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LT1528 3A Low Dropout Regulator for Microprocessor Applications
FEATURES
s s s s s s s s s s s s
DESCRIPTIO
Dropout Voltage: 0.6V at IOUT = 3A Fast Transient Response Output Current: 3A Quiescent Current: 400A No Protection Diodes Needed Fixed Output Voltage: 3.3V Controlled Quiescent Current in Dropout Shutdown IQ = 125A Stable with 3.3F Output Capacitor Reverse Battery Protection No Reverse Output Current Thermal Limiting
APPLICATIO S
s s s
Microprocessor Applications Post Regulator for Switching Supplies 5V to 3.3V Logic Regulator
The LT (R)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 400A. 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 3.3F, 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. The LT1528 has both reverse input and reverse output protection and includes a shutdown feature. Quiescent current drops to 125A in shutdown. The LT1528 is available in 5-lead TO-220 and 5-lead DD packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
5 IN LT1528 4 SHDN GND 3 SENSE 2 OUT 1
Microprocessor Supply with Shutdown
0.6
VOUT 15 J1 J2 68 J3
+
DROPOUT VOLTAGE (V)
VIN =5V
4 x 47F* SOLID TANTALUM
0.5 0.4 0.3 0.2 0.1 0
330
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
LT1528 * TA01
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Dropout Voltage
0 0.5 2.5 1.0 1.5 2.0 OUTPUT CURRENT (mA) 3.0
LT1528 * TA02
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LT1528
ABSOLUTE
AXI U
RATI GS
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
PACKAGE/ORDER I FOR ATIO
FRONT VIEW 5 4 TAB IS GND 3 2 1 Q PACKAGE 5-LEAD PLASTIC DD VIN SHDN GND SENSE OUTPUT
ORDER PART NUMBER LT1528CQ
TJMAX = 125C, JA = 30C/ W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25C.
PARAMETER Regulated Output Voltages (Notes 3, 4) Line Regulation (Note 4) Load Regulation (Note 4) Dropout Voltage (Note 5) CONDITIONS VIN = 3.8V, IOUT = 1mA 4.3V < VIN < 15V, 1mA < IOUT < 3A VIN = 3.8V to 15V, IOUT = 1mA ILOAD = 1mA to 3A, VIN = 4.3V ILOAD = 1mA to 3A, VIN = 4.3V ILOAD = 10mA ILOAD = 10mA ILOAD = 100mA ILOAD = 100mA ILOAD = 700mA ILOAD = 700mA ILOAD = 1.5A ILOAD = 1.5A ILOAD = 3A ILOAD = 3A
q q q q
2
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W
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(Note 1)
Output Short-Circuit Duration .......................... Indefinite Storage Temperature Range ................. - 65C to 150C Operating Junction Temperature Range LT1528C ............................................... 0C to 125C Lead Temperature (Soldering, 10 sec).................. 300C
*For applications requiring input voltage ratings greater than 15V, contact the factory.
TAB IS GND
FRONT VIEW 5 4 3 2 1 T PACKAGE 5-LEAD PLASTIC TO-220 TJMAX = 125C, JA = 50C/ W VIN SHDN GND SENSE OUTPUT
ORDER PART NUMBER LT1528CT
MIN 3.250 3.200
TYP 3.300 3.300 1.5 12 15 70 150
MAX 3.350 3.400 10 20 30 110 150 200 250 320 420 450 600 670 850
UNITS V V mV mV mV mV mV mV mV mV mV mV mV mV mV
q
280
q
390
q
570
q
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LT1528
ELECTRICAL CHARACTERISTICS
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25C.
PARAMETER GND Pin Current (Note 6) CONDITIONS ILOAD = 0mA ILOAD = 0mA, TJ = 125C (Note 7) ILOAD = 100mA ILOAD = 100mA, TJ = 125C (Note 7) ILOAD = 300mA ILOAD = 300mA, TJ = 125C (Note 7) ILOAD = 700mA ILOAD = 700mA, TJ = 125C (Note 7) ILOAD = 1.5A ILOAD = 3A SENSE Pin Current (Notes 4, 8) SHDN Threshold SHDN Pin Current (Note 9) Quiescent Current in Shutdown (Note 10) Ripple Rejection Current Limit Input Reverse Leakage Current Reverse Output Current (Note 11) VOUT = Off-to-On VOUT = On-to-Off VSHDN = 0V VIN = 6V, VSHDN = 0V VIN - VOUT = 1V(Avg), VRIPPLE = 0.5VP-P, fRIPPLE = 120Hz, ILOAD = 1.5A VIN - VOUT = 7V VIN = 4.3V, VOUT = - 0.1V VIN = - 15V, VOUT = 0V VOUT = 3.3V, VIN = 0V
q q q q q q
MIN
TYP 450 1.9 1.2 2.7 2.6 4.1 7.3 8.8
MAX 750 2.5 4.0 12.0 40 140 250 2.80 100 220
UNITS A mA mA mA mA mA mA mA mA mA A V V A A dB A A
q q
22 85 90 0.25 130 1.20 0.75 37 110 50 67 4.5 4.0
3.2
1.0 120 250
mA A
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. 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 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 > 75C. 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 (40A) and the GND pin current (70A). 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.
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LT1528 TYPICAL PERFOR A CE CHARACTERISTICS
Guaranteed Dropout Voltage
1.0 0.9 0.8 DROPOUT VOLTAGE (V) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 0.5 1.5 2.0 1.0 OUTPUT CURRENT (A) 2.5 3.0 TJ 125C TJ 25C = TEST POINTS
0.8 0.7
DROPOUT VOLTAGE (V)
0.6 0.5
ILOAD = 3A
QUIESCENT CURRENT (mA)
Quiescent Current
2000 1750 ILOAD = 0 RLOAD =
SENSE PIN VOLTAGE (V)
QUIESCENT CURRENT (A)
GND PIN CURRENT (mA)
1500 1250 1000 750 500 250 0 0 1 2 34567 INPUT VOLTAGE (V) 8 9 10 VSHDN = OPEN (HIGH) VSHDN = 0V
GND Pin Current
100 90 TJ = 25C VOUT = VSENSE *FOR VOUT = 3.3V
GND PIN CURRENT (mA)
GND PIN CURRENT (mA)
TJ = 125C
SHDN PIN THRESHOLD (V)
80 70 60 50 40 30 20 10 0 0 1 2 RL = 2.2 ILOAD = 1.5A*
RL = 1.1 ILOAD = 3A* RL = 4.7 ILOAD = 700mA*
34567 INPUT VOLTAGE (V)
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LT1528 * TPC01
LT1528 * TPC04
Dropout Voltage
2.00 1.75 1.50 1.25 1.00 0.75 0.50 0.25
125
Quiescent Current
VIN = 4.3V RL =
ILOAD = 1.5A 0.4 0.3 0.2 0.1 0 -50 -25 0 ILOAD = 300mA ILOAD = 10mA 75 50 25 TEMPERATURE (C) 100 ILOAD = 700mA
VSHDN = OPEN VSHDN = 0V 0 50 75 25 TEMPERATURE (C) 100 125
0 -50 -25
LT1528 * TPC02
LT1528 * TPC03
SENSE Pin Voltage
3.400 ILOAD = 1mA 3.375 3.350 3.325 3.300 3.275 3.250 3.225 3.200 -50 -25 0 75 50 25 TEMPERATURE (C) 100 125 7 6 5 4 3 2 1
GND Pin Current
TJ = 25C VOUT = VSENSE *FOR VOUT = 3.3V RL = 6.6 ILOAD = 500mA* RL = 11 ILOAD = 300mA* RL = 33 ILOAD = 100mA*
RL = 330: ILOAD = 10mA* 0 0 1 2 7 3 456 INPUT VOLTAGE (V) 8 9 10
LT1528 * TPC05
LT1528 * TPC06
GND Pin Current
100 90 80 70 60 50 40 30 20 10 0
8 9 10
SHDN Pin Threshold (On-to-Off)
2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 ILOAD = 1mA
VIN = 3.3V DEVICE IS OPERATING IN DROPOUT
TJ = 25C
TJ = -50C
0
0.5
1.5 2.0 1.0 OUTPUT CURRENT (A)
2.5
3.0
0 -50 -25
50 0 75 25 TEMPERATURE (C)
100
125
LT1528 * TPC07
LT1528 * TPC08
LT1528 * TPC09
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LT1528 TYPICAL PERFOR A CE CHARACTERISTICS
SHDN Pin Threshold (Off-to-On)
2.0 1.8 100 90
SHDN PIN THRESHOLD (V)
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 -50 -25 50 0 75 25 TEMPERATURE (C) 100 125 ILOAD = 1mA
SHDN PIN CURRENT (A)
1.6
ILOAD = 3A
80 70 60 50 40 30 20 10 0 -50 -25 50 0 75 25 TEMPERATURE (C) 100 125
SHDN PIN INPUT CURRENT (mA)
SENSE Pin Current
200 175
SENSE PIN CURRENT (A) OUTPUT CURRENT (A)
CURRENT FLOWS INTO SENSE PIN
150 125 100 75 50 25 0 -50 -25 0 75 50 25 TEMPERATURE (C) 100 125
200 150 100 50 0 -50 -25
SHORT-CIRCUIT CURRENT (A)
Current Limit
6 5
OUTPUT CURRENT (A)
SHORT-CIRCUIT CURRENT (A)
RIPPLE REJECITON (dB)
4 3 2 1
0 -50 -25
VIN = 7V VOUT = 0V 50 25 75 0 TEMPERATURE (C) 100 125
UW
LT1528 * TPC10
SHDN Pin Current
VSHDN = 0V
SHDN Pin Input Current
25
20
15
10
5
0 0 1 2 7 3 5 6 4 SHDN PIN VOLTAGE (V) 8 9
LT1528 * TPC11
LT1528 * TPC12
Reverse Output Current
300 250 VIN = 0V VOUT = VSENSE 6 5 4 3 2 1 0
Current Limit
VOUT = 0V
50 25 75 0 TEMPERATURE (C)
100
125
0
1
4 3 5 2 INPUT VOLTAGE (V)
6
7
LT1528 * TPC13
LT1528 * TPC14
LT1528 * TPC15
Reverse Output Current
1000 TJ = 25C, VIN = 0V 900 VOUT =VSENSE 800 CURRENT FLOWS INTO DEVICE 700 600 500 400 300 200 100 0 0 1 2 345678 OUTPUT VOLTAGE (V) 9 10
Ripple Rejection
70 68 66 64 62 60 58 56 -50 -25 VIN(AVG) = 4.3V VRIPPLE = 0.5VP-P AT f = 120Hz IL = 1.5A
50 25 75 0 TEMPERATURE (C)
100
125
LT1528 * TPC16
LT1528 * TPC17
LT1528 * TPC18
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LT1528 TYPICAL PERFOR A CE CHARACTERISTICS
Ripple Rejection
80 70
LOAD REGULATION (mV)
RIPPLE REJECTION (dB)
60 50 40 30 20 10 0 10 100 1k 10k FREQUENCY (Hz) 100k 1M IOUT = 1.5A VIN = 6V + 50mVRMS RIPPLE COUT = 4 x 47F SOLID TANTALUM COUT = 47F SOLID TANTALUM
Transient Response
OUTPUT VOLTAGE DEVIATION (mV) OUTPUT VOLTAGE DEVIATION (mV)
100 50 0 -50 -100 VIN = 5V CIN = 3.3F COUT = 47F 100 50 0 -50 -100
LOAD CURRENT (A)
3 2 1 0 0 20 40 60 80 100 120 140 160 180 200 TIME (s)
LT1528 * TPC21
LOAD CURRENT (A)
PI FU CTIO S
OUTPUT (Pin 1): The OUTPUT pin supplies power to the load. A minimum output capacitor of 3.3F 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 150A 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.
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Load Regulation
0 -5 -10 -15 -20 -25 -30 -50 -25 VIN = VOUT(NOMINAL) + 1V ILOAD = 1mA TO 3A
50 25 75 0 TEMPERATURE (C)
100
125
LT1528 * TPC19
LT1528 * TPC20
Transient Response
VIN = 5V CIN = 3.3F COUT = 4 x 47F
3 2 1 0 0 20 40 60 80 100 120 140 160 180 200 TIME (s)
LT1528 * TPC22
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LT1528
PI FU CTIO S
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 60A. 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. VIN (Pin 5): Power is supplied to the device through the input pin. The input pin should be bypassed to ground if 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 LT1528 4 SHDN GND 3 RP
LT1528 * F01
APPLICATIO S I FOR ATIO
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 400A. In shutdown, the quiescent current drops to only 125A. 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, 130A at 25C, flows through R2 into the
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OUT
1
RP
+
VIN
SENSE
2
+
LOAD
Figure 1. Kelvin Sense Connection
SENSE pin. The output voltage can be calculated using the formula in Figure 2. The value of R1 should be less than 330 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 LT1528 4 SHDN GND 3 R1 SENSE 2 OUT 1 VOUT
+
VIN R2
VOUT = 3.3V 1 + R2 + (ISENSE + R2) R1 VSENSE = 3.3V ISENSE = 130A AT 25C OUTPUT RANGE = 3.3V TO 14V
LT1528 * F02
)
)
Figure 2. Adjustable Operation
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LT1528
APPLICATIO S I FOR ATIO
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 (125C). 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. 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 125C 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. 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.
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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* BACKSIDE BOARD AREA 2500 sq mm 2500 sq mm 2500 sq mm 2500 sq mm 2500 sq mm 1000 sq mm 2500 sq mm 125 sq mm 2500 sq mm THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 23C/W 25C/W 33C/W *Device is mounted on topside.
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Table 1b. T Package, 5-Lead TO-220
Thermal Resistance (Junction-to-Case) 2.5C/W
Calculating Junction Temperature 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 50C, what will the maximum junction temperature be? The power dissipated by the device will be equal to: IOUT(MAX) * (VIN(MAX) - VOUT) + [IGND * VIN(MAX)] where, IOUT(MAX) = 500mA VIN(MAX) = 5.5V IGND at (IOUT = 500mA, VIN = 5.5V) = 4mA 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 23C/W to 33C/W depending on the copper area. So the junction temperature rise above ambient will be approximately equal to: 1.12W * 28C/W = 31.4C
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LT1528
APPLICATIO S I FOR ATIO
The maximum junction temperature will be equal to the maximum junction temperature rise above ambient plus the maximum ambient temperature or: TJMAX = 50C + 31.4C = 81.4C Output Capacitance and Transient Performance The LT1528 is designed to be stable with a wide range of output capacitors. The minimum recommended value is 3.3F with an ESR of 2 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 47F solid tantalum surface mount capacitors are recommended for decoupling at the microprocessor. These capacitors should have an ESR of approximately 0.1 to 0.2 to minimize transient response under worst-case load deltas. The Typical Application shows connections needed to supply power for several
Table 2. Fault Conditions
INPUT PIN < VOUT (Nominal) < VOUT (Nominal) Open Open 0.8V 0.8V > 1.5V - 15V < VIN < 15V SHDN PIN Open (High) Grounded Open (High) Grounded Open (High) Grounded Open (High) Grounded
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different processors. This application allows the output voltage to be jumper selectable. Protection Features 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 125C. 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 100A) 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.
RESULTING CONDITIONS Reverse Output Current 150A (See Figure 3) Input Current 1A (See Figure 4) Reverse Output Current 150A (See Figure 3) Input Current 1A (See Figure 4) Reverse Output Current 150A (See Figure 3) Reverse Output Current 150A (See Figure 3) Output Current = 0 Output Current = 0 Output Current = Short-Circuit Current Output Current = 0
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OUTPUT/SENSE PINS Forced to VOUT (Nominal) Forced to VOUT (Nominal) > 1V > 1V 0V 0V 0V 0V
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LT1528
APPLICATIO S I FOR ATIO
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
1000 900 800
OUTPUT CURRENT (A)
700 600 500 400 300 200 100 0
INPUT CURRENT (A)
TJ = 25C, VIN = 0V VOUT = VSENSE CURRENT FLOWS INTO DEVICE
0
1
2
345678 OUTPUT VOLTAGE (V)
9
10
LT1528 * F03
Figure 3. Reverse Output Current
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effect on the reverse output current when the input pin is floating. 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 2A (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.
5 VOUT = 3.3V 4 3 2 1 0 0 0.5 1.0 1.5 2.0 2.5 INPUT VOLTAGE (V) 3.0 3.5
LT1528 * F04
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Figure 4. Input Current
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LT1528
PACKAGE DESCRIPTIO
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 0.067 (1.70) 0.028 - 0.038 BSC (0.711 - 0.965) 0.013 - 0.023 (0.330 - 0.584)
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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Q Package 5-Lead Plastic DD Pak
(Reference LTC DWG # 05-08-1461)
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) +0.008 0.004 -0.004 0.330 - 0.370 (8.382 - 9.398) 0.059 (1.499) TYP
(
+0.203 0.102 -0.102
)
0.095 - 0.115 (2.413 - 2.921) 0.050 0.012 (1.270 0.305)
Q(DD5) 1098
(
+0.305 3.632 -0.508
)
1528fa
11
LT1528
PACKAGE DESCRIPTIO
0.390 - 0.415 (9.906 - 10.541)
0.147 - 0.155 (3.734 - 3.937) DIA 0.230 - 0.270 (5.842 - 6.858)
0.460 - 0.500 (11.684 - 12.700)
0.330 - 0.370 (8.382 - 9.398)
BSC
0.067 (1.70)
0.028 - 0.038 (0.711 - 0.965)
RELATED PARTS
PART NUMBER LTC 1265 LTC1266 LT1521 LT1584 LT1585
(R)
DESCRIPTION High Efficiency Step-Down Switching Regulator Synchronous Switching Controller 300mA Micropower Low Dropout Regulator 7A Low Dropout Fast Transient Response Regulator 4.6A Low Dropout Fast Transient Response Regulator
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507
q
U
T Package 5-Lead Plastic TO-220 (Standard)
(Reference LTC DWG # 05-08-1421)
0.165 - 0.180 (4.191 - 4.572) 0.045 - 0.055 (1.143 - 1.397) 0.570 - 0.620 (14.478 - 15.748) 0.700 - 0.728 (17.78 - 18.491) 0.620 (15.75) TYP SEATING PLANE 0.152 - 0.202 0.260 - 0.320 (3.861 - 5.131) (6.60 - 8.13) 0.095 - 0.115 (2.413 - 2.921) 0.155 - 0.195* (3.937 - 4.953) 0.013 - 0.023 (0.330 - 0.584) 0.135 - 0.165 (3.429 - 4.191) * MEASURED AT THE SEATING PLANE
T5 (TO-220) 0399
COMMENTS >90% Efficient 1A, 5V to 3.3V Conversion >90% Efficient High Current Microprocessor Supply 15A Quiescent Current For High Performance Microprocessors For High Performance Microprocessors
1528fa LT/TP 1201 1.5K REV A * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 1995

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