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 capaci-
tor 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 drop-
out. 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 microproces-
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.
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.
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
s
s
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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
+
V
IN
=5V
DROPOUT VOLTAGE (V)
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
LT1528 • TA01
0
U
U
U
Dropout Voltage
0.5
2.5
1.0
1.5
2.0
OUTPUT CURRENT (mA)
3.0
LT1528 • TA02
1
LT1528
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.
PACKAGE/ORDER INFORMATION
FRONT VIEW
TAB
IS
GND
5
4
3
2
1
V
IN
SHDN
GND
SENSE
OUTPUT
ORDER PART
NUMBER
LT1528CQ
Q PACKAGE
5-LEAD PLASTIC DD PAK
T
JMAX
= 125°C,
θ
JA
= 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)
CONDITIONS
V
IN
= 3.8V, I
OUT
= 1mA, T
J
= 25°C
4.3V < V
IN
< 15V, 1mA < I
OUT
< 3A
∆V
IN
= 3.8V to 15V, I
OUT
= 1mA
∆I
LOAD
= 1mA to 3A, V
IN
= 4.3V,T
J
= 25°C
∆I
LOAD
= 1mA to 3A, V
IN
= 4.3V
I
LOAD
= 10mA, T
J
= 25°C
I
LOAD
= 10mA
I
LOAD
= 100mA, T
J
= 25°C
I
LOAD
= 100mA
I
LOAD
= 700mA, T
J
= 25°C
I
LOAD
= 700mA
I
LOAD
= 1.5A, T
J
= 25°C
I
LOAD
= 1.5A
I
LOAD
= 3A, T
J
= 25°C
I
LOAD
= 3A
q
q
q
q
2
U
U
W
W W
U
W
TAB IS
GND
FRONT VIEW
5
4
3
2
1
T PACKAGE
5-LEAD PLASTIC TO-220
V
IN
SHDN
GND
SENSE
OUTPUT
ORDER PART
NUMBER
LT1528CT
T
JMAX
= 125°C,
θ
JA
= 50°C/ W
MIN
3.250
3.200
TYP
3.300
3.300
1.5
12
15
70
150
q
280
q
390
q
570
q
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)
CONDITIONS
I
LOAD
= 0mA, T
J
= 25°C
I
LOAD
= 0mA, T
J
= 125°C (Note 6)
I
LOAD
= 100mA, T
J
= 25°C
I
LOAD
= 100mA, T
J
= 125°C (Note 6)
I
LOAD
= 300mA, T
J
= 25°C
I
LOAD
= 300mA, T
J
= 125°C (Note 6)
I
LOAD
= 700mA, T
J
= 25°C
I
LOAD
= 700mA, T
J
= 125°C (Note 6)
I
LOAD
= 1.5A
I
LOAD
= 3A
T
J
= 25°C
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, T
J
= 25°C
V
IN
= 4.3V,
∆V
OUT
= – 0.1V
V
IN
= – 15V, V
OUT
= 0V
V
OUT
= 3.3V, V
IN
= 0V
MIN
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
4.5
4.0
120
1.0
250
MAX
750
2.5
4.0
12.0
40
140
250
2.80
100
220
UNITS
µA
mA
mA
mA
mA
mA
mA
mA
mA
mA
µA
V
V
µA
µA
dB
A
A
mA
µA
q
q
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)
90
q
q
q
q
0.25
50
q
q
3.2
The
q
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.
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: (V
IN
– V
DROPOUT
).
Note 5:
Ground 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 Ground pin current. The Ground
pin current will decrease slightly at higher input voltages.
Note 6:
Ground 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 7:
Sense pin current flows into the Sense pin.
Note 8:
Shutdown pin current at V
SHDN
= 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.
3
LT1528
TYPICAL PERFORMANCE CHARACTERISTICS
Guaranteed Dropout Voltage
1.0
0.9
0.8
DROPOUT VOLTAGE (V)
0.8
= TEST POINTS
DROPOUT VOLTAGE (V)
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
0.5
T
J
≤
125°C
0.6
0.5
I
LOAD
= 3A
QUIESCENT CURRENT (mA)
T
J
≤
25°C
1.5
2.0
1.0
OUTPUT CURRENT (A)
Quiescent Current
2000
1750
QUIESCENT CURRENT (µA)
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
50
75
25
TEMPERATURE (°C)
100
125
GROUND PIN CURRENT (mA)
Ground Pin Current
100
90
T
J
= 25°C
V
OUT
= V
SENSE
*FOR V
OUT
= 3.3V
100
90
SHUTDOWN PIN THRESHOLD (V)
GROUND PIN CURRENT (mA)
GROUND PIN CURRENT (mA)
80
70
60
50
40
30
20
10
0
0
1
2
R
L
= 2.2Ω
I
LOAD
= 1.5A*
R
L
= 1.1Ω
I
LOAD
= 3A*
R
L
= 4.7Ω
I
LOAD
= 700mA*
3 4 5 6 7
INPUT VOLTAGE (V)
4
U W
2.5
LT1528 • TPC01
Dropout Voltage
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
Quiescent Current
V
IN
= 4.3V
R
L
=
∞
0.7
I
LOAD
= 1.5A
0.4
0.3
0.2
0.1
I
LOAD
= 300mA
I
LOAD
= 10mA
–25
0
75
50
25
TEMPERATURE (°C)
100
125
I
LOAD
= 700mA
V
SHDN
= OPEN
V
SHDN
= 0V
–25
0
75
50
25
TEMPERATURE (°C)
100
125
3.0
0
–50
0
–50
LT1528 • TPC02
LT1528 • TPC03
Sense Pin Voltage
3.400
I
LOAD
= 0
R
LOAD
=
∞
7
Ground Pin Current
6
5
4
3
2
1
R
L
= 330Ω: I
LOAD
= 10mA*
0
0
1
2
3
7
4 5 6
INPUT VOLTAGE (V)
8
9
10
R
L
= 11Ω
I
LOAD
= 300mA*
R
L
= 33Ω
I
LOAD
= 100mA*
T
J
= 25°C
V
OUT
= V
SENSE
*FOR V
OUT
= 3.3V
R
L
= 6.6Ω
I
LOAD
= 500mA*
3.375
I
LOAD
= 1mA
LT1528 • TPC04
LT1528 • TPC05
LT1528 • TPC06
Ground Pin Current
2.0
V
IN
= 3.3V
DEVICE IS OPERATING
IN DROPOUT
Shutdown Pin Threshold
(On-to-Off)
1.8
T
J
= 125°C
I
LOAD
= 1mA
80
70
60
50
40
30
20
10
0
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
T
J
= 25°C
T
J
= –50°C
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
LT1528 • TPC07
LT1528 • TPC08
LT1528 • TPC09
LT1528
TYPICAL PERFORMANCE CHARACTERISTICS
Shutdown Pin Threshold
(Off-to-On)
2.0
1.8
SHUTDOWN PIN THRESHOLD (V)
SHUTDOWN 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
SHUTDOWN PIN INPUT CURRENT (mA)
I
LOAD
= 1mA
50
25
0
75
TEMPERATURE (°C)
Sense Pin Current
200
175
CURRENT FLOWS INTO SENSE PIN
OUTPUT 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
SHORT-CIRCUIT CURRENT (A)
SENSE PIN CURRENT (µA)
Current Limit
6
5
OUTPUT CURRENT (µA)
SHORT-CIRCUIT CURRENT (A)
RIPPLE REJECITON (dB)
4
3
2
1
V
IN
= 7V
V
OUT
= 0V
50
25
75
0
TEMPERATURE (°C)
100
125
0
–50 –25
U W
100
LT1528 • TPC10
LT1528 • TPC13
Shutdown Pin Current
100
90
V
SHDN
= 0V
Shutdown Pin Input Current
25
20
15
10
5
125
0
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
0
0
1
7
3
8
2
5
6
4
SHUTDOWN PIN VOLTAGE (V)
9
LT1528 • TPC11
LT1528 • TPC12
Reverse Output Current
300
250
V
IN
= 0V
V
OUT
= V
SENSE
6
Current Limit
V
OUT
= 0V
5
4
3
2
1
0
50
25
75
0
TEMPERATURE (°C)
100
125
0
1
4
3
5
2
INPUT VOLTAGE (V)
6
7
LT1528 • TPC14
LT1528 • TPC15
Reverse Output Current
1000
900
800
700
600
500
400
300
200
100
0
0
1
2
3 4 5 6 7 8
OUTPUT VOLTAGE (V)
9
10
T
J
= 25°C, V
IN
= 0V
V
OUT
=V
SENSE
CURRENT FLOWS
INTO DEVICE
70
68
66
64
62
60
58
Ripple Rejection
V
IN(AVG)
= 4.3V
V
RIPPLE
= 0.5V
P-P
AT f = 120Hz
I
L
= 1.5A
56
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
LT1528 • TPC16
LT1528 • TPC17
LT1528
• TPC18
5
FPGA/CPLD
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