Datasheet LT1585-1.5, LT1585A-1.5 Datasheet (Linear Technology)

FEATURES

LT1585-1.5/LT1585A-1.5

Fixed 1.5V, 4.6A and 5A

Low Dropout, Fast Response

GTL+ Regulators

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DESCRIPTIO

■

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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APPLICATIO S

■

GTL+ Power Supply

■

Low Voltage Logic Supplies

■

Battery-Powered Circuitry

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TYPICAL APPLICATIO

The LT®1585-1.5/LT1585A-1.5 are low dropout, 3-termi­nal regulators with 4.6A and 5A output current capability
respectively, and a fixed 1.5V output voltage. The designs
are optimized for low voltage applications where transient
response and minimum input voltage are critical. Similar to
the LT1084, they have lower dropout and faster transient
response. These improvements make them ideal for low
voltage microprocessor applications, especially as the
regulator in an Intel 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 LT1585-1.5/LT1585A-1.5 are available in the through­hole 3-pin TO-220 power package and 3-pin plastic DD.

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

3.3V

LT1585A-1.5

V

C1, C2

+

100µF
10V

NOTE: LTC RECOMMENDS CENTRALLY
LOCATING THE LT1585A-1.5 TO MINIMIZE

DISTRIBUTION DROPS AND USING

V

TT

SEPARATE V
BUS END

V

IN

OUT

GND

GENERATORS AT EACH

REF

+

V
5A

TT

= 1.5V

C3 TO C6
100µF
10V

Intel Processor GTL+ Supply

C7 TO
C12
1µF

RX

TX

RX

R1
75Ω

V

REF

R2
150Ω

TX

C13

0.1µF

Q1

Q3

R5
100ΩR7100ΩR8100ΩR6100Ω

•

•

•

142 TOTAL SIGNAL LINES

R3

V

75Ω

REF

R4
150Ω

Q2

Q4

C14

0.1µF

RX

TX

RX

TX

1585-1.5 • TA01

1

LT1585-1.5/LT1585A-1.5

WW

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ABSOLUTE MAXIMUM RATINGS

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(Note 1)

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

Operating Junction Temperature Range

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

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

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PACKAGE/ORDER INFORMATION

FRONT VIEW

TAB

IS

OUTPUT

Consult factory for Industrial and Military grade parts.

3

2

1

M PACKAGE

3-LEAD PLASTIC DD

θJA = 30°C/W*

*WITH PACKAGE
SOLDERED TO 0.5

V

IN

SQUARE INCH COPPER
AREA OVER BACKSIDE

V

OUT

GROUND PLANE OR
INTERNAL POWER PLANE.

GND

CAN VARY FROM

θ

JA

20°C/W TO >40°C/W
WITH OTHER MOUNTING
TECHNIQUES

ORDER PART

NUMBER

LT1585CM-1.5
LT1585ACM-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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ORDER PART

IN

OUT

LT1585CT-1.5
LT1585ACT-1.5

TAB IS

OUTPUT

FRONT VIEW

3

2

1

T PACKAGE

3-LEAD PLASTIC TO-220

θJA = 50°C/W

V

V

GND

NUMBER

ELECTRICAL CHARACTERISTICS

The ● denotes specifications which apply over the specified operating

temperature range, otherwise specifications are at TA = 25°C.

PARAMETER CONDITIONS MIN TYP MAX UNITS

Output Voltage (Note 4) VIN = 5V, TJ = 25°C, I

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

(Notes 2, 3, 4) ● 0.05 0.5 %
Dropout Voltage (Note 4) ∆V
Current Limit LT1585-1.5, (V

Quiescent Current V
Ripple Rejection (Note 4) 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

Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.

Note 2: 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 3: Line and load regulation are guaranteed up to the maximum
power dissipation (25W for the LT1585-1.5 in T package and 27.5W for

OUT

)

≤ 7V, 0mA ≤ I

3V ≤ V

IN

= 1%, I

OUT

LT1585A-1.5, (V

= 5V ● 713 mA

IN

OUT

IN

OUT

= 0mA 1.485 (–1%) 1.5 1.515 (+1%) V

OUT

≤ I

OUT

FULL LOAD

= 0mA 0.005 0.2 %

OUT

≤ I

OUT

FULL LOAD

= I

FULL LOAD

– V

) = 5.5V ● 4.60 5.25 A

OUT

– V

IN

= 25µF Tant., VIN = 4.5V, I

) = 5.5V ● 5.00 6.00 A

OUT

= I

OUT

FULL LOAD

the LT1585A-1.5). Power 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 4: I

FULL LOAD

as a function of input-to-output voltage. I
LT1585-1.5 and 5A for the LT1585A-1.5. The LT1585-1.5/LT1585A-1.5
have constant current limit with changes in input-to-output voltage.

● 1.470 (–2%) 1.5 1.530 (+2%) V

0.05 0.3 %

● 1.200 1.400 V

● 60 72 dB

is defined as the maximum value of output load current

FULL LOAD

is equal to 4.6A for the

2

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TEMPERATURE (°C)

–0.20

OUTPUT VOLTAGE DEVIATION (%)

–0.10

0

0.10

–0.15

–0.05

0.05

–25 25 75 125

1585-1.5 G03

175–50–75 0 50 100 150

∆I = I

FULL LOAD

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TYPICAL PERFORMANCE CHARACTERISTICS

LT1585-1.5/LT1585A-1.5

LT1585A-1.5 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

0

T = 25°C

1

2

OUTPUT CURRENT (A)

3

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

T = –5°C

T = 125°C

4

5

1585-1.5 G01

TEMPERATURE (°C)

LT1585A-1.5 Short-Circuit Current
vs Temperature

6.0

5.5

5.0

4.5

SHORT-CIRCUIT CURRENT (A)

4.0
–50

–75

1585-1.5 G04

–25

175–50–75 0 50 100 150

50

75

0

25

TEMPERATURE (°C)

100

Load Regulation vs Temperature

125

175

150

1585-1.5 G02

Quiescent Current vs Temperature

13
12
11
10

9
8
7
6

QUIESCENT CURRENT (mA)

5
4
3

–25

0

–50 150

–75

25

50

TEMPERATURE (°C)

75

100

125

175

1585-1.5 G05

Ripple Rejection vs Frequency

90

80

70

60

50

40

30

RIPPLE REJECTION (dB)

20

(VIN – V

0.5V ≤ V

10

I

OUT

0

10 1k 10k 100k

OUT

= I

FULL LOAD

100

RIPPLE

) ≤ 3V

≤ 2V

FREQUENCY (Hz)

1585-1.5 G06

Maximum Power Dissipation*

30

25

20

15

POWER (W)

10

5

0

*AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE

50

LT1585A-1.5

LT1585-1.5

90 110 120 130 140 150

80 100

60 70

CASE TEMPERATURE (˚C)

1585-1.5 G07

3

LT1585-1.5/LT1585A-1.5

WW

SI PLIFIED SCHE ATIC

V

IN

THERMAL

LIMIT

GND

+

–

V

OUT

1585-1.5 SS

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APPLICATIONS INFORMATION

General

The LT1585-1.5/LT1585A-1.5 3-terminal regulators are
easy to use and have all the protection features expected
in high performance linear regulators. The devices are
short-circuit protected, safe-area protected and provide
thermal shutdown to turn off the regulators if the junction
temperature exceeds about 150°C.

The ICs are pin compatible with the LT1083/LT1084/LT1085
family of linear regulators but offer 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 LT1585-

1.5/LT1585A-1.5 regulators require 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 LT1585-1.5/LT1585A-1.5 are specifi­cally designed to meet the fast current load step require-

ments of these applications and save total cost by needing
less output capacitance in order to maintain regulation.

Stability

The circuit design in the LT1585-1.5/LT1585A-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
LT1585-1.5/LT1585A-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 LT1585-1.5/
LT1585A-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

4

LT1585-1.5/LT1585A-1.5

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APPLICATIONS INFORMATION

stability and transient response of the LT1585-1.5/
LT1585A-1.5.

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 LT1585-1.5/
LT1585A-1.5 essentially have a flat current limit over the

CAPACITANCE
EFFECTS

1585-1.5 F01

range of input supply voltage. The lower current limit rating
and 7V maximum supply voltage rating for this device
permit this characteristic. Current limit oscillations are
typically nonexistent unless the input and output decou­pling capacitors for the regulators are mounted several
inches from the terminals.

Protection Diodes

In normal operation, the LT1585-1.5/LT1585A-1.5 do 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 LT1585-1.5/LT1585A-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
5000µF, and with the input pin instantaneously shorted to
ground can damage occur. A crowbar circuit at the input of
the LT1585-1.5/LT1585A-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)

LT1585-1.5

V

IN

+ +

C1
10µF

IN OUT

GND

Figure 2

C2
10µF

V

OUT

1585-1.5 F02

Ripple Rejection

The typical curve for ripple rejection reflects values for the
LT1585-1.5/LT1585A-1.5 as a function of frequency. In
applications that require improved ripple rejection, use the
adjustable LT1585/LT1585A. A bypass capacitor from the
adjust pin to ground reduces the output ripple by the ratio
of V

OUT

/1.25V.

5

LT1585-1.5/LT1585A-1.5

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APPLICATIONS INFORMATION

Load Regulation

It is not possible to provide true remote load sensing
because the LT1585-1.5/LT1585A-1.5 are 3-terminal de­vices. Load 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 GND pin of the device returned
to the negative side of the load. This is illustrated in
Figure 3.

R

P

PARASITIC

V

IN

LT1585-1.5

IN OUT

GND

LINE RESISTANCE

1585-1.5 F03

R

L

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 LT1585-1.5/LT1585A-1.5.

For example, using an LT1585ACT-1.5 (TO-220, commer­cial) and assuming:

V

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

IN

I

= 5A

OUT

TA = 70°C, θ

HEAT SINK

= 3°C/W

OUT

= 1.5V

Figure 3. Connection for Best Load Regulation

Thermal Considerations

The LT1585-1.5/LT1585A-1.5 protect 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 junction-to-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 junction­to-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.

θ

CASE-TO-HEAT SINK

= 1°C/W (with Thermal Compound)

Power dissipation under these conditions is equal to:

PD = (V

IN

– V

OUT

)(I

) = (3.465 – 1.5)(5A) = 9.825W

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 + 9.825W (3°C/W + 1°C/W + 0.7°C/W) = 116.2°C

116.2°C < 125°C = T

(Control Section Commercial

JMAX

Range)

For the Power Transistor:

TJ = 70°C + 9.825W (3°C/W + 1°C/W + 3°C/W) = 138.8°C

138.8°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

LT1585-1.5/LT1585A-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)

BSC

0.390 – 0.415

(9.906 – 10.541)

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

(4.191 – 4.572)

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)

± 0.012

0.050

(1.270 ± 0.305)

M (DD3) 1098

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)

0.100

(2.540)

BSC

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

(4.191 – 4.572)

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) 1098

7

LT1585-1.5/LT1585A-1.5

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or Adjustable

OUT

8

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone]

●

www.linear-tech.com

158515fa LT/TP 0100 2K REV A • PRINTED IN USA

 LINEAR TECHNOLOGY CORPORATION 1996