Device

Tested

Operating

Temp.

Range

Package

LT1585A

SILICON MONOLITHIC

INTEGRATED CIRCUIT

5A LOW DROPOUT FAST

RESPONSE POSITIVE

ADJUSTABLE AND FIXED

VOLTAGE REGULATOR

ORDERING INFORMATION

LT1585ACT

0 to 125

TO220

Order this document by LT1585A/D

T SUFFIX

PLASTIC PACKAGE

CASE 221A

LT1585ACM

0 to 125

D2PAK

CM SUFFIX

PLASTIC PACKAGE

CASE 936

(D2PAK)

Adjustable output:
Pin 1. Adjust

2. Vout

3. Vin

Fixed 1.5V output:
Pin 1. Gnd

2. Vout

3. Vin

LT1585ACT1.5 0 to 125

TO220

Output

Voltage

Type

ADJ.

FIXED

1.5V

LT1585ACM1.5 0 to 125

D2PAK

FIXED

1.5V

MOTOROLA ANALOG IC DEVICE DATA

5A Low Dropout Fast Response

Positive Adjustable and Fixed

Voltage Regulators

The LT1585A is a low dropout 3terminal voltage regulator with 5A output

current capability.

Design has been optimized for low voltage applications where transient

response and minimum input voltage are critical. This voltage regulator
features a low dropout voltage and fast transient response. These
improvements make them ideal for low voltage microprocessor applications
requiring a regulated 2.5V to 3.6V output with an input supply below 7V.

Current limits is trimmed to ensure specified output current and controlled

shortcircuit current. Onchip thermal limiting provides protection against
any combination of overload that would create excessive junction
temperatures. The LT1585A is available in the industry standard 3pin
TO220 and D2PAK power package.

Features

Fast Transient Response

Guaranteed Dropout Voltage at Multiple Currents

Load Regulation: 0.05% Typ

Trimmed Current Limit

OnChip Thermal Limiting

Standard 3Pin Power Package

Applications

Pentium

Processor Supplies

Power PC

Supplies

Other 2.5V to 3.6V Microprocessor Supplies

Low Voltage Logic Supplies

BatteryPowered Circuitry

Post Regulator for Switching Supply

Simplified Block Diagram

Vin

Vout

Thermal

Limit

Adjust

Motorola, Inc. 1999

Rev 0

LT1585A

MOTOROLA ANALOG IC DEVICE DATA

ABSOLUTE MAXIMUM RATINGS

(

Absolute Maximum Ratings indicate limits beyond which damage to the device may occur)

Rating

Symbol

Pin #

Value

Unit

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Maximum Supply Voltage

ÁÁÁÁÁ

Vin

ÁÁÁ

ÁÁÁÁÁÁÁÁ

ÁÁÁ

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Power Dissipation

ÁÁÁÁÁ

ÁÁÁ

ÁÁÁÁÁÁÁÁ

ÁÁÁ

Case 221A (TO220) (TJ = +25

Internally Limited

Thermal Resistance, JunctiontoAmbient

C/W

Thermal Resistance, JunctiontoCase

5.0

C/W

Case 936 (D2PAK) (TJ = +25

Internally Limited

Thermal Resistance, JunctiontoAmbient

C/W

Thermal Resistance, JunctiontoCase

5.0

C/W

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Storage Temperature Range

ÁÁÁÁÁ

Tstg

ÁÁÁ

ÁÁÁÁÁÁÁÁ

65 to 150

ÁÁÁ

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Minimum ESD Rating (Human Body Model: C = 100pF, R = 1.5 k

)

ÁÁÁÁÁ

ÁÁÁ

ÁÁÁÁÁÁÁÁ

3.0

ÁÁÁ

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Lead Temperature (Soldering, 10 sec.)

ÁÁÁÁÁ

ÁÁÁ

ÁÁÁÁÁÁÁÁ

260

ÁÁÁ

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Maximum Junction Temperature

ÁÁÁÁÁ

ÁÁÁ

ÁÁÁÁÁÁÁÁ

150

ÁÁÁ

OPERATING RATINGS

(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)

Rating

Symbol

Pin #

Value

Unit

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Operating Junction Temperature Range

ÁÁÁÁÁ

ÁÁÁ

ÁÁÁÁÁÁÁÁ

0 to +125

ÁÁÁ

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Supply Voltage

ÁÁÁÁÁ

ÁÁÁ

ÁÁÁÁÁ

ÁÁÁ

ÁÁ

ÁÁÁ

ÁÁÁÁÁÁÁÁ

ÁÁÁÁÁÁ

ÁÁÁÁÁÁÁÁ

7.0

ÁÁÁ

ELECTRICAL CHARACTERISTICS

(0 < TJ < +125

C, unless otherwise noted)

Characteristic

Symbol

Pin #

Min

Typ

Max

Unit

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Reference Voltage (LT1585A)

ÁÁÁÁÁ

Vref

ÁÁÁ

ÁÁÁÁ

ÁÁÁ

(VinVout) = 3V, Iout = 10mA, TJ = 25

1.238

1.250

1.262

1.5V

(VinVout)

5.75V, 10mA

Iout

1.225

1.250

1.275

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Output Voltage (LT1585A1.5)

ÁÁÁÁÁ

ÁÁÁ

ÁÁÁÁ

ÁÁÁ

Vin = 5V, TJ = 25

C, Iout = 0mA

1.485

1.5

1.515

Vin

7V, 0mA

Iout

1.470

1.5

1.530

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Line Regulation [Notes 1, 2]

ÁÁÁÁÁ

Regline

ÁÁÁ

ÁÁÁÁ

ÁÁÁ

LT1585A: 2.75V

Vin

7V, Iout = 10mA

0.005

0.2

LT1585A1.5: 3V

Vin

7V, Iout = 0mA

0.005

0.2

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Load Regulation [Notes 1, 2]

ÁÁÁÁÁ

Regload

ÁÁÁ

ÁÁÁÁ

ÁÁÁ

LT1585A: (VinVout) = 3V, TJ = 25

C, 10mA

Iout

0.05

0.3

LT1585A1.5: Vin = 5V, TJ = 25

C, 0mA

Iout

0.05

0.3

LT1585A: (VinVout) = 3V, 10mA

Iout

0.05

0.5

LT1585A1.5: Vin = 5V, 0mA

Iout

0.05

0.5

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Dropout Voltage

ÁÁÁÁÁ

VinVout

ÁÁÁ

ÁÁÁÁ

ÁÁÁ

LT1585A:

VREF = 1%, IOUT = 3A

1.150

1.300

LT1585A1.5:

VOUT = 1%, IOUT = 3A

1.150

1.300

LT1585A:

VREF = 1%, IOUT = 5A

1.200

1.400

LT1585A1.5:

VOUT = 1%, IOUT = 5A

1.200

1.400

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Current Limit [Note 3]

ÁÁÁÁÁ

ILimit

ÁÁÁ

ÁÁÁÁ

ÁÁÁ

(VinVout) = 5.5V

5.0

6.0

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Adjust Pin Current (LT1585A)

ÁÁÁÁÁ

IAdj

ÁÁÁ

ÁÁÁÁ

ÁÁÁ

120

ÁÁÁ

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Adjust Pin Current Change (LT1585A) [Note 3]

ÁÁÁÁÁ

ÁÁÁ

ÁÁÁÁ

ÁÁÁ

1.5V

(VinVout)

5.75V, 10mA

Iout

0.2

5.0

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Minimum Load Current (LT1585A) 1.5V

(VinVout)

5.75V

ÁÁÁÁÁ

ILoad min

ÁÁÁ

ÁÁÁÁ

2.0

ÁÁÁ

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Quiescent Current (LT1585A1.5) Vin = 5V

ÁÁÁÁÁ

ÁÁÁ

ÁÁÁÁ

7.0

ÁÁÁ

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Ripple Rejection

ÁÁÁÁÁ

ÁÁÁ

ÁÁÁÁ

ÁÁÁ

LT1585A: f = 120Hz, Cout = 25

F Tant., (VinVout) = 3V, Iout = 5A

LT1585A1.5: f = 120Hz, Cout = 25

F Tant., Vin = 4.5V, Iout = 5A

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Thermal Regulation TJ = 25

C, 30ms Pulse

ÁÁÁÁÁ

Reg

ÁÁÁ

ÁÁÁÁ

0.004

ÁÁÁ

%/W

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Temperature Stability

ÁÁÁÁÁ

Stab

ÁÁÁ

ÁÁÁÁ

0.5

ÁÁÁ

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

Long Term Stability TJ = 125

C, 1000 Hrs

ÁÁÁÁÁ

ÁÁÁ

ÁÁÁÁ

0.03

ÁÁÁ

1.0

ÁÁÁ

ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ

RMS Output Noise (% of Vout) TJ = 25

C, 10Hz

10kHz

ÁÁÁÁÁ

ÁÁÁ

ÁÁÁÁ

0.003

ÁÁÁ

NOTES 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.

2. Line and load regulations are guaranteed up to the maximum power dissipation 28.8W for the LT1585A in Tpackage. 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.

3. The LT1585A has constant current limit with changes in inputtooutput voltage.

LT1585A

MOTOROLA ANALOG IC DEVICE DATA

Figure 7. LT1585A Adjust Pin Current vs

Temperature

Figure 8. Ripple Rejection vs Frequency

100,000

TEMPERATURE (

10,000

100

1000

(V)

ref

160

TEMPERATURE (

100

140

120

(

adj

OPERATING DESCRIPTION

APPLICATIONS INFORMATION
General

The LT1585A 3terminal adjustable positive voltage

regulator is easy to use and has all the protection features
expected in high performance linear regulators. The device is
shortcircuit protected, safearea protected and provides
thermal shutdown to turn off the regulator should the junction
temperature exceed about 150

The LT1585A voltage 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 cycle load current

from almost zero to amps in tens of nanoseconds. Output
voltage tolerances are tighter and include transient response
as part of the specification.

The LT1585A is specifically designed to meet the fast

current loadstep requirements of these microprocessors
and save total cost by needing less output capacitance in
order to maintain regulation.
Stability

The circuit design in the LT1585A requires the use of an

output capacitor as part of the frequency compensation. For
all operating conditions, the addition of a 22

F solid tantalum

or a 100

F aluminium electrolytic on the output ensures

stability. Normally, the LT1585A 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 LT1585A frequency compensation optimizes
frequency response with low ESR capacitors. In general, use
capacitors with an ESR of less than 1

On the LT1585A, bypassing the adjust pin improves ripple

rejection and transient response. Bypassing the adjust pin
increases the required output capacitor value. The value of
22

F tantalum or 100

F aluminium covers all cases of

bypassing the adjust terminal. With no adjust pin bypassing,
smaller values of capacitors provide equally good results.

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 LT1585A.

Large load current changes are exactly the situation

presented by modern microprocessors. 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 =

ESR). The

ESL of the output capacitors produces a droop proportional
to the rate of change of output current (V = L

t). The

output capacitance produces a change in output voltage
proportional to the time until the regulator can respond (

V =

l/C). These transient effects are illustrated in Figure 9.

Figure 9.

ESR
Effects

ESL
Effects

Capacitance
Effects

Slope, V

+ D

Point at which

Regulator Takes Control

LT1585A

MOTOROLA ANALOG IC DEVICE DATA

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 microprocessors.
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 processor pins because
trace runs from the decoupling capacitors to the processor
pins are inductive. The ideal location for the decoupling
network is actually inside the microprocessor socket cavity.
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 LT1585A
essentially has a flat current limit over the range of input
supply voltage. The lower current limit rating and 12V
maximum supply voltage rating for these devices 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 LT1585A does not require any

protection diodes. Older 3terminal regulators require
protection diodes between the output pin and the input pin or
between the adjust pin and the output pin to prevent die
overstress.

Builtin internal resistors limit internal current paths on the

adjust pin. Therefore, even with bypass capacitors on the
adjust pin, no protection diode is needed to ensure device
safety under shortcircuit conditions.

A protection diode between the input and output pins is

usually not needed. An internal diode between the input and
output pins on the LT1585A 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 1000

F to 500

F, and with the input pin

instantaneously shorted to ground can damage occur. A
crowbar circuit at the input of the LT1585A can generate
those levels of current, and a diode from output to input is
then recommended. This is shown in Figure 10. Usually,
normal power supply cycling or system "hot plugging and
unplugging" will not generate current large enough to do any
damage.

The adjust pin can be driven on a transient basis

7V with

respect to the output, without any device degradation. As
w i t h a n y I C r e g u l a t o r, e x c e e d i n g t h e m a x i m u m
inputtooutput voltage differential causes the internal
transistors to break down and none of the protection circuitry
is then functional.

Vout

Vin

LT1585A

ADJ

OUT

1N4002

(Optional)

C2
10

Figure 10.

Ripple Rejection

A bypass capacitor from the adjust pin to ground reduces

the output ripple by the ratio of VOUT

/1.25 V. The impedance

of the adjust pin capacitor at the ripple frequency should be
less than the value of R1 (typically in the rage of 100

120

) in the feedback divider network in Figure 10.

Therefore, the value of the required adjust pin capacitor is a
function of the input ripple frequency. For example, if R1
equals 100

and the ripple frequency equals 120Hz, the

adjust pin capacitor should be 22

F. At 10kHz, only 0.22

F is

needed.
Output Voltage

The LT1585A adjustable regulator develops a 1.25V

reference voltage between the output pin and the adjust pin
(see Figure 11). Placing a resistor R1 between these two
terminals causes a constant current to flow through R1 and
down through R2 to set the overall output voltage. Normally,
this current is the specified minimum load current of 10mA.
The current out of the adjust pin adds to the current from R1
and is typically 55

A. Its output voltage contribution is small

and only needs consideration when very precise output
voltage setting is required.

Part Number LT1585A