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LM2590HV中文资料

LM2590HV

SIMPLE SWITCHER ?Power Converter 150kHz 1A Step-Down Voltage Regulator,with Features

General Description

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.

This series of switching regulators is similar to the LM2591HV with additional supervisory and performance fea-tures.

Requiring a minimum number of external components,these regulators are simple to use and include internal frequency compensation ?,improved line and load specifications,fixed-frequency oscillator,Shutdown/Soft-start,output error flag and flag delay.

The LM2590HV operates at a switching frequency of 150kHz thus allowing smaller sized filter components than what would be needed with lower frequency switching regulators.Available in a standard 7-lead TO-220package with several different lead bend options,and a 7-lead TO-263Surface mount package.

Other features include a guaranteed ±4%tolerance on out-put voltage under all conditions of input voltage and output load conditions,and ±15%on the oscillator frequency.Ex-ternal shutdown is included,featuring typically 90μA standby current.Self protection features include a two stage current limit for the output switch and an over temperature shutdown for complete protection under fault conditions.

Features

n 3.3V,5V,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-220and TO-263(surface mount)Package

n Input voltage range up to 60V

n 150kHz fixed frequency internal oscillator n Shutdown/Soft-start

n Out of regulation error flag n Error flag delay

n Low power standby mode,I Q typically 90μA n High Efficiency

n Thermal shutdown and current limit protection

Applications

n Simple high-efficiency step-down (buck)regulator n Efficient pre-regulator for linear regulators n On-card switching regulators n

Positive to Negative converter

Note:?Patent Number 5,382,918.

Typical Application

(Fixed Output Voltage Versions)

10134701

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

December 2001

LM2590HV SIMPLE SWITCHER Power Converter 150kHz 1A Step-Down Voltage Regulator,with Features

?2001National Semiconductor Corporation https://www.wendangku.net/doc/6016639801.html,

Absolute Maximum Ratings

(Note 1)If Military/Aerospace specified devices are required,please contact the National Semiconductor Sales Office/Distributors for availability and specifications.Maximum Supply Voltage (V IN )63V SD /SS Pin Input Voltage (Note 2)6V Delay Pin Voltage (Note 2) 1.5V

Flag Pin Voltage ?0.3≤V ≤45V Feedback Pin Voltage ?0.3≤V ≤+25V

Output Voltage to Ground (Steady State)?1V

Power Dissipation

Internally limited Storage Temperature Range

?65?C to +150?C

ESD Susceptibility

Human Body Model (Note 3)2kV

Lead Temperature S Package

Vapor Phase (60sec.)+215?C Infrared (10sec.)

+245?C T Package (Soldering,10sec.)+260?C Maximum Junction Temperature

+150?C Operating Conditions

Temperature Range ?40?C ≤T J ≤+125?C

Supply Voltage

4.5V to 60V

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)

(Note 5)

SYSTEM PARAMETERS (Note 6)Test Circuit Figure 1V OUT

Output Voltage

4.75V ≤V IN ≤60V,0.2A ≤I LOAD ≤1A

3.3

V 3.168/3.135V(min)3.432/3.465

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 1V OUT

Output Voltage

7V ≤V IN ≤60V,0.2A ≤I LOAD ≤1A

V 4.800/4.750V(min)5.200/5.250

V(max)η

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)

(Note 5)

SYSTEM PARAMETERS (Note 6)Test Circuit Figure 1V FB

Feedback Voltage

4.5V ≤V IN ≤60V,0.2A ≤I LOAD ≤1A 1.230

V V OUT programmed for 3V.Circuit of Figure 1.

1.193/1.180V(min)1.267/1.280

V(max)

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LM2590HV 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

(Note4)(Note5)

ηEfficiency V IN=12V,V OUT=3V,I LOAD=1A76%

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 the3.3V,5V,and Adjustable version.I LOAD=500mA

Symbol Parameter Conditions LM2590HV-XX Units

(Limits)

Typ Limit

(Note4)(Note5)

DEVICE PARAMETERS

I b Feedback Bias Current Adjustable Version Only,V FB=1.3V10nA

50/100nA(max)

f O Oscillator Frequency(Note7)150kHz

127/110kHz(min)

173/173kHz(max)

V SAT Saturation Voltage I OUT=1A(Note8)(Note9)0.95V

1.2/1.3V(max)

DC Max Duty Cycle(ON)(Note9)100% Min Duty Cycle(OFF)(Note10)0

I CLIM Switch current Limit Peak Current,(Note8)(Note9) 1.9A

1.3/1.2A(min)

2.8/

3.0A(max)

I L Output Leakage Current(Note8)(Note10)(Note11)Output=0V50μA(max)

Output=?1V5mA

30mA(max)

I Q Operating Quiescent SD/SS Pin Open(Note10)5mA

Current10mA(max)

I STBY Standby Quiescent SD/SS pin=0V(Note11)90μA

Current200/250μA(max)

θJC Thermal Resistance TO220or TO263Package,Junction to Case2?C/W

θJA TO220Package,Juncton to Ambient(Note12)50?C/W

θJA TO263Package,Juncton to Ambient(Note13)50?C/W

θJA TO263Package,Juncton to Ambient(Note14)30?C/W

θJA TO263Package,Juncton to Ambient(Note15)20?C/W SHUTDOWN/SOFT-START CONTROL Test Circuit of Figure1

V SD Shutdown Threshold 1.3V Voltage Low,(Shutdown Mode)0.6V(max)

High,(Soft-start Mode)2V(min)

V SS Soft-start Voltage V OUT=20%of Nominal Output Voltage2V

V OUT=100%of Nominal Output Voltage3

I SD Shutdown Current V SHUTDOWN=0.5V5μA

10μA(max)

I SS Soft-start Current V Soft-start=2.5V 1.5μA

5μA(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 =500mA Symbol

Parameter

Conditions

LM2590HV-XX Units (Limits)

Typ Limit (Note 4)

(Note 5)

FLAG/DELAY CONTROL Test Circuit of Figure 1

Regulator Dropout Detector Low (Flag ON)

%Threshold Voltage

92%(min)98

%(max)VF SAT Flag Output Saturation I SINK =3mA 0.3

V Voltage

V DELAY =0.5V 0.7/1.0

V(max)IF L

Flag Output Leakage Current V FLAG =60V

0.3μA Delay Pin Threshold 1.25

V Voltage

Low (Flag ON)

1.21V(min)High (Flag OFF)and V OUT Regulated 1.29

V(max)Delay Pin Source Current V DELAY =0.5V 3

μA 6

μA(max)Delay Pin Saturation

Low (Flag ON)

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 1mA.Note 3:The human body model is a 100pF 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 1test 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 IN =60V.

Note 12:Junction to ambient thermal resistance (no external heat sink)for the package mounted TO-220package mounted vertically,with the leads soldered to a printed circuit board with (1oz.)copper area of approximately 1in 2.

Note 13:Junction to ambient thermal resistance with the TO-263package tab soldered to a single sided printed circuit board with 0.5in 2of (1oz.)copper area.Note 14:Junction to ambient thermal resistance with the TO-263package tab soldered to a single sided printed circuit board with 2.5in 2of (1oz.)copper area.Note 15:Junction to ambient thermal resistance with the TO-263package tab soldered to a double sided printed circuit board with 3in 2of (1oz.)copper area on the LM2590HVS side of the board,and approximately 16in 2of 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 https://www.wendangku.net/doc/6016639801.html,.

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Typical Performance Characteristics

(Circuit of Figure 1)

NormalizedOutput Voltage

Line Regulation

Efficiency

101347021013470310134704

Switch SaturationVoltage Switch Current Limit Dropout Voltage

10134705

10134706

10134707

Operating

Quiescent Current

Shutdown Quiescent Current

Minimum Operating Supply Voltage

101347081013470910134710

LM2590HV

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Typical Performance Characteristics

(Circuit of Figure 1)(Continued)

Feedback Pin Bias Current

Flag Saturation Voltage

Switching Frequency

101347111013471210134713

Soft-start

Shutdown /Soft-start

Current

Delay Pin Current

10134714

1013471510134716

Soft-start Response

Shutdown/Soft-start Threshold Voltage

Internal Gain-Phase Characteristics

10134718

10134753

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Typical Performance Characteristics(Circuit of Figure1)(Continued)

Continuous Mode Switching Waveforms

V IN=20V,V OUT=5V,I LOAD=1A

L=52μH,C OUT=100μF,C OUT ESR=100m?

Discontinuous Mode Switching Waveforms

V IN=20V,V OUT=5V,I LOAD=250mA

L=15μH,C OUT=150μF,C OUT ESR=90m?

10134720

Horizontal Time Base:2μs/div.

A:Output Pin Voltage,10V/div.

B:Inductor Current0.5A/div.

C:Output Ripple Voltage,50mV/div.

10134719

Horizontal Time Base:2μs/div.

A:Output Pin Voltage,10V/div.

B:Inductor Current0.25A/div.

C:Output Ripple Voltage,100mV/div.

Load Transient Response for Continuous Mode

V IN=20V,V OUT=5V,I LOAD=250mA to1A

L=52μH,C OUT=100μF,C OUT ESR=100m?

Load Transient Response for Discontinuous Mode

V IN=20V,V OUT=5V,I LOAD=250mA to1A

L=15μH,C OUT=150μF,C OUT ESR=90m?

10134721

Horizontal Time Base:50μs/div.

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

B:250mA to1A Load Pulse

10134722

Horizontal Time Base:200μs/div.

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

B:250mA to1A 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

Order Number LM2590HVT-3.3,LM2590HVT-5.0,

or LM2590HVT-ADJ

See NS Package Number TA07B

10134723

Order Number LM2590HVS-3.3,LM2590HVS-5.0,

or LM2590HVS-ADJ

See NS Package Number TS7B

LM2590HV

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Test Circuit and Layout Guidelines

Fixed Output Voltage Versions

10134724

Component Values shown are for V IN =15V,V OUT =5V,I LOAD =1A.C IN —470μF,50V,Aluminum Electrolytic Nichicon “PM Series”C OUT —

220μF,25V Aluminum Electrolytic,Nichicon “PM Series”D1—2A,60V Schottky Rectifier,21DQ06(International Rectifier)L1

—68μH,See Inductor Selection Procedure

Adjustable Output Voltage Versions

10134725

Select R 1to be approximately 1k ?,use a 1%resistor for best https://www.wendangku.net/doc/6016639801.html,ponent Values shown are for V IN =20V,V OUT =10V,I LOAD =1A.C IN :—470μF,35V,Aluminum Electrolytic Nichicon “PM Series”C OUT :

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

D1—2A,60V Schottky Rectifier,21DQ06(International Rectifier)L1—100μH,See Inductor Selection Procedure R 1—1k ?,1%R 2—7.15k,1%C FF —3.3nF

Typical Values

C SS —0.1μF C DELAY —0.1μF

R PULL UP —4.7k (use 22k if V OUT 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 (C FF not being able to discharge immediately will drag feedback pin below ground).Required if V IN >40V

FIGURE 1.Standard Test Circuits and Layout Guides

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Block Diagram

10134730

PIN FUNCTIONS

+V IN(Pin1)—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(Pin2)—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(Pin3)—Open collector output that goes active low(≤1.0V)when the output of the switching regulator is out of regulation(less than95%of its nominal value).In this state it can sink maximum3mA.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(Pin5).The maximum rating of this pin should not be exceeded,so if the rail to which it will be pulled-up to is higher than45V,a resistive divider must be used instead of a single pull-up resistor,as indicated in Figure1.

Ground(Pin4)—Circuit ground.

Delay(Pin5)—This sets a programmable power-up delay from the moment that the output reaches regulation,to the high signal output(power good)on Pin3.A capacitor on this pin starts charging up by means on an internal()3μA) current source when the regulated output rises to within5% of its nominal value.Pin3goes high(with an external pull-up)when the voltage on the capacitor on Pin5exceeds 1.3V.The voltage on this pin is clamped internally to about 1.7V.If the regulated output drops out of regulation(less than95%of its nominal value),the capacitor on Pin5is rapidly discharged internally and Pin3will be forced low in about1/1000th of the set power-up delay time.

Feedback(Pin6)—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 to1.23V

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

above40V whenever a feedforward capacitor is present

(See Figure1).Feedforward capacitor values larger than0.1

μF are not recommended for the same reason,whatever be

the DC input voltage.

Shutdown/Soft-start(Pin7)—The regulator is in shut-

down mode,drawing about90μA,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 is1.3V and the pin

is internally clamped to a maximum of about7V.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

exceed1mA.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 at2.8V 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 about5μA when the pin is

below1.3V but is reduced to only1.6μA above1.3V,so as

to allow the use of smaller softstart capacitors.

LM2590HV

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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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INDUCTOR VALUE SELECTION GUIDES

(For Continuous Mode Operation)

10134732

FIGURE 3.Timing Diagram for 5V Output

10134726

FIGURE 4.LM2590HV-3.3

LM2590HV

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INDUCTOR VALUE SELECTION GUIDES

(For Continuous Mode Operation)(Continued)

10134729

FIGURE 6.LM2590HV-ADJ

L M 2590H V

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

10134765

FIGURE7.Current Ripple Ratio

Coilcraft Inc.Phone(USA):1-800-322-2645

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Coilcraft Inc.,Europe Phone(UK):1-236-730595

Web Address https://www.wendangku.net/doc/6016639801.html,

Pulse Engineering Inc.Phone(USA):1-858-674-8100

Web Address https://www.wendangku.net/doc/6016639801.html,

Pulse Engineering Inc.,Phone(UK):1-483-401700

Europe Web Address https://www.wendangku.net/doc/6016639801.html,

Renco Electronics Inc.Phone(USA):1-321-637-1000

Web Address https://www.wendangku.net/doc/6016639801.html,

Schott Corp.Phone(USA):1-952-475-1173

Web Address https://www.wendangku.net/doc/6016639801.html,

Cooper Electronic Tech. (Coiltronics)Phone(USA):1-888-414-2645 Web Address https://www.wendangku.net/doc/6016639801.html,

FIGURE8.Contact Information for Suggested Inductor Manufacturers

LM2590HV

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Application Information

INDUCTOR SELECTION PROCEDURE

Application Note AN-1197titled’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 Figure4to Figure6.To widen the choice of the

Designer to a more general selection of available inductors,

the nomographs provide the required inductance and also

the energy in the core expressed in microjoules(μJ),as an

alternative to just prescribing custom parts.The following

points need to be highlighted:

1.The Energy values shown on the nomographs apply to

steady operation at the corresponding x-coordinate

(rated maximum load current).However under start-up,

without soft-start,or a short-circuit on the output,the

current in the inductor will momentarily/repetitively hit

the current limit I CLIM of the device,and this current

could be much higher than the rated load,I LOAD.This

represents an overload situation,and can cause the

Inductor to saturate(if it has been designed only to

handle the energy of steady operation).However most

types of core structures used for such applications have

a large inherent air gap(for example powdered iron

types or ferrite rod inductors),and so the inductance

does not fall off too sharply under an overload.The

device is usually able to protect itself by not allowing the

current to ever exceed I CLIM.But if the DC input voltage

to the regulator is over40V,the current can slew up so

fast under core saturation,that the device may not be

able to act fast enough to restrict the current.The cur-

rent can then rise without limit till destruction of the

device takes place.Therefore to ensure reliability,it is

recommended,that if the DC Input Voltage exceeds

40V,the inductor must ALWAYS be sized to handle an

instantaneous current equal to I CLIM without saturating,

irrespective of the type of core structure/material.

2.The Energy under steady operation is

where L is inμH and I PEAK is the peak of the inductor current

waveform with the regulator delivering I LOAD.These are the

energy values shown in the nomographs.See Example1

below.

3.The Energy under overload is

If V IN>40V,the inductor should be sized to handle e CLIM

instead of the steady energy values.The worst case I CLIM for

the LM2590HV is3A.The Energy rating depends on the

Inductance.See Example2below.

4.The nomographs were generated by allowing a greater

amount of percentage current ripple in the Inductor as

the maximum rated load decreases(see Figure7).This

was done to permit the use of smaller inductors at light

loads.Figure7however 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-1197for

detailed calculations if a certain maximum inductor cur-

rent ripple is required for various possible reasons.Also

consider the rather wide tolerance on the nominal induc-

tance of commercial inductors.

5.Figure6shows 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 inμsecs.See Example3below.

Example1:(V IN≤40V)LM2590HV-5.0,V IN=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(Figure5)and

a current rating equal to the maximum load current.We

therefore quick-select a100μH/0.8A inductor(designed for

150kHz operation)for this application.

2.We should confirm that it is rated to handle50μJ(see

Figure5)by either estimating the peak current or by a

detailed calculation as shown in AN-1197,and also that the

losses are acceptable.

Example2:(V IN>40V)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(Figure5)and

a current rating equal to I CLIM.We therefore quick-select a

100μH/3A inductor(designed for150kHz operation)for this

application.

2.We should confirm that it is rated to handle e CLIM by the

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

able.Here e CLIM is:

Example3:(V IN≤40V)LM2590HV-ADJ,V IN=20V,Output

10V@1A

1.Since input voltage is less than40V,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 Figure6and a current rating

equal to the maximum load.But we first need to calculate Et

for the given application.The Duty cycle is

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

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

And the switch ON time is

where f is the switching frequency in Hz.So

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Application Information

(Continued)

Therefore,looking at Figure 4we quick-select a 100μH/1A inductor (designed for 150kHz operation)for this applica-tion.

2.We should confirm that it is rated to handle 100μJ (see Figure 6)by the procedure shown in AN-1197and that the losses are acceptable.(If the DC Input voltage had been greater than 40V we would need to consider e CLIM as in Example 2above).

Note that we have taken V SAT 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 8provides helpful contact information on suggested Inductor manufacturers who may be able to recommend suitable parts,if the require-ments are known.

FEEDFORWARD CAPACITOR

(Adjustable Output Voltage Version)

C FF -A Feedforward Capacitor C FF ,shown across R2in Figure 1is used when the output voltage is greater than 10V or when C OUT has a very low ESR.This capacitor adds lead compensation to the feedback loop and increases the phase margin for better loop stability.

If the output voltage ripple is large (>5%of the nominal output voltage),this ripple can be coupled to the feedback pin through the feedforward capacitor and cause the error comparator to trigger the error flag.In this situation,adding a resistor,R FF ,in series with the feedforward capacitor,ap-proximately 3times R1,will attenuate the ripple voltage at the feedback pin.

INPUT CAPACITOR

C IN —A low ESR aluminum or tantalum bypass capacitor is needed between the input pin and ground pin.It must be located near the regulator using short leads.This capacitor prevents large voltage transients from appearing at the in-put,and provides the instantaneous current needed each time the switch turns on.

The important parameters for the Input capacitor are the voltage rating and the RMS current rating.Because of the

relatively high RMS currents flowing in a buck regulator’s input capacitor,this capacitor should be chosen for its RMS current rating rather than its capacitance or voltage ratings,although the capacitance value and voltage rating are di-rectly related to the RMS current rating.The voltage rating of the capacitor and its RMS ripple current capability must never be exceeded.OUTPUT CAPACITOR

C OUT —An output capacitor is required to filter the output and provide regulator loop stability.Low impedance or low ESR Electrolytic or solid tantalum capacitors designed for switching regulator applications must be used.When select-ing an output capacitor,the important capacitor parameters are;the 100kHz 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 100m ?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 charac-teristic may cause instability or EMI problems.Ultra-fast recovery diodes typically have reverse recovery times of 50ns or less.The diode must be chosen for its average/RMS current rating and maximum voltage rating.The voltage rating of the diode must be greater than the DC input voltage (not the output voltage).SHUTDOWN /SOFT-START

This reduction in start up current is useful in situations where the input power source is limited in the amount of current it can deliver.In some applications Soft-start can be used to replace undervoltage lockout or delayed startup functions.If a very slow output voltage ramp is desired,the Soft-start capacitor can be made much larger.Many seconds or even minutes are possible.

If only the shutdown feature is needed,the Soft-start capaci-tor can be eliminated.

LM2590HV

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Application Information

(Continued)

lNVERTING REGULATOR

The circuit in Figure 10converts 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-5to generate a ?5V output,but other output voltages are possible by selecting other output voltage versions,including the adjustable ver-sion.Since this regulator topology can produce an output voltage that is either greater than or less than the input voltage,the maximum output current greatly depends on both the input and output voltage.

To determine how much load current is possible before the internal device current limit is reached (and power limiting

occurs),the system must be evaluated as a buck-boost configuration rather than as a buck.The peak switch current in Amperes,for such a configuration is given as:

where L is in μH and f is in Hz.The maximum possible load current I LOAD is limited by the requirement that I PEAK ≤I CLIM .While checking for this,take I CLIM to be the lowest possible current limit value (min across tolerance and temperature is 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-

10134743

FIGURE 10.Inverting ?5V Regulator With Shutdown and Soft-start

L M 2590H V

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Application Information(Continued) suming100%efficiency,which is never so.Therefore expect I PEAK to be an additional10-20%higher than calculated from the above equation.

The reader is also referred to Application Note AN-1157for 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 of60V.In this example,when converting+20V to?5V,the regulator would see25V be-tween the input pin and ground pin.The LM2590HV has a maximum input voltage rating of60V.

An additional diode is required in this regulator configuration. Diode D1is used to isolate input voltage ripple or noise from

coupling through the C IN capacitor to the output,under light or no load conditions.Also,this diode isolation changes the topology to closely resemble a buck configuration thus pro-viding good closed loop stability.A Schottky diode is recom-mended for low input voltages,(because of its lower voltage drop)but for higher input voltages,a IN5400diode 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,a33μH, 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 (approximately3.0A)are needed for2ms 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 Figure10is recommended. Also shown in Figure10are several shutdown methods for the inverting configuration.With the inverting configuration, some level shifting is required,because the ground pin of the regulator is no longer at ground,but is now at the negative output voltage.The shutdown methods shown accept ground referenced shutdown signals.

UNDERVOLTAGE LOCKOUT

Some applications require the regulator to remain off until the input voltage reaches a predetermined voltage.Figure11 contains a undervoltage lockout circuit for a buck configura-tion,while Figure12and Figure13are for the inverting types (only the circuitry pertaining to the undervoltage lockout is shown).Figure11uses 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 R2hold 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 approximately1.5V greater than the zener voltage.

Figure12and Figure13apply the same feature to an

inverting circuit.Figure12features 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

13has 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

internal7V zener clamp,R2is needed to limit the current into

this pin to approximately1mA when Q1is on.

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

Figure1,the wires indicated by heavy lines should be wide

printed circuit traces and should be kept as short as

10134745

FIGURE11.Undervoltage Lockout for a Buck

Regulator

10134747

FIGURE12.Undervoltage Lockout Without

Hysteresis for an Inverting Regulator

10134746

FIGURE13.Undervoltage Lockout With

Hysteresis for an Inverting Regulator

LM2590HV

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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 OUT wiring can cause problems.

When using the adjustable version,special care must be taken as to the location of the feedback resistors and the associated wiring.Physically locate both resistors near the IC,and route the wiring away from the inductor,especially an open core type of inductor.

L M 2590H V

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LM2590HV Physical Dimensions inches(millimeters)

unless otherwise noted Array

7-Lead TO-220Bent and Staggered Package

Order Number LM2590HVT-3.3,LM2590HVT-5.0or LM2590HVT-ADJ

NS Package Number TA07B

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Physical Dimensions

inches (millimeters)unless otherwise noted (Continued)

7-Lead TO-263Bent and Formed Package

Order Number LM2590HVS-3.3,LM2590HVS-5.0or LM2590HVS-ADJ

NS Package Number TS7B

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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.

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Tel:81-3-5639-7560Fax:81-3-5639-7507

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L M 2590H V S I M P L E S W I T C H E R P o w e r C o n v e r t e r 150k H z 1A S t e p -D o w n V o l t a g e R e g u l a t o r ,w i t h F e a t u r e s

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