LT1528 [Linear]
3A Low Dropout Regulator for Microprocessor Applications; 3A低压降稳压器为微处理器应用
| 型号： | LT1528 |
| 厂家： | 
Linear |
| 描述： | 3A Low Dropout Regulator for Microprocessor Applications |
| 文件： | 总12页 (文件大小：249K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
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FEATURES
DESCRIPTION
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 capaci-
tor ESR. Dropout voltage is 75mV at 10mA, rising to
300mVat1Aand600mVat3A. Thedevicehasaquiescent
current of 400µA. Quiescent current is well controlled; it
does not increase significantly as the device enters drop-
out. The regulator can operate with output capacitors as
small as 3.3µF, although larger capacitors will be needed
toachievetheperformancerequiredinmostmicroproces-
sor 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
■
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
5
1
V
OUT
IN
OUT
0.5
+
4 × 47µF*
SOLID TANTALUM
15Ω
68Ω
J3
V
=5V
LT1528
IN
0.4
0.3
0.2
0.1
0
J1
J2
4
2
SHDN
SENSE
GND
3
330Ω
*CHOOSE CAPACITORS
TO MEET PROCESSOR
REQUIREMENTS
V
(PIN 4)
<0.25
>2.80
NC
OUTPUT
SHORTING
V
SHDN
OUT
OFF
ON
ON
J1
J2
J3
3.30
3.45
4.00
LT1528 • TA01
0
1.0
1.5
2.0
2.5
3.0
0.5
OUTPUT CURRENT (mA)
LT1528 • TA02
1
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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
TAB IS
GND
FRONT VIEW
ORDER PART
NUMBER
ORDER PART
FRONT VIEW
T PACKAGE
NUMBER
V
IN
5
4
3
2
1
5
4
3
2
1
V
IN
TAB
IS
GND
SHDN
GND
SENSE
OUTPUT
SHDN
LT1528CQ
LT1528CT
GND
SENSE
OUTPUT
Q PACKAGE
5-LEAD PLASTIC DD PAK
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
CONDITIONS
= 3.8V, I
MIN
TYP
MAX
UNITS
Regulated Output Voltages (Notes 2, 3)
V
IN
= 1mA, T = 25°C
3.250
3.200
3.300
3.300
1.5
12
15
70
3.350
3.400
10
20
30
110
150
200
250
320
420
450
600
670
850
V
V
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
OUT
J
4.3V < V < 15V, 1mA < I
< 3A
●
●
IN
OUT
Line Regulation (Note 3)
Load Regulation (Note 3)
∆V = 3.8V to 15V, I
= 1mA
OUT
IN
∆I
∆I
= 1mA to 3A, V = 4.3V,T = 25°C
= 1mA to 3A, V = 4.3V
LOAD
LOAD
IN
J
●
●
●
●
●
●
IN
Dropout Voltage (Note 4)
I
I
= 10mA, T = 25°C
= 10mA
LOAD
LOAD
J
I
I
= 100mA, T = 25°C
= 100mA
150
280
390
570
LOAD
LOAD
J
I
I
= 700mA, T = 25°C
= 700mA
LOAD
LOAD
J
I
I
= 1.5A, T = 25°C
= 1.5A
LOAD
LOAD
J
I
I
= 3A, T = 25°C
= 3A
LOAD
LOAD
J
2
ELECTRICAL CHARACTERISTICS
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Ground Pin Current (Note 5)
I
I
= 0mA, T = 25°C
450
1.9
750
µA
mA
LOAD
LOAD
J
= 0mA, T = 125°C (Note 6)
J
I
I
I
I
= 100mA, T = 25°C
1.2
2.7
2.6
4.1
2.5
4.0
mA
mA
mA
mA
LOAD
LOAD
J
= 100mA, T = 125°C (Note 6)
J
= 300mA, T = 25°C
LOAD
LOAD
J
= 300mA, T = 125°C (Note 6)
J
I
I
= 700mA, T = 25°C
7.3
8.8
12.0
mA
mA
LOAD
LOAD
J
= 700mA, T = 125°C (Note 6)
J
I
I
= 1.5A
= 3A
●
●
22
85
130
1.20
0.75
40
mA
mA
µA
V
V
LOAD
LOAD
140
250
2.80
Sense Pin Current (Notes 3, 7)
Shutdown Threshold
T = 25°C
V
V
90
J
= Off-to-On
= On-to-Off
●
●
OUT
OUT
0.25
Shutdown Pin Current (Note 8)
Quiescent Current in Shutdown (Note 9)
Ripple Rejection
V
V
V
= 0V
●
●
37
110
67
100
220
µA
µA
dB
SHDN
= 6V, V
= 0V
SHDN
IN
IN
– V
= 1V(Avg), V
= 120Hz, I
= 0.5V ,
P-P
50
OUT
RIPPLE
= 1.5A
f
RIPPLE
LOAD
Current Limit
V
V
– V
= 4.3V, ∆V
= –15V, V
= 3.3V, V = 0V
= 7V, T = 25°C
4.5
4.0
A
A
mA
IN
IN
OUT
J
= –0.1V
●
●
3.2
OUT
Input Reverse Leakage Current
Reverse Output Current (Note 10)
V
V
= 0V
1.0
250
IN
OUT
120
µA
OUT
IN
Note 4: Dropout voltage is the minimum input/output voltage required to
The
● denotes specifications which apply over the full operating
maintain regulation at the specified output current. In dropout the output
temperature range.
voltage will be equal to: (V – V
).
IN
DROPOUT
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 5: Ground pin current is tested with V = V
(nominal) and a
OUT
IN
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 T > 75°C. This is due to internal
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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 V
= 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).
SHDN
Note 3: The LT1528 is tested and specified with the Sense pin connected
to the Output pin.
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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TYPICAL PERFORMANCE CHARACTERISTICS
Guaranteed Dropout Voltage
Dropout Voltage
Quiescent Current
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
V
= 4.3V
= TEST POINTS
IN
L
R
= ∞
I
= 3A
LOAD
T
≤ 125°C
J
I
= 1.5A
LOAD
I
= 700mA
LOAD
T
≤ 25°C
J
V
SHDN
= OPEN
I
= 300mA
LOAD
V
= 0V
SHDN
I
= 10mA
LOAD
–25
0
50
75 100 125
–25
0
50
75 100 125
–50
25
–50
25
0
0.5
1.5
2.0
2.5
3.0
1.0
TEMPERATURE (°C)
TEMPERATURE (°C)
OUTPUT CURRENT (A)
LT1528 • TPC03
LT1528 • TPC02
LT1528 • TPC01
Quiescent Current
Sense Pin Voltage
Ground Pin Current
2000
1750
1500
1250
1000
750
3.400
7
6
I
= 0
T
V
= 25°C
LOAD
J
I
= 1mA
LOAD
3.375
3.350
3.325
3.300
3.275
3.250
3.225
3.200
R
=
∞
= V
LOAD
OUT
SENSE
*FOR V
= 3.3V
OUT
5
R
I
= 6.6Ω
L
= 500mA*
LOAD
4
3
2
1
R
LOAD
= 11Ω
L
I
= 300mA*
R
I
= 33Ω
LOAD
L
= 100mA*
500
V
SHDN
= OPEN (HIGH)
250
V
SHDN
= 0V
R
3
= 330Ω: I
= 10mA*
L
LOAD
0
0
0
1
2
3
4
5
6
7
8
9
10
–50
–25
0
25
50
75 100 125
0
5
6
7
8
9
10
1
2
4
INPUT VOLTAGE (V)
TEMPERATURE (°C)
INPUT VOLTAGE (V)
LT1528 • TPC04
LT1528 • TPC05
LT1528 • TPC06
Shutdown Pin Threshold
(On-to-Off)
Ground Pin Current
Ground Pin Current
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
T
= 25°C
V
= 3.3V
IN
J
V
I
= 1mA
LOAD
= V
DEVICE IS OPERATING
IN DROPOUT
OUT
SENSE
*FOR V
= 3.3V
OUT
T
= 125°C
J
T
= 25°C
R
L
LOAD
= 1.1Ω
= 3A*
J
I
R
I
= 2.2Ω
LOAD
L
T = –50°C
J
R
LOAD
= 4.7Ω
L
= 1.5A*
I
= 700mA*
0
1
2
3
4
5
6
7
8
9
10
50
TEMPERATURE (°C)
125
–50
0
25
75 100
–25
0
0.5
1.5
2.0
2.5
3.0
1.0
INPUT VOLTAGE (V)
OUTPUT CURRENT (A)
LT1528 • TPC07
LT1528 • TPC09
LT1528 • TPC08
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TYPICAL PERFORMANCE CHARACTERISTICS
Shutdown Pin Threshold
(Off-to-On)
Shutdown Pin Current
Shutdown Pin Input Current
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
100
90
80
70
60
50
40
30
20
10
0
25
20
V
= 0V
SHDN
I
= 3A
LOAD
15
I
= 1mA
LOAD
10
5
0
–50
0
25
50
75 100 125
–50
0
25
50
75 100 125
–25
–25
0
1
2
3
4
5
6
7
8
9
TEMPERATURE (°C)
TEMPERATURE (°C)
SHUTDOWN PIN VOLTAGE (V)
LT1528 • TPC10
LT1528 • TPC11
LT1528 • TPC12
Sense Pin Current
Reverse Output Current
Current Limit
200
175
150
125
100
75
300
250
200
150
100
50
6
5
4
3
2
1
0
V
V
= 0V
OUT
V
= 0V
OUT
CURRENT FLOWS INTO SENSE PIN
IN
= V
SENSE
50
25
0
0
–25
0
50
75 100 125
–50
25
50
0
TEMPERATURE (°C)
100 125
4
6
7
–50 –25
25
75
0
1
2
3
5
TEMPERATURE (°C)
INPUT VOLTAGE (V)
LT1528 • TPC13
LT1528 • TPC14
LT1528 • TPC15
Current Limit
Reverse Output Current
Ripple Rejection
6
5
4
3
2
1
0
1000
900
800
700
600
500
400
300
200
100
0
70
68
V
V
I
= 4.3V
T
= 25°C, V = 0V
IN(AVG)
J
IN
= 0.5V AT f = 120Hz
V
=V
RIPPLE
= 1.5A
P-P
OUT
SENSE
L
CURRENT FLOWS
INTO DEVICE
66
64
62
60
58
V
V
= 7V
IN
OUT
= 0V
56
50
TEMPERATURE (°C)
100 125
–50 –25
0
25
75
50
0
TEMPERATURE (°C)
100 125
0
1
2
3
4
5
6
7
8
9
10
–50 –25
25
75
OUTPUT VOLTAGE (V)
LT1528 • TPC17
LT1528 • TPC16
LT1528 • TPC18
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TYPICAL PERFORMANCE CHARACTERISTICS
Ripple Rejection
Load Regulation
80
0
–5
V
= V (NOMINAL) + 1V
OUT
IN
70
60
50
∆I
= 1mA TO 3A
LOAD
–10
–15
–20
–25
–30
C
= 4 × 47µF
OUT
SOLID TANTALUM
40
30
20
10
0
C
OUT
= 47µF
SOLID TANTALUM
I
= 1.5A
OUT
IN
V
= 6V + 50mV
RIPPLE
10k
RMS
10
100
1k
100k
1M
50
TEMPERATURE (°C)
100 125
–50 –25
0
25
75
FREQUENCY (Hz)
LT1528 • TPC19
LT1528 • TPC20
Transient Response
Transient Response
V
C
C
= 5V
V
C
C
= 5V
IN
IN
IN
IN
100
50
100
50
= 3.3µF
= 4 × 47µF
= 3.3µF
= 47µF
OUT
OUT
0
0
–50
–100
–50
–100
3
2
1
0
3
2
1
0
0
20 40 60 80 100 120 140 160 180 200
0
20 40 60 80 100 120 140 160 180 200
TIME (µs)
TIME (µs)
LT1528 • TPC21
LT1528 • TPC22
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PIN FUNCTIONS
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).
OUTPUT (Pin 1): The Output pin supplies power to the
load. A minimum output capacitor of 3.3µF is required to
preventoscillations.Largervalueswillbeneededtoachieve
the transient performance required by high speed micro-
processors. See the Applications Information section for
more on output capacitance and reverse output character-
istics.
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
theOutputpinattheregulator.Incriticalapplicationssmall
voltage drops caused by the resistance (RP) of PC traces
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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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
theShutdownpinisactivelypulledlow. TheShutdownpin
current with the pin pulled to ground will be 60µA. The
Shutdown pin is internally clamped to 7V and –0.6V (one
VBE). ThisallowstheShutdownpintobedrivendirectlyby
5V logic or by open collector logic with a pull-up resistor.
The pull-up resistor is only required to supply the leakage
currentoftheopencollectorgate, normallyseveralmicro-
amperes. 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.
the device is more than six inches away from the main
input filter capacitor. TheLT1528 is designedto 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.
R
P
1
5
IN
OUT
LT1528
+
+
2
4
V
LOAD
IN
SHDN
SENSE
GND
3
R
P
LT1528 • 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
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APPLICATIONS INFORMATION
The LT1528 is a 3A low dropout regulator optimized for formula in Figure 2. The value of R1 should be less than
microprocessorapplications.Dropoutvoltageisonly0.6V 330Ω to minimize errors in the output voltage caused by
at 3A output current. With the Sense pin shorted to the the Sense pin current. Note that in shutdown the output is
Output pin, the output voltage is set to 3.3V. The device turned off and the divider current will be zero. Curves of
operates with a quiescent current of 400µA. In shutdown,
Sense Pin Voltage vs Temperature and Sense Pin Current
the quiescent current drops to only 125µA. The LT1528 vs Temperature appear in the Typical Performance Char-
incorporatesseveralprotectionfeatures,includingprotec- acteristics section.
tion against reverse input voltages. If the output is held at
5
4
1
2
V
IN
OUT
OUT
theratedoutputvoltagewhentheinputispulledtoground,
the LT1528 acts like it has a diode in series with its output
and prevents reverse current flow.
+
R2
V
LT1528
IN
SHDN
SENSE
GND
3
Adjustable Operation
R1
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
thenequalto3.3V/R1.ThecurrentinR2isequaltothesum
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
R2
V
V
= 3.3V 1 +
+ (I
+ R2)
SENSE
OUT
)
)
R1
= 3.3V
SENSE
SENSE
I
= 130µA AT 25°C
LT1528 • F02
OUTPUT RANGE = 3.3V TO 14V
Figure 2. Adjustable Operation
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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. Specifica-
tions for output voltage greater than 3.3V will be propor-
tional 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:
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
interactionswithothercomponentsaswellasboardsizeand
shape.Someexperimentationwillbenecessarytodetermine
the actual value.
(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:
Table 1a. Q-Package, 5-Lead DD
COPPER AREA
TOPSIDE* BACKSIDE
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
BOARD AREA
1. Output current multiplied by the input/output voltage
2500 sq mm 2500 sq mm 2500 sq mm
1000 sq mm 2500 sq mm 2500 sq mm
125 sq mm 2500 sq mm 2500 sq mm
23°C/W
25°C/W
33°C/W
differential, IOUT × (VIN – VOUT), and
2. Ground pin current multiplied by the input voltage,
IGND × VIN.
*Device is mounted on topside.
Table 1b. T Package, 5-Lead TO-220
Thermal Resistance (Junction-to-Case)
The Ground pin current can be found by examining the
Ground Pin Current curves in the Typical Performance
Characteristics. Powerdissipationwillbeequaltothesum
of the two components listed above.
2.5°C/W
Calculating Junction Temperature
Example:Givenanoutputvoltageof3.3V, aninputvoltage
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 LT1528 has internal thermal limiting designed to
protect the device during overload conditions. For
continuousnormalloadconditionsthemaximumjunction
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.
The power dissipated by the device will be equal to:
I
OUT(MAX) × (VIN(MAX) – VOUT) + [IGND × VIN(MAX)
where,
IOUT(MAX) = 500mA
]
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 electri-
cally 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.
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
8
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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
T
JMAX = 50°C + 31.4°C = 81.4°C
TheLT1528incorporatesseveralprotectionfeatures,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.
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 capaci-
tance. See the Transient Response curves in the Typical
Performance Characteristics. Larger values of output ca-
pacitance will decrease the peak deviations and provide
improved output transient response for larger load tran-
sients. Bypass capacitors, used to decouple individual
components powered by the LT1528, will increase the
effective value of the output capacitor.
Current limit protection and thermal overload protection
are intended to protect the device against overload condi-
tions. For normal operation the junction temperatures
should not exceed 125°C.
The input of the device will withstand reverse voltages of
15V. Currentflowintothedevicewillbelimitedtolessthan
1mA (typically less than 100µA) and no negative voltage
will appear at the output. The device will protect both itself
and the load.
Microprocessor Applications
The Sense pin is internally clamped to one diode drop
belowground.IftheSensepinispulledbelowground,with
theinputopenorgrounded, currentmustbelimitedtoless
than 5mA.
The LT1528 has been optimized for microprocessor
applications, withthefastesttransientresponseofcurrent
PNP low dropout regulators. In order to deal with the large
load transients associated with current generation
microprocessors, output capacitance must be increased.
Tomeetworst-casevoltagespecificationsformanypopular
processors, four 47µF solid tantalum surface mount
capacitors are recommended for decoupling at the
microprocessor. These capacitors should have an ESR of
approximately0.1Ωto0.2Ωtominimizetransientresponse
under worst-case load deltas. The Typical Application
shows connections needed to supply power for several
Several different input/output conditions can occur in
regulatorcircuits. Theoutputvoltagemaybeheldupwhile
the input is either pulled to ground, pulled to some inter-
mediate 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 manage-
ment. The following information summarized in Table 2
will help optimize power usage.
Table 2. Fault Conditions
INPUT PIN
SHDN PIN
OUTPUT/SENSE PINS
RESULTING CONDITIONS
< V
< V
(Nominal)
Open (High)
Forced to V
(Nominal)
Reverse Output Current ≈ 150µA (See Figure 3)
Input Current ≈ 1µA (See Figure 4)
OUT
OUT
(Nominal)
Grounded
Forced to V
(Nominal)
Reverse Output Current ≈ 150µA (See Figure 3)
Input Current ≈ 1µA (See Figure 4)
OUT
OUT
Open
Open (High)
Grounded
> 1V
> 1V
≤ 0V
≤ 0V
≤ 0V
≤ 0V
Reverse Output Current ≈ 150µA (See Figure 3)
Reverse Output Current ≈ 150µA (See Figure 3)
Output Current = 0
Open
≤ 0.8V
≤ 0.8V
> 1.5V
Open (High)
Grounded
Output Current = 0
Open (High)
Grounded
Output Current = Short-Circuit Current
Output Current = 0
–15V < V < 15V
IN
9
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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.
When the input of the LT1528 is forced to a voltage below
its nominal output voltage and its output is held high, the
outputcurrentwillfollowthecurveshowninFigure3.This
canhappeniftheinputoftheLT1528isconnectedtoalow
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
reverseoutputcurrentwhentheoutputispulledabovethe
input.
Insomeapplicationsitmaybenecessarytoleavetheinput
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
outputcurrentalsofollowsthecurveinFigure3iftheinput
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.
5
1000
V
= 3.3V
T
= 25°C, V = 0V
IN
OUT
J
900
800
700
600
500
400
300
200
100
0
V
=V
OUT
SENSE
4
3
2
1
0
CURRENT FLOWS
INTO DEVICE
0
1
2
3
4
5
6
7
8
9
10
3.5
0
1.0 1.5
2.0
INPUT VOLTAGE (V)
2.5 3.0
0.5
OUTPUT VOLTAGE (V)
LT1528 • F03
LT1528 • F04
Figure 3. Reverse Output Current
Figure 4. Input Current
10
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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
0.045 – 0.055
(4.191 – 4.572)
(1.143 – 1.397)
15° TYP
+0.008
0.004
–0.004
0.059
(1.499)
TYP
0.330 – 0.370
(8.382 – 9.398)
+0.203
–0.102
0.102
(
)
0.095 – 0.115
(2.413 – 2.921)
0.057 – 0.077
(1.447 – 0.955)
0.050 ± 0.012
(1.270 ± 0.305)
0.013 – 0.023
(0.330 – 0.584)
+0.012
0.143
–0.020
0.028 – 0.038
(0.711 – 0.965)
+0.305
3.632
(
)
–0.508
DD5 0694
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 represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
11
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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)
0.620
(15.75)
TYP
0.460 – 0.500
(11.684 – 12.700)
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
(3.860 – 5.130)
0.260 – 0.320
(6.604 – 8.128)
0.013 – 0.023
(0.330 – 0.584)
0.057 – 0.077
(1.448 – 1.956)
0.135 – 0.165
(3.429 – 4.191)
0.155 – 0.195
(3.937 – 4.953)
0.028 – 0.038
(0.711 – 0.965)
T5 (FORMED) 0694
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LT1585
LT/GP 0595 10K • PRINTED IN USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
12
●
●
(408) 432-1900 FAX: (408) 434-0507 TELEX: 499-3977
LINEAR TECHNOLOGY CORPORATION 1995
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