LM2590HV [NSC]

SIMPLE SWITCHER Power Converter 150 kHz 1A Step-Down Voltage Regulator, with Features; SIMPLE SWITCHER系列电源转换器150千赫1A降压型稳压器，具有特色


型号：	LM2590HV
厂家：	National Semiconductor
描述：	SIMPLE SWITCHER Power Converter 150 kHz 1A Step-Down Voltage Regulator, with Features SIMPLE SWITCHER系列电源转换器150千赫1A降压型稳压器，具有特色转换器稳压器
文件：	总20页 (文件大小：753K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

December 2001

LM2590HV

SIMPLE SWITCHER^®Power Converter 150 kHz 1A

Step-Down Voltage Regulator, with Features

General Description

Features

n 3.3V, 5V, and adjustable output versions

The LM2590HV 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

1A 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.

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

This series of switching regulators is similar to the

LM2591HV with additional supervisory and performance fea-

tures.

n Input voltage range up to 60V

n 150 kHz fixed frequency internal oscillator

n Shutdown/Soft-start

Requiring a minimum number of external components, these

regulators are simple to use and include internal frequency

n Out of regulation error flag

n Error flag delay

n Low power standby mode, I_Qtypically 90 µA

n High Efficiency

n Thermal shutdown and current limit protection

†

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.

Applications

n Simple high-efficiency step-down (buck) regulator

n Efficient pre-regulator for linear regulators

n On-card switching regulators

Other features include a guaranteed 4% tolerance on out-

n Positive to Negative converter

put voltage under all conditions of input voltage and output

†

Note: Patent Number 5,382,918.

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.

Typical Application (Fixed Output Voltage Versions)

10134701

SIMPLE SWITCHER^®and Switchers Made Simple^®are registered trademarks of National Semiconductor Corporation.

DS101347

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.

ESD Susceptibility

Human Body Model (Note 3)

Lead Temperature

2 kV

S Package

Maximum Supply Voltage (V_IN

)

63V

Vapor Phase (60 sec.)

Infrared (10 sec.)

+215˚C

+245˚C

+260˚C

+150˚C

SD /SS Pin Input Voltage (Note 2)

Delay Pin Voltage (Note 2)

Flag Pin Voltage

1.5V

T Package (Soldering, 10 sec.)

Maximum Junction Temperature

−0.3 ≤ V ≤45V

−0.3 ≤ V ≤+25V

Feedback Pin Voltage

Output Voltage to Ground

(Steady State)

Operating Conditions

Temperature Range

Supply Voltage

−1V

Internally limited

−65˚C to +150˚C

−40˚C ≤ T_J≤ +125˚C

Power Dissipation

4.5V to 60V

Storage Temperature Range

LM2590HV-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

LM2590HV-3.3

Units

(Limits)

Typ

Limit

(Note 4)

3.3

(Note 5)

SYSTEM PARAMETERS (Note 6) Test Circuit Figure 1

V_OUT

Output Voltage

4.75V ≤ V_IN≤ 60V, 0.2A ≤ I_LOAD≤ 1A

3.168/3.135

3.432/3.465

V(min)

V(max)

Efficiency

V_IN= 12V, I_LOAD= 1A

LM2590HV-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

LM2590HV-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≤ 1A

4.800/4.750

5.200/5.250

V(min)

V(max)

Efficiency

V_IN= 12V, I_LOAD= 1A

LM2590HV-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

LM2590HV-ADJ

Units

(Limits)

Typ

Limit

(Note 4)

1.230

(Note 5)

SYSTEM PARAMETERS (Note 6) Test Circuit Figure 1

V_FB

Feedback Voltage

4.5V ≤ V_IN≤ 60V, 0.2A ≤ I_LOAD≤ 1A

V_OUTprogrammed for 3V. Circuit of Figure 1.

1.193/1.180

1.267/1.280

V(min)

V(max)

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LM2590HV-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

LM2590HV-ADJ

Units

(Limits)

Typ

Limit

(Note 4)

(Note 5)

Efficiency

V_IN= 12V, V_OUT= 3V, I_LOAD= 1A

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

LM2590HV-XX

Typ Limit

Units

(Limits)

(Note 4) (Note 5)

DEVICE PARAMETERS

I_b

Feedback Bias Current

Adjustable Version Only, V_FB= 1.3V

(Note 7)

50/100

150

nA (max)

kHz

f_O

Oscillator Frequency

Saturation Voltage

127/110

kHz(min)

173/173 kHz(max)

V_SAT

I_OUT= 1A (Note 8) (Note 9)

0.95

1.2/1.3

V(max)

Max Duty Cycle (ON)

Min Duty Cycle (OFF)

Switch current Limit

(Note 9)

100

(Note 10)

I_CLIM

Peak Current, (Note 8) (Note 9)

1.9

1.3/1.2

2.8/3.0

A(min)

A(max)

µA(max)

I_L

Output Leakage Current

(Note 8) (Note 10) (Note 11)

SD /SS Pin Open (Note 10)

Output = 0V

Output = −1V

mA(max)

I_Q

Operating Quiescent

Current

mA(max)

µA

I_STBY

Standby Quiescent

Current

SD /SS pin = 0V

(Note 11)

200/250

µA(max)

˚C/W

θ_JC

θ_JA

Thermal Resistance

TO220 or TO263 Package, Junction to Case

TO220 Package, Juncton to Ambient (Note 12)

TO263 Package, Juncton to Ambient (Note 13)

TO263 Package, Juncton to Ambient (Note 14)

TO263 Package, Juncton to Ambient (Note 15)

˚C/W

SHUTDOWN/SOFT-START CONTROL Test Circuit of Figure 1

V_SD

Shutdown Threshold

Voltage

1.3

Low, (Shutdown Mode)

0.6

V(max)

V(min)

High, (Soft-start Mode)

V_SS

I_SD

I_SS

Soft-start Voltage

Shutdown Current

Soft-start Current

V_OUT= 20% of Nominal Output Voltage

V_OUT= 100% of Nominal Output Voltage

V_SHUTDOWN= 0.5V

µA

µA(max)

µA

V_Soft-start= 2.5V

1.5

µA(max)

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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

LM2590HV-XX

Typ Limit

Units

(Limits)

(Note 4) (Note 5)

FLAG/DELAY CONTROL Test Circuit of Figure 1

Regulator Dropout Detector

Threshold Voltage

Low (Flag ON)

%(min)

%(max)

VF_SAT

IF_L

Flag Output Saturation

Voltage

I_SINK= 3 mA

V_DELAY= 0.5V

V_FLAG= 60V

0.3

0.7/1.0

0.3

V(max)

µA

Flag Output Leakage Current

Delay Pin Threshold

Voltage

1.25

1.21

1.29

Low (Flag ON)

V(min)

V(max)

µA

High (Flag OFF) and V_OUTRegulated

V_DELAY= 0.5V

Delay Pin Source Current

Delay Pin Saturation

µA(max)

Low (Flag ON)

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: V = 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 in .

Note 13: Junction to ambient thermal resistance with the TO-263 package tab soldered to a single sided printed circuit board with 0.5 in of (1 oz.) copper area.

Note 14: Junction to ambient thermal resistance with the TO-263 package tab soldered to a single sided printed circuit board with 2.5 in of (1 oz.) copper area.

Note 15: Junction to ambient thermal resistance with the TO-263 package tab soldered to a double sided printed circuit board with 3 in of (1 oz.) copper area on

the LM2590HVS side of the board, and approximately 16 in 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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Typical Performance Characteristics (Circuit of Figure 1)

NormalizedOutput Voltage

Line Regulation

Efficiency

10134702

10134703

10134704

Switch SaturationVoltage

Switch Current Limit

Dropout Voltage

10134706

10134705

10134707

Operating

Quiescent Current

Minimum Operating

Supply Voltage

Shutdown Quiescent Current

10134708

10134709

10134710

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Typical Performance Characteristics (Circuit of Figure 1) (Continued)

Feedback Pin Bias Current

Flag Saturation Voltage

Switching Frequency

10134711

10134712

10134713

Shutdown /Soft-start

Current

Soft-start

Delay Pin Current

10134714

10134715

10134716

Shutdown/Soft-start

Threshold Voltage

Soft-start Response

Internal Gain-Phase Characteristics

10134718

10134753

10134778

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Typical Performance Characteristics (Circuit of Figure 1) (Continued)

Continuous Mode Switching Waveforms

V_IN= 20V, V_OUT= 5V, I_LOAD= 1A

Discontinuous Mode Switching Waveforms

V_IN= 20V, V_OUT= 5V, I_LOAD= 250 mA

L = 52 µH, C_OUT= 100 µF, C_OUTESR = 100 mΩ

L = 15 µH, C_OUT= 150 µF, C_OUTESR = 90 mΩ

10134720

10134719

Horizontal Time Base: 2 µs/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 Continuous Mode

V_IN= 20V, V_OUT= 5V, I_LOAD= 250 mA to 1A

L = 52 µH, C_OUT= 100 µF, C_OUTESR = 100 mΩ

Load Transient Response for Discontinuous Mode

V_IN= 20V, V_OUT= 5V, I_LOAD= 250 mA to 1A

L = 15 µH, C_OUT= 150 µF, C_OUTESR = 90 mΩ

10134722

Horizontal Time Base: 200 µs/div.

10134721

A: Output Voltage, 100 mV/div. (AC)

B: 250 mA to 1A Load Pulse

Horizontal Time Base: 50 µs/div.

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

Order Number LM2590HVS-3.3, LM2590HVS-5.0,

or LM2590HVS-ADJ

See NS Package Number TA07B

See NS Package Number TS7B

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Test Circuit and Layout Guidelines

Fixed Output Voltage Versions

10134724

Component Values shown are for V = 15V,

= 5V, I

= 1A.

LOAD

OUT

—

470 µF, 50V, Aluminum Electrolytic Nichicon “PM Series”

220 µF, 25V Aluminum Electrolytic, Nichicon “PM Series”

2A, 60V Schottky Rectifier, 21DQ06 (International Rectifier)

—

OUT

—

68 µH, See Inductor Selection Procedure

Adjustable Output Voltage Versions

10134725

Select R to be approximately 1 kΩ, use a 1% resistor for best stability.

Component Values shown are for V = 20V,

= 10V, I

= 1A.

LOAD

OUT

— 470 µF, 35V, Aluminum Electrolytic Nichicon “PM Series”

— 220 µF, 35V Aluminum Electrolytic, Nichicon “PM Series”

OUT

D1 — 2A, 60V Schottky Rectifier, 21DQ06 (International Rectifier)

L1 — 100 µH, See Inductor Selection Procedure

— 1 kΩ, 1%

— 7.15k, 1%

— 3.3 nF

Typical Values

†

— 0.1 µF

DELAY

PULL UP

— 0.1 µF

— 4.7k (use 22k if V

is ≥ 45V)

OUT

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 (C not being able to discharge immediately will

drag feedback pin below ground). Required if V

40V

FIGURE 1. Standard Test Circuits and Layout Guides

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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 (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.

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.

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-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.

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^thof the set power-up delay time.

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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.

10134731

FIGURE 2. Soft-Start, Delay, Error Output

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10134732

FIGURE 3. Timing Diagram for 5V Output

INDUCTOR VALUE SELECTION GUIDES

(For Continuous Mode Operation)

10134726

FIGURE 4. LM2590HV-3.3

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INDUCTOR VALUE SELECTION GUIDES (For Continuous Mode Operation) (Continued)

10134727

FIGURE 5. LM2590HV-5.0

10134729

FIGURE 6. LM2590HV-ADJ

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INDUCTOR VALUE SELECTION GUIDES (For Continuous Mode Operation) (Continued)

10134765

FIGURE 7. Current Ripple Ratio

Coilcraft Inc.

Phone

(USA): 1-800-322-2645

http://www.coilcraft.com

(UK): 1-236-730595

Web Address

Phone

Coilcraft Inc., Europe

Pulse Engineering Inc.

Web Address

Phone

http://www.coilcraft-europe.com

(USA): 1-858-674-8100

http://www.pulseeng.com

(UK): 1-483-401700

Web Address

Phone

Pulse Engineering Inc.,

Europe

Web Address

Phone

http://www.pulseeng.com

(USA): 1-321-637-1000

http://www.rencousa.com

(USA): 1-952-475-1173

http://www.shottcorp.com

(USA): 1-888-414-2645

http://www.cooperet.com

Renco Electronics Inc.

Web Address

Phone

Schott Corp.

Web Address

Phone

Cooper Electronic Tech.

(Coiltronics)

Web Address

FIGURE 8. Contact Information for Suggested Inductor Manufacturers

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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 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:

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) LM2590HV-5.0, V_IN= 24V, Output

5V 0.8A

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_CLIMof 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_CLIMwithout saturating,

irrespective of the type of core structure/material.

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: (V_IN40V) LM2590HV-5.0, V_IN= 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 I_CLIM. 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 e_CLIMby the

procedure shown in AN-1197 and that the losses are accept-

able. Here e_CLIMis:

2. The Energy under steady operation is

Example 3: (V_IN≤ 40V) LM2590HV-ADJ, V_IN= 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 I_PEAKis 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_CLIMfor

the LM2590HV is 3A. The Energy rating depends on the

Inductance. See Example 2 below.

where V_Dis the drop across the Catch Diode () 0.5V for a

Schottky) and V_SATthe drop across the switch ()1.5V). So

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

And the switch ON time is

where f is the switching frequency in Hz. So

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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.

Application Information (Continued)

Therefore, looking at Figure 4 we quick-select a 100µH/1A

inductor (designed for 150 kHz operation) for this applica-

tion.

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 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.

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 e_CLIMas in

Example 2 above).

Note that we have taken V_SATas 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 require-

ments are known.

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.

FEEDFORWARD CAPACITOR

(Adjustable Output Voltage Version)

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).

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_OUThas 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.

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.

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.

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.

The important parameters for the Input capacitor are the

voltage rating and the RMS current rating. Because of the

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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

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:

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 LM2590HV-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.

where L is in µH and f is in Hz. The maximum possible load

current I_LOADis limited by the requirement that I_PEAK≤ I_CLIM

While checking for this, take I_CLIMto be the lowest possible

current limit value (min across tolerance and temperature is

1.2A for the LM2590HV). 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-

To determine how much load current is possible before the

internal device current limit is reached (and power limiting

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Application Information (Continued)

suming 100% efficiency, which is never so. Therefore expect

I_PEAKto 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 LM2590HV has a

maximum input voltage rating of 60V.

10134745

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_INcapacitor 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.

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 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.

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 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.

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 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.

10134746

FIGURE 13. Undervoltage Lockout With

Hysteresis for an Inverting Regulator

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

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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.

Application Information (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 induc-

tor. Allowing the inductor flux to intersect sensitive feedback,

lC groundpath and C_OUTwiring can cause problems.

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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

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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

LIFE SUPPORT POLICY

NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT

DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL

COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or

systems which, (a) are intended for surgical implant

into the body, or (b) support or sustain life, and

whose failure to perform when properly used in

accordance with instructions for use provided in the

labeling, can be reasonably expected to result in a

significant injury to the user.

2. A critical component is any component of a life

support device or system whose failure to perform

can be reasonably expected to cause the failure of

the life support device or system, or to affect its

safety or effectiveness.

National Semiconductor

Corporation

Americas

National Semiconductor

Europe

National Semiconductor

Asia Pacific Customer

Response Group

Tel: 65-2544466

Fax: 65-2504466

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Tel: 81-3-5639-7560

Fax: 81-3-5639-7507

Fax: +49 (0) 180-530 85 86

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Email: ap.support@nsc.com

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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.

LM2590HV [NSC]

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