Datasheet LT1587-1.5 Datasheet (Linear Technology)

LT1587-1.5

C2, C3
100µF
10V
AVX TPS

C1
100µF
10V
AVX TPS

+

C4 TO 
C6
1µF

C8, C9
100µF
10V
AVX TPS

C10 TO C12
1µF

C7
100µF
10V
AVX TPS

R1
75Ω

R5
100Ω

R2
150Ω

V

REF

R4
150Ω

V

REF

R7
100Ω

R8
100Ω

R6
100Ω

R3
75Ω

Q1

Q3

+

+

V

OUT

V

IN

GND

LT1587-1.5

3.3V 3.3V

V

TT

= 1.5V

3A

V

TT

= 1.5V

3A

V

IN

V

OUT

GND

LT1587-1.5

142 TOTAL SIGNAL LINES

•

•

•

C13

0.1µF

C14

0.1µF

Q4

Q2

+

LT1587 • TA01

RX

TX

RX

TX

RX

TX

RX

TX

NOTE: LTC RECOMMENDS SEPARATE 
V

TT

GENERATORS AT EACH BUS END
TO ENSURE CURRENT SHARING
BETWEEN THE REGULATORS AND TO
MINIMIZE V

TT

DISTRIBUTION DROPS



FEATURES

■

Fast Transient Response

■

Guaranteed Dropout Voltage at Multiple Currents

■

Load Regulation: 0.05% Typ

■

Trimmed Current Limit

■

On-Chip Thermal Limiting

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APPLICATIONS

■

Intel Pentium® Pro Processor GTL+ Supply

■

Low Voltage Logic Supplies

■

Battery-Powered Circuitry

Fixed 1.5V, 3A

Low Dropout

Fast Response

GTL+ Regulator

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DESCRIPTION

The LT®1587-1.5 is a low dropout 3-terminal regulator
with a fixed 1.5V output voltage and 3A output current
capability. The design is optimized for low voltage applica­tions where transient response and minimum input voltage
are critical. Similar to the LT1085, it has lower dropout and
faster transient response. These improvements make it
ideal for low voltage microprocessor applications, espe­cially as the regulator in an Intel Pentium Pro processor
GTL+ supply.

Current limit is trimmed to ensure specified output current
and controlled short-circuit current. On-chip thermal lim­iting provides protection against any combination of over­load that creates excessive junction temperatures.

The LT1587-1.5 is available in both the through-hole and
surface mount versions of the industry standard 3-pin
TO-220 power package.

, LTC and LT are registered trademarks of Linear Technology Corporation.

Pentium is a registered trademark of Intel Corporation

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TYPICAL APPLICATION

Intel Pentium Pro Processor GTL+ Supply

1

LT1587-1.5

WW

W

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ABSOLUTE MAXIMUM RATINGS

VIN............................................................................. 7V

Operating Junction Temperature Range

Control Section.................................... 0°C to 125°C

Power Transistor ................................. 0°C to 150°C

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W



PACKAGE/ORDER INFORMATION

FRONT VIEW

3



2



1

M PACKAGE

3-LEAD PLASTIC DD

θJA = 30°C/W*

* With package soldered to 0.5 square inch copper area over backside

ground plane or internal power plane. θ
>40°C/W with other mounting techniques.

VIN

V

OUT


GND



can vary from 20°C/W to

JA

ORDER PART

NUMBER

LT1587CM-1.5

Storage Temperature Range ................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec).................. 300°C

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PRECONDITIONI G

100% Thermal Limit Functional Test

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FRONT VIEW

3

2

1

T PACKAGE

3-LEAD PLASTIC TO-220

θJA = 50°C/W

Consult factory for Industrial and Military grade parts.

VIN

V

OUT

GND



ORDER PART

NUMBER

LT1587CT-1.5

ELECTRICAL CHARACTERISTICS

PARAMETER CONDITIONS MIN TYP MAX UNITS

Output Voltage VIN = 5V, TJ = 25°C, I

Line Regulation (Notes 1, 2) 3V ≤ VIN ≤ 7V, I
Load Regulation VIN = 5V, TJ = 25°C, 0mA ≤ I

(Notes 1, 2, 3)
Dropout Voltage ∆V
Current Limit (Note 3) (V
Quiescent Current V
Ripple Rejection f = 120Hz, C
Thermal Regulation TA = 25°C, 30ms pulse 0.004 0.02 %/W
Temperature Stability ● 0.5 %
Long-Term Stability TA = 125°C, 1000 Hrs. 0.03 1.0 %
RMS Output Noise TA = 25°C, 10Hz ≤ f ≤ 10kHz 0.003 %

(% of V
Thermal Resistance T Package: Control Circuitry/Power Transistor 0.7/3.0 °C/W

Junction to Case M Package: Control Circuitry/Power Transistor 0.7/3.0 °C/W

The ● denotes specifications which apply over the specified operating
temperature range.

Note 1: See thermal regulation specifications for changes in output voltage
due to heating effects. Load and line regulation are measured at a constant
junction temperature by low duty cycle pulse testing.

Note 2: Line and load regulation are guaranteed up to the maximum
power dissipation (17W for the LT1587-1.5 in T package). Power

OUT

)

3V ≤ V

≤ 7V, 0mA ≤ I

IN

= 1%, I

OUT

– V

IN

= 5V ● 713 mA

IN

OUT

) = 5.5V ● 3.100 3.750 A

OUT

OUT

= 0mA 1.485 (–1%) 1.5 1.515 (+1%) V

OUT

≤ 3A ● 1.470 (–2%) 1.5 1.530 (+2%) V

OUT

= 0mA 0.005 0.2 %

OUT

≤ I

OUT

FULL LOAD

= 3A ● 1.150 1.300 V

= 25µF Tant., VIN = 4.5V, I

= 3A ● 60 72 dB

OUT

dissipation is determined by input/output differential and the output
current. Guaranteed maximum output power will not be available over
the full input/output voltage range.

Note 3: I

FULL LOAD

as a function of input-to-output voltage. I
LT1587-1.5 has constant current limit with changes in input-to-output
voltage.

● 0.05 0.5 %

is defined as the maximum value of output load current

0.05 0.3 %

FULL LOAD

is equal to 3A. The

2

W

TEMPERATURE (°C)

–0.20

OUTPUT VOLTAGE DEVIATION (%)

–0.10

0

0.10

–0.15

–0.05

0.05

–25 25 75 125

LT1587 • TPC03

175–50–75 0 50 100 150

∆I = 3A

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TYPICAL PERFORMANCE CHARACTERISTICS

Short-Circuit Current

Dropout Voltage vs Output Current

1.5
GUARANTEED

1.4

TEST POINTS

1.3

1.2

1.1

1.0

0.9

0.8

DROPOUT VOLTAGE (V)

0.7

0.6

0.5

T = 25°C

T = 125°C

0

0.5

1.5 2.0

1.0

OUTPUT CURRENT (A)

T = –5°C

2.5

LT1587 • TPC01

3.0

vs Temperature

5.0

4.5

4.0

3.5

SHORT-CIRCUIT CURRENT (A)

3.0
–50

–25

–75

0

25

TEMPERATURE (°C)

50

75

100

125

LT1587 • TPC02

150

LT1587-1.5

Load Regulation vs Temperature

175

Output Voltage vs Temperature

1.53

1.52

1.51

1.50

1.49

OUTPUT VOLTAGE (V)

1.48

1.47
–25 25 75 125

TEMPERATURE (°C)

Ripple Rejection vs Frequency

90

80

70

60

50

40

30

RIPPLE REJECTION (dB)



20

LT1587-1.5: (V

0.5V ≤ V

10

= I

I

OUT

0

10 1k 10k 100k

IN

≤ 2V

RIPPLE

FULL LOAD

100

FREQUENCY (Hz)

– V

OUT

) ≤ 3V

LT1587 • TPC04

LT1587 • TPC06

Quiescent Current vs Temperature

13
12
11
10

9
8
7
6

QUIESCENT CURRENT (mA)

5
4

175–50– 75 0 50 100 150

3

–25

–75

–50 150

0
TEMPERATURE (°C)

75

25

100

50

125

LT1587 • TPC05

175

Maximum Power Dissipation*

30

25

20

LT1587-1.5

15

POWER (W)

10

5

0

50

60 70

*AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE

90 110 120 130 140 150

80 100

CASE TEMPERATURE (˚C)

LT1587 • TPC07

3

LT1587-1.5

WW

SI PLIFIED SCHE ATIC

V

IN

THERMAL

LIMIT

GND

+

–

V

OUT

LT1587 • BD

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APPLICATIONS INFORMATION

General

The LT1587-1.5 3-terminal regulator is easy to use and
has all the protection features expected in a high perfor­mance linear regulator. The device is short-circuit pro­tected, safe-area protected and provides thermal shut­down to turn off the regulator if the junction temperature
exceeds about 150°C.

The IC is pin compatible with the LT1083/LT1084/LT1085
family of linear regulators but offers lower dropout voltage
and faster transient response. The trade-off for this im­proved performance is a 7V maximum supply voltage.
Similar to the LT1083/LT1084/LT1085 family, the LT1587-

1.5 regulator requires an output capacitor for stability.
However, the improved frequency compensation permits
the use of capacitors with much lower ESR while still
maintaining stability. This is critical in addressing the needs
of modern low voltage, high speed microprocessors.

Current generation microprocessors and their associated
circuitry cycle load current from almost zero to several
amps in tens of nanoseconds. Output voltage tolerances
are tighter and include transient response as part of the
specification. The LT1587-1.5 is specifically designed to
meet the fast current load step requirements of these

applications and saves total cost by needing less output
capacitance in order to maintain regulation.

Stability

The circuit design in the LT1587-1.5 requires the use of an
output capacitor as part of the frequency compensation.
For all operating conditions, the addition of a 22µF solid
tantalum or a 100µF aluminum electrolytic on the output
ensures stability. Normally, the LT1587-1.5 can use smaller
value capacitors. Many different types of capacitors are
available and have widely varying characteristics. These
capacitors differ in capacitor tolerance (sometimes rang­ing up to ±100%), equivalent series resistance, equivalent
series inductance and capacitance temperature coefficient.
The LT1587-1.5 frequency compensation optimizes fre­quency response with low ESR capacitors. In general, use
capacitors with an ESR of less than 1Ω.

Normally, capacitor values on the order of several hundred
microfarads are used on the output of the regulators to
ensure good transient response with heavy load current
changes. Output capacitance can increase without limit
and larger values of output capacitance further improve the
stability and transient response of the LT1587-1.5.

4

LT1587-1.5

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APPLICATIONS INFORMATION

Large load current changes are exactly the situation pre­sented by modern microprocessors and their peripheral
circuitry. The load current step contains higher order
frequency components that the output decoupling network
must handle until the regulator throttles to the load current
level. Capacitors are not ideal elements and contain para­sitic resistance and inductance. These parasitic elements
dominate the change in output voltage at the beginning of
a transient load step change. The ESR of the output
capacitors produces an instantaneous step in output volt­age [∆V = ∆I(ESR)]. The ESL of the output capacitors
produces a droop proportional to the rate of change of
output current [V = L(∆I/∆t)]. The output capacitance
produces a change in output voltage proportional to the
time until the regulator can respond [∆V = ∆t(∆I/C)]. These
transient effects are illustrated in Figure 1.

ESR
EFFECTS

ESL
EFFECTS

V

SLOPE, =

∆I

t

C

POINT AT WHICH REGULATOR

TAKES CONTROL

Figure 1

The use of capacitors with low ESR, low ESL and good high
frequency characteristics is critical in meeting the output
voltage tolerances of these high speed microprocessor
applications. These requirements dictate a combination of
high quality surface mount tantalum capacitors and ce­ramic capacitors. The location of the decoupling network is
critical to transient response performance. Place the
decoupling network as close as possible to the micropro­cessor control circuitry because a trace run from the
decoupling capacitors to the actual circuitry is inductive. In
addition, use large power and ground plane areas to
minimize distribution drops.

A possible stability problem that occurs in monolithic linear
regulators is current limit oscillations. The LT1587-1.5
essentially has a flat current limit over the range of input
supply voltage. The lower current limit rating and 7V
maximum supply voltage rating for this device permits this
characteristic. Current limit oscillations are typically non­existent unless the input and output decoupling capacitors

CAPACITANCE
EFFECTS

LT1587 • F01

for the regulators are mounted several inches from the
terminals.

Protection Diodes

In normal operation, the LT1587-1.5 does not require any
protection diodes. Older 3-terminal regulators require
protection diodes between the output pin and the input pin
to prevent die overstress.

A protection diode between the input and output pins is
usually not needed. An internal diode between the input
and output pins on the LT1587-1.5 can handle microsec­ond surge currents of 50A to 100A. Even with large value
output capacitors it is difficult to obtain those values of
surge currents in normal operation. Only with large values
of output capacitance, such as 1000µF to 5000µ F, and with
the input pin instantaneously shorted to ground can dam­age occur. A crowbar circuit at the input of the LT1587-1.5
can generate those levels of current, and a diode from
output to input is then recommended. This is shown in
Figure 2. Usually, normal power supply cycling or system
“hot plugging and unplugging” will not generate current
large enough to do any damage.

D1

1N4002

(OPTIONAL)

LT1587-1.5

V

IN

+

C1
10µF

IN OUT

GND



Figure 2



V

+

OUT

C2
10µF

LT1587 • F02

Ripple Rejection

The typical curve for ripple rejection reflects values for the
LT1587-1.5 as a function of frequency. In applications that
require improved ripple rejection, use the adjustable
LT1587. A bypass capacitor from the adjust pin to ground
reduces the output ripple by the ratio of V

OUT

/1.25V.

Load Regulation

It is not possible to provide true remote load sensing
because the LT1587-1.5 is a 3-terminal device. Load

5

LT1587-1.5

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APPLICATIONS INFORMATION

regulation is limited by the resistance of the wire connect­ing the regulators to the load. Load regulation per the data
sheet specification is measured at the bottom of the
package.

For fixed voltage devices, negative side sensing is a true
Kelvin connection with the Ground pin of the device re­turned to the negative side of the load. This is illustrated in
Figure 3.

R



P

PARASITIC

LINE RESISTANCE

LT1587 • F03

R

L

IN

LT1587-1.5

IN OUT

GND

V

Figure 3. Connection for Best Load Regulation

Thermal Considerations

The LT1587-1.5 protects the device under overload condi­tions with internal power and thermal limiting circuitry.
However, for normal continuous load conditions, do not
exceed maximum junction temperature ratings. It is impor­tant to consider all sources of thermal resistance from
junction-to-ambient. These sources include the junction­to-case resistance, the case-to-heat sink interface resis­tance, and the heat sink resistance. Thermal resistance
specifications have been developed to more accurately
reflect device temperature and ensure safe operating tem­peratures. The electrical characteristics section provides a
separate thermal resistance and maximum junction tem­perature for both the control circuitry and the power
transistor. Older regulators with a single junction-to-case
thermal resistance specification, use an average of the two
values provided here and allow excessive junction tem­peratures under certain conditions of ambient temperature
and heat sink resistance. Calculate the maximum junction
temperature for both sections to ensure that both thermal
limits are met.

Junction-to-case thermal resistance is specified from the
IC junction to the bottom of the case directly below the die.
This is the lowest resistance path for heat flow. Proper
mounting ensures the best thermal flow from this area of
the package to the heat sink. Linear Technology strongly
recommends thermal compound at the case-to-heat sink
interface. Use a thermally conductive spacer if the case of
the device must be electrically isolated and include its
contribution to the total thermal resistance. Please consult
“Mounting Considerations for Power Semiconductors”

1990 Linear Applications Handbook, Volume I

, Pages
RR3-1 to RR3-20. The output connects to the case of the
device in the LT1587-1.5.

For example, using an LT1587CT-1.5 (TO-220, commer­cial) and assuming:

VIN(Max Continuous) = 3.465V (3.3V + 5%), V
I

= 3A

OUT

TA = 70°C, θ

θ

CASE-TO-HEAT SINK

HEAT SINK

= 7°C/W

= 1°C/W (with Thermal Compound)

OUT

= 1.5V

Power dissipation under these conditions is equal to:

PD = (V

IN

– V

OUT

)(I

) = (3.465 – 1.5)(3A) = 5.895W

OUT

Junction temperature will be equal to:

TJ = TA + PD(θ

HEAT SINK

+ θ

CASE-TO-HEAT SINK

+ θJC)

For the Control Section:

TJ = 70°C + 5.895W (7°C/W + 1°C/W + 0.7°C/W) = 121.3°C

121.3°C < 125°C = T

(Control Section Commercial

JMAX

Range)

For the Power Transistor:

TJ = 70°C + 5.895W (7°C/W + 1°C/W + 3°C/W) = 134.8°C

134.8°C < 150°C = T

(Power Transistor Commercial

JMAX

Range)

In both cases the junction temperature is below the maxi­mum rating for the respective sections, ensuring reliable
operation.

6

PACKAGE DESCRIPTION

LT1587-1.5

U

Dimensions in inches (millimeters) unless otherwise noted.

M Package

3-Lead Plastic DD Pak

(LTC DWG # 05-08-1460)

0.256

(6.502)

0.060

(1.524)

0.300

(7.620)

BOTTOM VIEW OF DD PAK

HATCHED AREA IS SOLDER PLATED

COPPER HEAT SINK

(1.524)

(1.905)

0.060

0.075

0.183

(4.648)

0.060

(1.524)

TYP

0.330 – 0.370

(8.382 – 9.398)

+0.012

0.143
–0.020

+0.305

3.632

()

–0.508

0.050 

(1.270)

TYP

0.390 – 0.415

(9.906 – 10.541)

(4.191 – 4.572)

15° TYP

0.090 – 0.110

(2.286 – 2.794)

T Package

3-Lead Plastic TO-220

(LTC DWG # 05-08-1420)

0.165 – 0.180

0.059

(1.499)

TYP

0.013 – 0.023

(0.330 – 0.584)

0.045 – 0.055

(1.143 – 1.397)

+0.008

0.004
–0.004

+0.203

0.102

()

–0.102

0.095 – 0.115

(2.413 – 2.921)

0.050 ± 0.012

(1.270 ± 0.305)

M (DD3) 0695

0.390 – 0.415

(9.906 – 10.541)

0.460 – 0.500

(11.684 – 12.700)

0.980 – 1.070

(24.892 – 27.178)

0.520 – 0.570

(13.208 – 14.478)

0.147 – 0.155

(3.734 – 3.937)

DIA

0.230 – 0.270

(5.842 – 6.858)

0.570 – 0.620

(14.478 – 15.748)

0.330 – 0.370

(8.382 – 9.398)

0.218 – 0.252

(5.537 – 6.401)

0.090 – 0.110

(2.286 – 2.794)

0.028 – 0.038

(0.711 – 0.965)

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen­tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

0.050

(1.270)

TYP

0.165 – 0.180

(4.293 – 4.699)

0.013 – 0.023

(0.330 – 0.584)

0.045 – 0.055

(1.143 – 1.397)

0.095 – 0.115

(2.413 – 2.921)

T3 (TO-220) 0595

7

LT1587-1.5

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PART NUMBER DESCRIPTION COMMENTS

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or Adjustable

OUT

8

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone]

●

FAX

: [phone]

●

TELEX

: 499-3977

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