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Download LT1528 3A Low Dropout Regulator for Microprocessor Applications DESCRIPTION
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LT1528 3A Low Dropout Regulator for Microprocessor Applications FEATURES DESCRIPTION n The LT ®1528 is a 3A low dropout regulator optimized to handle the large load current transients associated with the current generation of microprocessors. This device has the fastest transient response of currently available PNP regulators and is very tolerant of variations in capacitor ESR. Dropout voltage is 75mV at 10mA, rising to 300mV at 1A and 600mV at 3A. The device has a quiescent current of 400μA. Quiescent current is well controlled; it does not increase significantly as the device enters dropout. The regulator can operate with output capacitors as small as 3.3μF, although larger capacitors will be needed to achieve the performance required in most microprocessor applications. The LT1528 is available with a fixed output voltage of 3.3V. An external SENSE pin allows adjustment to output voltages greater than 3.3V, using a simple resistive divider. This allows the device to be adjusted over a wide range of output voltages, including the 3.3V to 4.2V range required by a variety of processors from Intel, IBM, AMD, and Cyrix. n n n n n n n n n n n Dropout Voltage: 0.6V at IOUT = 3A Fast Transient Response Output Current: 3A Quiescent Current: 400μA No Protection Diodes Needed Fixed Output Voltage: 3.3V Controlled Quiescent Current in Dropout Shutdown IQ = 125μA Stable with 3.3μF Output Capacitor Reverse Battery Protection No Reverse Output Current Thermal Limiting APPLICATIONS n n n Microprocessor Applications Post Regulator for Switching Supplies 5V to 3.3V Logic Regulator The LT1528 has both reverse input and reverse output protection and includes a shutdown feature. Quiescent current drops to 125μA in shutdown. The LT1528 is available in 5-lead TO-220 and 5-lead DD-PAK packages. L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION Microprocessor Supply with Shutdown Dropout Voltage 0.6 IN VIN =5V OUT 1 VOUT 15Ω 68Ω J2 J3 LT1528 4 SHDN SENSE 2 J1 + 4 × 47μF* SOLID TANTALUM GND 330Ω 3 VSHDN (PIN 4) <0.25 >2.80 NC OUTPUT OFF ON ON SHORTING J1 J2 J3 VOUT 3.30 3.45 4.00 *CHOOSE CAPACITORS TO MEET PROCESSOR REQUIREMENTS 1528 TA01 0.5 DROPOUT VOLTAGE (V) 5 0.4 0.3 0.2 0.1 0 0 0.5 2.5 1.0 1.5 2.0 OUTPUT CURRENT (mA) 3.0 1528 TA02 1528fb 1 LT1528 ABSOLUTE MAXIMUM RATINGS (Note 1) Input Voltage........................................................ ±15V* OUTPUT Pin Reverse Current ................................10mA SENSE Pin Current .................................................10mA SHDN Pin Input Voltage (Note 2) ..................6.5V, – 0.3V SHDN Pin Input Current (Note 2) .............................5mA Output Short-Circuit Duration .......................... Indefinite Storage Temperature Range................... –65°C to 150°C Operating Junction Temperature Range LT1528C................................................ 0°C to 125°C Lead Temperature (Soldering, 10 sec) .................. 300°C *For applications requiring input voltage ratings greater than 15V, contact the factory. PIN CONFIGURATION TAB IS GND FRONT VIEW TAB IS GND 5 VIN 4 SHDN 3 FRONT VIEW 5 VIN 4 SHDN GND 3 GND 2 SENSE 2 SENSE 1 OUTPUT 1 OUTPUT Q PACKAGE 5-LEAD PLASTIC DD T PACKAGE 5-LEAD PLASTIC TO-220 TJMAX = 125°C, θJA = 50°C/ W TJMAX = 125°C, θJA = 30°C/ W ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LT1528CQ#PBF LT1528CQ#TRPBF LT1528CQ 5-Lead Plastic DD-PAK 0°C to 125°C LT1528CT#PBF LT1528CT#TRPBF LT1528CT 5-Lead Plastic TO-220 0°C to 125°C LEAD BASED FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LT1528CQ LT1528CQ#TR LT1528CQ 5-Lead Plastic DD-PAK 0°C to 125°C LT1528CT LT1528CT#TR LT1528CT 5-Lead Plastic TO-220 0°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25°C. PARAMETER CONDITIONS MIN TYP MAX UNITS Regulated Output Voltages (Notes 3, 4) VIN = 3.8V, IOUT = 1mA 4.3V < VIN < 15V, 1mA < IOUT < 3A l 3.250 3.200 3.300 3.300 3.350 3.400 V V Line Regulation (Note 4) ΔVIN = 3.8V to 15V, IOUT = 1mA l 1.5 1.0 mV Load Regulation (Note 4) ΔILOAD = 1mA to 3A, VIN = 4.3V ΔILOAD = 1mA to 3A, VIN = 4.3V l 12 15 20 30 mV mV Dropout Voltage (Note 5) ILOAD = 10mA ILOAD = 10mA l 70 110 150 mV mV 1528fb 2 LT1528 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25°C. PARAMETER CONDITIONS Dropout Voltage (Note 5) ILOAD = 100mA ILOAD = 100mA l ILOAD = 700mA ILOAD = 700mA l ILOAD = 1.5A ILOAD = 1.5A l ILOAD = 3A ILOAD = 3A l GND Pin Current (Note 6) MIN TYP MAX UNITS 150 200 250 mV mV 280 320 420 mV mV 390 450 600 mV mV 570 670 850 mV mV ILOAD = 0mA ILOAD = 0mA, TJ = 125°C (Note 7) 450 1.9 750 μA mA ILOAD = 100mA ILOAD = 100mA, TJ = 125°C (Note 7) 1.2 2.7 2.5 mA mA ILOAD = 300mA ILOAD = 300mA, TJ = 125°C (Note 7) 2.6 4.1 4.0 mA mA ILOAD = 700mA ILOAD = 700mA, TJ = 125°C (Note 7) 7.3 8.8 12.0 mA mA ILOAD = 1.5A l 22 40 mA ILOAD = 3A l 85 140 mA 90 130 250 μA 1.20 0.75 2.80 0.25 V V SENSE Pin Current (Notes 4, 8) SHDN Threshold VOUT = Off-to-On VOUT = On-to-Off l l SHDN Pin Current (Note 9) VSHDN = 0V l 37 100 μA Quiescent Current in Shutdown (Note 10) VIN = 6V, VSHDN = 0V l 110 220 μA Ripple Rejection VIN – VOUT = 1V(Avg), VRIPPLE = 0.5VP-P, fRIPPLE = 120Hz, ILOAD = 1.5A Current Limit VIN – VOUT = 7V VIN = 4.3V, ΔVOUT = – 0.1V l Input Reverse Leakage Current VIN = – 15V, VOUT = 0V l Reverse Output Current (Note 11) VOUT = 3.3V, VIN = 0V Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The SHDN pin input voltage rating is required for a low impedance source. Internal protection devices connected to the SHDN pin will turn on and clamp the pin to approximately 7V or – 0.6V. This range allows the use of 5V logic devices to drive the pin directly. For high impedance sources or logic running on supply voltages greater than 5.5V, the maximum current driven into the SHDN pin must be less than 5mA. Note 3: Operating conditions are limited by maximum junction temperature. The regulated output voltage specification will not apply for all possible combinations of input voltage and output current. When operating at maximum input voltage, the output current must be limited. When operating at maximum output current, the input voltage range must be limited. Note 4: The LT1528 is tested and specified with the SENSE pin connected to the OUTPUT pin. Note 5: Dropout voltage is the minimum input/output voltage required to 50 67 dB 3.2 4.5 4.0 A A 120 1.0 mA 250 μA maintain regulation at the specified output current. In dropout the output voltage will be equal to: (VIN – VDROPOUT ). Note 6: GND pin current is tested with VIN = VOUT (nominal) and a current source load. This means that the device is tested while operating in its dropout region. This is the worst-case GND pin current. The GND pin current will decrease slightly at higher input voltages. Note 7: GND pin current will rise at TJ > 75°C. This is due to internal circuitry designed to compensate for leakage currents in the output transistor at high temperatures. This allows quiescent current to be minimized at lower temperatures, yet maintain output regulation at high temperatures with light loads. See quiescent current curve in typical performance characteristics section. Note 8: SENSE pin current flows into the SENSE pin. Note 9: SHDN pin current at VSHDN = 0V flows out of the SHDN pin. Note 10: Quiescent current in shutdown is equal to the total sum of the SHDN pin current (40μA) and the GND pin current (70μA). Note 11: Reverse output current is tested with the input pin grounded and the OUTPUT pin forced to the rated output voltage. This current flows into the OUTPUT pin and out of the GND pin. 1528fb 3 LT1528 TYPICAL PERFORMANCE CHARACTERISTICS Guaranteed Dropout Voltage Dropout Voltage DROPOUT VOLTAGE (V) DROPOUT VOLTAGE (V) 0.8 0.7 TJ ≤ 125°C 0.6 0.5 TJ ≤ 25°C 0.4 0.3 0.2 2.00 0.7 1.75 ILOAD = 3A 0.6 0.5 ILOAD = 1.5A 0.4 ILOAD = 700mA 0.3 0.2 ILOAD = 300mA 0.1 0.1 0 0.5 0 1.5 2.0 1.0 OUTPUT CURRENT (A) 2.5 ILOAD = 10mA 0 –50 3.0 –25 75 50 25 TEMPERATURE (°C) 0 1000 750 VSHDN = OPEN (HIGH) VSHDN = 0V 0 3 4 5 6 7 INPUT VOLTAGE (V) 8 ILOAD = 1mA 9 10 3.350 3.325 3.300 3.275 3.250 40 RL = 2.2Ω ILOAD = 1.5A* 30 20 RL = 4.7Ω ILOAD = 700mA* 100 80 75 50 25 TEMPERATURE (°C) 0 100 125 8 9 10 1528 TPC07 RL = 33Ω ILOAD = 100mA* 2 0 1 2 3 4 5 6 7 INPUT VOLTAGE (V) 1.8 TJ = 25°C 50 40 TJ = –50°C 30 9 10 1528 TPC06 2.0 TJ = 125°C 60 8 SHDN Pin Threshold (On-to-Off) 70 20 0 3 4 5 6 7 INPUT VOLTAGE (V) RL = 11Ω ILOAD = 300mA* RL = 330Ω: ILOAD = 10mA* VIN = 3.3V DEVICE IS OPERATING IN DROPOUT 90 0 2 RL = 6.6Ω ILOAD = 500mA* 1528 TPC05 10 1 125 TJ = 25°C VOUT = VSENSE *FOR VOUT = 3.3V 3 0 10 0 100 4 3.200 –50 –25 GND PIN CURRENT (mA) GND PIN CURRENT (mA) RL = 1.1Ω ILOAD = 3A* 75 50 25 TEMPERATURE (°C) 0 5 GND Pin Current 70 50 VSHDN = 0V 1 TJ = 25°C VOUT = VSENSE *FOR VOUT = 3.3V 60 0.25 3.225 GND Pin Current 80 VSHDN = OPEN 6 1528 TPC04 90 0.50 GND Pin Current 3.375 SENSE PIN VOLTAGE (V) 1250 100 0.75 7 GND PIN CURRENT (mA) QUIESCENT CURRENT (μA) 1500 2 1.00 0 –50 –25 125 3.400 ILOAD = 0 RLOAD = ∞ 1 1.25 SENSE Pin Voltage 1750 0 1.50 1528 TPC03 Quiescent Current 2000 250 100 VIN = 4.3V RL = ∞ 1528 TPC02 1528 TPC01 500 QUIESCENT CURRENT (mA) = TEST POINTS 0.9 Quiescent Current 0.8 SHDN PIN THRESHOLD (V) 1.0 ILOAD = 1mA 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0.5 1.5 2.0 1.0 OUTPUT CURRENT (A) 2.5 3.0 1528 TPC08 0 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 125 1528 TPC09 1528fb 4 LT1528 TYPICAL PERFORMANCE CHARACTERISTICS 1.8 90 ILOAD = 3A 1.4 1.2 ILOAD = 1mA 1.0 0.8 0.6 70 60 50 40 30 20 0.2 10 –25 50 25 0 75 TEMPERATURE (°C) 100 VSHDN = 0V 80 0.4 0 –50 0 –50 125 25 SHDN PIN INPUT CURRENT (mA) 100 1.6 SHDN Pin Input Current SHDN Pin Current 2.0 SHDN PIN CURRENT (μA) –25 50 25 0 75 TEMPERATURE (°C) 100 300 100 75 50 200 150 100 50 25 75 50 25 TEMPERATURE (°C) 100 0 –50 –25 125 50 25 75 0 TEMPERATURE (°C) 100 Current Limit OUTPUT CURRENT (μA) SHORT-CIRCUIT CURRENT (A) 3 2 1 0 –50 –25 VOUT = 0V 3 2 1 0 1 4 3 5 2 INPUT VOLTAGE (V) 6 7 1528 TPC15 Ripple Rejection 70 TJ = 25°C, VIN = 0V 900 VOUT =VSENSE 800 CURRENT FLOWS INTO DEVICE 700 68 600 500 400 300 200 VIN = 7V VOUT = 0V 9 4 0 125 1000 5 8 5 Reverse Output Current 4 7 3 5 6 4 SHDN PIN VOLTAGE (V) 1528 TPC14 1528 TPC13 6 2 Current Limit SHORT-CIRCUIT CURRENT (A) OUTPUT CURRENT (μA) SENSE PIN CURRENT (μA) 125 1 1528 TPC12 6 250 150 0 5 0 VIN = 0V VOUT = VSENSE CURRENT FLOWS INTO SENSE PIN 175 –25 10 Reverse Output Current SENSE Pin Current 0 –50 15 1528 TPC11 1528 TPC10 200 20 0 125 RIPPLE REJECTION (dB) SHDN PIN THRESHOLD (V) SHDN Pin Threshold (Off-to-On) VIN(AVG) = 4.3V VRIPPLE = 0.5VP-P AT f = 120Hz IL = 1.5A 66 64 62 60 58 100 50 25 75 0 TEMPERATURE (°C) 100 125 1528 TPC16 0 0 1 2 3 4 5 6 7 8 OUTPUT VOLTAGE (V) 9 10 1528 TPC17 56 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 125 1528 TPC18 1528fb 5 LT1528 TYPICAL PERFORMANCE CHARACTERISTICS Ripple Rejection Load Regulation 80 0 VIN = VOUT(NOMINAL) + 1V ΔILOAD = 1mA TO 3A –5 LOAD REGULATION (mV) RIPPLE REJECTION (dB) 70 60 50 COUT = 4 × 47μF SOLID TANTALUM 40 COUT = 47μF SOLID TANTALUM 30 20 0 10 100 1k 10k FREQUENCY (Hz) –15 –20 –25 IOUT = 1.5A VIN = 6V + 50mVRMS RIPPLE 10 –10 100k –30 –50 –25 1M 50 25 75 0 TEMPERATURE (°C) 1528 TPC19 –50 –100 3 2 1 0 0 20 40 60 80 100 120 140 160 180 200 TIME (μs) 1528 TPC21 OUTPUT VOLTAGE DEVIATION (mV) 0 LOAD CURRENT (A) OUTPUT VOLTAGE DEVIATION (mV) LOAD CURRENT (A) Transient Response VIN = 5V CIN = 3.3μF COUT = 47μF 50 125 1528 TPC20 Transient Response 100 100 VIN = 5V CIN = 3.3μF COUT = 4 × 47μF 100 50 0 –50 –100 3 2 1 0 0 20 40 60 80 100 120 140 160 180 200 TIME (μs) 1528 TPC22 PIN FUNCTIONS OUTPUT (Pin 1): The OUTPUT pin supplies power to the load. A minimum output capacitor of 3.3μF is required to prevent oscillations. Larger values will be needed to achieve the transient performance required by high speed microprocessors. See the Applications Information section for more on output capacitance and reverse output characteristics. SENSE (Pin 2): The SENSE pin is the input to the error amplifier. Optimum regulation will be obtained at the point where the SENSE pin is connected to the OUTPUT pin. For most applications the SENSE pin is connected directly to the OUTPUT pin at the regulator. In critical applications small voltage drops caused by the resistance (RP) of PC traces between the regulator and the load, which would normally degrade regulation, may be eliminated by connecting the SENSE pin to the OUTPUT pin at the load as shown in Figure 1 (Kelvin Sense Connection). Note that the voltage drop across the external PC traces will add to the dropout voltage of the regulator. The SENSE pin bias current is 150μA at the nominal regulated output voltage. See SENSE Pin Current vs Temperature in the Typical Performance Characteristics section. This pin is internally clamped to – 0.6V (one VBE). The SENSE pin can also be used with a resistor divider to achieve output voltages above 3.3V. See the Applications Information section for information on adjustable operation. 1528fb 6 LT1528 PIN FUNCTIONS SHDN (Pin 4): This pin is used to put the device into shutdown. In shutdown the output of the device is turned off. This pin is active low. The device will be shut down if the SHDN pin is actively pulled low. The SHDN pin current with the pin pulled to ground will be 60μA. The SHDN pin is internally clamped to 7V and – 0.6V (one VBE). This allows the SHDN pin to be driven directly by 5V logic or by open collector logic with a pull-up resistor. The pull-up resistor is only required to supply the leakage current of the open collector gate, normally several microamperes. Pull-up current must be limited to a maximum of 5mA. A curve of SHDN pin input current as a function of voltage appears in the Typical Performance Characteristics section. If the SHDN pin is not used it can be left open circuit. The device will be active output on if the SHDN pin is not connected. the device is more than six inches away from the main input filter capacitor. The LT1528 is designed to withstand reverse voltages on the input pin with respect to ground and the OUTPUT pin. In the case of reversed input, the LT1528 will act as if there is a diode in series with its input. There will be no reverse current flow into the LT1528 and no reverse voltage will appear at the load. The device will protect both itself and the load. 5 IN RP 1 OUT LT1528 + 4 VIN SHDN + 2 SENSE LOAD GND 3 RP 1528 F01 VIN (Pin 5): Power is supplied to the device through the input pin. The input pin should be bypassed to ground if Figure 1. Kelvin Sense Connection APPLICATIONS INFORMATION The LT1528 is a 3A low dropout regulator optimized for microprocessor applications. Dropout voltage is only 0.6V at 3A output current. With the SENSE pin shorted to the OUTPUT pin, the output voltage is set to 3.3V. The device operates with a quiescent current of 400μA. In shutdown, the quiescent current drops to only 125μA. The LT1528 incorporates several protection features, including protection against reverse input voltages. If the output is held at the rated output voltage when the input is pulled to ground, the LT1528 acts like it has a diode in series with its output and prevents reverse current flow. Adjustable Operation The LT1528 can be used as an adjustable regulator with an output voltage range of 3.3V to 14V. The output voltage is set by the ratio of two external resistors as shown in Figure 2. The device servos the output voltage to maintain the voltage at the SENSE pin at 3.3V. The current in R1 is then equal to 3.3V/R1. The current in R2 is equal to the sum of the current in R1 and the SENSE pin current. The SENSE pin current, 130μA at 25°C, flows through R2 into the SENSE pin. The output voltage can be calculated using the formula in Figure 2. The value of R1 should be less than 330Ω to minimize errors in the output voltage caused by the SENSE pin current. Note that in shutdown the output is turned off and the divider current will be zero. Curves of SENSE Pin Voltage vs Temperature and SENSE Pin Current vs Temperature appear in the Typical Performance Characteristics section. 5 IN OUT 1 VOUT + VIN R2 LT1528 4 SHDN SENSE 2 GND R1 3 ) ) VOUT = 3.3V 1 + R2 + (ISENSE)(R2) R1 VSENSE = 3.3V ISENSE = 130μA AT 25°C OUTPUT RANGE = 3.3V TO 14V 1528 F02 Figure 2. Adjustable Operation 1528fb 7 LT1528 APPLICATIONS INFORMATION The LT1528 is specified with the SENSE pin tied to the OUTPUT pin. This sets the output voltage to 3.3V. Specifications for output voltage greater than 3.3V will be proportional to the ratio of the desired output voltage to 3.3V (VOUT/3.3V). For example, load regulation for an output current change of 1mA to 1.5A is – 5mV (typical) at VOUT = 3.3V. At VOUT = 12V, load regulation would be: (12V/3.3V) • (–5mV) = (–18mV) Thermal Considerations The power handling capability of the device will be limited by the maximum rated junction temperature (125°C). The power dissipated by the device will be made up of two components: 1. Output current multiplied by the input/output voltage differential, IOUT • (VIN – VOUT), and 2. GND pin current multiplied by the input voltage, IGND • VIN. The GND pin current can be found by examining the GND Pin Current curves in the Typical Performance Characteristics. Power dissipation will be equal to the sum of the two components listed above. Table 1a lists thermal resistance for the DD package. For the TO-220 package (Table 1b) thermal resistance is given for junction-to-case only since this package is usually mounted to a heat sink. Measured values of thermal resistance for several different copper areas are listed for the DD package. All measurements were taken in still air on 3/32" FR-4 board with one ounce copper. This data can be used as a rough guideline in estimating thermal resistance. The thermal resistance for each application will be affected by thermal interactions with other components as well as board size and shape. Some experimentation will be necessary to determine the actual value. Table 1a. Q-Package, 5-Lead DD COPPER AREA TOPSIDE* THERMAL RESISTANCE BACKSIDE BOARD AREA (JUNCTION-TO-AMBIENT) 2500 sq mm 2500 sq mm 2500 sq mm 23°C/W 1000 sq mm 2500 sq mm 2500 sq mm 25°C/W 125 sq mm 33°C/W 2500 sq mm 2500 sq mm *Device is mounted on topside. Table 1b. T Package, 5-Lead TO-220 Thermal Resistance (Junction-to-Case) 2.5°C/W Calculating Junction Temperature The LT1528 has internal thermal limiting designed to protect the device during overload conditions. For continuous normal load conditions the maximum junction temperature rating of 125°C must not be exceeded. It is important to give careful consideration to all sources of thermal resistance from junction-to-ambient. Additional heat sources mounted nearby must also be considered. Example: Given an output voltage of 3.3V, an input voltage range of 4.5V to 5.5V, an output current range of 0mA to 500mA and a maximum ambient temperature of 50°C, what will the maximum junction temperature be? For surface mount devices heat sinking is accomplished by using the heat spreading capabilities of the PC board and its copper traces. Experiments have shown that the heat spreading copper layer does not have to be electrically connected to the tab of the device. The PC material can be very effective at transmitting heat between the pad area, attached to the tab of the device, and a ground or power plane either inside or on the opposite side of the board. Although the actual thermal resistance of the PC material is high, the length/area ratio of the thermal resistor between layers is small. Copper board stiffeners and plated through holes can also be used to spread the heat generated by power devices. where, IOUT(MAX) = 500mA VIN(MAX) = 5.5V IGND at (IOUT = 500mA, VIN = 5.5V) = 4mA The power dissipated by the device will be equal to: IOUT(MAX) • (VIN(MAX) – VOUT) + [IGND • VIN(MAX)] so, P = 500mA • (5.5V – 3.3V) + (4mA • 5.5V) = 1.12W If we use a DD package, the thermal resistance will be in the range of 23°C/W to 33°C/W depending on the copper area. So the junction temperature rise above ambient will be approximately equal to: 1.12W • 28°C/W = 31.4°C 1528fb 8 LT1528 APPLICATIONS INFORMATION The maximum junction temperature will be equal to the maximum junction temperature rise above ambient plus the maximum ambient temperature or: several different processors. This application allows the output voltage to be jumper selectable. Protection Features TJMAX = 50°C + 31.4°C = 81.4°C Output Capacitance and Transient Performance The LT1528 is designed to be stable with a wide range of output capacitors. The minimum recommended value is 3.3μF with an ESR of 2Ω or less. The LT1528 output transient response will be a function of output capacitance. See the Transient Response curves in the Typical Performance Characteristics. Larger values of output capacitance will decrease the peak deviations and provide improved output transient response for larger load transients. Bypass capacitors, used to decouple individual components powered by the LT1528, will increase the effective value of the output capacitor. Microprocessor Applications The LT1528 has been optimized for microprocessor applications, with the fastest transient response of current PNP low dropout regulators. In order to deal with the large load transients associated with current generation microprocessors, output capacitance must be increased. To meet worst-case voltage specifications for many popular processors, four 47μF solid tantalum surface mount capacitors are recommended for decoupling at the microprocessor. These capacitors should have an ESR of approximately 0.1Ω to 0.2Ω to minimize transient response under worst-case load deltas. The Typical Application shows connections needed to supply power for The LT1528 incorporates several protection features, such as current limiting and thermal limiting, in addition to the normal protection features associated with monolithic regulators. The device is protected against reverse input voltages and reverse voltages from output to input. Current limit protection and thermal overload protection are intended to protect the device against overload conditions. For normal operation the junction temperatures should not exceed 125°C. The input of the device will withstand reverse voltages of 15V. Current flow into the device will be limited to less than 1mA (typically less than 100μA) and no negative voltage will appear at the output. The device will protect both itself and the load. The SENSE pin is internally clamped to one diode drop below ground. If the SENSE pin is pulled below ground, with the input open or grounded, current must be limited to less than 5mA. Several different input/output conditions can occur in regulator circuits. The output voltage may be held up while the input is either pulled to ground, pulled to some intermediate voltage or is left open circuit. Current flow back into the output will vary depending on the conditions. Many circuits incorporate some form of power management. The following information summarized in Table 2 will help optimize power usage. Table 2. Fault Conditions INPUT PIN SHDN PIN OUTPUT/SENSE PINS < VOUT (Nominal) Open (High) Forced to VOUT (Nominal) Reverse Output Current ≈ 150μA (See Figure 3) Input Current ≈ 1μA (See Figure 4) < VOUT (Nominal) Grounded Forced to VOUT (Nominal) Reverse Output Current ≈ 150μA (See Figure 3) Input Current ≈ 1μA (See Figure 4) Open Open (High) > 1V Reverse Output Current ≈ 150μA (See Figure 3) Open Grounded > 1V Reverse Output Current ≈ 150μA (See Figure 3) ≤ 0.8V Open (High) ≤ 0V Output Current = 0 ≤ 0.8V Grounded ≤ 0V Output Current = 0 > 1.5V Open (High) ≤ 0V Output Current = Short-Circuit Current – 15V < VIN < 15V Grounded ≤ 0V Output Current = 0 RESULTING CONDITIONS 1528fb 9 LT1528 APPLICATIONS INFORMATION The reverse output current will follow the curve in Figure 3 when the input is pulled to ground. This current flows through the OUTPUT pin to ground. The state of the SHDN pin will have no effect on output current when the input pin is pulled to ground. In some applications it may be necessary to leave the input on the LT1528 unconnected when the output is held high. This can happen when the LT1528 is powered from a rectified AC source. If the AC source is removed, then the input of the LT1528 is effectively left floating. The reverse output current also follows the curve in Figure 3 if the input pin is left open. The state of the SHDN pin will have no effect on the reverse output current when the input pin is floating. 1000 5 TJ = 25°C, VIN = 0V VOUT = VSENSE CURRENT FLOWS INTO DEVICE 900 VOUT = 3.3V 4 INPUT CURRENT (μA) 800 OUTPUT CURRENT (μA) When the input of the LT1528 is forced to a voltage below its nominal output voltage and its output is held high, the output current will follow the curve shown in Figure 3. This can happen if the input of the LT1528 is connected to a low voltage and the output is held up by a second regulator circuit. When the input pin is forced below the 0utput pin or the OUTPUT pin is pulled above the input pin, the input current will typically drop to less than 2μA (see Figure 4). The state of the SHDN pin will have no effect on the reverse output current when the output is pulled above the input. 700 600 500 400 300 3 2 1 200 100 0 0 0 1 2 3 4 5 6 7 8 OUTPUT VOLTAGE (V) 9 10 0 0.5 1.0 1.5 2.0 2.5 INPUT VOLTAGE (V) 3.0 1528 F03 Figure 3. Reverse Output Current 3.5 1528 F04 Figure 4. Input Current 1528fb 10 LT1528 PACKAGE DESCRIPTION Q Package 5-Lead Plastic DD Pak (Reference LTC DWG # 05-08-1461) .256 (6.502) .060 (1.524) TYP .060 (1.524) .390 – .415 (9.906 – 10.541) .165 – .180 (4.191 – 4.572) .045 – .055 (1.143 – 1.397) 15° TYP .060 (1.524) .183 (4.648) +.008 .004 –.004 +0.203 0.102 –0.102 .059 (1.499) TYP .330 – .370 (8.382 – 9.398) ( ) .095 – .115 (2.413 – 2.921) .075 (1.905) .300 (7.620) +.012 .143 –.020 +0.305 3.632 –0.508 ( BOTTOM VIEW OF DD PAK HATCHED AREA IS SOLDER PLATED COPPER HEAT SINK .067 (1.702) .028 – .038 BSC (0.711 – 0.965) TYP ) Q(DD5) 0502 .420 .276 .080 .420 .050 ± .012 (1.270 ± 0.305) .013 – .023 (0.330 – 0.584) .325 .350 .205 .565 .565 .320 .090 .090 .067 .042 RECOMMENDED SOLDER PAD LAYOUT NOTE: 1. DIMENSIONS IN INCH/(MILLIMETER) 2. DRAWING NOT TO SCALE .067 .042 RECOMMENDED SOLDER PAD LAYOUT FOR THICKER SOLDER PASTE APPLICATIONS 1528fb 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. 11 LT1528 PACKAGE DESCRIPTION T Package 5-Lead Plastic TO-220 (Standard) (Reference LTC DWG # 05-08-1421) .165 – .180 (4.191 – 4.572) .147 – .155 (3.734 – 3.937) DIA .390 – .415 (9.906 – 10.541) .045 – .055 (1.143 – 1.397) .230 – .270 (5.842 – 6.858) .570 – .620 (14.478 – 15.748) .460 – .500 (11.684 – 12.700) .620 (15.75) TYP .330 – .370 (8.382 – 9.398) .700 – .728 (17.78 – 18.491) SEATING PLANE .152 – .202 .260 – .320 (3.861 – 5.131) (6.60 – 8.13) .095 – .115 (2.413 – 2.921) .155 – .195* (3.937 – 4.953) .013 – .023 (0.330 – 0.584) BSC .067 (1.70) .028 – .038 (0.711 – 0.965) .135 – .165 (3.429 – 4.191) * MEASURED AT THE SEATING PLANE T5 (TO-220) 0801 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC ®1265 High Efficiency Step-Down Switching Regulator >90% Efficient 1A, 5V to 3.3V Conversion LTC1266 Synchronous Switching Controller >90% Efficient High Current Microprocessor Supply LT1521 300mA Micropower Low Dropout Regulator 15μA Quiescent Current LT1584 7A Low Dropout Fast Transient Response Regulator For High Performance Microprocessors LT1585 4.6A Low Dropout Fast Transient Response Regulator For High Performance Microprocessors 1528fb 12 Linear Technology Corporation LT 0508 REV B • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 1995