LT1528
3A Low Dropout Regulator
for Microprocessor Applications
FEATURES
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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 capacitor
ESR. Dropout voltage is 75mV at 10mA, rising to 300mV
at 1A and 600mV at 3A. The device has a quiescent cur-
rent 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 resis-
tive 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 125μA in shutdown. The LT1528 is avail-
able 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.
Dropout Voltage: 0.6V at I
OUT
= 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 I
Q
= 125μA
Stable with 3.3μF Output Capacitor
Reverse Battery Protection
No Reverse Output Current
Thermal Limiting
APPLICATIONS
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Microprocessor Applications
Post Regulator for Switching Supplies
5V to 3.3V Logic Regulator
TYPICAL APPLICATION
Microprocessor Supply with Shutdown
0.6
5
IN
LT1528
4
SHDN
GND
3
330Ω
SENSE
2
J1
J2
J3
OUT
1
15Ω
68Ω
V
OUT
Dropout Voltage
+
DROPOUT VOLTAGE (V)
V
IN
=5V
4
×
47μF*
SOLID TANTALUM
0.5
0.4
0.3
0.2
0.1
0
V
SHDN
(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
1528 TA01
0
0.5
2.5
1.0
1.5
2.0
OUTPUT CURRENT (mA)
3.0
1528 TA02
1528fb
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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
FRONT VIEW
5
4
TAB IS
GND
3
2
1
Q PACKAGE
5-LEAD PLASTIC DD
T
JMAX
= 125°C,
θ
JA
= 30°C/ W
TAB IS
GND
V
IN
SHDN
GND
SENSE
OUTPUT
FRONT VIEW
5
4
3
2
1
T PACKAGE
5-LEAD PLASTIC TO-220
T
JMAX
= 125°C,
θ
JA
= 50°C/ W
V
IN
SHDN
GND
SENSE
OUTPUT
ORDER INFORMATION
LEAD FREE FINISH
LT1528CQ#PBF
LT1528CT#PBF
LEAD BASED FINISH
LT1528CQ
LT1528CT
TAPE AND REEL
LT1528CQ#TRPBF
LT1528CT#TRPBF
TAPE AND REEL
LT1528CQ#TR
LT1528CT#TR
PART MARKING
LT1528CQ
LT1528CT
PART MARKING
LT1528CQ
LT1528CT
PACKAGE DESCRIPTION
5-Lead Plastic DD-PAK
5-Lead Plastic TO-220
PACKAGE DESCRIPTION
5-Lead Plastic DD-PAK
5-Lead Plastic TO-220
TEMPERATURE RANGE
0°C to 125°C
0°C to 125°C
TEMPERATURE RANGE
0°C to 125°C
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
PARAMETER
Regulated Output Voltages (Notes 3, 4)
Line Regulation (Note 4)
Load Regulation (Note 4)
Dropout Voltage (Note 5)
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
J
= 25°C.
CONDITIONS
V
IN
= 3.8V, I
OUT
= 1mA
4.3V < V
IN
< 15V, 1mA < I
OUT
< 3A
ΔV
IN
= 3.8V to 15V, I
OUT
= 1mA
ΔI
LOAD
= 1mA to 3A, V
IN
= 4.3V
ΔI
LOAD
= 1mA to 3A, V
IN
= 4.3V
I
LOAD
= 10mA
I
LOAD
= 10mA
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MIN
3.250
3.200
TYP
3.300
3.300
1.5
12
15
70
MAX
3.350
3.400
1.0
20
30
110
150
UNITS
V
V
mV
mV
mV
mV
mV
1528fb
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LT1528
ELECTRICAL CHARACTERISTICS
PARAMETER
Dropout Voltage (Note 5)
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
J
= 25°C.
CONDITIONS
I
LOAD
= 100mA
I
LOAD
= 100mA
I
LOAD
= 700mA
I
LOAD
= 700mA
I
LOAD
= 1.5A
I
LOAD
= 1.5A
I
LOAD
= 3A
I
LOAD
= 3A
GND Pin Current (Note 6)
I
LOAD
= 0mA
I
LOAD
= 0mA, T
J
= 125°C (Note 7)
I
LOAD
= 100mA
I
LOAD
= 100mA, T
J
= 125°C (Note 7)
I
LOAD
= 300mA
I
LOAD
= 300mA, T
J
= 125°C (Note 7)
I
LOAD
= 700mA
I
LOAD
= 700mA, T
J
= 125°C (Note 7)
I
LOAD
= 1.5A
I
LOAD
= 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)
V
OUT
= Off-to-On
V
OUT
= On-to-Off
V
SHDN
= 0V
V
IN
= 6V, V
SHDN
= 0V
V
IN
– V
OUT
= 1V(Avg), V
RIPPLE
= 0.5V
P-P
,
f
RIPPLE
= 120Hz, I
LOAD
= 1.5A
V
IN
– V
OUT
= 7V
V
IN
= 4.3V, ΔV
OUT
= – 0.1V
V
IN
= – 15V, V
OUT
= 0V
V
OUT
= 3.3V, V
IN
= 0V
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MIN
TYP
150
280
390
570
450
1.9
1.2
2.7
2.6
4.1
7.3
8.8
22
85
MAX
200
250
320
420
450
600
670
850
750
2.5
4.0
12.0
40
140
250
2.80
100
220
UNITS
mV
mV
mV
mV
mV
mV
mV
mV
μA
mA
mA
mA
mA
mA
mA
mA
mA
mA
μA
V
V
μA
μA
dB
A
A
90
0.25
130
1.20
0.75
37
110
50
67
4.5
4.0
1.0
120
250
3.2
mA
μA
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
maintain regulation at the specified output current. In dropout the output
voltage will be equal to: (V
IN
– V
DROPOUT
).
Note 6:
GND pin current is tested with V
IN
= V
OUT
(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 T
J
> 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 V
SHDN
= 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.
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LT1528
TYPICAL PERFORMANCE CHARACTERISTICS
Guaranteed Dropout Voltage
1.0
0.9
0.8
= TEST POINTS
0.8
0.7
Dropout Voltage
2.00
1.75
I
LOAD
= 3A
Quiescent Current
V
IN
= 4.3V
R
L
=
∞
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
T
J
≤ 25°C
T
J
≤ 125°C
DROPOUT VOLTAGE (V)
0.6
0.5
QUIESCENT CURRENT (mA)
1.50
1.25
1.00
0.75
0.50
0.25
V
SHDN
= OPEN
V
SHDN
= 0V
0
75
50
25
TEMPERATURE (°C)
100
125
I
LOAD
= 1.5A
0.4
0.3
0.2
0.1
0
–50
–25
0
I
LOAD
= 300mA
I
LOAD
= 10mA
75
50
25
TEMPERATURE (°C)
100
125
I
LOAD
= 700mA
0
–50 –25
1528 TPC01
1528 TPC02
1528 TPC03
Quiescent Current
2000
1750
I
LOAD
= 0
R
LOAD
=
∞
SENSE Pin Voltage
3.400
I
LOAD
= 1mA
3.375
GND Pin Current
7
6
GND PIN CURRENT (mA)
QUIESCENT CURRENT (μA)
T
J
= 25°C
V
OUT
= V
SENSE
*FOR V
OUT
= 3.3V
R
L
= 6.6Ω
I
LOAD
= 500mA*
R
L
= 11Ω
I
LOAD
= 300mA*
R
L
= 33Ω
I
LOAD
= 100mA*
SENSE PIN VOLTAGE (V)
1500
1250
1000
750
500
250
0
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
V
SHDN
= OPEN (HIGH)
V
SHDN
= 0V
3.350
3.325
3.300
3.275
3.250
3.225
3.200
–50 –25
0
75
50
25
TEMPERATURE (°C)
100
125
5
4
3
2
1
R
L
= 330Ω: I
LOAD
= 10mA*
0
0
1
2
3 4 5 6
7
INPUT VOLTAGE (V)
8
9
10
1528 TPC04
1528 TPC05
1528 TPC06
GND Pin Current
100
90
GND PIN CURRENT (mA)
GND Pin Current
T
J
= 25°C
V
OUT
= V
SENSE
*FOR V
OUT
= 3.3V
GND PIN CURRENT (mA)
100
90
80
70
60
50
40
30
20
10
0
T
J
= –50°C
T
J
= 25°C
V
IN
= 3.3V
DEVICE IS OPERATING
IN DROPOUT
T
J
= 125°C
SHDN
Pin Threshold
(On-to-Off)
2.0
1.8
I
LOAD
= 1mA
SHDN
PIN THRESHOLD (V)
80
70
60
50
40
30
20
10
0
0
1
2
R
L
= 2.2Ω
I
LOAD
= 1.5A*
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
R
L
= 1.1Ω
I
LOAD
= 3A*
R
L
= 4.7Ω
I
LOAD
= 700mA*
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
0
0.5
1.5
2.0
1.0
OUTPUT CURRENT (A)
2.5
3.0
0
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
1528 TPC07
1528 TPC08
1528 TPC09
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LT1528
TYPICAL PERFORMANCE CHARACTERISTICS
SHDN
Pin Threshold
(Off-to-On)
2.0
1.8
100
90
SHDN
Pin Current
V
SHDN
= 0V
SHDN
Pin Input Current
25
SHDN
PIN THRESHOLD (V)
SHDN
PIN CURRENT (μA)
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
–50
–25
I
LOAD
= 3A
80
70
60
50
40
30
20
10
SHDN
PIN INPUT CURRENT (mA)
–25
50
25
0
75
TEMPERATURE (°C)
100
125
20
I
LOAD
= 1mA
15
10
5
50
25
0
75
TEMPERATURE (°C)
100
125
0
–50
0
0
1
2
7
3
5
6
4
SHDN
PIN VOLTAGE (V)
8
9
1528 TPC10
1528 TPC11
1528 TPC12
SENSE Pin Current
200
175
Reverse Output Current
300
V
IN
= 0V
V
OUT
= V
SENSE
SHORT-CIRCUIT CURRENT (A)
Current Limit
6
5
4
3
2
1
0
V
OUT
= 0V
CURRENT FLOWS INTO SENSE PIN
250
OUTPUT CURRENT (μA)
SENSE PIN CURRENT (μA)
150
125
100
75
50
25
0
–50
–25
0
75
50
25
TEMPERATURE (°C)
100
125
200
150
100
50
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
0
1
4
3
5
2
INPUT VOLTAGE (V)
6
7
1528 TPC13
1528 TPC14
1528 TPC15
Current Limit
6
5
Reverse Output Current
1000
T
J
= 25°C, V
IN
= 0V
900 V
OUT
=V
SENSE
800 CURRENT FLOWS
INTO DEVICE
700
600
500
400
300
200
70
68
RIPPLE REJECTION (dB)
Ripple Rejection
V
IN(AVG)
= 4.3V
V
RIPPLE
= 0.5V
P-P
AT f = 120Hz
I
L
= 1.5A
SHORT-CIRCUIT CURRENT (A)
OUTPUT CURRENT (μA)
4
3
2
1
66
64
62
60
58
56
–50 –25
0
–50 –25
V
IN
= 7V
V
OUT
= 0V
50
25
75
0
TEMPERATURE (°C)
100
125
100
0
0
1
2
3 4 5 6 7 8
OUTPUT VOLTAGE (V)
9
10
50
25
75
0
TEMPERATURE (°C)
100
125
1528 TPC16
1528 TPC17
1528 TPC18
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