ETC LT1121HVIS8

LT1121/LT1121-3.3/LT1121-5
Micropower Low Dropout
Regulators with Shutdown
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FEATURES
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DESCRIPTIO
0.4V Dropout Voltage
150mA Output Current
30µA Quiescent Current
No Protection Diodes Needed
Adjustable Output from 3.8V to 30V
3.3V and 5V Fixed Output Voltages
Controlled Quiescent Current in Dropout
Shutdown
16µA Quiescent Current in Shutdown
Stable with 0.33µF Output Capacitor
Reverse Battery Protection
No Reverse Current with Input Low
Thermal Limiting
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APPLICATIO S
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Low Current Regulator
Regulator for Battery-Powered Systems
Post Regulator for Switching Supplies
The LT®1121/LT1121-3.3/LT1121-5 are micropower low
dropout regulators with shutdown. These devices are
capable of supplying 150mA of output current with a
dropout voltage of 0.4V. Designed for use in batterypowered systems, the low quiescent current, 30µA operating and 16µA 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.
Other features of the LT1121/LT1121-3.3/LT1121-5 include the ability to operate with very small output capacitors. They are stable with only 0.33µF on the output while
most older devices require between 1µF and 100µF for
stability. Small ceramic capacitors can be used, enhancing
manufacturability. Also the input may be connected to
ground or a reverse voltage without reverse current flow
from output to input. This makes the LT1121 series ideal
for backup power situations where the output is held high
and the input is at ground or reversed. Under these
conditions only 16µA will flow from the output pin to
ground.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATIO
5V Battery-Powered Supply with Shutdown
Dropout Voltage
0.5
IN
OUT
1
LT1121-3.3
5V
5
3.3VOUT
150mA
+
SHDN
GND
3
VSHDN (PIN 5) OUTPUT
<0.25
OFF
>2.8
ON
NC
ON
0.4
1µF
SOLID TANTALUM
DROPOUT VOLTAGE (V)
8
0.3
0.2
0.1
LT1121 • TA01
0
0
20
40 60 80 100 120 140 160
OUTPUT CURRENT (mA)
LT1121 • TA02
1
LT1121/LT1121-3.3/LT1121-5
W W
W
AXI U
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ABSOLUTE
RATI GS (Note 1)
Input Voltage
LT1121 ............................................................. ±30V
LT1121HV ............................................. +36V, – 30V
Output Pin Reverse Current ................................. 10mA
Adjust Pin Current ............................................... 10mA
Shutdown Pin Input Voltage (Note 2) ........ 6.5V, – 0.6V
Shutdown Pin Input Current (Note 2) .................. 20mA
Output Short-Circuit Duration ......................... Indefinite
Operating Junction Temperature Range (Note 3)
LT1121C-X ........................................... 0°C to 125°C
LT1121I-X ....................................... – 40°C to 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
W
U
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PACKAGE/ORDER I FOR ATIO
TOP VIEW
OUT 1
8 IN
NC/ADJ* 2
7 NC**
GND 3
6 NC**
NC 4
5 SHDN
N8 PACKAGE
8-LEAD PDIP
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 150°C, θJA ≈ 120°C/ W (N8, S8)
TJMAX = 150°C, θJA ≈ 70°C/ W (AS8)
* PIN 2 = NC FOR LT1121-3.3/LT1121-5
= ADJ FOR LT1121
** PINS 6 AND 7 ARE FLOATING (NO
INTERNAL CONNECTION) ON THE
STANDARD S8 PACKAGE.
PINS 6 AND 7 CONNECTED TO GROUND
ON THE A VERSION OF THE LT1121 (S8 ONLY).
CONNECTING PINS 6 AND 7 TO THE
GROUND PLANE WILL REDUCE THERMAL
RESISTANCE. SEE THERMAL RESISTANCE
TABLES IN THE APPLICATIONS INFORMATION
SECTION.
ORDER PART NUMBER
LT1121CN8
LT1121CN8-3.3
LT1121CN8-5
LT1121IN8
LT1121IN8-3.3
LT1121IN8-5
LT1121CS8
LT1121CS8-3.3
LT1121CS8-5
LT1121HVCS8
LT1121IS8
LT1121IS8-3.3
LT1121IS8-5
LT1121HVIS8
LT1121ACS8
LT1121ACS8-3.3
LT1121ACS8-5
LT1121AHVCS8
LT1121AIS8
LT1121AIS8-3.3
LT1121AIS8-5
LT1121AHVIS8
Consult factory for Military grade parts.
2
S8 PART
MARKING
1121
11213
11215
1121H
1121I
121I3
121I5
121IH
1121A
121A3
121A5
121AH
121AI
121AI3
121AI5
121AIH
BOTTOM VIEW
FRONT VIEW
TAB IS
GND
3
OUTPUT
2
GND
1
VIN
3
2
1
IN
GND
OUT
ST PACKAGE
3-LEAD PLASTIC SOT-223
Z PACKAGE
3-LEAD PLASTIC TO-92
TJMAX = 150°C, θJA ≈ 50°C/ W
TJMAX = 150°C, θJA ≈ 150°C/ W
ORDER PART
NUMBER
ORDER PART
NUMBER
LT1121CST-3.3
LT1121IST-3.3
LT1121CST-5
LT1121IST-5
LT1121CZ-3.3
LT1121IZ-3.3
LT1121CZ-5
LT1121IZ-5
LT1121/LT1121-3.3/LT1121-5
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the operating temperature
range, otherwise specifications are at TA = 25°C.
PARAMETER
CONDITIONS
Regulated Output Voltage
(Note 4)
LT1121-3.3
LT1121-5
LT1121 (Note 5)
Line Regulation
LT1121-3.3
LT1121-5
LT1121 (Note 5)
Load Regulation
LT1121-3.3
LT1121-5
LT1121 (Note 5)
Dropout Voltage
(Note 6)
Ground Pin Current
(Note 7)
TYP
MAX
UNITS
VIN = 3.8V, IOUT = 1mA, TJ = 25°C
4.3V < VIN < 20V, 1mA < IOUT < 150mA
●
3.250
3.200
3.300
3.300
3.350
3.400
V
V
VIN = 5.5V, IOUT = 1mA, TJ = 25°C
6V < VIN < 20V, 1mA < IOUT < 150mA
●
4.925
4.850
5.000
5.000
5.075
5.150
V
V
VIN = 4.3V, IOUT = 1mA, TJ = 25°C
4.8V < VIN < 20V, 1mA < IOUT < 150mA
●
3.695
3.640
3.750
3.750
3.805
3.860
V
V
∆VIN = 4.8V to 20V, IOUT = 1mA
∆VIN = 5.5V to 20V, IOUT = 1mA
●
1.5
10
mV
●
1.5
10
mV
∆VIN = 4.3V to 20V, IOUT = 1mA
∆ILOAD = 1mA to 150mA, TJ = 25°C
∆ILOAD = 1mA to 150mA
●
1.5
10
mV
●
– 12
– 20
– 25
– 40
mV
mV
∆ILOAD = 1mA to 150mA, TJ = 25°C
∆ILOAD = 1mA to 150mA
●
– 17
– 28
– 35
– 50
mV
mV
∆ILOAD = 1mA to 150mA, TJ = 25°C
∆ILOAD = 1mA to 150mA
●
– 12
– 18
– 25
– 40
mV
mV
0.13
0.16
0.25
V
V
0.30
0.35
0.50
V
V
0.37
0.45
0.60
V
V
0.42
0.55
0.70
V
V
30
50
µA
ILOAD = 1mA, TJ = 25°C
ILOAD = 1mA
●
ILOAD = 50mA, TJ = 25°C
LOAD = 50mA
●
ILOAD = 100mA, TJ = 25°C
ILOAD = 100mA
●
ILOAD = 150mA, TJ = 25°C
ILOAD = 150mA
●
ILOAD = 0mA
●
ILOAD = 1mA
●
90
120
µA
ILOAD = 10mA
●
350
500
µA
ILOAD = 50mA
●
1.5
2.5
mA
ILOAD = 100mA
●
4.0
7.0
mA
ILOAD = 150mA
●
7.0
14.0
mA
150
300
nA
1.2
0.75
2.8
V
V
6
10
µA
15
22
Adjust Pin Bias Current (Notes 5, 8)
TJ = 25°C
Shutdown Threshold
VOUT = Off to On
VOUT = On to Off
●
●
VSHDN = 0V
●
Quiescent Current in Shutdown (Note 10)
VIN = 6V, VSHDN = 0V
●
Ripple Rejection
VIN – VOUT = 1V (Avg), VRIPPLE = 0.5VP-P,
fRIPPLE = 120Hz, ILOAD = 0.1A
Current Limit
VIN – VOUT = 7V, TJ = 25°C
Input Reverse Leakage Current
VIN = –20V, VOUT = 0V
Reverse Output Current (Note 11)
LT1121-3.3
LT1121-5
LT1121 (Note 5)
Shutdown Pin Current (Note 9)
MIN
50
58
200
●
VOUT = 3.3V, VIN = 0V
VOUT = 5V, VIN = 0V
VOUT = 3.8V, VIN = 0V
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
0.25
16
16
16
µA
dB
500
mA
1.0
mA
25
25
25
µA
µA
µA
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
3
LT1121/LT1121-3.3/LT1121-5
ELECTRICAL CHARACTERISTICS
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 20mA.
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.
Note 5: The LT1121 (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 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 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 sum total of the
shutdown pin current (6µA) and the ground pin current (9µA).
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 PERFOR A CE CHARACTERISTICS
0.6
TJ ≤ 125°C
0.5
TJ ≤ 25°C
0.3
0.2
0.1
10
ILOAD = 150mA
QUIESCENT CURRENT (µA)
0.6
0.4
Quiescent Current
Dropout Voltage
0.7
DROPOUT VOLTAGE (V)
DROPOUT VOLTAGE (V)
Guaranteed Dropout Voltage
0.7
ILLOAD = 100mA
0.5
0.4
0.3
ILOAD = 50mA
0.2
ILOAD = 1mA
VIN = 6V
RLOAD = ∞
40
VSHDN = OPEN
30
20
VSHDN = 0V
10
0.1
= TEST POINTS
0
0
0
–50
40 60 80 100 120 140 160
OUTPUT CURRENT (mA)
20
50
0
75
25
TEMPERATURE (°C)
–25
100
1121 G27
120
TJ = 25°C
RLOAD = ∞
VSHDN = OPEN
60
40
20
80
VSHDN = OPEN
60
40
20
VSHDN = 0V
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
1121 G04
80
VSHDN = OPEN
60
40
20
VSHDN = 0V
0
0
TJ = 25°C
RLOAD = ∞
VOUT = VADJ
100
QUIESCENT CURRENT (µA)
100
QUIESCENT CURRENT (µA)
QUIESCENT CURRENT (µA)
100
125
LT1121
Quiescent Current
120
TJ = 25°C
RLOAD = ∞
80
100
1121 G11
LT1121-5
Quiescent Current
120
50
0
75
25
TEMPERATURE (°C)
1121 G14
LT1121-3.3
Quiescent Current
4
0
–50 –25
125
VSHDN = 0V
0
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
1121 G02
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
1121 G03
LT1121/LT1121-3.3/LT1121-5
U W
TYPICAL PERFOR A CE CHARACTERISTICS
LT1121-3.3
Output Voltage
LT1121-5
Output Voltage
3.83
5.08
3.38
IOUT = 1mA
IOUT = 1mA
5.06
3.81
3.34
5.04
3.79
3.32
3.30
3.28
3.26
OUTPUT VOLTAGE (V)
3.36
OUTPUT VOLTAGE (V)
5.02
5.00
4.98
4.96
50
25
0
75
TEMPERATURE (°C)
–25
100
4.92
–50
125
50
0
75
25
TEMPERATURE (°C)
–25
100
LT1121-3.3
Ground Pin Current
800
RLOAD = 130Ω
ILOAD = 25mA*
500
RLOAD = 330Ω
ILOAD = 10mA*
300
*FOR VOUT = 3.3V
200
RLOAD = 3.3k
ILOAD = 1mA*
100
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
500
RLOAD = 500Ω
ILOAD = 10mA*
400
300
*FOR VOUT = 5V
200
RLOAD = 5k
ILOAD = 1mA*
10
TJ = 25°C
RLOAD = 33Ω
ILOAD = 100mA*
5
4
3
RLOAD = 66Ω
ILOAD = 50mA*
2
1
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
1
2
9
300
*FOR VOUT = 3.75V
200
3 4 5 6 7
INPUT VOLTAGE (V)
9
10
1121 G09
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
1121 G08
TJ = 25°C
9 VOUT = VADJ
6
RLOAD = 50Ω
ILOAD = 100mA*
5
4
3
RLOAD = 100Ω
ILOAD = 50mA*
2
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
RLOAD = 25Ω
ILOAD = 150mA*
7
6
5
RLOAD = 38Ω
ILOAD = 100mA*
4
3
RLOAD = 75Ω
ILOAD = 50mA*
2
1
*FOR VOUT = 5V
0
10
10
RLOAD = 33Ω
ILOAD = 150mA*
7
9
LT1121
Ground Pin Current
8
0
8
RLOAD = 3.8k
ILOAD = 1mA*
0
10
TJ = 25°C
1
*FOR VOUT = 3.3V
0
GROUND PIN CURRENT (mA)
GROUND PIN CURRENT (mA)
6
RLOAD = 380Ω
ILOAD = 10mA*
400
100
9
RLOAD = 22Ω
ILOAD = 150mA*
7
500
LT1121-5
Ground Pin Current
9
8
600
1121 G06
LT1121-3.3
Ground Pin Current
10
RLOAD = 150Ω
ILOAD = 25mA*
0
0
1121 G10
0
TJ = 25°C
700 VOUT = VADJ
RLOAD = 200Ω
ILOAD = 25mA*
600
10
125
100
LT1121
Ground Pin Current
0
1
50
0
75
25
TEMPERATURE (°C)
–25
800
100
0
0
3.71
1121 G24
TJ = 25°C
700
GROUND PIN CURRENT (µA)
GROUND PIN CURRENT (µA)
700
400
3.73
LT1121-5
Ground Pin Current
TJ = 25°C
600
3.75
1121 G23
1121 G22
800
3.77
3.67
–50
125
GROUND PIN CURRENT (µA)
3.22
–50
IOUT = 1mA
3.69
4.94
3.24
GROUND PIN CURRENT (mA)
OUTPUT VOLTAGE (V)
LT1121
Adjust Pin Voltage
8
9
10
1121 G05
0
*FOR VOUT = 3.75V
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
1121 G07
5
LT1121/LT1121-3.3/LT1121-5
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Shutdown Pin Threshold
(On-to-Off)
Ground Pin Current
2.0
VIN = 3.3V (LT1121-3.3)
VIN = 5V (LT1121-5)
12 V = 3.75V (LT1121)
IN
DEVICE IS OPERATING
10 IN DROPOUT
TJ = 25°C
6
TJ = –55°C
4
2
1.8
1.6
SHUTDOWN THRESHOLD (V)
TJ = 125°C
8
2.0
ILOAD = 1mA
1.8
SHUTDOWN THRESHOLD (V)
GROUND PIN CURRENT (mA)
14
Shutdown Pin Threshold
(Off-to-On)
1.4
1.2
1.0
0.8
0.6
0.4
0
20
0
–50
40 60 80 100 120 140 160
OUTPUT CURRENT (mA)
50
0
75
25
TEMPERATURE (°C)
–25
100
1121 G29
6
5
4
3
2
1
–25
50
0
75
25
TEMPERATURE (°C)
100
20
15
10
5
0
1
7
3
8
2
5
6
4
SHUTDOWN PIN VOLTAGE (V)
10
5
200
150
100
50
125
–25
50
0
75
25
TEMPERATURE (°C)
100
125
1121 G25
Current Limit
VOUT = 0V
350
VIN = 7V
350 VOUT = 0V
300
300
250
200
150
100
250
200
150
100
50
0
100
1121 G13
6
250
400
50
50
25
0
75
TEMPERATURE (°C)
125
300
0
–50
9
CURRENT LIMIT (mA)
SHORT-CIRCUIT CURRENT (mA)
OUTPUT PIN CURRENT (µA)
15
100
350
Current Limit
400
20
50
0
75
25
TEMPERATURE (°C)
1121 G28
Reverse Output Current
VIN = 0V
VOUT = 5V (LT1121-5)
25 VOUT = 3.3V (LT1121-3.3)
VOUT = 3.8V (LT1121)
–25
400
0
125
30
–25
0.4
LT1121
Adjust Pin Bias Current
1121 G15
0
–50
0.6
1121 G17
ADJUST PIN BIAS CURRENT (nA)
7
0
–50
0.8
0
–50
125
25
VSHDN = 0V
8
ILOAD = 1mA
1.0
Shutdown Pin Input Current
SHUTDOWN PIN INPUT CURRENT (mA)
SHUTDOWN PIN CURRENT (µA)
9
1.2
1121 G16
Shutdown Pin Current
10
ILOAD = 150mA
1.4
0.2
0.2
0
1.6
0
1
4
2
5
3
INPUT VOLTAGE (V)
6
7
1121 G20
0
–50
–25
50
0
75
25
TEMPERATURE (°C)
100
125
1121 G19
LT1121/LT1121-3.3/LT1121-5
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Ripple Rejection
64
62
RIPPLE REJECTION (dB)
LT1121
(VOUT = VADJ)
60
50
40
LT1121-3.3
30
80
60
58
56
54
0
52
LT1121-5
60
50
40
30
COUT = 1µF
SOLID TANTALUM
0
1
2
3 4 5 6 7 8
OUTPUT VOLTAGE (V)
9
10
50
–50
10
0
–25
50
0
75
25
TEMPERATURE (°C)
∆ILOAD = 1mA TO 150mA
OUTPUT VOLTAGE
DEVIATION (V)
–5
LT1121*
125
10
LT1121-3.3
–15
–20
100
1k
10k
FREQUENCY (Hz)
100k
1M
1121 G26
LT1121-5
Load Transient Response
Load Regulation
–10
100
1121 G18
1121 G01
0
COUT = 47µF
SOLID TANTALUM
70
20
20
10
LT1121-5
Load Transient Response
VIN = 6V
0.2 CIN = 0.1µF
= 1µF
C
0.1 OUT
0
–0.1
–0.2
VIN = 6V
0.2 CIN = 0.1µF
COUT = 3.3µF
0.1
0
–0.1
–0.2
LT1121-5
–30
–35
* ADJ PIN TIED TO
OUTPUT PIN
–40
–50
–25
50
0
75
25
TEMPERATURE (°C)
100
125
1121 G21
LOAD CURRENT
(mA)
–25
LOAD CURRENT
(mA)
LOAD REGULATION (mV)
IOUT = 100mA
90 VIN = 6V + 50mVRMS RIPPLE
VIN = VOUT (NOMINAL) + 1V
+ 0.5VP-P RIPPLE AT f = 120Hz
IOUT = 100mA
OUTPUT VOLTAGE
DEVIATION (V)
OUTPUT PIN CURRENT (µA)
TJ = 25°C
90 VIN = 0V
CURRENT FLOWS
80 INTO OUTPUT PIN
70
Ripple Rejection
100
RIPPLE REJECTION (dB)
Reverse Output Current
100
150
100
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
TIME (ms)
1121 G30
150
100
50
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
TIME (ms)
1121 G31
7
LT1121/LT1121-3.3/LT1121-5
U
U
U
PI FU CTIO S
Input Pin: 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 a
battery rises with frequency so it is usually adviseable to
include a bypass capacitor in battery-powered circuits. A
bypass capacitor in the range of 0.1µF to 1µF is sufficient.
The LT1121 is designed to withstand reverse voltages on
the input pin with respect to both ground and the output
pin. In the case of a reversed input, which can happen if a
battery is plugged in backwards, the LT1121 will act as if
there is a diode in series with its input. There will be no
reverse current flow into the LT1121 and no reverse
voltage will appear at the load. The device will protect both
itself and the load.
Output Pin: The output pin supplies power to the load. An
output capacitor is required to prevent oscillations. See
the Applications Information section for recommended
value of output capacitance and information on reverse
output characteristics.
Shutdown Pin: This pin is used to put the device into
shutdown. In shutdown the output of the device is turned
8
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 6µA. 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 pullup 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
20mA. A curve of 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.
Adjust Pin: For the adjustable LT1121, 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 150nA
which flows into the pin. See Bias Current curve in the
Typical Performance Characteristics. 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 30V.
LT1121/LT1121-3.3/LT1121-5
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APPLICATIO S I FOR ATIO
The LT1121 is a micropower low dropout regulator with
shutdown, capable of supplying up to 150mA of output
current at a dropout voltage of 0.4V. The device operates
with very low quiescent current (30µA). In shutdown the
quiescent current drops to only 16µA. In addition to the
low quiescent current the LT1121 incorporates several
protection features which make it ideal for use in batterypowered 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 LT1121 acts like it has a diode in series with its output
and prevents reverse current flow.
Adjustable Operation
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 voltage 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 150mA is –12mV typical
at VOUT = 3.75V. At VOUT = 12V, load regulation would be:
 12V 

 • –12mV = –38mV
 3.75V 
(
) (
)
Thermal Considerations
The adjustable version of the LT1121 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 1. 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, 150nA at 25°C, flows through R2 into the
adjust pin. The output voltage can be calculated according
to the formula in Figure 1. 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
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 slight positive temperature coefficient of
IN
VOUT
OUT
LT1121
R2
SHDN
ADJ
+
R1
GND
1121 • F01
(
approximately 15ppm/°C. The adjust pin bias current has
a negative temperature coefficient. These effects are small
and will tend to cancel each other.
)
(
)
VOUT = 3.75V 1 + R2 + IADJ • R2
R1
VADJ = 3.75V
IADJ = 150nA AT 25°C
OUTPUT RANGE = 3.75V TO 30V
Figure 1. Adjustable Operation
Power handling capability will be limited by maximum
rated junction temperature (125°C). 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 LT1121 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.
Heat sinking, for surface mount devices, 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. Tables 1 through 5 list thermal
resistances for each package. Measured values of thermal
resistance for several different board sizes and copper
areas are listed for each package. All measurements were
9
LT1121/LT1121-3.3/LT1121-5
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APPLICATIO S I FOR ATIO
taken in still air, on 3/32" FR-4 board with 1oz copper. All
NC leads were connected to the ground plane.
Table 1. N8 Package*
COPPER AREA
TOPSIDE
BACKSIDE
THERMAL RESISTANCE
BOARD AREA (JUNCTION-TO-AMBIENT)
2500 sq mm
2500 sq. mm
2500 sq. mm
80°C/W
1000 sq mm
2500 sq. mm
2500 sq. mm
80°C/W
225 sq mm
2500 sq. mm
2500 sq. mm
85°C/W
1000 sq mm
1000 sq. mm
1000 sq. mm
91°C/W
Table 5. TO-92 Package
THERMAL
RESISTANCE
Package alone
220°C/W
Package soldered into PC board with plated
through holes only
175°C/W
Package soldered into PC board with 1/4 sq. inch of
copper trace per lead
145°C/W
Package soldered into PC board with plated through holes
in board, no extra copper trace, and a clip-on type
heat sink:
Thermalloy type 2224B
Aavid type 5754
160°C/W
135°C/W
* Device is mounted on topside. Leads are through hole and are soldered
to both sides of board.
Calculating Junction Temperature
Table 2. S8 Package
COPPER AREA
TOPSIDE*
BACKSIDE
THERMAL RESISTANCE
BOARD AREA (JUNCTION-TO-AMBIENT)
2500 sq. mm 2500 sq. mm
2500 sq. mm
120°C/W
1000 sq. mm 2500 sq. mm
2500 sq. mm
120°C/W
225 sq. mm
2500 sq. mm
2500 sq. mm
25°C/W
100 sq. mm
1000 sq. mm
1000 sq. mm
131°C/W
* Device is mounted on topside.
COPPER AREA
BACKSIDE
BOARD AREA
2500 sq. mm
1000 sq. mm 2500 sq. mm
2500 sq. mm
60°C/W
225 sq. mm
2500 sq. mm
2500 sq. mm
68°C/W
100 sq. mm
2500 sq. mm
2500 sq. mm
74°C/W
60°C/W
* Pins 3, 6, and 7 are ground.
** Device is mounted on topside.
2500 sq. mm 2500 sq. mm
THERMAL RESISTANCE
BOARD AREA (JUNCTION-TO-AMBIENT)
2500 sq. mm
50°C/W
1000 sq. mm 2500 sq. mm
2500 sq. mm
50°C/W
225 sq. mm
2500 sq. mm
2500 sq. mm
58°C/W
100 sq. mm
2500 sq. mm
2500 sq. mm
64°C/W
1000 sq. mm 1000 sq. mm
1000 sq. mm
57°C/W
1000 sq. mm
1000 sq. mm
60°C/W
BACKSIDE
0
* Tab of device attached to topside copper
10
P = 100mA • (7V – 3.3V) + (5mA • 7V)
= 0.405W
If we use an SOT-223 package, then the thermal resistance
will be in the range of 50°C/W to 65°C/W depending on
copper area. So the junction temperature rise above
ambient will be less than or equal to:
0.405W • 60°C/W = 24°C
Table 4. SOT-223 Package
(Thermal Resistance Junction-to-Tab 20°C/W)
COPPER AREA
IOUT MAX • (VIN MAX – VOUT) + (IGND • VIN)
so,
2500 sq. mm 2500 sq. mm
TOPSIDE*
Power dissipated by the device will be equal to:
where, IOUT MAX = 100mA
VIN MAX = 7V
IGND at (IOUT = 100mA, VIN = 7V) = 5mA
Table 3. AS8 Package*
TOPSIDE**
Example: given an output voltage of 3.3V, an input voltage
range of 4.5V to 7V, an output current range of 0mA to
100mA, and a maximum ambient temperature of 50°C,
what will the maximum junction temperature be?
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 + 24°C = 74°C
Output Capacitance and Transient Performance
The LTC1121 is designed to be stable with a wide range of
output capacitors. The minimum recommended value is
1µF with an ESR of 3Ω or less. For applications where
space is very limited, capacitors as low as 0.33µF can be
used if combined with a small series resistor. Assuming
LT1121/LT1121-3.3/LT1121-5
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APPLICATIO S I FOR ATIO
Table 5.
OUTPUT CAPACITANCE
0.33µF
0.47µF
0.68µF
>1µF
SUGGESTED SERIES
RESISTOR
2Ω
1Ω
1Ω
None Needed
Protection Features
The LT1121 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 temperature should not exceed 125°C.
The input of the device will withstand reverse voltages of
30V. 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 backwards.
For fixed voltage versions of the device, the output can be
pulled below ground without damaging the device. If the
input is 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 a 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.
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
6 summarizes the following information.
The reverse output current will follow the curve in Figure
2 when the input pin 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
to the LT1121 unconnected when the output is held high.
This can happen when the LT1121 is powered from a
rectified AC source. If the AC source is removed, then the
input of the LT1121 is effectively left floating. The reverse
output current also follows the curve in Figure 2 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.
100
OUTPUT PIN CURRENT (µA)
that the ESR of the capacitor is low (ceramic) the suggested series resistor is shown in Table 5. The LT1121 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. Bypass capacitors, used to decouple individual
components powered by the LT1121, will increase the
effective value of the output capacitor.
TJ = 25°C
90 VIN < VOUT
CURRENT FLOWS
80
INTO OUTPUT PIN
70 TO GROUND
LT1121
(VOUT = VADJ)
60
50
40
LT1121-3.3
30
20
LT1121-5
10
0
0
1
2
3 4 5 6 7 8
OUTPUT VOLTAGE (V)
9
10
1121• F02
Figure 2. Reverse Output Current
11
LT1121/LT1121-3.3/LT1121-5
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APPLICATIO S I FOR ATIO
5
VOUT = 3.3V (LT1121-3.3)
VOUT = 5V (LT1121-5)
4
INPUT CURRENT (µA)
When the input of the LT1121 is forced to a voltage below
its nominal output voltage and its output is held high, the
reverse output current will still follow the curve in Figure
2. This condition can occur if the input of the LT1121 is
connected to a discharged (low voltage) battery and the
output is held up by either a backup battery or by a 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 3). The state of the shutdown pin will have no effect
on the reverse output current when the output is pulled
above the input.
3
2
1
0
0
1
3
2
INPUT VOLTAGE (V)
4
1121 F03
Figure 3. Input Current
Table 6. Fault Conditions
INPUT PIN
SHDN PIN
OUTPUT PIN
< VOUT (Nominal)
Open (Hi)
Forced to VOUT (Nominal)
Reverse Output Current ≈ 15µA (See Figure 2)
Input Current ≈ 1µA (See Figure 3)
< VOUT (Nominal)
Grounded
Forced to VOUT (Nominal)
Reverse Output Current ≈ 15µA (See Figure 2)
Input Current ≈ 1µA (See Figure 3)
Open
Open (Hi)
Forced to VOUT (Nominal)
Reverse Output Current ≈ 15µA (See Figure 2)
Reverse Output Current ≈ 15µA (See Figure 2)
Open
Grounded
Forced to VOUT (Nominal)
≤ 0.8V
Open (Hi)
≤ 0V
Output Current = 0
≤ 0.8V
Grounded
≤ 0V
Output Current = 0
> 1.5V
Open (Hi)
≤ 0V
Output Current = Short-Circuit Current
– 30V < VIN < 30V
Grounded
≤ 0V
Output Current = 0
12
5
LT1121/LT1121-3.3/LT1121-5
U
PACKAGE DESCRIPTIO
Dimensions in inches (millimeters) unless otherwise noted.
N8 Package
8-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
0.400*
(10.160)
MAX
8
7
6
5
1
2
3
4
0.255 ± 0.015*
(6.477 ± 0.381)
0.300 – 0.325
(7.620 – 8.255)
0.065
(1.651)
TYP
0.009 – 0.015
(0.229 – 0.381)
(
+0.035
0.325 –0.015
8.255
+0.889
–0.381
0.130 ± 0.005
(3.302 ± 0.127)
0.045 – 0.065
(1.143 – 1.651)
)
0.125
(3.175) 0.020
MIN (0.508)
MIN
0.018 ± 0.003
0.100
(2.54)
BSC
(0.457 ± 0.076)
N8 1098
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
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)
TYP
*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
2
3
4
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
BSC
SO8 1298
13
LT1121/LT1121-3.3/LT1121-5
U
PACKAGE DESCRIPTIO
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)
0.114 – 0.124
(2.90 – 3.15)
0.264 – 0.287
(6.70 – 7.30)
0.130 – 0.146
(3.30 – 3.71)
0.033 – 0.041
(0.84 – 1.04)
0.0905
(2.30)
NOM
10° – 16°
0.010 – 0.014
(0.25 – 0.36)
10°
MAX
0.071
(1.80)
MAX
10° – 16°
0.024 – 0.033
(0.60 – 0.84)
0.181
(4.60)
NOM
14
0.012
(0.31)
MIN
0.0008 – 0.0040
(0.0203 – 0.1016)
ST3 (SOT-233) 1298
LT1121/LT1121-3.3/LT1121-5
U
PACKAGE DESCRIPTIO
Dimensions in inches (millimeters) unless otherwise noted.
Z Package
3-Lead Plastic TO-92 (Similar to TO-226)
(LTC DWG # 05-08-1410)
0.060 ± 0.005
(1.524± 0.127)
DIA
0.180 ± 0.005
(4.572 ± 0.127)
0.180 ± 0.005
(4.572 ± 0.127)
0.060 ± 0.010
(1.524 ± 0.254)
0.90
(2.286)
NOM
0.140 ± 0.010
(3.556 ± 0.127)
Z3 (TO-92) 1098
0.500
(12.70)
MIN
0.050 UNCONTROLLED
(1.270) LEAD DIMENSION
MAX
5°
NOM
10° NOM
0.015 ± 0.002
(0.381 ± 0.051)
0.050
(1.27)
BSC
0.016 ± 0.003
(0.406 ± 0.076)
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.
15
LT1121/LT1121-3.3/LT1121-5
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Burst Mode is a trademark of Linear Technology Corporation.
16
Linear Technology Corporation
1121fb LT/LCG 0900 2K REV B • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com
 LINEAR TECHNOLOGY CORPORATION 1994