LINER LT1521IST-3

LT1521/LT1521-3
LT1521-3.3/LT1521-5
300mA Low Dropout
Regulators with Micropower
Quiescent Current and Shutdown
U
DESCRIPTION
FEATURES
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The LT ®1521/LT1521-3/LT1521-3.3/LT1521-5 are low
dropout regulators with micropower quiescent current
and shutdown. These devices are capable of supplying
300mA of output current with a dropout voltage of 0.5V.
Designed for use in battery-powered systems, the low
quiescent current, 12µA operating and 6µA in
shutdown, makes them an ideal choice. The quiescent
current is well controlled; it does not rise in dropout as it
does with many other low dropout PNP regulators.
Dropout Voltage: 0.5V
Output Current: 300mA
Quiescent Current: 12µA
No Protection Diodes Needed
Adjustable Output from 3.8V to 20V
Fixed Output Voltages: 3V, 3.3V, 5V
Controlled Quiescent Current in Dropout
Shutdown IQ = 6µA
Reverse Battery Protection
No Reverse Current
Thermal Limiting
Other features of the LT1521/LT1521-3/LT1521-3.3/
LT1521-5 include the ability to operate with very small
output capacitors. They are stable with only 1.5µF on the
output while most older devices require between 10µF and
100µF for stability. Small ceramic capacitors can be used,
enhancing manufacturability. Also, the input may be connected to voltages lower than the output voltage, including
negative voltages, without reverse current flow from output to input. This makes the LT1521 series ideal for backup
power situations where the output is held high and the
input is low or reversed. Under these conditions only 5µA
will flow from the output pin to ground.
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APPLICATIONS
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Low Current Regulator
Regulator for Battery-Powered Systems
Post Regulator for Switching Supplies
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATION
Dropout Voltage
5V Battery-Powered Supply with Shutdown
8
IN
OUT
0.6
5V
300mA
1
+
1µF
5
SHDN
SENSE
0.5
1.5µF
LT1521-5
2
GND
3
VSHDN (PIN 5) OUTPUT
<0.25
OFF
>2.80
ON
NC
ON
DROPOUT VOLTAGE (V)
6V
0.4
0.3
0.2
0.1
LT1521 • TA01
0
0
50
100
150
200
250
OUTPUT CURRENT (mA)
300
LT1521 • TA02
1
LT1521/LT1521-3
LT1521-3.3/LT1521-5
U
W W
W
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Voltage ...................................................... ± 20V*
Output Pin Reverse Current .................................. 10mA
Adjust 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 (Note 2)
Commercial ........................................... 0°C to 125°C
Industrial ......................................... – 40°C to 125°C
Lead Temperature (Soldering, 10 sec).................. 300°C
*For applications requiring input voltage ratings greater than 20V, contact
the factory.
U
W
U
PACKAGE/ORDER INFORMATION
TOP VIEW
TOP VIEW
OUT
SENSE/ADJ*
NC
GND
8
7
6
5
1
2
3
4
IN
NC
NC
SHDN
MS8 PACKAGE
8-LEAD PLASTIC MSOP
*PIN 2 = SENSE FOR LT1521-3/
LT1521-3.3/LT1521-5
PIN 2 = ADJ FOR LT1521
8
IN
SENSE/ADJ* 2
7
GND
GND 3
6
GND
NC 4
5
SHDN
S8 PACKAGE
8-LEAD PLASTIC SO
TAB IS
GND
1
OUT
2
GND
3
IN
ST PACKAGE
3-LEAD PLASTIC SOT-223
*PIN 2 = SENSE FOR LT1521-3/LT1521-3.3/LT1521-5
= ADJ FOR LT1521
TJMAX = 125°C, θJA = 70°C/ W
SEE THE APPLICATIONS INFORMATION SECTION
TJMAX = 125 °C, θJA = 50°C/ W
SEE THE APPLICATIONS INFORMATION SECTION
ORDER PART NUMBER
ORDER PART NUMBER
ORDER PART NUMBER
LT1521CMS8
LT1521CMS8-3
LT1521CMS8-3.3
LT1521CMS8-5
LT1521CS8
LT1521CS8-3
LT1521CS8-3.3
LT1521CS8-5
LT1521IS8
LT1521IS8-3
LT1521IS8-3.3
LT1521IS8-5
LT1521CST-3
LT1521CST-3.3
LT1521CST-5
LT1521IST-3
LT1521IST-3.3
LT1521IST-5
TJMAX = 125°C, θJA = 125°C/ W
MS8 PART MARKING
LTEZ
LTFB
LTDU
LTFA
Consult factory for Military grade parts.
2
FRONT VIEW
OUT 1
S8 PART MARKING
1521
15213
152133
15215
1521I
1521I3
1521I33
1521I5
ST PART MARKING
15213
152133
15215
1521I3
1521I33
1521I5
LT1521/LT1521-3
LT1521-3.3/LT1521-5
ELECTRICAL CHARACTERISTICS
PARAMETER
Regulated Output Voltage
(Note 4)
Line Regulation
Load Regulation
Dropout Voltage (Note 6)
Ground Pin Current (Note 7)
Adjust Pin Bias Current (Notes 5, 8)
Shutdown Threshold
Shutdown Pin Current (Note 9)
Quiescent Current in Shutdown (Note 10)
Ripple Rejection
Current Limit
CONDITIONS
LT1521-3
VIN = 3.5V, IOUT = 1mA, TJ = 25°C
4V < VIN < 20V, 1mA < IOUT < 300mA
LT1521-3.3
VIN = 3.8V, IOUT = 1mA, TJ = 25°C
4.3V < VIN < 20V, 1mA < IOUT < 300mA
LT1521-5
VIN = 5.5V, IOUT = 1mA, TJ = 25°C
6V < VIN < 20V, 1mA < IOUT < 300mA
LT1521 (Note 5) VIN = 4.3V, IOUT = 1mA, TJ = 25°C
4.8V < VIN < 20V, 1mA < IOUT < 300mA
LT1521-3
∆VIN = 4.5 to 20V, IOUT = 1mA
LT1521-3.3
∆VIN = 4.8 to 20V, IOUT = 1mA
LT1521-5
∆VIN = 5.5 to 20V, IOUT = 1mA
LT1521 (Note 5) ∆VIN = 4.3 to 20V, IOUT = 1mA
LT1521-3
∆ILOAD = 1mA to 300mA, TJ ≤ 25°C
LT1521-3.3
∆ILOAD = 1mA to 300mA, TJ ≤ 25°C
LT1521-5
∆ILOAD = 1mA to 300mA, TJ ≤ 25°C
LT1521 (Note 5) ∆ILOAD = 1mA to 300mA, TJ ≤ 25°C
LT1521-3
∆ILOAD = 1mA to 300mA, TJ >25°C
LT1521-3.3
∆ILOAD = 1mA to 300mA, TJ > 25°C
LT1521-5
∆ILOAD = 1mA to 300mA, TJ > 25°C
LT1521 (Note 5) ∆ILOAD = 1mA to 300mA, TJ > 25°C
ILOAD = 1mA, TJ = 25°C
ILOAD = 1mA
ILOAD = 50mA, TJ = 25°C
ILOAD = 50mA
ILOAD = 100mA, TJ = 25°C
ILOAD = 100mA
ILOAD = 150mA, TJ = 25°C
ILOAD = 150mA
ILOAD = 300mA, TJ = 25°C
ILOAD = 300mA
ILOAD = 0mA
ILOAD = 1mA
ILOAD = 10mA
ILOAD = 50mA
ILOAD = 100mA
ILOAD = 150mA
ILOAD = 300mA
TJ = 25°C
VOUT = Off to On
VOUT = On to Off
VSHDN = 0V
VIN = VOUT (NOMINAL) + 1V, VSHDN = 0V
VIN – VOUT = 1V(Avg), VRIPPLE = 0.5VP–P,
fRIPPLE = 120Hz, ILOAD = 150mA
VIN – VOUT = 7V, TJ = 25°C
VIN = VOUT (NOMINAL) + 1.5V, ∆VOUT = – 0.1V
●
●
●
●
MIN
2.950
2.900
3.250
3.200
4.925
4.850
3.695
3.640
●
●
●
●
TYP
3.000
3.000
3.300
3.300
5.000
5.000
3.750
3.750
1.5
1.5
1.5
1.5
– 20
– 20
– 25
– 20
– 20
– 20
– 25
– 20
130
●
290
●
350
●
400
●
500
●
50
12
65
300
0.8
1.4
2.2
6.5
50
1.20
0.75
2.0
6
58
320
400
400
●
●
●
●
●
●
●
●
●
0.25
●
●
●
MAX
3.050
3.100
3.350
3.400
5.075
5.150
3.805
3.860
20
20
20
20
– 30
– 30
– 45
– 30
– 55
– 55
– 75
– 55
170
250
350
450
420
550
470
600
600
750
20
100
450
1.5
2.5
4.0
12.0
100
2.80
5.0
12
800
UNITS
V
V
V
V
V
V
V
V
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
µA
µA
µA
mA
mA
mA
mA
nA
V
V
µA
µA
dB
mA
mA
3
LT1521/LT1521-3
LT1521-3.3/LT1521-5
ELECTRICAL CHARACTERISTICS
PARAMETER
Input Reverse Leakage Current
Reverse Output Current (Note 11)
CONDITIONS
VIN = – 20V, VOUT = 0V
LT1521-3
VOUT = 3V, VIN < 3V, TJ = 25°C
LT1521-3.3
VOUT = 3.3V, VIN < 3.3V, TJ = 25°C
LT1521-5
VOUT = 5V, VIN < 5V, TJ = 25°C
LT1521 (Note 5) VOUT = 3.8V, VIN < 3.75V, TJ = 25°C
The ● denotes specifications which apply over the full operating
temperature range.
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: 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 limited to less
than 5mA.
Note 3: For junction temperatures greater than 110°C, a minimum load of
1mA is recommended. For TJ > 110°C and IOUT < 1mA, output voltage
may increase by 1%.
Note 4: 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 range must be
limited. When operating at maximum output current, the input voltage
range must be limited.
MIN
TYP
●
5
5
5
5
MAX
1.0
10
10
10
10
UNITS
mA
µA
µA
µA
µA
Note 5: The LT1521 (adjustable version) is tested and specified with the
adjust pin connected to the output pin.
Note 6: 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 7: Ground pin current is tested with VIN = VOUT (nominal) and a
current source load. This means 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 8: Adjust pin bias current flows into the adjust pin.
Note 9: Shutdown pin current at VSHDN = 0V flows out of the shutdown
pin.
Note 10: Quiescent current in shutdown is equal to the total sum of the
shutdown pin current (2µA) and the ground pin current (4µA).
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 ground pin.
U W
TYPICAL PERFORMANCE CHARACTERISTICS
Guaranteed Dropout Voltage
Dropout Voltage
Quiescent Current
0.8
0.8
15.0
= TEST POINTS
0.7
0.6
0.5
TJ ≤ 25°C
0.4
0.3
0.2
0.1
0
0
50
100
200
250
150
OUTPUT CURRENT (mA)
300
LT1521 • TPC01
4
0.5
ILOAD = 150mA
ILOAD = 100mA
0.4
0.3
0.2
ILOAD = 50mA
0.1
ILOAD = 1mA
0
–50 –25
VSHDN = OPEN
12.5
ILOAD = 300mA
0.6
0
50
75
25
TEMPERATURE (°C)
QUIESCENT CURRENT (µA)
TJ ≤ 125°C
DROPOUT VOLTAGE (V)
DROPOUT VOLTAGE (V)
0.7
10.0
7.5
2.5
100
125
LT1521 • TPC02
VSHDN = 0V
5.0
VIN = 6V
RL = ∞
ILOAD = 0
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
LT1521 • TPC03
LT1521/LT1521-3
LT1521-3.3/LT1521-5
U W
TYPICAL PERFORMANCE CHARACTERISTICS
LT1521-3
Output Voltage
LT1521-3.3
Output Voltage
3.38
3.36
3.04
3.34
OUTPUT VOLTAGE (V)
3.06
3.02
3.00
2.98
2.96
5.08
IOUT = 1mA
5.06
OUTPUT VOLTAGE (V)
3.08
3.32
3.30
3.28
3.26
3.24
2.94
2.92
–50
–25
0
50
75
25
TEMPERATURE (°C)
100
3.22
–50
125
75
50
25
TEMPERATURE (°C)
–25
3.75
3.73
3.71
30
25
20
15
0
100
VSHDN = OPEN
10
3.67
–50
125
VSHDN = 0V
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
25
20
15
10
8
9
0
10
QUIESCENT CURRENT (µA)
35
30
25
20
VSHDN = OPEN
10
VSHDN = 0V
8
9
10
LT1521 • TPC10
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
1000
40
35
30
25
20
15
TJ = 25°C
*FOR VOUT = 3V
900
VSHDN = OPEN
10
VSHDN = 0V
800
RLOAD = 60Ω
ILOAD = 50mA*
700
600
RLOAD = 120Ω
ILOAD = 25mA*
500
400
RLOAD = 300Ω
ILOAD = 10mA*
300
200
RLOAD = 3k
ILOAD = 1mA*
100
0
3 4 5 6 7
INPUT VOLTAGE (V)
1
LT1521 • TPC09
TJ = 25°C
RL = ∞
5
0
0
LT1521-3
Ground Pin Current
45
40
2
30
5
50
TJ = 25°C
RL = ∞
45
125
35
LT1521
Quiescent Current
50
1
40
LT1521 • TPC08
LT1521 • TPC07
LT1521-5
Quiescent Current
100
TJ = 25°C
RL = ∞
45
35
5
50
75
25
TEMPERATURE (°C)
50
75
25
TEMPERATURE (°C)
50
TJ = 25°C
RL = ∞
40
3.69
0
0
LT1521 • TPC06
QUIESCENT CURRENT (µA)
QUIESCENT CURRENT (µA)
OUTPUT VOLTAGE (V)
3.77
0
4.96
LT1521-3.3
Quiescent Current
45
3.79
5
4.98
4.92
–50 –25
125
50
ILOAD = 1mA
15
5.00
LT1521-3
Quiescent Current
3.83
–25
5.02
LT1521 • TPC05
LT1521
Adjust Pin Voltage
QUIESCENT CURRENT (µA)
100
0
LT1521 • TPC04
3.81
5.04
4.94
GROUND PIN CURRENT (µA)
OUTPUT VOLTAGE (V)
LT1521-5
Output Voltage
0
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
LT1521 • TPC11
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
LT1521 • TPC12
5
LT1521/LT1521-3
LT1521-3.3/LT1521-5
U W
TYPICAL PERFORMANCE CHARACTERISTICS
LT1521-3
Ground Pin Current
LT1521-3.3
Ground Pin Current
8
8
1000
GROUND PIN CURRENT (µA)
6
RLOAD = 10Ω
ILOAD = 300mA*
5
4
RLOAD = 20Ω
ILOAD = 150mA*
3
2
RLOAD = 30Ω
ILOAD = 100mA*
1
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
800
600
RLOAD = 132Ω
ILOAD = 25mA*
500
400
RLOAD = 330Ω
ILOAD = 10mA*
300
200
0
10
RLOAD = 3.3k
ILOAD = 1mA*
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
RLOAD = 200Ω
ILOAD = 25mA*
RLOAD = 500Ω
ILOAD = 10mA*
300
200
RLOAD = 5k
ILOAD = 1mA*
100
5
4
RLOAD = 33.3Ω
ILOAD = 150mA*
3
2
1
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
GROUND PIN CURRENT (mA)
4
RLOAD = 25Ω
ILOAD =150mA*
3
2
1
RLOAD = 37.5Ω
ILOAD =100mA*
0
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
800
10
LT1521 • TPC19
RLOAD = 75Ω
ILOAD = 50mA*
700
600
RLOAD = 150Ω
ILOAD = 25mA*
500
400
RLOAD = 375Ω
ILOAD = 10mA*
300
200
0
8
9
10
RLOAD = 3.8k
ILOAD = 1mA*
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
LT1521 • TPC18
Shutdown Pin Threshold
(On-to-Off)
8
7
6
5
TJ = 25°C
4
1.8
TJ = 125°C
TJ = 55°C
3
2
ILOAD = 1mA
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
1
9
10
9
2.0
VIN = 3V (LT1521-3)
VIN = 3.3V (LT1521-3.3)
VIN = 5V (LT1521-5)
VIN = 3.75V (LT1521)
DEVICE IS OPERATING
IN DROPOUT
9
5
8
VOUT = VADJ
*FOR VOUT = 3.75V
100
10
RLOAD = 12.5Ω
ILOAD =300mA*
6
3 4 5 6 7
INPUT VOLTAGE (V)
LT1521 • TPC17
8
7
2
TJ = 25°C
900
Ground Pin Current
TJ = 25°C
VOUT = VADJ
*FOR VOUT = 3.75V
1
LT1521 • TPC15
RLOAD = 50Ω
ILOAD = 100mA*
0
0
RLOAD = 33Ω
ILOAD = 100mA*
LT1521
Ground Pin Current
6
LT1521
Ground Pin Current
GROUND PIN CURRENT (mA)
10
RLOAD = 16.7Ω
ILOAD = 300mA*
LT1521 • TPC16
6
9
SHUTDOWN PIN THRESHOLD (V)
400
0
8
GROUND PIN CURRENT (µA)
GROUND PIN CURRENT (mA)
GROUND PIN CURRENT (µA)
700
500
2
1000
TJ = 25°C
*FOR VOUT = 5V
7
RLOAD = 100Ω
ILOAD = 50mA*
RLOAD = 22Ω
ILOAD = 150mA*
3
0
8
600
4
LT1521-5
Ground Pin Current
1000
800
RLOAD = 11Ω
ILOAD = 300mA*
5
LT1521 • TPC14
LT1521-5
Ground Pin Current
TJ = 25°C
*FOR VOUT = 5V
6
1
LT1521 • TPC13
900
TJ = 25°C
*FOR VOUT = 3.3V
7
RLOAD = 66Ω
ILOAD = 50mA*
700
100
0
0
TJ = 25°C
*FOR VOUT = 3.3V
900
GROUND PIN CURRENT (mA)
TJ = 25°C
*FOR VOUT = 3V
7
GROUND PIN CURRENT (mA)
LT1521-3.3
Ground Pin Current
0
0
50
250
150
200
100
OUTPUT CURRENT (mA)
300
LT1521 • TPC20
0
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
LT1521 • TPC21
LT1521/LT1521-3
LT1521-3.3/LT1521-5
U W
TYPICAL PERFORMANCE CHARACTERISTICS
Shutdown Pin Threshold
(Off-to-On)
3.0
25
SHUTDOWN PIN CURRENT (µA)
ILOAD = 300mA
1.6
1.4
1.2
ILOAD = 1mA
1.0
0.8
0.6
0.4
SHUTDOWN PIN INPUT CURRENT (mA)
VSHDN = 0V
1.8
SHUTDOWN PIN THRESHOLD (V)
Shutdown Pin Input Current
Shutdown Pin Current
2.0
2.5
2.0
1.5
1.0
0.5
0.2
0
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
0
–50 –25
125
50
25
75
0
TEMPERATURE (°C)
45
150
125
100
75
50
25
TJ = 25°C
VIN = 0V
CURRENT FLOWS
INTO OUTPUT PIN
VOUT = VSENSE
(LT1521-3/LT1521-3.3
LT1521-5)
VOUT = VADJ (LT1521)
40
35
30
25
100
15
Current Limit
LT1521-5
1
2
3 4 5 6 7 8
OUTPUT VOLTAGE (V)
9
0.2
0.1
0.1
125
LT1521 • TPC28
1
4
3
5
2
INPUT VOLTAGE (V)
6
5
6
7
Ripple Rejection
66
VIN = 0V
VOUT = 3V (LT1521-3)
VOUT = 3.3V (LT1521-3.3)
VOUT = 5V (LT1521-5)
VOUT = 3.75V (LT1521)
64
4
3
2
0
–50 –25
VIN = VOUT (NOMINAL) + 1V + 0.5VP-P
RIPPLE AT f = 120Hz
ILOAD = 150mA
62
60
58
56
54
1
100
0
LT1521 • TPC27
RIPPLE REJECITON (dB)
7
0.2
50
25
75
0
TEMPERATURE (°C)
0.3
Reverse Output Current
VIN = 7V
VOUT = 0V
0
–50 –25
0.4
0
10
8
OUTPUT PIN CURRENT (µA)
SHORT-CIRCUIT CURRENT (A)
VOUT = 0V
LT1521-3
0
9
0.5
LT1521 • TPC26
0.6
0.3
7
3
8
2
5
6
4
SHUTDOWN PIN VOLTAGE (V)
Current Limit
10
0
125
0.4
1
LT1521 • TPC24
LT1521
LT1521 • TPC25
0.5
0
0.6
LT1521-3.3
20
5
75
50
25
TEMPERATURE (°C)
5
0
125
SHORT-CIRCUIT CURRENT (A)
175
0
10
Reverse Output Current
50
REVERSE OUTPUT CURRENT (µA)
ADJUST PIN BIAS CURRENT (nA)
Adjust Pin Bias Current
200
–25
15
LT1521 • TPC23
LT1521 • TPC22
0
–50
100
20
75
50
25
TEMPERATURE (°C)
0
100
125
LT1521 • TPC29
52
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
LT1521 • TPC30
7
LT1521/LT1521-3
LT1521-3.3/LT1521-5
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TYPICAL PERFORMANCE CHARACTERISTICS
Load Regulation
Ripple Rejection
0
100
ILOAD = 150mA
VIN = 6V + 50mVRMS RIPPLE
90
–5
LOAD REGULATION (mV)
RIPPLE REJECTION (dB)
80
70
60
COUT = 33µF
SOLID TANTALUM
50
40
30
20
COUT = 3.3µF
SOLID TANTALUM
10
0
10
100
1k
10k
FREQUENCY (Hz)
100k
∆ILOAD = 1mA TO 300mA
–10
LT1521-5
LT1521-3
–15
LT1521*
–25
–30
–35
VIN = VOUT (NOMINAL + 1V)
*VADJ = VOUT
–40
–50 –25
1M
LT1521-3.3
–20
0
50
75
25
TEMPERATURE (°C)
LT1521 • TPC31
OUTPUT VOLTAGE
DEVIATION (V)
OUTPUT VOLTAGE
DEVIATION (V)
LT1521-5
Transient Response
VIN = 6V
CIN = 0.1µF
COUT = 1.5µF
0.1
0
–0.1
–0.2
0.2
0.1
VIN = 6V
CIN = 0.1µF
COUT = 33µF
0
–0.1
–0.2
LOAD CURRENT
(mA)
LOAD CURRENT
(mA)
125
LT1521 • TPC32
LT1521-5
Transient Response
0.2
100
150
100
50
0
50 100 150 200 250 300 350 400 450 500
TIME (µs)
LT1521 • TPC33
300
200
100
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
TIME (ms)
LT1521 • TPC34
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PIN FUNCTIONS
OUT (Pin 1): The output pin supplies power to the load. A
minimum output capacitor of 1.5µF is required to prevent
oscillations, but larger values of output capacitor will be
necessary to deal with larger load transients. See the
Applications Information section for more on output
capacitance and reverse output characteristics.
SENSE (Pin 2): For fixed voltage versions of the LT1521
(LT1521-3, LT1521-3.3, LT1521-5), 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
8
the output pin of 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 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 5µA
at the nominal regulated output voltage. This pin is internally clamped to – 0.6V (one VBE).
LT1521/LT1521-3
LT1521-3.3/LT1521-5
U
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PIN FUNCTIONS
5
+
VIN
IN
OUT
1
RP
LT1521
4
SHDN
SENSE
+
2
LOAD
GND
3
RP
LT1521 • F01
Figure 1. Kelvin Sense Connection
ADJ (Pin 2): For adjustable LT1521, the adjust pin is the
input to the error amplifier. This pin is internally clamped
to 6V and – 0.6V (one VBE). It has a bias current of 50nA
which flows into the pin. See Adjust Pin Bias Current vs
Temperature in the Typical Performance Characteristics
section. The adjust pin reference voltage is 3.75V referenced to ground. The output voltage range that can be
produced by this device is 3.75V to 20V.
SHDN (Pin 5): The shutdown 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 pulled low. The shutdown pin
current with the pin pulled to ground will be 1.7µA. 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 the shutdown pin input current as a
function of voltage appears in the Typical Performance
Characteristics. 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.
IN (Pin 8): 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. In general, the output impedance of
battery rises with frequency, so it is advisable to include a
bypass capacitor in battery-powered circuits. A bypass
capacitor in the range of 1µF to 10µF is sufficient. The
LT1521 is designed to withstand reverse voltages on the
input pin with respect to ground and the output pin. In the
case of reversed input, which can happen if a battery is
plugged in backwards, the LT1521 will act as if there is a
diode in series with its input. There will be no reverse
current flow into the LT1521 and no reverse voltage will
appear at the load. The device will protect both itself and
the load.
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APPLICATIONS INFORMATION
The LT1521 is a 300mA low dropout regulator with
micropower quiescent current and shutdown. The device
is capable of supplying 300mA at a dropout of 0.5V and
operates with very low quiescent current (12µA). In shutdown, the quiescent current drops to only 6µA. In addition
to the low quiescent current, the LT1521 incorporates
several protection features which make it ideal for use in
battery-powered systems. The device is protected against
both reverse input voltages and reverse output voltages.
In battery backup applications where the output can be
held up by a backup battery when the input is pulled to
ground, the LT1521 acts like it has a diode in series with
its output and prevents reverse current flow.
Adjustable Operation
The adjustable version of the LT1521 has an output
voltage range of 3.75V to 20V. 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 adjust pin at 3.75V. The current in R1 is then equal to
3.75V/R1. The current in R2 is equal to the sum of the
current in R1 and the adjust pin bias current. The adjust pin
bias current, 50nA at 25°C, flows through R2 into the
adjust pin. The output voltage can be calculated using the
formula in Figure 2. The value of R1 should be less than
400k to minimize errors in the output voltage caused by
the adjust pin bias current. Note that in shutdown the
9
LT1521/LT1521-3
LT1521-3.3/LT1521-5
U
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APPLICATIONS INFORMATION
IN
VOUT
OUT
+
VIN
R2
LT1521
SHDN
ADJ
GND
) )
R1
VOUT = 3.75V 1 + R2 + (IADJ + R2)
R1
VADJ = 3.75V
IADJ = 50nA AT 25°C
OUTPUT RANGE = 3.75V TO 20V
LT1521 • F01
Figure 2. Adjustable Operation
output is turned off and the divider current will be zero.
Curves of Adjust Pin Voltage vs Temperature and Adjust
Pin Bias Current vs Temperature appear in the Typical
Performance Characteristics. The reference voltage at the
adjust pin has a positive temperature coefficient of approximately 15ppm/°C. The adjust pin bias current has a
negative temperature coefficient. These effects will tend to
cancel each other.
The adjustable device is specified with the adjust pin tied
to the output pin. This sets the output voltage to 3.75V.
Specifications for output voltages greater than 3.75V will
be proportional to the ratio of the desired output voltage
to 3.75V; (VOUT/3.75V). For example: load regulation for
an output current change of 1mA to 300mA is –20mV
typical at VOUT = 3.75V. At VOUT = 12V, load regulation
would be:
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 LT1521 series regulators have 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. Copper board stiffeners and plated
through-holes can also be used to spread the heat generated by power devices.
The following tables list thermal resistance for each package. Measured values of thermal resistance for several
different board sizes and copper areas are listed for each
package. All measurements were taken in still air on
3/32" FR-4 board with one ounce copper. All NC leads were
connected to the ground plane.
Table 1. MS8 Package
COPPER AREA
TOPSIDE**
BACKSIDE
BOARD AREA
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
2500mm2
2500mm2
2500mm2
110°C/W
1000mm2
2500mm2
2500mm2
115°C/W
Thermal Considerations
225mm2
2500mm2
2500mm2
120°C/W
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:
100mm2
2500mm2
2500mm2
130°C/W
(12V/3.75V)(– 20mV) = – 64mV
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)
* Pin 4 is ground. ** Device is mounted on topside.
Table 2. S8 Package*
COPPER AREA
TOPSIDE** BACKSIDE
THERMAL RESISTANCE
BOARD AREA (JUNCTION-TO-AMBIENT)
2500mm2
2500mm2
2500mm2
60°C/W
1000mm2
2500mm2
2500mm2
60°C/W
225mm2
2500mm2
2500mm2
68°C/W
100mm2
2500mm2
2500mm2
74°C/W
* Pins 3, 6, 7 are ground. ** Device is mounted on topside.
10
LT1521/LT1521-3
LT1521-3.3/LT1521-5
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APPLICATIONS INFORMATION
Table 3. SOT-223 Package
(Thermal Resistance Junction-to-Tab 20°C/W)
COPPER AREA
TOPSIDE*
BACKSIDE
BOARD AREA
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
2500mm2
2500mm2
2500mm2
50°C/W
1000mm2
2500mm2
2500mm2
50°C/W
225mm2
2500mm2
2500mm2
58°C/W
100mm2
2500mm2
2500mm2
64°C/W
1000mm2
1000mm2
1000mm2
57°C/W
2
60°C/W
1000mm
2
0
1000mm
is required to prevent oscillations. The LT1521 is a
micropower device and 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 current deltas. Bypass capacitors, used to decouple individual components powered by
the LT1521, will increase the effective value of the output
capacitor.
* Tab of device attached to topside copper.
Calculating Junction Temperature
Example: Given an output voltage of 3.3V, an input voltage
range of 4.5V to 7V, an output current range of 0mA to
150mA 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) = 150mA
VIN(MAX) = 7V
IGND at (IOUT = 150mA, VIN = 7V) = 2.1mA
So,
P = 150mA(7V – 3.3V) + (2.1mA)(7V) = 0.57W
If we use a SOT-223 package, then the thermal resistance
will be in the range of 50°C/W to 65°C/W depending on the
copper area. So the junction temperature rise above
ambient will be approximately equal to:
0.57W(60°C/W) = 34.2°C
The maximum junction temperature will then be equal to the
maximum junction temperature rise above ambient plus the
maximum ambient temperature or:
TJMAX = 50°C + 34.2°C = 84.2°C
Output Capacitance and Transient Performance
The LT1521 is designed to be stable with a wide range of
output capacitors. A minimum output capacitor of 1.5µF
Protection Features
The LT1521 incorporates several protection features which
make it ideal for use in battery-powered circuits. In
addition to the normal protection features associated with
monolithic regulators, such as current limiting and thermal limiting, the device is protected against reverse input
voltages, reverse output voltages and reverse voltages
from output to input.
Current limit protection and thermal overload protection
are intended to protect the device against current overload
conditions at the output of the device. For normal operation, the junction temperatures should not exceed 125°C.
The input of the device will withstand reverse voltages of
20V. 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. This provides protection against
batteries that can be plugged in backward.
For fixed voltage versions of the device, the output can be
pulled below ground without damaging the device. If the
input is left open circuit or grounded, the output can be
pulled below ground by 20V. The output will act like an
open circuit, no current will flow out of the pin. If the input
is powered by voltage source, the output will source the
short-circuit current of the device and will protect itself by
thermal limiting. For the adjustable version of the device,
the output pin is internally clamped at one diode drop
below ground. Reverse current for the adjustable device
must be limited to 5mA.
11
LT1521/LT1521-3
LT1521-3.3/LT1521-5
U
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APPLICATIONS INFORMATION
In circuits where a backup battery is required, several
different input/output conditions can occur. 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 battery-powered circuits
incorporate some form of power management. The following information will help optimize battery life. Table 4
summarizes the following 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 LT1521 unconnected when the output is held high.
This can happen when the LT1521 is powered from a
TJ = 25°C
VIN = 0V
CURRENT FLOWS
INTO OUTPUT PIN
VOUT = VSENSE
(LT1521-3/LT1521-3.3
LT1521-5)
VOUT = VADJ (LT1521)
45
40
35
30
25
5
LT1521
15
LT1521-3
10
LT1521-3.3
3
2
LT1521-3
LT1521-5
1
LT1521-5
5
0
VOUT = 3V (LT1521-3)
VOUT = 3.3V (LT1521-3.3)
VOUT = 5V (LT1521-5)
4
LT1521-3.3
20
When the input of the LT1521 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 LT1521 is connected to a
discharged (low voltage) battery and the output is held up
by either a backup battery or by second regulator circuit.
When the input pin is forced below the output 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.
INPUT CURRENT (µA)
REVERSE OUTPUT CURRENT (µA)
50
rectified AC source. If the AC source is removed, then the
input of the LT1521 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.
0
1
2
3 4 5 6 7 8
OUTPUT VOLTAGE (V)
9
10
0
0
1
3
2
INPUT VOLTAGE (V)
LT1521 • F03
Figure 3. Reverse Output Current
12
4
5
LT1521 • F04
Figure 4. Input Current
LT1521/LT1521-3
LT1521-3.3/LT1521-5
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APPLICATIONS INFORMATION
Table 4. Fault Conditions
INPUT PIN
SHDN PIN
OUTPUT/SENSE PINS
< VOUT (Nominal)
Open (High)
Forced to VOUT (Nominal)
Reverse Output Current ≈ 5µA (See Figure 3)
Input Current ≈ 1µA (See Figure 4)
< VOUT (Nominal)
Grounded
Forced to VOUT (Nominal)
Reverse Output Current ≈ 5µA (See Figure 3)
Input Current ≈ 1µA (See Figure 4)
Open
Open (High)
> 1V
Reverse Output Current ≈ 5µA (See Figure 3)
Open
Grounded
> 1V
Reverse Output Current ≈ 5µA (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
– 20V < VIN < 20V
Grounded
≤ 0V
Output Current = 0
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PACKAGE DESCRIPTION
RESULTING CONDITIONS
Dimensions in inches (millimeters) unless otherwise noted.
MS8 Package
8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
0.118 ± 0.004*
(3.00 ± 0.102)
8
7 6
5
0.118 ± 0.004**
(3.00 ± 0.102)
0.192 ± 0.004
(4.88 ± 0.10)
1
0.040 ± 0.006
(1.02 ± 0.15)
0.007
(0.18)
2 3
4
0.034 ± 0.004
(0.86 ± 0.102)
0° – 6° TYP
0.021 ± 0.006
(0.53 ± 0.015)
SEATING
PLANE 0.012
(0.30)
0.0256
REF
(0.65)
TYP
0.006 ± 0.004
(0.15 ± 0.102)
MSOP (MS8) 1197
* DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH,
PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
13
LT1521/LT1521-3
LT1521-3.3/LT1521-5
U
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 – 0.197*
(4.801 – 5.004)
8
7
6
5
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
1
0.010 – 0.020
× 45°
(0.254 – 0.508)
0.008 – 0.010
(0.203 – 0.254)
0.053 – 0.069
(1.346 – 1.752)
0°– 8° TYP
0.016 – 0.050
0.406 – 1.270
0.014 – 0.019
(0.355 – 0.483)
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
14
2
3
4
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
TYP
SO8 0996
LT1521/LT1521-3
LT1521-3.3/LT1521-5
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PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
ST Package
3-Lead Plastic SOT-223
(LTC DWG # 05-08-1630)
0.248 – 0.264
(6.30 – 6.71)
0.116 – 0.124
(2.95 – 3.15)
0.264 – 0.287
(6.71 – 7.29)
0.130 – 0.146
(3.30 – 3.71)
0.033 – 0.041
(0.84 – 1.04)
0.090
(2.29)
NOM
10° – 16°
0.010 – 0.014
(0.25 – 0.36)
10°
MAX
0.071
(1.80)
MAX
10° – 16°
0.025 – 0.033
(0.64 – 0.84)
0.181
(4.60)
NOM
0.012
(0.31)
MIN
0.0008 – 0.0040
(0.0203 – 0.1016)
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.
ST3 (SOT-233) 0792
15
LT1521/LT1521-3
LT1521-3.3/LT1521-5
RELATED PARTS
PART NUMBER
®
DESCRIPTION
COMMENTS
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425mA High Efficiency Step-Down Switching Regulator
>90% Efficiency, SO-8 Package
LT1175
500mA Micropower Low Dropout Negative Linear Regulator
Selectable Current Limit
LT1120A
125mA Micropower Low Dropout Linear Regulator
20µA Quiescent Current, Includes Comparator
LT1304
Micropower Step-Up DC/DC Converter
15µA Quiescent Current, 1.5 Minimum Input
LT1529
3A Micropower Low Dropout Regulator
50µA Quiescent Current
16
Linear Technology Corporation
1521335fa LT/TP 0299 REV A 2K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com
 LINEAR TECHNOLOGY CORPORATION 1995