LM2590HV
SIMPLE SWITCHER

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

Other features include a guaranteed

4% tolerance on out-

put voltage under all conditions of input voltage and output
load conditions, and

15% on the oscillator frequency. Ex-

ternal shutdown is included, featuring typically 90 µA
standby current. Self protection features include a two stage
current limit for the output switch and an over temperature
shutdown for complete protection under fault conditions.

Features

3.3V, 5V, and adjustable output versions

Adjustable version output voltage range, 1.2V to 57V

4% max over line and load conditions

Guaranteed 1A output load current

Available in 7-pin TO-220 and TO-263 (surface mount)
Package

Input voltage range up to 60V

150 kHz fixed frequency internal oscillator

Shutdown/Soft-start

Out of regulation error flag

Error flag delay

Low power standby mode, I

typically 90 µA

High Efficiency

Thermal shutdown and current limit protection

Applications

Simple high-efficiency step-down (buck) regulator

Efficient pre-regulator for linear regulators

On-card switching regulators

Positive to Negative converter

Note:

Patent Number 5,382,918.

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

150

kHz

Step-Down

oltage

Regulator

with

Features

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.

Maximum Supply Voltage (V

)

63V

SD /SS Pin Input Voltage (Note 2)

Delay Pin Voltage (Note 2)

1.5V

Flag Pin Voltage

-0.3

45V

Feedback Pin Voltage

-0.3

+25V

Output Voltage to Ground

(Steady State)

-1V

Power Dissipation

Internally limited

Storage Temperature Range

-65°C to +150°C

ESD Susceptibility

Human Body Model (Note 3)

2 kV

Lead Temperature

S Package

Vapor Phase (60 sec.)

+215°C

Infrared (10 sec.)

+245°C

T Package (Soldering, 10 sec.)

+260°C

Maximum Junction Temperature

+150°C

Operating Conditions

Temperature Range

-40°C

+125°C

Supply Voltage

4.5V to 60V

LM2590HV-3.3
Electrical Characteristics

Specifications with standard type face are for T

= 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 1

OUT

Output Voltage

4.75V

60V, 0.2A

LOAD

3.3

3.168/3.135

V(min)

3.432/3.465

V(max)

Efficiency

= 12V, I

LOAD

= 1A

LM2590HV-5.0
Electrical Characteristics

Specifications with standard type face are for T

= 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

OUT

Output Voltage

60V, 0.2A

LOAD

4.800/4.750

V(min)

5.200/5.250

V(max)

Efficiency

= 12V, I

LOAD

= 1A

LM2590HV-ADJ
Electrical Characteristics

Specifications with standard type face are for T

= 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 1

Feedback Voltage

4.5V

60V, 0.2A

LOAD

1.230

OUT

programmed for 3V. Circuit of

Figure 1.

1.193/1.180

V(min)

1.267/1.280

V(max)

LM2590HV

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LM2590HV-ADJ
Electrical Characteristics

(Continued)

Specifications with standard type face are for T

= 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

= 12V, V

OUT

= 3V, I

LOAD

= 1A

All Output Voltage Versions
Electrical Characteristics

Specifications with standard type face are for T

= 25°C, and those with boldface type apply over full Operating Tempera-

ture Range. Unless otherwise specified, V

= 12V for the 3.3V, 5V, and Adjustable version. I

LOAD

= 500 mA

Symbol

Parameter

Conditions

LM2590HV-XX

Units

(Limits)

Typ

Limit

(Note 4)

(Note 5)

DEVICE PARAMETERS

Feedback Bias Current

Adjustable Version Only, V

= 1.3V

50/100

nA (max)

Oscillator Frequency

(Note 7)

150

kHz

127/110

kHz(min)

173/173

kHz(max)

SAT

Saturation Voltage

OUT

= 1A (Note 8) (Note 9)

0.95

1.2/1.3

V(max)

Max Duty Cycle (ON)

(Note 9)

100

Min Duty Cycle (OFF)

(Note 10)

CLIM

Switch current Limit

Peak Current, (Note 8) (Note 9)

1.9

1.3/1.2

A(min)

2.8/3.0

A(max)

Output Leakage Current

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

Output = 0V

µA(max)

Output = -1V

mA(max)

Operating Quiescent

SD /SS Pin Open (Note 10)

Current

mA(max)

STBY

Standby Quiescent

SD /SS pin = 0V

(Note 11)

µA

Current

200/250

µA(max)

Thermal Resistance

TO220 or TO263 Package, Junction to Case

°C/W

TO220 Package, Juncton to Ambient (Note 12)

°C/W

TO263 Package, Juncton to Ambient (Note 13)

°C/W

TO263 Package, Juncton to Ambient (Note 14)

°C/W

TO263 Package, Juncton to Ambient (Note 15)

°C/W

SHUTDOWN/SOFT-START CONTROL Test Circuit of

Figure 1

Shutdown Threshold

1.3

Voltage

Low, (Shutdown Mode)

0.6

V(max)

High, (Soft-start Mode)

V(min)

Soft-start Voltage

OUT

= 20% of Nominal Output Voltage

OUT

= 100% of Nominal Output Voltage

Shutdown Current

SHUTDOWN

= 0.5V

µA

µA(max)

Soft-start Current

Soft-start

= 2.5V

1.5

µA

µA(max)

LM2590HV

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All Output Voltage Versions
Electrical Characteristics

(Continued)

Specifications with standard type face are for T

= 25°C, and those with boldface type apply over full Operating Tempera-

ture Range. Unless otherwise specified, V

= 12V for the 3.3V, 5V, and Adjustable version. I

LOAD

= 500 mA

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

%(min)

%(max)

SAT

Flag Output Saturation

SINK

= 3 mA

0.3

Voltage

DELAY

= 0.5V

0.7/1.0

V(max)

Flag Output Leakage Current

FLAG

= 60V

0.3

µA

Delay Pin Threshold

1.25

Voltage

Low (Flag ON)

1.21

V(min)

High (Flag OFF) and V

OUT

Regulated

1.29

V(max)

Delay Pin Source Current

DELAY

= 0.5V

µA

µA(max)

Delay Pin Saturation

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.

LM2590HV

www.national.com

Typical Performance Characteristics

(Circuit of

Figure 1) (Continued)

Continuous Mode Switching Waveforms

= 20V, V

OUT

= 5V, I

LOAD

= 1A

L = 52 µH, C

OUT

= 100 µF, C

OUT

ESR = 100 m

Discontinuous Mode Switching Waveforms

= 20V, V

OUT

= 5V, I

LOAD

= 250 mA

L = 15 µH, C

OUT

= 150 µF, C

OUT

ESR = 90 m

10134720

Horizontal Time Base: 2 µs/div.

A: Output Pin Voltage, 10V/div.

B: Inductor Current 0.5A/div.

C: Output Ripple Voltage, 50 mV/div.

10134719

Horizontal Time Base: 2 µs/div.

A: Output Pin Voltage, 10V/div.

B: Inductor Current 0.25A/div.

C: Output Ripple Voltage, 100 mV/div.

Load Transient Response for Continuous Mode

= 20V, V

OUT

= 5V, I

LOAD

= 250 mA to 1A

L = 52 µH, C

OUT

= 100 µF, C

OUT

ESR = 100 m

Load Transient Response for Discontinuous Mode

= 20V, V

OUT

= 5V, I

LOAD

= 250 mA to 1A

L = 15 µH, C

OUT

= 150 µF, C

OUT

ESR = 90 m

10134721

Horizontal Time Base: 50 µs/div.

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

B: 250 mA to 1A Load Pulse

10134722

Horizontal Time Base: 200 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

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

= 15V,

OUT

= 5V, I

LOAD

= 1A.

470 µF, 50V, Aluminum Electrolytic Nichicon "PM Series"

OUT

220 µF, 25V Aluminum Electrolytic, Nichicon "PM Series"

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

68 µH, See Inductor Selection Procedure

Adjustable Output Voltage Versions

10134725

Select R

to be approximately 1 k

, use a 1% resistor for best stability.

Component Values shown are for V

= 20V,

OUT

= 10V, I

LOAD

= 1A.

-- 470 µF, 35V, Aluminum Electrolytic Nichicon "PM Series"

OUT

-- 220 µF, 35V Aluminum Electrolytic, Nichicon "PM Series"

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

L1 -- 100 µH, See Inductor Selection Procedure

-- 1 k

, 1%

-- 7.15k, 1%

-- 3.3 nF

Typical Values

-- 0.1 µF

DELAY

-- 0.1 µF

PULL UP

-- 4.7k (use 22k if V

OUT

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

not being able to discharge immediately will

drag feedback pin below ground). Required if V

40V

FIGURE 1. Standard Test Circuits and Layout Guides

LM2590HV

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Block Diagram

10134730

PIN FUNCTIONS

(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

- V

SAT

) and approxi-

mately -0.5V, with a duty cycle of V

OUT

Error Flag (Pin 3) -- Open collector output that goes active
low (

1.0V) when the output of the switching regulator is out

of regulation (less than 95% of its nominal value). In this
state it can sink maximum 3mA. When not low, it can be
pulled high to signal that the output of the regulator is in
regulation (power good). During power-up, it can be pro-
grammed to go high after a certain delay as set by the Delay
pin (Pin 5). The maximum rating of this pin should not be
exceeded, so if the rail to which it will be pulled-up to is
higher than 45V, a resistive divider must be used instead of
a single pull-up resistor, as indicated in

Figure 1.

Ground (Pin 4) -- Circuit ground.

Delay (Pin 5) -- This sets a programmable power-up delay
from the moment that the output reaches regulation, to the
high signal output (power good) on Pin 3. A capacitor on this
pin starts charging up by means on an internal (

)

3 µA)

current source when the regulated output rises to within 5%
of its nominal value. Pin 3 goes high (with an external
pull-up) when the voltage on the capacitor on Pin 5 exceeds
1.3V. The voltage on this pin is clamped internally to about
1.7V. If the regulated output drops out of regulation (less
than 95% of its nominal value), the capacitor on Pin 5 is
rapidly discharged internally and Pin 3 will be forced low in
about 1/1000

of the set power-up delay time.

Feedback (Pin 6) -- Senses the regulated output voltage to
complete the feedback loop. This pin is directly connected to
the Output for the fixed voltage versions, but is set to 1.23V
by means of a resistive divider from the output for the
Adjustable version. If a feedforward capacitor is used (Ad-
justable version), then a negative voltage spike is generated
on this pin whenever the output is shorted. This happens
because the feedforward capacitor cannot discharge fast
enough, and since one end of it is dragged to Ground, the
other end goes momentarily negative. To prevent the energy
rating of this pin from being exceeded, a small-signal Schot-
tky diode to Ground is recommended for DC input voltages
above 40V whenever a feedforward capacitor is present
(See

Figure 1). Feedforward capacitor values larger than 0.1

µF are not recommended for the same reason, whatever be
the DC input voltage.

Shutdown /Soft-start (Pin 7) -- The regulator is in shut-
down mode, drawing about 90 µA, when this pin is driven to
a low level (

0.6V), and is in normal operation when this Pin

is left floating (internal-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.

LM2590HV

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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:

The Energy values shown on the nomographs apply to
steady operation at the corresponding x-coordinate
(rated maximum load current). However under start-up,
without soft-start, or a short-circuit on the output, the
current in the inductor will momentarily/repetitively hit
the current limit I

CLIM

of the device, and this current

could be much higher than the rated load, I

LOAD

. This

represents an overload situation, and can cause the
Inductor to saturate (if it has been designed only to
handle the energy of steady operation). However most
types of core structures used for such applications have
a large inherent air gap (for example powdered iron
types or ferrite rod inductors), and so the inductance
does not fall off too sharply under an overload. The
device is usually able to protect itself by not allowing the
current to ever exceed I

CLIM

. But if the DC input voltage

to the regulator is over 40V, the current can slew up so
fast under core saturation, that the device may not be
able to act fast enough to restrict the current. The cur-
rent can then rise without limit till destruction of the
device takes place.

Therefore to ensure reliability, it is

recommended, that if the DC Input Voltage exceeds
40V, the inductor must ALWAYS be sized to handle an
instantaneous current equal to I

CLIM

without saturating,

irrespective of the type of core structure/material.

The Energy under steady operation is

where L is in µH and I

PEAK

is the peak of the inductor current

waveform with the regulator delivering I

LOAD

. These are the

energy values shown in the nomographs. See

Example 1

below.

The Energy under overload is

If V

40V, the inductor should be sized to handle e

CLIM

instead of the steady energy values. The worst case I

CLIM

for

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

Example 2 below.

The nomographs were generated by allowing a greater
amount of percentage current ripple in the Inductor as
the maximum rated load decreases (see

Figure 7). This

was done to permit the use of smaller inductors at light
loads.

Figure 7 however shows only the 'median' value

of the current ripple. In reality there may be a great
spread around this because the nomographs approxi-
mate the exact calculated inductance to standard avail-
able values. It is a good idea to refer to AN-1197 for
detailed calculations if a certain maximum inductor cur-
rent ripple is required for various possible reasons. Also

consider the rather wide tolerance on the nominal induc-
tance of commercial inductors.

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

-V

SAT

-V

OUT

) multiplied by the time for

which the switch is on in µsecs. See Example 3 below.

Example 1: (V

40V) LM2590HV-5.0, V

= 24V, Output

0.8A

1. A first pass inductor selection is based upon

Inductance

and rated max load current. We choose an inductor with the
Inductance value indicated by the nomograph (

Figure 5) and

a current rating equal to the maximum load current. We
therefore quick-select a 100µH/0.8 A inductor (designed for
150 kHz operation) for this application.

2. We should confirm that it is rated to handle 50 µJ (see
Figure 5) by either estimating the peak current or by a
detailed calculation as shown in AN-1197, and also that the
losses are acceptable.

Example 2: (V

40V) LM2590HV-5.0, V

= 48V, Output

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

CLIM

by the

procedure shown in AN-1197 and that the losses are accept-
able. Here e

CLIM

is:

Example 3: (V

40V) LM2590HV-ADJ, V

= 20V, Output

10V

1. Since input voltage is less than 40V, a first pass inductor
selection is based upon Inductance and rated max load
current. We choose an inductor with the Inductance value
indicated by the nomograph

Figure 6 and a current rating

equal to the maximum load. But we first need to calculate Et
for the given application. The Duty cycle is

where V

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

LM2590HV

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Application Information

(Continued)

Therefore, looking at

Figure 4 we quick-select a 100µH/1A

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

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

CLIM

as in

Example 2 above).

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 8 provides helpful

contact information on suggested Inductor manufacturers
who may be able to recommend suitable parts, if the require-
ments are known.

FEEDFORWARD CAPACITOR

(Adjustable Output Voltage Version)

- A Feedforward Capacitor C

, shown across R2 in

Figure 1 is used when the output voltage is greater than 10V
or when C

OUT

has a very low ESR. This capacitor adds lead

compensation to the feedback loop and increases the phase
margin for better loop stability.

If the output voltage ripple is large (

5% of the nominal

output voltage), this ripple can be coupled to the feedback
pin through the feedforward capacitor and cause the error
comparator to trigger the error flag. In this situation, adding a
resistor, R

, in series with the feedforward capacitor, ap-

proximately 3 times R1, will attenuate the ripple voltage at
the feedback pin.

INPUT CAPACITOR

-- 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

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 m

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 50
ns or less. The diode must be chosen for its average/RMS
current rating and maximum voltage rating. The voltage
rating of the diode must be greater than the DC input voltage
(not the output voltage).

SHUTDOWN /SOFT-START

This reduction in start up current is useful in situations where
the input power source is limited in the amount of current it
can deliver. In some applications Soft-start can be used to
replace undervoltage lockout or delayed startup functions.

If a very slow output voltage ramp is desired, the Soft-start
capacitor can be made much larger. Many seconds or even
minutes are possible.

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

LM2590HV

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Application Information

(Continued)

lNVERTING REGULATOR

The circuit in

Figure 10 converts a positive input voltage to a

negative output voltage with a common ground. The circuit
operates by bootstrapping the regulator's ground pin to the
negative output voltage, then grounding the feedback pin,
the regulator senses the inverted output voltage and regu-
lates it.

This example uses the 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.

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

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-

10134742

FIGURE 9. Typical Circuit Using Shutdown /Soft-start and Error Flag Features

10134743

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

LM2590HV

www.national.com

Application Information

(Continued)

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

PEAK

to be an additional 10-20% higher than calculated from

the above equation.

The reader is also referred to Application Note AN-1157 for
examples based on positive to negative configuration.

The maximum voltage appearing across the regulator is the
absolute sum of the input and output voltage, and this must
be limited to a maximum of 60V. In this example, when
converting +20V to -5V, the regulator would see 25V be-
tween the input pin and ground pin. The LM2590HV has a
maximum input voltage rating of 60V.

An additional diode is required in this regulator configuration.
Diode D1 is used to isolate input voltage ripple or noise from
coupling through the C

capacitor to the output, under light

or no load conditions. Also, this diode isolation changes the
topology to closely resemble a buck configuration thus pro-
viding good closed loop stability. A Schottky diode is recom-
mended for low input voltages, (because of its lower voltage
drop) but for higher input voltages, a IN5400 diode could be
used.

Because of differences in the operation of the inverting
regulator, the standard design procedure is not used to
select the inductor value. In the majority of designs, a 33 µH,
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.

UNDERVOLTAGE LOCKOUT

Some applications require the regulator to remain off until
the input voltage reaches a predetermined voltage.

Figure 11

contains a undervoltage lockout circuit for a buck configura-
tion, while

Figure 12 and Figure 13 are for the inverting types

(only the circuitry pertaining to the undervoltage lockout is
shown).

Figure 11 uses a zener diode to establish the

threshold voltage when the switcher begins operating. When
the input voltage is less than the zener voltage, resistors R1
and R2 hold the Shutdown /Soft-start pin low, keeping the
regulator in the shutdown mode. As the input voltage ex-
ceeds the zener voltage, the zener conducts, pulling the
Shutdown /Soft-start pin high, allowing the regulator to begin
switching. The threshold voltage for the undervoltage lockout
feature is approximately 1.5V greater than the zener voltage.

Figure 12 and Figure 13 apply the same feature to an
inverting circuit.

Figure 12 features a constant threshold

voltage for turn on and turn off (zener voltage plus approxi-
mately one volt). If hysteresis is needed, the circuit in

Figure

13 has a turn ON voltage which is different than the turn OFF
voltage. The amount of hysteresis is approximately equal to
the value of the output voltage. Since the SD /SS pin has an
internal 7V zener clamp, R2 is needed to limit the current into
this pin to approximately 1 mA when Q1 is on.

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

10134745

FIGURE 11. Undervoltage Lockout for a Buck

Regulator

10134747

FIGURE 12. Undervoltage Lockout Without

Hysteresis for an Inverting Regulator

10134746

FIGURE 13. Undervoltage Lockout With

Hysteresis for an Inverting Regulator

LM2590HV

www.national.com

Physical Dimensions

inches (millimeters) unless otherwise noted (Continued)

7-Lead TO-263 Bent and Formed Package

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

NS Package Number TS7B

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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
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www.national.com

LM2590HV

SIMPLE

SWITCHER

Power

Converter

150

kHz

Step-Down

oltage

Regulator

with

Features

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.

Document Outline

Ð­Ð»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: LM2590HVS-ADJ

Document Outline

ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: LM2590HVS-ADJ