performance will be as shown in
Electrical Characteristics.
ELECTRICAL CHARACTERISTICS ALL OUTPUT VOLTAGE VERSIONS
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 LM2591HV-XX Units
(Limits)
Typ (1) Limit (2)
DEVICE PARAMETERS
IbFeedback Bias Current Adjustable Version Only, VFB = 1.3V 10 nA
50/100 nA (max)
fOOscillator Frequency See (3) 150 kHz
127/110 kHz(min)
173/173 kHz(max)
VSAT Saturation Voltage IOUT = 1A (4)(5) 0.95 V
1.2/1.3 V(max)
(1) Typical numbers are at 25°C and represent the most likely norm.
(2) All limits ensured 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 ensured via correlation using standard Statistical Quality Control
(SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).
(3) 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.
(4) No diode, inductor or capacitor connected to output pin.
(5) Feedback pin removed from output and connected to 0V to force the output transistor switch ON.
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ELECTRICAL CHARACTERISTICS ALL OUTPUT VOLTAGE VERSIONS (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 LM2591HV-XX Units
(Limits)
Typ (1) Limit (2)
DC Max Duty Cycle (ON) See (5)(6) 100 %
Min Duty Cycle (OFF) 0
ICLIM Switch current Limit Peak Current, (4)(5) 1.9 A
1.3/1.2 A(min)
2.8/3.0 A(max)
ILOutput Leakage Current Output = 0V 50 μA(max)
Output = −1V (4)(6)(7) 5 mA
30 mA(max)
IQOperating Quiescent SD /SS Pin Open (6) 5 mA
Current 10 mA(max)
ISTBY Standby Quiescent SD /SS pin = 0V (7) 90 μA
Current 200/250 μA(max)
θJC Thermal Resistance TO220 or TO263 Package, Junction to Case 2 °C/W
θJA TO220 Package, Junction to Ambient (8) 50 °C/W
θJA TO263 Package, Junction to Ambient (9) 50 °C/W
θJA TO263 Package, Junction to Ambient (10) 30 °C/W
θJA TO263 Package, Junction to Ambient (11) 20 °C/W
ON/OFF CONTROL Test Circuit Test Circuit and Layout Guidelines
ON /OFF Pin Logic Input 1.3 V
VIH Threshold Voltage Low (Regulator ON) 0.6 V(max)
VIL High (Regulator OFF) 2.0 V(min)
IHON /OFF Pin Input Current VLOGIC = 2.5V (Regulator OFF) 5 μA
15 μA(max)
ILVLOGIC = 0.5V (Regulator ON) 0.02 μA
5μA(max)
(6) 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.
(7) VIN = 60V.
(8) 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.
(9) 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.
(10) 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.
(11) 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 LM2591HVS side of the board, and approximately 16 in2of copper on the other side of the p-c board. See
APPLICATION INFORMATION in this data sheet and the thermal model in Switchers Made Simple available at
http://www.ti.com/lsds/ti/analog/powermanagement/power_portal.page.
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TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit of Test Circuit and Layout Guidelines)
Normalized
Output Voltage Line Regulation
Figure 2. Figure 3.
Switch Saturation
Efficiency Voltage
Figure 4. Figure 5.
Switch Current Limit Dropout Voltage
Figure 6. Figure 7.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
(Circuit of Test Circuit and Layout Guidelines)
Operating Shutdown
Quiescent Current Quiescent Current
Figure 8. Figure 9.
Minimum Operating Feedback Pin
Supply Voltage Bias Current
Figure 10. Figure 11.
Switching Frequency ON/OFF Threshold Voltage
Figure 12. Figure 13.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
(Circuit of Test Circuit and Layout Guidelines)
ON/OFF Pin Current (Sinking) Internal Gain-Phase Characteristics
Figure 14. Figure 15.
Continuous Mode Switching Waveforms Discontinuous Mode Switching Waveforms
VIN = 20V, VOUT = 5V, ILOAD = 1A VIN = 20V, VOUT = 5V, ILOAD = 250 mA
L = 52 μH, COUT = 100 μF, COUT ESR = 100 mΩL = 15 μH, COUT = 150 μF, COUT ESR = 90 mΩ
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.
Figure 16. Horizontal Time Base: 2 μs/div. Figure 17. Horizontal Time Base: 2 μs/div.
Load Transient Response for Continuous Mode Load Transient Response for Discontinuous Mode
VIN = 20V, VOUT = 5V, ILOAD = 250 mA to 1A VIN = 20V, VOUT = 5V, ILOAD = 250 mA to 1A
L = 52 μH, COUT = 100 μF, COUT ESR = 100 mΩL = 15 μH, COUT = 150 μF, COUT ESR = 90 mΩ
A: Output Voltage, 100 mV/div. (AC)
B: 250 mA to 1A Load Pulse
A: Output Voltage, 100 mV/div. (AC)
B: 250 mA to 1A Load Pulse
Figure 18. Horizontal Time Base: 50 μs/div. Figure 19. Horizontal Time Base: 200 μs/div.
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CONNECTION DIAGRAMS
Figure 20. Bent and Staggered Leads, Through Figure 21. Surface Mount Package
Hole Package 5-Lead TO-263 (KTT)
5-Lead TO-220 (NDH) See Package Number KTT0005B LM2591HV 7
See Package Number NDH0005D
Test Circuit and Layout Guidelines
Component Values shown are for VIN = 15V,
VOUT = 5V, ILOAD = 1A.
CIN — 470 μF, 50V, Aluminum Electrolytic Nichicon “PM Series”
COUT — 220 μF, 25V Aluminum Electrolytic, Nichicon “PM Series”
D1 — 2A, 60V Schottky Rectifier, 21DQ06 (International Rectifier)
L1 — 68 H, See INDUCTOR SELECTION PROCEDURE
Figure 22. Fixed Output Voltage Versions
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Select R1to be approximately 1 kΩ, use a 1% resistor for best stability.
Component Values shown are for VIN = 20V,
VOUT = 10V, ILOAD = 1A.
CIN: — 470 μF, 35V, Aluminum Electrolytic Nichicon “PM Series”
COUT: — 220 μF, 35V Aluminum Electrolytic, Nichicon “PM Series”
D1 — 2A, 60V Schottky Rectifier, 21DQ06 (International Rectifier)
See INDUCTOR SELECTION PROCEDURE L1 — 100 μH,
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)
† 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 23. Adjustable Output Voltage Versions
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BLOCK DIAGRAM
Figure 24.
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.
Ground (Pin 3)Circuit ground.
Feedback (Pin 4)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 Test Circuit and Layout Guidelines). Feedforward capacitor values
larger than 0.1 μF are not recommended for the same reason, whatever be the DC input voltage.
ON /OFF (Pin 5)The regulator is in shutdown mode, drawing about 90 μA, when this pin is driven to a high level
(≥2.0V), and is in normal operation when this Pin is left floating or driven to a low level (≤0.6V). The
typical value of the threshold is 1.3V and the voltage on this pin must not exceed 25V.
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Inductor Value Selection Guides
(For Continuous Mode Operation)
Figure 25. LM2591HV-3.3
Figure 26. LM2591HV-5.0
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(For Continuous Mode Operation)
Figure 27. LM2591HV-ADJ
Figure 28. Current Ripple Ratio
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(For Continuous Mode Operation)
Table 1. Contact Information for Suggested Inductor Manufacturers
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., Europe Phone (UK): 1-483-401700
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
TDK Phone (USA): 1-847-803-6100
Web Address http://www.componet.tdk.com
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eCLIM = 1
2x L x ICLIM2 PJ
e = 1
2x L x IPEAK2 PJ
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APPLICATION INFORMATION
INDUCTOR SELECTION PROCEDURE
Application Note AN-1197 SNVA038titled "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 25 to Figure 27. 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:
where
• L is in µH
• 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. (1)
3. The Energy under overload is
(2)
If VIN > 40V, the inductor should be sized to handle eCLIM instead of the steady energy values. The worst
case ICLIM for the LM2591HV is 3A. The Energy rating depends on the Inductance. See Example 2.
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 28). This was done to permit the use of smaller inductors
at light loads. However Figure 28 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 SNVA038 for detailed calculations if a certain
maximum inductor current ripple is required for various possible reasons. Also consider the rather wide
tolerance on the nominal inductance of commercial inductors.
5. Figure 27 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.
Example 1: (VIN ≤40V) LM2591HV-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 (see Figure 26) and a current rating equal to the
maximum load current. We therefore quick-select a 100μH/0.8A inductor (designed for 150 kHz operation) for
this application.
2. We should confirm that it is rated to handle 50 μJ (see Figure 26) by either estimating the peak current or by a
detailed calculation as shown in AN-1197 SNVA038, and also that the losses are acceptable.
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= (20 - 1.5 - 10) x 0.55
Et = (VIN - VSAT - VOUT) x tON
150000 x 106 VPsecs
= 31.3 VPsecs
tON = D
fx 106 Ps
D = 10 + 0.5
20 - 1.5 + 0.5 = 0.55
D = VOUT + VD
VIN - VSAT + VD
eCLIM = 1
2x 100 x 32 = 450 PJ
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Example 2: (VIN > 40V) LM2591HV-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 26) 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 SNVA038 and that the
losses are acceptable. Here eCLIM is:
(3)
Example 3: (VIN ≤40V) LM2591HV-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 27 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
• VDis the drop across the Catch Diode (≊0.5V for a Schottky)
• VSAT the drop across the switch (≊1.5V) (4)
So
(5)
And the switch ON time is
where
• f is the switching frequency in Hz (6)
So
(7)
Therefore, looking at Figure 25 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 27) by the procedure shown in AN-1197
SNVA038 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 SNVA038.Table 1 provides helpful contact information on
suggested Inductor manufacturers who may be able to recommend suitable parts, if the requirements are known.
FEEDFORWARD CAPACITOR
(Adjustable Output Voltage Version)
CFF - A Feedforward Capacitor CFF, shown across R2 in Test Circuit and Layout Guidelines 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.
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(Adjustable Output Voltage Version)
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.
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 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.
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 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 LM2591HV 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).
DELAYED STARTUP
The circuit in Figure 29 uses the ON /OFF pin to provide a time delay between the time the input voltage is
applied and the time the output voltage comes up (only the circuitry pertaining to the delayed start up is shown).
As the input voltage rises, the charging of capacitor C1 pulls the ON /OFF pin high, keeping the regulator off.
Once the input voltage reaches its final value and the capacitor stops charging, and resistor R2pulls the ON
/OFF pin low, thus allowing the circuit to start switching. Resistor R1is included to limit the maximum voltage
applied to the ON /OFF pin (maximum of 25V), reduces power supply noise sensitivity, and also limits the
capacitor, C1, discharge current. When high input ripple voltage exists, avoid long delay time, because this ripple
can be coupled into the ON /OFF pin and cause problems.
This delayed startup feature is useful in situations where the input power source is limited in the amount of
current it can deliver. It allows the input voltage to rise to a higher voltage before the regulator starts operating.
Buck regulators require less input current at higher input voltages.
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(Adjustable Output Voltage Version)
Figure 29. Delayed Startup
UNDERVOLTAGE LOCKOUT
Some applications require the regulator to remain off until the input voltage reaches a predetermined voltage. An
undervoltage lockout feature applied to a buck regulator is shown in Figure 30, while Figure 31 and Figure 32
applies the same feature to an inverting circuit. The circuit in Figure 31 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 32
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. If zener voltages greater than 25V are used, an additional 47 kΩresistor
is needed from the ON /OFF pin to the ground pin to stay within the 25V maximum limit of the ON /OFF pin.
Figure 30. Undervoltage Lockout for Buck Regulator
This circuit has an ON/OFF threshold of approximately 13V.
Figure 31. Undervoltage Lockout for Inverting Regulator
Copyright © 2001–2013, Texas Instruments Incorporated Submit Documentation Feedback 17
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( )
6
IN OUT IN OUT
PEAK LOAD
IN IN OUT
V V V V 10
I I
V2 L f V V
æ ö
+ ´ ´
= ´ +
ç ÷ ´ ´ ´ +
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LM2591HV
SNVS074D –MAY 2001–REVISED APRIL 2013
www.ti.com
(Adjustable Output Voltage Version)
lNVERTING REGULATOR
The circuit in Figure 33 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 LM2591HV-5.0 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 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 (8)
While checking for this, take ICLIM to be the lowest possible current limit value (min across tolerance and
temperature is 1.2A for the LM2591HV). Also to account for inductor tolerances, we should take the min value of
Inductance for L in Equation 8 (typically 20% less than the nominal value). Further, Equation 8 disregards the
drop across the Switch and the diode. This is equivalent to assuming 100% efficiency, which is never so.
Therefore expect IPEAK to be an additional 10-20% higher than calculated from Equation 8.
The reader is also referred to Application Note AN-1157 SNVA022 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. For example, when converting +20V to −12V, the regulator would see
32V between the input pin and ground pin. The LM2591HV has a maximum input voltage spec of 60V.
Additional diodes are 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 closley 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 fast recovery diode could be used.
Without diode D3, when the input voltage is first applied, the charging current of CIN can pull the output positive
by several volts for a short period of time. Adding D3 prevents the output from going positive by more than a
diode voltage.
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(Adjustable Output Voltage Version)
This circuit has hysteresis
Regulator starts switching at VIN= 13V
Regulator stops switching at VIN= 8V
Figure 32. Undervoltage Lockout with Hysteresis for Inverting Regulator
CIN —68 μF/25V Tant. Sprague 595D
470 μF/50V Elec. Panasonic HFQ
COUT—47 μF/20V Tant. Sprague 595D
220 μF/25V Elec. Panasonic HFQ
Figure 33. Inverting −5V Regulator with Delayed Startup
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 LM2591HV current limit (approx 4A) are needed for at least 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 delayed startup feature (C1, R1and R2) shown in Figure 33 is
recommended. By delaying the regulator startup, the input capacitor is allowed to charge up to a higher voltage
before the switcher begins operating. A portion of the high input current needed for startup is now supplied by the
input capacitor (CIN). For severe start up conditions, the input capacitor can be made much larger than normal.
lNVERTING REGULATOR SHUTDOWN METHODS
To use the ON /OFF pin in a standard buck configuration is simple, pull it below 1.3V (@25°C, referenced to
ground) to turn regulator ON, pull it above 1.3V to shut the regulator OFF. With the inverting configuration, some
level shifting is required, because the ground pin of the regulator is no longer at ground, but is now setting at the
negative output voltage level. Two different shutdown methods for inverting regulators are shown in Figure 34
and Figure 35.
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(Adjustable Output Voltage Version)
Figure 34. Inverting Regulator Ground Referenced Shutdown
Figure 35. Inverting Regulator Ground Referenced Shutdown using Opto Device
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 Test Circuit and Layout Guidelines, 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
inductor. Allowing the inductor flux to intersect sensitive feedback, lC groundpath and COUT 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.
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SNVS074D –MAY 2001–REVISED APRIL 2013
REVISION HISTORY
Changes from Revision C (April 2013) to Revision D Page
• Changed layout of National Data Sheet to TI format .......................................................................................................... 20
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TAPE AND REEL INFORMATION
*All dimensions are nominal
Device Package
Type Package
Drawing Pins SPQ Reel
Diameter
(mm)
Reel
Width
W1 (mm)
A0
(mm) B0
(mm) K0
(mm) P1
(mm) W
(mm) Pin1
Quadrant
LM2591HVSX-3.3/NOPB DDPAK/
TO-263 KTT 5 500 330.0 24.4 10.75 14.85 5.0 16.0 24.0 Q2
LM2591HVSX-5.0 DDPAK/
TO-263 KTT 5 500 330.0 24.4 10.75 14.85 5.0 16.0 24.0 Q2
LM2591HVSX-5.0/NOPB DDPAK/
TO-263 KTT 5 500 330.0 24.4 10.75 14.85 5.0 16.0 24.0 Q2
LM2591HVSX-ADJ DDPAK/
TO-263 KTT 5 500 330.0 24.4 10.75 14.85 5.0 16.0 24.0 Q2
LM2591HVSX-ADJ/NOPB DDPAK/
TO-263 KTT 5 500 330.0 24.4 10.75 14.85 5.0 16.0 24.0 Q2
PACKAGE MATERIALS INFORMATION
www.ti.com 23-Sep-2013
Pack Materials-Page 1
*All dimensions are nominal
Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)
LM2591HVSX-3.3/NOPB DDPAK/TO-263 KTT 5 500 367.0 367.0 45.0
LM2591HVSX-5.0 DDPAK/TO-263 KTT 5 500 367.0 367.0 45.0
LM2591HVSX-5.0/NOPB DDPAK/TO-263 KTT 5 500 367.0 367.0 45.0
LM2591HVSX-ADJ DDPAK/TO-263 KTT 5 500 367.0 367.0 45.0
LM2591HVSX-ADJ/NOPB DDPAK/TO-263 KTT 5 500 367.0 367.0 45.0
PACKAGE MATERIALS INFORMATION
www.ti.com 23-Sep-2013
Pack Materials-Page 2
MECHANICAL DATA
NDH0005D
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MECHANICAL DATA
KTT0005B
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BOTTOM SIDE OF PACKAGE
TS5B (Rev D)
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