LINER LT1528CQ 3a low dropout regulator for microprocessor application Datasheet

LT1528
3A Low Dropout Regulator
for Microprocessor Applications
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DESCRIPTION
FEATURES
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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.
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
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APPLICATIONS
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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 packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATION
Dropout Voltage
Microprocessor Supply with Shutdown
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
V OUT
3.30
3.45
4.00
*CHOOSE CAPACITORS
TO MEET PROCESSOR
REQUIREMENTS
0.5
DROPOUT VOLTAGE (V)
5
0.4
0.3
0.2
0.1
0
LT1528 • TA01
0
0.5
2.5
1.0
1.5
2.0
OUTPUT CURRENT (mA)
3.0
LT1528 • TA02
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LT1528
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ABSOLUTE MAXIMUM RATINGS
Input Voltage ....................................................... ±15V*
Output Pin Reverse Current .................................. 10mA
Sense Pin Current ................................................. 10mA
Shutdown Pin Input Voltage (Note 1) .......... 6.5V, – 0.6V
Shutdown Pin Input Current (Note 1) ..................... 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.
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PACKAGE/ORDER INFORMATION
ORDER PART
NUMBER
FRONT VIEW
TAB
IS
GND
5
4
3
2
1
VIN
SHDN
GND
SENSE
OUTPUT
TAB IS
GND
5
4
3
2
1
LT1528CQ
Q PACKAGE
5-LEAD PLASTIC DD PAK
ORDER PART
NUMBER
FRONT VIEW
VIN
SHDN
GND
LT1528CT
SENSE
OUTPUT
T PACKAGE
5-LEAD PLASTIC TO-220
TJMAX = 125°C, θJA = 50°C/ W
TJMAX = 125°C, θJA = 30°C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
PARAMETER
Regulated Output Voltages (Notes 2, 3)
Line Regulation (Note 3)
Load Regulation (Note 3)
Dropout Voltage (Note 4)
2
CONDITIONS
VIN = 3.8V, IOUT = 1mA, TJ = 25°C
4.3V < VIN < 15V, 1mA < IOUT < 3A
∆VIN = 3.8V to 15V, IOUT = 1mA
∆ILOAD = 1mA to 3A, VIN = 4.3V,TJ = 25°C
∆ILOAD = 1mA to 3A, VIN = 4.3V
ILOAD = 10mA, TJ = 25°C
ILOAD = 10mA
ILOAD = 100mA, TJ = 25°C
ILOAD = 100mA
ILOAD = 700mA, TJ = 25°C
ILOAD = 700mA
ILOAD = 1.5A, TJ = 25°C
ILOAD = 1.5A
ILOAD = 3A, TJ = 25°C
ILOAD = 3A
●
●
●
MIN
3.250
3.200
TYP
3.300
3.300
1.5
12
15
70
●
150
●
280
●
390
●
570
●
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
LT1528
ELECTRICAL CHARACTERISTICS
PARAMETER
Ground Pin Current (Note 5)
Sense Pin Current (Notes 3, 7)
Shutdown Threshold
Shutdown Pin Current (Note 8)
Quiescent Current in Shutdown (Note 9)
Ripple Rejection
Current Limit
Input Reverse Leakage Current
Reverse Output Current (Note 10)
CONDITIONS
ILOAD = 0mA, TJ = 25°C
ILOAD = 0mA, TJ = 125°C (Note 6)
ILOAD = 100mA, TJ = 25°C
ILOAD = 100mA, TJ = 125°C (Note 6)
ILOAD = 300mA, TJ = 25°C
ILOAD = 300mA, TJ = 125°C (Note 6)
ILOAD = 700mA, TJ = 25°C
ILOAD = 700mA, TJ = 125°C (Note 6)
ILOAD = 1.5A
ILOAD = 3A
TJ = 25°C
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, TJ = 25°C
VIN = 4.3V, ∆VOUT = – 0.1V
VIN = – 15V, VOUT = 0V
VOUT = 3.3V, VIN = 0V
The ● denotes specifications which apply over the full operating
temperature range.
Note 1: The Shutdown pin input voltage rating is required for a low
impedance source. Internal protection devices connected to the Shutdown
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 Shutdown pin must be less than
5mA.
Note 2: 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 3: The LT1528 is tested and specified with the Sense pin connected
to the Output pin.
MIN
50
TYP
450
1.9
1.2
2.7
2.6
4.1
7.3
8.8
22
85
130
1.20
0.75
37
110
67
3.2
4.5
4.0
●
●
90
●
●
0.25
●
●
●
●
120
MAX
750
2.5
4.0
12.0
40
140
250
2.80
100
220
1.0
250
UNITS
µA
mA
mA
mA
mA
mA
mA
mA
mA
mA
µA
V
V
µA
µA
dB
A
A
mA
µA
Note 4: 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 5: Ground 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 Ground pin current. The Ground
pin current will decrease slightly at higher input voltages.
Note 6: Ground 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 7: Sense pin current flows into the Sense pin.
Note 8: Shutdown pin current at VSHDN = 0V flows out of the Shutdown pin.
Note 9: Quiescent current in shutdown is equal to the total sum of the
Shutdown pin current (40µA) and the Ground pin current (70µA).
Note 10: 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 Ground pin.
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LT1528
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TYPICAL PERFORMANCE CHARACTERISTICS
Guaranteed Dropout Voltage
Dropout Voltage
= TEST POINTS
0.9
DROPOUT VOLTAGE (V)
TJ ≤ 125°C
0.7
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)
0
–50
3.0
2.5
ILOAD = 10mA
–25
75
50
25
TEMPERATURE (°C)
0
Quiescent Current
1000
750
VSHDN = OPEN (HIGH)
3 4 5 6 7
INPUT VOLTAGE (V)
ILOAD = 1mA
3.350
3.325
3.300
3.275
3.250
8
9
10
–25
0
50
75
25
TEMPERATURE (°C)
70
RL = 1.1Ω
ILOAD = 3A*
RL = 2.2Ω
ILOAD = 1.5A*
30
20
RL = 4.7Ω
ILOAD = 700mA*
80
60
4
8
9
10
LT1528 • TPC07
TJ = 125°C
TJ = 25°C
TJ = –50°C
30
20
0
3 4 5 6 7
INPUT VOLTAGE (V)
RL = 11Ω
ILOAD = 300mA*
3
RL = 33Ω
ILOAD = 100mA*
2
0
1
2
3
7
4 5 6
INPUT VOLTAGE (V)
8
9
10
LT1528 • TPC06
1.8
40
0
2
RL = 6.6Ω
ILOAD = 500mA*
Shutdown Pin Threshold
(On-to-Off)
50
10
1
TJ = 25°C
VOUT = VSENSE
*FOR VOUT = 3.3V
0
125
70
10
0
125
2.0
VIN = 3.3V
DEVICE IS OPERATING
IN DROPOUT
90
GROUND PIN CURRENT (mA)
GROUND PIN CURRENT (mA)
100
100
40
100
0
5
Ground Pin Current
TJ = 25°C
VOUT = VSENSE
*FOR VOUT = 3.3V
50
75
50
25
TEMPERATURE (°C)
–25
LT1528 • TPC05
100
60
VSHDN = 0V
1
3.200
–50
Ground Pin Current
80
0.25
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LT1528 • TPC04
90
VSHDN = OPEN
RL = 330Ω: ILOAD = 10mA*
0
2
0.50
Ground Pin Current
3.225
VSHDN = 0V
1
0.75
LT1528 • TPC03
GROUND PIN CURRENT (mA)
SENSE PIN VOLTAGE (V)
QUIESCENT CURRENT (µA)
1250
0
1.00
7
3.375
1500
250
1.25
Sense Pin Voltage
ILOAD = 0
RLOAD = ∞
500
1.50
0
–50
125
3.400
2000
1750
VIN = 4.3V
RL = ∞
LT1528 • TPC02
LT1528 • TPC01
4
100
SHUTDOWN PIN THRESHOLD (V)
DROPOUT VOLTAGE (V)
0.8
0.8
QUIESCENT CURRENT (mA)
1.0
Quiescent Current
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
LT1528 • TPC08
0
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
LT1528 • TPC09
LT1528
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TYPICAL PERFORMANCE CHARACTERISTICS
Shutdown Pin Current
100
1.8
90
ILOAD = 3A
1.6
1.4
1.2
ILOAD = 1mA
1.0
0.8
0.6
0.4
0.2
25
VSHDN = 0V
80
70
60
50
40
30
20
10
0
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
0
–50 –25
125
50
25
0
75
TEMPERATURE (°C)
LT1528 • TPC10
Sense Pin Current
125
100
75
50
75
50
25
TEMPERATURE (°C)
100
VIN = 0V
VOUT = VSENSE
150
100
50
25
75
0
TEMPERATURE (°C)
LT1528 • TPC13
100
3
2
1
0
125
OUTPUT CURRENT (µA)
800
2
700
68
600
500
400
300
200
VIN = 7V
VOUT = 0V
4
3
5
2
INPUT VOLTAGE (V)
6
7
70
RIPPLE REJECITON (dB)
5
3
1
Ripple Rejection
TJ = 25°C, VIN = 0V
VOUT =VSENSE
CURRENT FLOWS
INTO DEVICE
900
4
0
LT1528 • TPC15
1000
50
25
75
0
TEMPERATURE (°C)
4
Reverse Output Current
6
0
–50 –25
5
LT1528 • TPC14
Current Limit
SHORT-CIRCUIT CURRENT (A)
VOUT = 0V
200
0
–50 –25
125
9
Current Limit
50
25
0
7
3
8
2
5
6
4
SHUTDOWN PIN VOLTAGE (V)
LT1528 • TPC12
SHORT-CIRCUIT CURRENT (A)
OUTPUT CURRENT (µA)
SENSE PIN CURRENT (µA)
150
1
6
250
–25
5
Reverse Output Current
CURRENT FLOWS INTO SENSE PIN
0
–50
10
0
300
175
15
0
125
100
20
LT1528 • TPC11
200
1
Shutdown Pin Input Current
SHUTDOWN PIN INPUT CURRENT (mA)
2.0
SHUTDOWN PIN CURRENT (µA)
SHUTDOWN PIN THRESHOLD (V)
Shutdown 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
100
125
LT1528 • TPC16
0
0
1
2
3 4 5 6 7 8
OUTPUT VOLTAGE (V)
9
10
LT1528 • TPC17
56
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
LT1528 • TPC18
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LT1528
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TYPICAL PERFORMANCE CHARACTERISTICS
Ripple Rejection
Load Regulation
80
0
VIN = VOUT(NOMINAL) + 1V
∆ILOAD = 1mA TO 3A
–5
60
50
LOAD REGULATION (mV)
RIPPLE REJECTION (dB)
70
COUT = 4 × 47µF
SOLID TANTALUM
40
COUT = 47µF
SOLID TANTALUM
30
20
0
10
100
–15
–20
–25
IOUT = 1.5A
VIN = 6V + 50mVRMS RIPPLE
10
–10
1k
10k
FREQUENCY (Hz)
100k
–30
–50 –25
1M
50
25
75
0
TEMPERATURE (°C)
LT1528 • TPC19
–100
3
2
1
0
0
20 40 60 80 100 120 140 160 180 200
TIME (µs)
LT1528 • TPC21
OUTPUT VOLTAGE
DEVIATION (mV)
0
–50
LOAD CURRENT (A)
OUTPUT VOLTAGE
DEVIATION (mV)
LOAD CURRENT (A)
Transient Response
VIN = 5V
CIN = 3.3µF
COUT = 47µF
50
125
LT1528 • 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)
LT1528 • TPC22
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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
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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.
LT1528
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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 Shutdown pin is actively pulled low. The Shutdown pin
current with the pin pulled to ground will be 60µA. The
Shutdown pin is internally clamped to 7V and – 0.6V (one
VBE). This allows the Shutdown 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 Shutdown pin input current as a
function of voltage appears in the Typical Performance
Characteristics section. If the Shutdown pin is not used it
can be left open circuit. The device will be active output on
if the Shutdown 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
OUT
1
RP
LT1528
+
4
VIN
SHDN
SENSE
+
2
LOAD
GND
3
RP
LT1528 • F01
Figure 1. Kelvin Sense Connection
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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.
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
VOUT
+
VIN
R2
LT1528
4
SHDN
SENSE
2
GND
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
1
R1
3
)
)
VOUT = 3.3V 1 + R2 + (ISENSE + R2)
R1
VSENSE = 3.3V
ISENSE = 130µA AT 25°C
OUTPUT RANGE = 3.3V TO 14V
LT1528 • F02
Figure 2. Adjustable Operation
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LT1528
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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. Ground pin current multiplied by the input voltage,
IGND × VIN.
The Ground pin current can be found by examining the
Ground 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 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.
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
THERMAL RESISTANCE
(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 2500 sq mm
2500 sq mm
33°C/W
*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
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?
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 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
LT1528
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APPLICATIONS INFORMATION
The maximum junction temperature will be equal to the
maximum junction temperature rise above ambient plus
the maximum ambient temperature or:
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 several
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)
RESULTING CONDITIONS
< 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
9
LT1528
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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
Shutdown 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 Shutdown pin will have no
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 2µA (see Figure 4).
The state of the Shutdown pin will have no effect on the
reverse output current when the output is pulled above the
input.
5
1000
700
4
INPUT CURRENT (µA)
800
OUTPUT CURRENT (µA)
VOUT = 3.3V
TJ = 25°C, VIN = 0V
VOUT =VSENSE
CURRENT FLOWS
INTO DEVICE
900
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)
LT1528 • F03
Figure 3. Reverse Output Current
10
3.0
3.5
LT1528 • F04
Figure 4. Input Current
LT1528
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PACKAGE DESCRIPTION
Dimension in inches (millimeters) unless otherwise noted.
Q Package
5-Lead Plastic DD
0.060
(1.524)
TYP
0.390 – 0.415
(9.906 – 10.541)
0.165 – 0.180
(4.191 – 4.572)
15° TYP
0.059
(1.499)
TYP
0.330 – 0.370
(8.382 – 9.398)
0.045 – 0.055
(1.143 – 1.397)
(
+0.008
0.004 –0.004
+0.203
0.102 –0.102
)
0.095 – 0.115
(2.413 – 2.921)
(
+0.012
0.143 –0.020
+0.305
3.632 –0.508
)
0.057 – 0.077
(1.447 – 0.955)
0.028 – 0.038
(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.
0.050 ± 0.012
(1.270 ± 0.305)
DD5 0694
11
LT1528
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PACKAGE DESCRIPTION
Dimension in inches (millimeters) unless otherwise noted.
T Package
5-Lead TO-220
0.165 – 0.180
(4.293 – 4.572)
0.147 – 0.155
(3.734 – 3.937)
DIA
0.390 – 0.415
(9.906 – 10.541)
0.045 – 0.055
(1.143 – 1.397)
0.230 – 0.270
(5.842 – 6.858)
0.570 – 0.620
(14.478 – 15.748)
0.460 – 0.500
(11.684 – 12.700)
0.620
(15.75)
TYP
0.330 – 0.370
(8.382 – 9.398)
0.700 – 0.728
(17.780 – 18.491)
0.095 – 0.115
(2.413 – 2.921)
0.152 – 0.202
0.260 – 0.320 (3.860 – 5.130)
(6.604 – 8.128)
0.013 – 0.023
(0.330 – 0.584)
0.057 – 0.077
(1.448 – 1.956)
0.028 – 0.038
(0.711 – 0.965)
0.135 – 0.165
(3.429 – 4.191)
0.155 – 0.195
(3.937 – 4.953)
T5 (FORMED) 0694
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12
Linear Technology Corporation
LT/GP 0595 10K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977
 LINEAR TECHNOLOGY CORPORATION 1995
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