LINER LT1587CT-1.5

LT1587-1.5
U
DESCRIPTION
FEATURES
■
■
■
■
■
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.
Fast Transient Response
Guaranteed Dropout Voltage at Multiple Currents
Load Regulation: 0.05% Typ
Trimmed Current Limit
On-Chip Thermal Limiting
U
APPLICATIONS
■
■
■
Fixed 1.5V, 3A
Low Dropout
Fast Response
GTL+ Regulator
Intel Pentium® Pro Processor GTL+ Supply
Low Voltage Logic Supplies
Battery-Powered Circuitry
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
U
TYPICAL APPLICATION
Intel Pentium Pro Processor GTL+ Supply
VTT = 1.5V
3A
LT1587-1.5
VIN
VOUT
3.3V
VTT = 1.5V
3A
C4 TO
C6
1µF
GND
+
C1
100µF
10V
AVX TPS
+
C2, C3
100µF
10V
AVX TPS
R1
75Ω
R2
150Ω
R5
100Ω
VREF
R7
100Ω
R8
100Ω
R6
100Ω
VREF
C13
0.1µF
R3
75Ω
C14
0.1µF
LT1587-1.5
VOUT
VIN
3.3V
GND
C10 TO C12
1µF
R4
150Ω
C9
+ C8,
100µF
+
10V
AVX TPS
C7
100µF
10V
AVX TPS
RX
RX
TX
Q1
RX
TX
TX
Q2
RX
Q3
Q4
•
•
•
142 TOTAL SIGNAL LINES
TX
NOTE: LTC RECOMMENDS SEPARATE
VTT GENERATORS AT EACH BUS END
TO ENSURE CURRENT SHARING
BETWEEN THE REGULATORS AND TO
MINIMIZE VTT DISTRIBUTION DROPS
LT1587 • TA01
1
LT1587-1.5
W W
U
W
ABSOLUTE MAXIMUM RATINGS
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
UU
U
VIN ............................................................................. 7V
Operating Junction Temperature Range
Control Section.................................... 0°C to 125°C
Power Transistor ................................. 0°C to 150°C
PRECONDITIONI G
100% Thermal Limit Functional Test
U
W
U
PACKAGE/ORDER INFORMATION
FRONT VIEW
3
VIN
2
VOUT
1
GND
3
LT1587CM-1.5
VIN
2
VOUT
1
GND
M PACKAGE
3-LEAD PLASTIC DD
T PACKAGE
3-LEAD PLASTIC TO-220
θJA = 30°C/W*
θJA = 50°C/W
* With package soldered to 0.5 square inch copper area over backside
ground plane or internal power plane. θJA can vary from 20°C/W to
> 40°C/W with other mounting techniques.
ORDER PART
NUMBER
FRONT VIEW
ORDER PART
NUMBER
LT1587CT-1.5
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
PARAMETER
CONDITIONS
Output Voltage
VIN = 5V, TJ = 25°C, IOUT = 0mA
3V ≤ VIN ≤ 7V, 0mA ≤ IOUT ≤ 3A
●
Line Regulation (Notes 1, 2)
3V ≤ VIN ≤ 7V, IOUT = 0mA
Load Regulation
(Notes 1, 2, 3)
VIN = 5V, TJ = 25°C, 0mA ≤ IOUT ≤ IFULL LOAD
Dropout Voltage
∆VOUT = 1%, IOUT = 3A
●
Current Limit (Note 3)
(VIN – VOUT) = 5.5V
●
Quiescent Current
VIN = 5V
●
Ripple Rejection
f = 120Hz, COUT = 25µF Tant., VIN = 4.5V, IOUT = 3A
●
Thermal Regulation
TA = 25°C, 30ms pulse
MIN
TYP
MAX
1.485 (– 1%)
1.470 (– 2%)
1.5
1.5
1.515 (+ 1%)
1.530 (+ 2%)
V
V
0.005
0.2
%
0.05
0.05
0.3
0.5
%
%
1.150
1.300
●
3.100
3.750
60
72
7
0.004
Temperature Stability
●
TA = 125°C, 1000 Hrs.
0.03
RMS Output Noise
(% of VOUT)
TA = 25°C, 10Hz ≤ f ≤ 10kHz
0.003
Thermal Resistance
Junction to Case
T Package: Control Circuitry/Power Transistor
M Package: Control Circuitry/Power Transistor
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
2
V
A
13
mA
dB
0.02
%/W
1.0
%
0.5
Long-Term Stability
UNITS
%
%
0.7/3.0
0.7/3.0
°C/W
°C/W
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: IFULL LOAD is defined as the maximum value of output load current
as a function of input-to-output voltage. IFULL LOAD is equal to 3A. The
LT1587-1.5 has constant current limit with changes in input-to-output
voltage.
LT1587-1.5
U W
TYPICAL PERFORMANCE CHARACTERISTICS
Short-Circuit Current
vs Temperature
Dropout Voltage vs Output Current
0.10
1.3
1.2
T = –5°C
1.1
1.0
T = 25°C
0.9
T = 125°C
0.8
0.7
OUTPUT VOLTAGE DEVIATION (%)
SHORT-CIRCUIT CURRENT (A)
GUARANTEED
TEST POINTS
1.4
4.5
4.0
3.5
∆I = 3A
0.05
0
–0.05
–0.10
–0.15
0.6
0.5
1.5
2.0
1.0
OUTPUT CURRENT (A)
2.5
3.0
3.0
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
–0.20
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1587 • TPC03
LT1587 • TPC02
LT1587 • TPC01
Output Voltage vs Temperature
Quiescent Current vs Temperature
1.53
13
12
QUIESCENT CURRENT (mA)
1.52
1.51
1.50
1.49
1.48
11
10
9
8
7
6
5
4
1.47
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
3
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1587 • TPC04
LT1587 • TPC05
Ripple Rejection vs Frequency
Maximum Power Dissipation*
90
30
80
25
70
60
20
POWER (W)
0.5
OUTPUT VOLTAGE (V)
0
RIPPLE REJECTION (dB)
DROPOUT VOLTAGE (V)
Load Regulation vs Temperature
5.0
1.5
50
40
30
LT1587-1.5
15
10
20
LT1587-1.5: (VIN – VOUT) ≤ 3V
0.5V ≤ VRIPPLE ≤ 2V
IOUT = IFULL LOAD
10
0
10
100
1k
10k
FREQUENCY (Hz)
5
100k
LT1587 • TPC06
0
50 60 70 80 90 100 110 120 130 140 150
CASE TEMPERATURE (˚C)
LT1587 • TPC07
*AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE
3
LT1587-1.5
W
W
SI PLIFIED SCHE ATIC
VIN
+
–
THERMAL
LIMIT
VOUT
GND
LT1587 • BD
U
W
U
U
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 LT15871.5 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
4
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.
LT1587-1.5
U
W
U
U
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
CAPACITANCE
EFFECTS
LT1587 • F01
SLOPE,
V ∆I
=
t
C
POINT AT WHICH REGULATOR
TAKES CONTROL
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 5000µF, 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.
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
D1
1N4002
(OPTIONAL)
VIN
+
IN
C1
10µF
LT1587-1.5
OUT
GND
+
VOUT
C2
10µF
LT1587 • F02
Figure 2
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 VOUT/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
U
W
U U
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.
VIN
LT1587-1.5
IN
OUT
RP
PARASITIC
LINE RESISTANCE
GND
RL
LT1587 • F03
Figure 3. Connection for Best Load Regulation
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%), VOUT = 1.5V
IOUT = 3A
Thermal Considerations
TA = 70°C, θHEAT SINK = 7°C/W
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.
θCASE-TO-HEAT SINK = 1°C/W (with Thermal Compound)
6
Power dissipation under these conditions is equal to:
PD = (VIN – VOUT)(IOUT) = (3.465 – 1.5)(3A) = 5.895W
Junction temperature will be equal to:
TJ = TA + PD(θHEAT SINK + θCASE-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 = TJMAX (Control Section Commercial
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 = TJMAX (Power Transistor Commercial
Range)
In both cases the junction temperature is below the maximum rating for the respective sections, ensuring reliable
operation.
LT1587-1.5
U
PACKAGE DESCRIPTION
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)
TYP
0.060
(1.524)
0.390 – 0.415
(9.906 – 10.541)
0.165 – 0.180
(4.191 – 4.572)
0.045 – 0.055
(1.143 – 1.397)
15° TYP
0.060
(1.524)
0.183
(4.648)
0.059
(1.499)
TYP
0.330 – 0.370
(8.382 – 9.398)
(
+0.008
0.004 –0.004
+0.203
0.102 –0.102
)
0.095 – 0.115
(2.413 – 2.921)
0.075
(1.905)
0.300
(7.620)
(
+0.305
3.632 –0.508
BOTTOM VIEW OF DD PAK
HATCHED AREA IS SOLDER PLATED
COPPER HEAT SINK
0.090 – 0.110
(2.286 – 2.794)
+0.012
0.143 – 0.020
)
0.050
(1.270)
TYP
0.013 – 0.023
(0.330 – 0.584)
0.050 ± 0.012
(1.270 ± 0.305)
M (DD3) 0695
T Package
3-Lead Plastic TO-220
(LTC DWG # 05-08-1420)
0.147 – 0.155
(3.734 – 3.937)
DIA
0.390 – 0.415
(9.906 – 10.541)
0.165 – 0.180
(4.293 – 4.699)
0.045 – 0.055
(1.143 – 1.397)
0.230 – 0.270
(5.842 – 6.858)
0.460 – 0.500
(11.684 – 12.700)
0.570 – 0.620
(14.478 – 15.748)
0.330 – 0.370
(8.382 – 9.398)
0.980 – 1.070
(24.892 – 27.178)
0.520 – 0.570
(13.208 – 14.478)
0.090 – 0.110
(2.286 – 2.794)
0.028 – 0.038
(0.711 – 0.965)
0.218 – 0.252
(5.537 – 6.401)
0.013 – 0.023
(0.330 – 0.584)
0.050
(1.270)
TYP
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.
0.095 – 0.115
(2.413 – 2.921)
T3 (TO-220) 0595
7
LT1587-1.5
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC ® 1392
Micropower Temperature, Power Supply and Differential Voltage Monitor
Micropower Data Acquisition to Monitor System
LTC1430
High Power Step-Down Switching Regulator Controller
5V to 3.3V at 10A or More
LTC1472
Protected PCMCIA VCC and VPP Switching Matrix
Single-Slot Power Switch
LT1580
Very Low Dropout 7A Linear Regulator
0.54V Dropout at 7A, Fixed 2.5VOUT or Adjustable
8
Linear Technology Corporation
LT/GP 0995 10K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977
 LINEAR TECHNOLOGY CORPORATION 1995