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LT1587-1.5 Fixed 1.5V, 3A Low Dropout Fast Response GTL+ Regulator
FEATURES
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DESCRIPTION
The LT (R)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
Fast Transient Response Guaranteed Dropout Voltage at Multiple Currents Load Regulation: 0.05% Typ Trimmed Current Limit On-Chip Thermal Limiting
APPLICATIONS
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Intel Pentium(R) Pro Processor GTL+ Supply Low Voltage Logic Supplies Battery-Powered Circuitry
TYPICAL APPLICATION
Intel Pentium Pro Processor GTL+ Supply
3.3V LT1587-1.5 VIN VOUT GND VTT = 1.5V 3A C4 TO C6 1F R1 75 R2 150 R5 100 C13 0.1F R7 100 R8 100 R6 100 VREF C14 0.1F R3 75 R4 150 VTT = 1.5V 3A LT1587-1.5 VOUT VIN GND C10 TO C12 1F 3.3V
+
C1 100F 10V AVX TPS
+
C2, C3 100F 10V AVX TPS
VREF
RX
TX
Q1
Q2
RX
RX 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
TX
Q3 * * *
Q4
TX
142 TOTAL SIGNAL LINES
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+ C8, C9 100F
10V AVX TPS
+
C7 100F 10V AVX TPS
RX
TX
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LT1587-1.5
ABSOLUTE MAXIMUM RATINGS
PRECONDITIONI G
100% Thermal Limit Functional Test VIN ............................................................................. 7V Operating Junction Temperature Range Control Section.................................... 0C to 125C Power Transistor ................................. 0C to 150C
PACKAGE/ORDER INFORMATION
FRONT VIEW 3 2 1 M PACKAGE 3-LEAD PLASTIC DD VIN VOUT GND
ORDER PART NUMBER LT1587CM-1.5
FRONT VIEW 3 2 1 T PACKAGE 3-LEAD PLASTIC TO-220 VIN VOUT GND
JA = 30C/W*
JA = 50C/W
* With package soldered to 0.5 square inch copper area over backside ground plane or internal power plane. JA can vary from 20C/W to > 40C/W with other mounting techniques.
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
PARAMETER Output Voltage Line Regulation (Notes 1, 2) Load Regulation (Notes 1, 2, 3) Dropout Voltage Current Limit (Note 3) Quiescent Current Ripple Rejection Thermal Regulation Temperature Stability Long-Term Stability RMS Output Noise (% of VOUT) Thermal Resistance Junction to Case TA = 125C, 1000 Hrs. TA = 25C, 10Hz f 10kHz T Package: Control Circuitry/Power Transistor M Package: Control Circuitry/Power Transistor CONDITIONS VIN = 5V, TJ = 25C, IOUT = 0mA 3V VIN 7V, 0mA IOUT 3A 3V VIN 7V, IOUT = 0mA VIN = 5V, TJ = 25C, 0mA IOUT IFULL LOAD
q q
MIN 1.485 (- 1%) 1.470 (- 2%)
VOUT = 1%, IOUT = 3A (VIN - VOUT) = 5.5V VIN = 5V f = 120Hz, COUT = 25F Tant., VIN = 4.5V, IOUT = 3A TA = 25C, 30ms pulse
q q q q
3.100 60
q
The q 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
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.
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Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER LT1587CT-1.5
TYP 1.5 1.5 0.005 0.05 0.05 1.150 3.750 7 72 0.004 0.5 0.03 0.003
MAX 1.515 (+ 1%) 1.530 (+ 2%) 0.2 0.3 0.5 1.300 13 0.02 1.0
UNITS V V % % % V A mA dB %/W % % %
0.7/3.0 0.7/3.0
C/W C/W
LT1587-1.5 TYPICAL PERFORMANCE CHARACTERISTICS
Dropout Voltage vs Output Current
1.5 1.4 1.3 GUARANTEED TEST POINTS SHORT-CIRCUIT CURRENT (A)
OUTPUT VOLTAGE DEVIATION (%)
DROPOUT VOLTAGE (V)
1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0 0.5 1.5 2.0 1.0 OUTPUT CURRENT (A) T = 125C T = 25C
Output Voltage vs Temperature
1.53 1.52 13 12
QUIESCENT CURRENT (mA)
OUTPUT VOLTAGE (V)
1.51 1.50 1.49 1.48 1.47 -75 -50 -25 0 25 50 75 100 125 150 175 TEMPERATURE (C)
LT1587 * TPC04
Ripple Rejection vs Frequency
90 80
RIPPLE REJECTION (dB)
70 60 50 40 30 20 10 0 10 LT1587-1.5: (VIN - VOUT) 3V 0.5V VRIPPLE 2V IOUT = IFULL LOAD 100 1k 10k FREQUENCY (Hz) 100k
LT1587 * TPC06
POWER (W)
UW
T = -5C 2.5
LT1587 * TPC01
Short-Circuit Current vs Temperature
5.0
Load Regulation vs Temperature
0.10 0.05 0 -0.05 -0.10 -0.15 -0.20 -75 -50 -25 0 25 50 75 100 125 150 175 TEMPERATURE (C)
LT1587 * TPC03
I = 3A
4.5
4.0
3.5
3.0
3.0 -75 -50 -25 0 25 50 75 100 125 150 175 TEMPERATURE (C)
LT1587 * TPC02
Quiescent Current vs Temperature
11 10 9 8 7 6 5 4 3 -75 -50 -25 0 25 50 75 100 125 150 175 TEMPERATURE (C)
LT1587 * TPC05
Maximum Power Dissipation*
30 25 20 15 10 5 0 50 60 70 80 90 100 110 120 130 140 150 CASE TEMPERATURE (C)
LT1587 * TPC07
LT1587-1.5
*AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE
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LT1587-1.5
SI PLIFIED SCHE ATIC
VIN
GND
LT1587 * BD
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 150C. 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 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 22F solid tantalum or a 100F 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 1. 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.
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+ -
THERMAL LIMIT
VOUT
LT1587-1.5
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 I = t C CAPACITANCE EFFECTS
LT1587 * F01
SLOPE,
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
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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 1000F to 5000F, 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)
VIN
+
IN C1 10F
LT1587-1.5 OUT GND
+
VOUT C2 10F
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
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LT1587-1.5
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.
LT1587-1.5 IN OUT GND RL RP PARASITIC LINE RESISTANCE
VIN
LT1587 * F03
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.
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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 TA = 70C, HEAT SINK = 7C/W CASE-TO-HEAT SINK = 1C/W (with Thermal Compound) 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(HEAT SINK + CASE-TO-HEAT SINK + JC) For the Control Section: TJ = 70C + 5.895W (7C/W + 1C/W + 0.7C/W) = 121.3C 121.3C < 125C = TJMAX (Control Section Commercial Range) For the Power Transistor: TJ = 70C + 5.895W (7C/W + 1C/W + 3C/W) = 134.8C 134.8C < 150C = 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
PACKAGE DESCRIPTION
0.256 (6.502)
0.060 (1.524)
0.060 (1.524)
0.183 (4.648)
0.075 (1.905) 0.300 (7.620) BOTTOM VIEW OF DD PAK HATCHED AREA IS SOLDER PLATED COPPER HEAT SINK +0.012 0.143 - 0.020 0.090 - 0.110 (2.286 - 2.794) 0.050 (1.270) TYP
0.013 - 0.023 (0.330 - 0.584)
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)
0.090 - 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.
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Dimensions in inches (millimeters) unless otherwise noted. M Package 3-Lead Plastic DD Pak
(LTC DWG # 05-08-1460)
0.060 (1.524) TYP
0.390 - 0.415 (9.906 - 10.541) 15 TYP
0.165 - 0.180 (4.191 - 4.572)
0.045 - 0.055 (1.143 - 1.397)
0.330 - 0.370 (8.382 - 9.398)
0.059 (1.499) TYP
(
+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)
(
+0.305 3.632 -0.508
)
M (DD3) 0695
T Package 3-Lead Plastic TO-220
(LTC DWG # 05-08-1420)
0.147 - 0.155 (3.734 - 3.937) DIA 0.230 - 0.270 (5.842 - 6.858) 0.570 - 0.620 (14.478 - 15.748) 0.330 - 0.370 (8.382 - 9.398)
0.165 - 0.180 (4.293 - 4.699)
0.045 - 0.055 (1.143 - 1.397)
0.218 - 0.252 (5.537 - 6.401) 0.013 - 0.023 (0.330 - 0.584) 0.050 (1.270) TYP
0.095 - 0.115 (2.413 - 2.921)
T3 (TO-220) 0595
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LT1587-1.5 RELATED PARTS
PART NUMBER LTC (R) 1392 LTC1430 LTC1472 LT1580 DESCRIPTION Micropower Temperature, Power Supply and Differential Voltage Monitor High Power Step-Down Switching Regulator Controller Protected PCMCIA VCC and VPP Switching Matrix Very Low Dropout 7A Linear Regulator COMMENTS Micropower Data Acquisition to Monitor System 5V to 3.3V at 10A or More Single-Slot Power Switch 0.54V Dropout at 7A, Fixed 2.5VOUT or Adjustable
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977
LT/GP 0995 10K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1995

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