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LT1461 Datasheet

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Datasheet

LT1461
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For more information www.linear.com/LT1461
Typical applicaTion
FeaTures DescripTion
Micropower Precision
Low Dropout Series
Voltage Reference Family
The LT
®
1461 is a family of low dropout micropower band-
gap references that combine very high accuracy and low
drift with low supply current and high output drive. These
series references use advanced curvature compensation
techniques to obtain low temperature coefficient and
trimmed precision thin-film resistors to achieve high
output accuracy. The LT1461 family draws only 35µA
of supply current, making them ideal for low power and
portable applications, however their high 50mA output
drive makes them suitable for higher power requirements,
such as precision regulators.
In low power applications, a dropout voltage of less than
300mV ensures maximum battery life while maintaining
full reference performance. Line regulation is nearly im-
measurable, while the exceedingly good load and ther-
mal regulation will not add significantly to system error
budgets. The shutdown feature can be used to switch full
load currents and can be used for system power down.
Thermal shutdown protects the part from overload condi-
tions. The LT1461 is available in 2.5V, 3V, 3.3V 4.096V
and 5V options.
applicaTions
n Trimmed to High Accuracy: 0.04% Max
n Low Drift: 3ppm/°C Max
n Low Supply Current: 50µA Max
n High Output Current: 50mA Min
n Low Dropout Voltage: 300mV Max
n Excellent Thermal Regulation
n Power Shutdown
n Thermal Limiting
n All Parts Guaranteed Functional from –40°C to 125°C
n Voltage Options: 2.5V, 3V, 3.3V, 4.096V and 5V
n A/D and D/A Converters
n Precision Regulators
n Handheld Instruments
n Power Supplies
L, LT, LTC , LT M , Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
LT1461-2.5 Load Regulation, PDISS = 200mWBasic Connection
CIN
1µF
V
OUT
(V
OUT + 0.3V) ≤ VIN ≤ 20V
CL
2µF
1461 TA01
LT1461
VOUT
1461 TA02
10ms/DIV
0mA
20mA
V
OUT LOAD REG
1mV/DIV
LT1461
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For more information www.linear.com/LT1461
pin conFiguraTionabsoluTe MaxiMuM raTings
Input Voltage ............................................................20V
Output Short-Circuit Duration .......................... Indefinite
Operating Temperature Range
(Note 2) ............................................. 40°C to 125°C
Storage Temperature Range (Note 3) ..... 6C to 150°C
Specified Temperature Range
Commercial ............................................. C to 70°C
Industrial .............................................40°C to 8C
High ................................................... 40°C to 125°C
Lead Temperature (Soldering, 10 sec) ...................30C
(Note 1)
1
2
3
4
8
7
6
5
TOP VIEW
*DNC: DO NOT CONNECT
DNC*
DNC*
VOUT
DNC*
DNC*
VIN
SHDN
GND
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 150°C, θJA = 190°C/W
(Note 3)
orDer inForMaTion
LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION SPECIFIED TEMPERATURE RANGE
LT1461ACS8-2.5#PBF LT1461ACS8-2.5#TRPBF 461A25 8-LEAD PLASTIC SO 0°C to 70°C
LT1461ACS8-3#PBF LT1461ACS8-3#TRPBF 1461A3 8-LEAD PLASTIC SO 0°C to 70°C
LT1461ACS8-3.3#PBF LT1461ACS8-3.3#TRPBF 461A33 8-LEAD PLASTIC SO 0°C to 70°C
LT1461ACS8-4#PBF LT1461ACS8-4#TRPBF 1461A4 8-LEAD PLASTIC SO 0°C to 70°C
LT1461ACS8-5#PBF LT1461ACS8-5#TRPBF 1461A5 8-LEAD PLASTIC SO 0°C to 70°C
LT1461BCS8-2.5#PBF LT1461BCS8-2.5#TRPBF 461B25 8-LEAD PLASTIC SO 0°C to 70°C
LT1461BCS8-3#PBF LT1461BCS8-3#TRPBF 1461B3 8-LEAD PLASTIC SO 0°C to 70°C
LT1461BCS8-3.3#PBF LT1461BCS8-3.3#TRPBF 461B33 8-LEAD PLASTIC SO 0°C to 70°C
LT1461BCS8-4#PBF LT1461BCS8-4#TRPBF 1461B4 8-LEAD PLASTIC SO 0°C to 70°C
LT1461BCS8-5#PBF LT1461BCS8-5#TRPBF 1461B5 8-LEAD PLASTIC SO 0°C to 70°C
LT1461CCS8-2.5#PBF LT1461CCS8-2.5#TRPBF 461C25 8-LEAD PLASTIC SO 0°C to 70°C
LT1461CCS8-3#PBF LT1461CCS8-3#TRPBF 1461C3 8-LEAD PLASTIC SO 0°C to 70°C
LT1461CCS8-3.3#PBF LT1461CCS8-3.3#TRPBF 461C33 8-LEAD PLASTIC SO 0°C to 70°C
LT1461CCS8-4#PBF LT1461CCS8-4#TRPBF 1461C4 8-LEAD PLASTIC SO 0°C to 70°C
LT1461CCS8-5#PBF LT1461CCS8-5#TRPBF 1461C5 8-LEAD PLASTIC SO 0°C to 70°C
LT1461AIS8-2.5#PBF LT1461AIS8-2.5#TRPBF 61AI25 8-LEAD PLASTIC SO –40°C to 85°C
LT1461AIS8-3#PBF LT1461AIS8-3#TRPBF 461AI3 8-LEAD PLASTIC SO –40°C to 85°C
LT1461AIS8-3.3#PBF LT1461AIS8-3.3#TRPBF 61AI33 8-LEAD PLASTIC SO –40°C to 85°C
LT1461AIS8-4#PBF LT1461AIS8-4#TRPBF 461AI4 8-LEAD PLASTIC SO –40°C to 85°C
LT1461AIS8-5#PBF LT1461AIS8-5#TRPBF 461AI5 8-LEAD PLASTIC SO –40°C to 85°C
LT1461BIS8-2.5#PBF LT1461BIS8-2.5#TRPBF 61BI25 8-LEAD PLASTIC SO –40°C to 85°C
LT1461BIS8-3#PBF LT1461BIS8-3#TRPBF 461BI3 8-LEAD PLASTIC SO –40°C to 85°C
LT1461BIS8-3.3#PBF LT1461BIS8-3.3#TRPBF 61BI33 8-LEAD PLASTIC SO –40°C to 85°C
LT1461BIS8-4#PBF LT1461BIS8-4#TRPBF 461BI4 8-LEAD PLASTIC SO –40°C to 85°C
LT1461BIS8-5#PBF LT1461BIS8-5#TRPBF 461BI5 8-LEAD PLASTIC SO –40°C to 85°C
LT1461CIS8-2.5#PBF LT1461CIS8-2.5#TRPBF 61CI25 8-LEAD PLASTIC SO –40°C to 85°C
LT1461CIS8-3#PBF LT1461CIS8-3#TRPBF 461CI3 8-LEAD PLASTIC SO –40°C to 85°C
LT1461CIS8-3.3#PBF LT1461CIS8-3.3#TRPBF 61CI33 8-LEAD PLASTIC SO –40°C to 85°C
LT1461
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For more information www.linear.com/LT1461
elecTrical characTerisTics
available opTions
orDer inForMaTion
PARAMETER CONDITIONS MIN TYP MAX UNITS
Output Voltage (Note 4) LT1461ACS8/LT1461AIS8
LT1461BCS8/LT1461BIS8
LT1461CCS8/LT1461CIS8
LT1461DHS8
–0.04
–0.06
–0.08
–0.15
0.04
0.06
0.08
0.15
%
%
%
%
Output Voltage Temperature Coefficient (Note 5) LT1461ACS8/LT1461AIS8
LT1461BCS8/LT1461BIS8
LT1461CCS8/LT1461CIS8
LT1461DHS8
l
l
l
l
1
3
5
7
3
7
12
20
ppm/°C
ppm/°C
ppm/°C
ppm/°C
Line Regulation (VOUT + 0.5V) ≤ VIN ≤ 20V
l
2 8
12
ppm/V
ppm/V
LT1461DHS8 l15 50 ppm/V
Load Regulation Sourcing (Note 6) VIN = VOUT + 2.5V
0 ≤ IOUT ≤ 50mA
l
12
30
40
ppm/mA
ppm/mA
LT1461DHS8, 0 ≤ IOUT ≤ 10mA l50 ppm/mA
The l denotes the specifications which apply over the specified
temperature range, otherwise specifications are at TA = 25°C. VIN – VOUT = 0.5V, Pin 3 = 2.4V, CL = 2µF, unless otherwise specified.
LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION SPECIFIED TEMPERATURE RANGE
LT1461CIS8-4#PBF LT1461CIS8-4#TRPBF 461CI4 8-LEAD PLASTIC SO –40°C to 85°C
LT1461CIS8-5#PBF LT1461CIS8-5#TRPBF 461CI5 8-LEAD PLASTIC SO –40°C to 85°C
LT1461DHS8-2.5#PBF LT1461DHS8-2.5#TRPBF 61DH25 8-LEAD PLASTIC SO –40°C to 125°C
LT1461DHS8-3#PBF LT1461DHS8-3#TRPBF 461DH3 8-LEAD PLASTIC SO –40°C to 125°C
LT1461DHS8-3.3#PBF LT1461DHS8-3.3#TRPBF 61DH33 8-LEAD PLASTIC SO –40°C to 125°C
LT1461DHS8-4#PBF LT1461DHS8-4#TRPBF 461DH4 8-LEAD PLASTIC SO –40°C to 125°C
LT1461DHS8-5#PBF LT1461DHS8-5#TRPBF 461DH5 8-LEAD PLASTIC SO –40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on nonstandard lead based finish parts.
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/
INITIAL
ACCURACY
TEMPERATURE
COEFFICIENT
TEMPERATURE
RANGE
OUTPUT VOLTAGE
2.5V 3.0V 3.3V 4.096V 5.0V
0.04% Max 3ppm/°C Max 0°C to 70°C LT1461ACS8-2.5 LT1461ACS8-3 LT1461ACS8-3.3 LT1461ACS8-4 LT1461ACS8-5
0.04% Max 3ppm/°C Max –40°C to 85°C LT1461AIS8-2.5 LT1461AIS8-3 LT1461AIS8-3.3 LT1461AIS8-4 LT1461AIS8-5
0.06% Max 7ppm/°C Max 0°C to 70°C LT1461BCS8-2.5 LT1461BCS8-3 LT1461BCS8-3.3 LT1461BCS8-4 LT1461BCS8-5
0.06% Max 7ppm/°C Max –40°C to 85°C LT1461BIS8-2.5 LT1461BIS8-3 LT1461BIS8-3.3 LT1461BIS8-4 LT1461BIS8-5
0.08% Max 12ppm/°C Max 0°C to 70°C LT1461CCS8-2.5 LT1461CCS8-3 LT1461CCS8-3.3 LT1461CCS8-4 LT1461CCS8-5
0.08% Max 12ppm/°C Max –40°C to 85°C LT1461CIS8-2.5 LT1461CIS8-3 LT1461CIS8-3.3 LT1461CIS8-4 LT1461CIS8-5
0.15% Max 20ppm/°C Max –40°C to 125°C LT1461DHS8-2.5 LT1461DHS8-3 LT1461DHS8-3.3 LT1461DHS8-4 LT1461DHS8-5
LT1461
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For more information www.linear.com/LT1461
elecTrical characTerisTics
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 LT1461 is guaranteed functional over the operating
temperature range of –40°C to 125°C.
Note 3: Output may shift due to thermal hysteresis. Thermal hysteresis
affects parts during storage as well as operation.
Note 4: ESD (Electrostatic Discharge) sensitive device. Extensive use of
ESD protection devices are used internal to the LT1461, however, high
electrostatic discharge can damage or degrade the device. Use proper ESD
handling precautions.
Note 5: Temperature coefficient is calculated from the minimum and
maximum output voltage measured at TMIN, Room and TMAX as follows:
TC = (VOMAX – VOMIN)/(TMAX – TMIN)
Incremental slope is also measured at 25°C.
Note 6: Load regulation is measured on a pulse basis from no load to the
specified load current. Output changes due to die temperature change
must be taken into account separately.
Note 7: Peak-to-peak noise is measured with a single pole highpass filter
at 0.1Hz and a 2-pole lowpass filter at 10Hz. The unit is enclosed in a still-
air environment to eliminate thermocouple effects on the leads. The test
time is 10 seconds. RMS noise is measured with a single pole highpass
filter at 10Hz and a 2-pole lowpass filter at 1kHz. The resulting output is
full-wave rectified and then integrated for a fixed period, making the final
reading an average as opposed to RMS. A correction factor of 1.1 is used
to convert from average to RMS and a second correction of 0.88 is used to
correct for the nonideal bandpass of the filters.
Note 8: Long-term drift typically has a logarithmic characteristic and
therefore, changes after 1000 hours tend to be much smaller than before
that time. Total drift in the second thousand hours is normally less than
one third that of the first thousand hours with a continuing trend toward
reduced drift with time. Long-term drift will also be affected by differential
stresses between the IC and the board material created during board
assembly. See the Applications Information section.
Note 9: Hysteresis in output voltage is created by package stress
that depends on whether the IC was previously at a higher or lower
temperature. Output voltage is always measured at 25°C, but the IC is
cycled hot or cold before successive measurements. Hysteresis is roughly
proportional to the square of the temperature change. Hysteresis is not
normally a problem for operational temperature excursions where the
instrument might be stored at high or low temperature. See Applications
Information section.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Dropout Voltage VIN – VOUT, VOUT Error = 0.1%
IOUT = 0mA
IOUT = 1mA
IOUT = 10mA
IOUT = 50mA, I and C Grades Only
l
l
l
0.06
0.13
0.20
1.50
0.3
0.4
2.0
V
V
V
V
Output Current Short VOUT to GND 100 mA
Shutdown Pin Logic High Input Voltage
Logic High Input Current, Pin 3 = 2.4V
l
l
2.4
2
15
V
µA
Logic Low Input Voltage
Logic Low Input Current, Pin 3 = 0.8V
l
l
0.5 0.8
4
V
µA
Supply Current No Load
l
35 50
70
µA
µA
Shutdown Current RL = 1k
l
25 35
55
µA
µA
Output Voltage Noise (Note 7) 0.1Hz ≤ f ≤ 10Hz
10Hz ≤ f ≤ 1kHz
8
9.6
ppmP-P
ppmRMS
Long-Term Drift of Output Voltage, SO-8 Package (Note 8) See Applications Information 60 ppm/√kHr
Thermal Hysteresis (Note 9) ∆T = 0°C to 70°C
∆T = –40°C to 85°C
∆T = –40°C to 125°C
40
75
120
ppm
ppm
ppm
The l denotes the specifications which apply over the specified
temperature range, otherwise specifications are at TA = 25°C. VIN – VOUT = 0.5V, Pin 3 = 2.4V, CL = 2µF, unless otherwise specified.
LT1461
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Typical perForMance characTerisTics
2.5V Output Impedance
vs Frequency 2.5V Turn-On Time 2.5V Turn-On Time
2.5V Minimum Input/Output
Voltage Differential vs Load Current
2.5V Supply Current
vs Input Voltage
2.5V Ripple Rejection Ratio
vs Frequency
2.5V Reference Voltage
vs Temperature 2.5V Load Regulation
2.5V Line Regulation
vs Temperature
Characteristic curves are similar for most LT1461s.
Curves from the LT1461-2.5 and the LT1461-5 represent the extremes of the voltage options. Characteristic curves for other output
voltages fall between these curves and can be estimated based on their output.
TEMPERATURE (°C)
60 –40 –20
2.4980
REFERENCE VOLTAGE (V)
2.4985
2.4995
2.5000
2.5005
60 80 100
1461 G01
2.4990
0 20 40
120
2.5010
2.5015
2.5020
TEMPCO –60°C TO 120°C
3 TYPICAL PARTS
OUTPUT CURRENT (mA)
0.1
800
OUTPUT VOLTAGE CHANGE (ppm)
1200
1600
1 10
100
1461 G02
400
0
125°C
25°C
55°C
VIN = 7.5V
TEMPERATURE (°C)
40 –20
LINE REGULATION (ppm/V)
4
2
120
1461 G03
6
8 040 80 100
20 60
0
5
3
7
1
SUPPLY ∆ = 15V
5V – 20V
OUTPUT CURRENT (mA)
0.1
0.1
1
1 10
55°C
25°C
125°C
INPUT VOLTAGE (V)
SUPPLY CURRENT (µA)
1000
1461 G05
10
100
5 252015100
125°C
55°C
25°C
FREQUENCY (kHz)
0.01
40
RIPPLE REJECTION RATIO (dB)
50
60
70
80
0.1 1 10010
1000
1641 G06
30
20
10
0
90
100
FREQUENCY (kHz)
0.01
1
OUTPUT IMPEDANCE (Ω)
10
100
1000
0.1 1 10
1461 G07
COUT = 2µF
COUT = 1µF
TIME (100µs/DIV)
VOLTAGE (V)
VIN
20
10
0
2
1
0
1461 G08
CIN = 1µF
CL = 2µF
RL =
VOUT
TIME (100µs/DIV)
VOLTAGE (V)
VIN
20
10
0
2
1
0
1461 G09
CIN = 1µF
CL = 2µF
RL = 50Ω
VOUT
LT1461
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For more information www.linear.com/LT1461
5V Minimum Input/Output Voltage
Differential vs Load Current
5V Supply Current
vs Input Voltage
5V Ripple Rejection Ratio
vs Frequency
5V Reference Voltage
vs Temperature 5V Load Regulation
5V Line Regulation
vs Temperature
Typical perForMance characTerisTics
Characteristic curves are similar for most LT1461s.
Curves from the LT1461-2.5 and the LT1461-5 represent the extremes of the voltage options. Characteristic curves for other output
voltages fall between these curves and can be estimated based on their output.
TEMPERATURE (°C)
60
REFERENCE VOLTAGE (V)
5.0040
5.0030
5.0020
5.0010
5.0000
4.9990
4.9980
4.9970
4.9960
4.9950
4.9940
4.9930 20 20 40
1461 G13
40 060 80 100 120
TEMPCO –60°C TO 120°C
3 TYPICAL PARTS
OUTPUT CURRENT (mA)
0.1
800
LOAD REGULATION (ppm)
1200
1600
1 10
100
1461 G14
400
0
2000
VIN = 10V 125°C
125°C
25°C
25°C
55°C
55°C
TEMPERATURE (°C)
–40
LINE REGULATION (ppm/V)
4
2
120
1461 G15
6
8 040 80
20 20 60 100
0
5
3
7
1
SUPPLY ∆ = 14V
6V TO 20V
OUTPUT CURRENT (mA)
0.1
0.01
0.1
1
1 10
125°C
55°C
25°C
INPUT VOLTAGE (V)
10
SUPPLY CURRENT (µA)
100
1000
10000
0 10 15 20
1525
1461 G17
125°C
55°C 25°C
FREQUENCY (kHz)
0.01
40
RIPPLE REJECTION RATIO (dB)
50
60
70
80
0.1 1 10010
1000
1461 G18
30
20
10
0
90
100
2.5V Transient Response to 10mA
Load Step 2.5V Line Transient Response
2.5V Output Noise
0.1Hz ≤ f ≤ 10Hz
1461 G10
C
L
= 2µF
VOUT
50mV/DIV
IOUT
0mA
10mA/DIV
1461 G11
CIN = 0.1µF
VOUT
50mV/DIV
5V
4V
VIN
TIME (2SEC/DIV)
OUTPUT NOISE (10µV/DIV)
1461 G12
LT1461
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Supply Current
vs Temperature Current Limit vs Temperature
SHDN Pin Current
vs SHDN Input Voltage
5V Transient Response to 10mA
Load Step 5V Line Transient Response
5V Output Noise
0.1Hz ≤ f ≤ 10Hz
5V Output Impedance vs
Frequency 5V Turn-On Time 5V Turn-On Time
Typical perForMance characTerisTics
Characteristic curves are similar for most LT1461s.
Curves from the LT1461-2.5 and the LT1461-5 represent the extremes of the voltage options. Characteristic curves for other output
voltages fall between these curves and can be estimated based on their output.
FREQUENCY (kHz)
0.01
1
OUTPUT IMPEDANCE (Ω)
10
100
1000
0.1 1 10
1461 G19
COUT = 2µF COUT = 1µF
200µs/DIV
VIN
2V/DIV
6
4
2
0
4
2
0
1461 G20
VOUT
CIN = 1µF
COUT = 2µF
IOUT = 0
200µs/DIV
VIN
2V/DIV
6
4
2
0
4
2
0
1461 G21
VOUT
CIN = 1µF
COUT = 2µF
IOUT = 50mA
1461 G22
C
L
= 2µF
VOUT
50mV/DIV
0mA
10mA
I
OUT
1461 G23
C
IN
= 0.1µF
VOUT
50mV/DIV
7V
6V
VIN
TIME (2SEC/DIV)
OUTPUT NOISE (10µV/DIV)
1461 G24
TEMPERATURE (°C)
40
SUPPLY CURRENT (µA)
30
40
50
IS
20 60
120
1461 G25
20
10
020 0 40 80 100
IS(SHDN)
TEMPERATURE (°C)
50 –25
40
CURRENT LIMIT (mA)
80
140
050 75
1461 G26
60
120
100
25 100 125
SHDN PIN INPUT VOLTAGE (V)
0
0
SHDN PIN CURRENT (µA)
20
60
80
100
200
140
10
1461 G27
40
160
125°C
55°C
180
120
515 20
25°C
LT1461
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For more information www.linear.com/LT1461
–40°C to 85°C Hysteresis
–40°C to 125°C Hysteresis
0°C to 70°C Hysteresis
Typical perForMance characTerisTics
Characteristic curves are similar for most LT1461s.
Curves from the LT1461-2.5 and the LT1461-5 represent the extremes of the voltage options. Characteristic curves for other output
voltages fall between these curves and can be estimated based on their output.
HYSTERESIS (ppm)
100
NUMBER OF UNITS
12
16
20
WORST-CASE HYSTERESIS
ON 35 UNITS
1461 G29
8
4
10
14
18
6
2
080 –60 –40
0°C TO 25°C
70°C TO 25°C
20 0 20 40 60 80 100
HYSTERESIS (ppm)
100
NUMBER OF UNITS
12
16
20
WORST-CASE HYSTERESIS
ON 35 UNITS
8
4
10
14
18
6
2
080 60 40 –20 0 20 40 60 80 100
40°C TO 25°C85°C TO 25°C
1461 G30
HYSTERESIS (ppm)
–200
NUMBER OF UNITS
12
16
WORST-CASE HYSTERESIS
ON 35 UNITS
8
4
10
14
6
2
0–160 –120 –80 –40 0 40 80 120 160
200
40°C TO 25°C125°C TO 25°C
1461 G31
LT1461
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For more information www.linear.com/LT1461
Long-Term Drift (Number of Data Points Reduced at 650 Hours)*
Typical perForMance characTerisTics
Characteristic curves are similar for most LT1461s.
Curves from the LT1461-2.5 and the LT1461-5 represent the extremes of the voltage options. Characteristic curves for other output
voltages fall between these curves and can be estimated based on their output.
HOURS
*SEE APPLICATIONS INFORMATION FOR DETAILED EXPLANATION OF LONG-TERM DRIFT
50
ppm
50
150
250
0
100
200
400 800 1200 1600
1461 G28
2000
200 600 1000 1400 1800
0
LT1461S8
3 TYPICAL PARTS SOLDERED ONTO PCB
TA = 30°C
LT1461
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applicaTions inForMaTion
Examples shown in this Applications section use the
LT1461-2.5. The response of other voltage options can
be estimated by proper scaling.
Bypass and Load Capacitors
The LT1461 family requires a capacitor on the input and
on the output for stability. The capacitor on the input is
a supply bypass capacitor and if the bypass capacitors
from other components are close (within 2 inches) they
Figure 2. 50mA Load Step with CL = 2µFFigure 1. 1mA Load Step with CL = 1µF
should be sufficient. The output capacitor acts as frequency
compensation for the reference and cannot be omitted.
For light loads ≤1mA, aF nonpolar output capacitor is
usually adequate, but for higher loads (up to 75mA), the
output capacitor should beF or greater. Figures 1 and
2 show the transient response to a 1mA load step with
aF output capacitor and a 50mA load step with aF
output capacitor.
1461 F01
0mA
1mA
VOUT
20mV/DIV
IOUT
1mA/DIV
1461 F02
VOUT
200mV/DIV
IOUT
50mA/DIV
LT1461
11
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For more information www.linear.com/LT1461
applicaTions inForMaTion
Precision Regulator
The LT1461 will deliver 50mA with VIN = VOUT + 2.5V and
higher load current with higher VIN. Load regulation is
typically 12ppm/mA, which means for a 50mA load step,
the output will change by only 1.5mV. Thermal regulation,
caused by die temperature gradients and created from
load current or input voltage changes, is not measurable.
This often overlooked parameter must be added to normal
line and load regulation errors. The load regulation photo,
on the first page of this data sheet, shows the output
response to 200mW of instantaneous power dissipation
and the reference shows no sign of thermal errors. The
reference has thermal shutdown and will turn off if the
junction temperature exceeds 150°C.
Shutdown
The shutdown (Pin 3 low) serves to shut off load current
when the LT1461 is used as a regulator. The LT1461 op-
erates normally with Pin 3 open or greater than or equal
to 2.4V. In shutdown, the reference draws a maximum
supply current of 35µA. Figure 3 shows the transient
response of shutdown while the part is delivering 25mA.
After shutdown, the reference powers up in about 200µs.
Figure 3. Shutdown While Delivering 25mA, RL = 100Ω
PC Board Layout
In 13- to 16-bit systems where initial accuracy and
temperature coefficient calibrations have been done, the
mechanical and thermal stress on a PC board (in a card
cage for instance) can shift the output voltage and mask
the true temperature coefficient of a reference. In addition,
the mechanical stress of being soldered into a PC board
can cause the output voltage to shift from its ideal value.
Surface mount voltage references are the most susceptible
to PC board stress because of the small amount of plastic
used to hold the lead frame.
A simple way to improve the stress-related shifts is to
mount the reference near the short edge of the PC board,
or in a corner. The board edge acts as a stress boundary,
or a region where the flexure of the board is minimum.
The package should always be mounted so that the leads
absorb the stress and not the package. The package is
generally aligned with the leads parallel to the long side
of the PC board as shown in Figure 5a.
A qualitative technique to evaluate the effect of stress on
voltage references is to solder the part into a PC board and
deform the board a fixed amount as shown in Figure 4.
The flexure #1 represents no displacement, flexure #2 is
concave movement, flexure #3 is relaxation to no displace-
ment and finally, flexure #4 is a convex movement. This
motion is repeated for a number of cycles and the relative
Figure 4. Flexure Numbers
1461 F03
5V
0V
0V
VOUT
PIN 3
1
2
3
4
1461 F04
LT1461
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For more information www.linear.com/LT1461
applicaTions inForMaTion
The most effective technique to improve PC board stress
is to cut slots in the board around the reference to serve
as a strain relief. These slots can be cut on three sides of
the reference and the leads can exit on the fourth side. This
“tongue” of PC board material can be oriented in the long
direction of the board to further reduce stress transferred
to the reference.
The results of slotting the PC boards of Figures 5a and
5b are shown in Figures 6a and 6b. In this example the
slots can improve the output shift from about 100ppm
to nearly zero.
output deviation is noted. The result shown in Figure 5a is
for two LT1461S8-2.5s mounted vertically and Figure 5b
is for two LT1461S8-2.5s mounted horizontally. The parts
oriented in Figure 5a impart less stress into the package
because stress is absorbed in the leads. Figures 5a and
5b show the deviation to be between 125µV and 250µV
and implies a 50ppm and 100ppm change respectively.
This corresponds to a 13- to 14-bit system and is not a
problem for most 10- to 12-bit systems unless the sys-
tem has a calibration. In this case, as with temperature
hysteresis, this low level can be important and even more
careful techniques are required.
Figure 6a. Same Tw o LT1461S8-2.5s in Figure 5a, but with Slots
Figure 6b. Same Tw o LT1461S8-2.5s in Figure 5b, but with Slots
Figure 5a. Tw o Typical LT1461S8-2.5s,
Vertical Orientation without Slots
Figure 5b. Tw o Typical LT1461S8-2.5s,
Horizontal Orientation without Slots
LONG DIMENSION
2
1
0
0
40
3020
FLEXURE NUMBER
10
1461 F05a
1
OUTPUT DEVIATION (mV)
FLEXURE NUMBER 1461 F05b
LONG DIMENSION
2
1
0
0
40
302010
1
OUTPUT DEVIATION (mV)
SLOT
2
1
0
0
40
3020
FLEXURE NUMBER
10
1461 F06a
1
OUTPUT DEVIATION (mV)
SLOT
2
1
0
0
40
3020
FLEXURE NUMBER
10
1461 F06b
1
OUTPUT DEVIATION (mV)
LT1461
13
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applicaTions inForMaTion
Long-Term Drift
Long-term drift cannot be extrapolated from accelerated
high temperature testing. This erroneous technique gives
drift numbers that are wildly optimistic. The only way
long-term drift can be determined is to measure it over
the time interval of interest. The erroneous technique
uses the Arrhenius Equation to derive an acceleration fac-
tor from elevated temperature readings. The equation is:
A
F
=e
EA
K
1
T1
1
T2
where: EA = Activation Energy (Assume 0.7)
K = Boltzmann’s Constant
T2 = Test Condition in °Kelvin
T1 = Use Condition Temperature in °Kelvin
To show how absurd this technique is, compare the LT1461
data. Typical 1000 hour long-term drift at 30°C = 60ppm.
The typical 1000 hour long-term drift at 130°C = 120ppm.
From the Arrhenius Equation the acceleration factor is:
A
F
=e
0.7
0.0000863
1
303
1
403
=767
The erroneous projected long-term drift is:
120ppm/767 = 0.156ppm/1000 hr
For a 2.5V reference, this corresponds to a 0.39µV shift
after 1000 hours. This is pretty hard to determine (read
impossible) if the peak-to-peak output noise is larger than
this number. As a practical matter, one of the best laboratory
references available is the Fluke 732A and its long-term
drift is 1.5µV/mo. This performance is only available from
the best subsurface zener references utilizing specialized
heater techniques.
The LT1461 long-term drift data was taken with parts that
were soldered onto PC boards similar to areal world”
application. The boards were then placed into a constant
temperature oven with TA = 30°C, their outputs were
scanned regularly and measured with an 8.5 digit DVM.
As an additional accuracy check on the DVM, a Fluke 732A
laboratory reference was also scanned. Figure 7 shows
the long-term drift measurement system. The data taken
is shown at the end of the Typical Performance Charac-
teristics section of this data sheet. The long-term drift is
the trend line that asymptotes to a value at 2000 hours.
Note the slope in output shift between 0 hours and 1000
hours compared to the slope between 1000 hours and
2000 hours. Long-term drift is affected by differential
stresses between the IC and the board material created
during board assembly.
Figure 7. Long-Term Drift Measurement Setup
Hysteresis
The hysteresis curves found in the Typical Performance
Characteristics represent the worst-case data taken on
35 typical parts after multiple temperature cycles. As
expected, the parts that are cycled over the wider –40°C
to 125°C temperature range have more hysteresis than
those cycled over lower ranges. Note that the hysteresis
coming from 125°C to 25°C has an influence on the –40°C
to 25°C hysteresis. The –40°C to 25°C hysteresis is differ-
ent depending on the part’s previous temperature. This is
because not all of the high temperature stress is relieved
during the 25°C measurement.
The typical performance hysteresis curves are for parts
mounted in a socket and represent the performance of the
PCB3
SCANNER
1461 F07
FLUKE
732A
LABORATORY
REFERENCE
PCB2
PCB1
COMPUTER
8.5 DIGIT
DVM
LT1461
14
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For more information www.linear.com/LT1461
applicaTions inForMaTion
parts alone. What is more interesting are parts IR soldered
onto a PC board. If the PC board is then temperature cycled
several times from –40°C to 85°C, the resulting hysteresis
curve is shown in Figure 8. This graph shows the influence
of the PC board stress on the reference.
When the LT1461 is soldered onto a PC board, the output
shifts due to thermal hysteresis. Figure 9 shows the effect
of soldering 40 pieces onto a PC board using standard
IR reflow techniques. The average output voltage shift is
–110ppm. Remeasurement of these parts after 12 days
shows the outputs typically shift back 45ppm toward their
initial value. This second shift is due to the relaxation of
stress incurred during soldering.
Figure 9. Typical Distribution of Output Voltage Shift After Soldering Onto PC Board
Figure 8. –40°C to 85°C Hysteresis of 35 Parts Soldered Onto a PC Board
The LT1461 is capable of dissipating high power, i.e.,
for the LT1461-2.5, 17.5V 50mA = 875mW. The SO-8
package has a thermal resistance of 190°C/W and this
dissipation causes a 166°C internal rise producing a junc-
tion temperature of TJ = 25°C + 166°C = 191°C. What will
actually occur is the thermal shutdown will limit the junc-
tion temperature to around 150°C. This high temperature
excursion will cause the output to shift due to thermal
hysteresis. Under these conditions, a typical output shift is
–135ppm, although this number can be higher. This high
dissipation can cause the 25°C output accuracy to exceed
its specified limit. For best accuracy and precision, the
LT1461 junction temperature should not exceed 125°C.
HYSTERESIS (ppm)
200
NUMBER OF UNITS
12
8
4
10
6
2
11
7
3
9
5
1
0160 –120 80 40 0 40 80 120 160
200
40°C TO 25°C85°C TO 25°C
1461 F08
WORST-CASE HYSTERESIS
ON 35 UNITS
OUTPUT VOLTAGE SHIFT (ppm)
–300
0
NUMBER OF UNITS
2
4
6
8
12
–200 –100 0 100
1461 F09
200
300
10
LT1461
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For more information www.linear.com/LT1461
siMpliFieD scheMaTic
4GND
1461 SS
6V
OUT
3
SHDN
100k
2VIN
LT1461
16
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For more information www.linear.com/LT1461
package DescripTion
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
.016 – .050
(0.406 – 1.270)
.010 – .020
(0.254 – 0.508)× 45°
0°– 8° TYP
.008 – .010
(0.203 – 0.254)
SO8 REV G 0212
.053 – .069
(1.346 1.752)
.014 – .019
(0.355 – 0.483)
TYP
.004 – .010
(0.101 0.254)
.050
(1.270)
BSC
1234
.150 – .157
(3.810 – 3.988)
NOTE 3
8765
.189 – .197
(4.801 – 5.004)
NOTE 3
.228 – .244
(5.791 – 6.197)
.245
MIN .160 ±.005
RECOMMENDED SOLDER PAD LAYOUT
.045 ±.005
.050 BSC
.030
±.005
TYP
INCHES
(MILLIMETERS)
NOTE:
1. DIMENSIONS IN
2. DRAWING NOT TO SCALE
3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
4. PIN 1 CAN BE BEVEL EDGE OR A DIMPLE
S8 Package
8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610 Rev G)
LT1461
17
1461fb
For more information www.linear.com/LT1461
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
revision hisTory
REV DATE DESCRIPTION PAGE NUMBER
A 04/15 Features modified
Correction to VIN description, Typical Application schematic
Order Information updated
Note 3 thermal hysteresis description updated
Related Parts list updated
1
1
2
4
18
B 09/15 Removed unneeded Pin Functions section 10
LT1461
18
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For more information www.linear.com/LT1461
LINEAR TECHNOLOGY CORPORATION 1999
LT 0915 REV B • PRINTED IN USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507 www.linear.com/LT1461
relaTeD parTs
Typical applicaTion
Low Power 16-Bit A/D
PART NUMBER DESCRIPTION COMMENTS
LT1460 Micropower Series References 0.075% Accuracy, 10ppm/°C Drift, 20mA Drive
LT1790 Micropower Series References 0.05% Accuracy, 10ppm/°C Drift, 60µA Supply Current
LTC
®
1798 Micropower Series Reference 200mV Dropout at 10mA Drive, Sinks 2mA, 4μA Supply Current
LT6650 Micropower Reference and Buffer 0.5% Accuracy, 5.6μA Supply Current, SOT23 Package
LTC6652 Micropower Series Reference 0.05% Accuracy, 5ppm/°C Drift, –40°C to 125°C Operation
LT6654 All Purpose, Rugged and Precise Micropower References 0.05% Accuracy, 10ppm/°C Drift, –55°C to 125°C Operation, ±10mA Output
Drive, 100mV Dropout, 1.6ppmP-P Noise
LT6656 1µA Precision Voltage Reference 0.05% Accuracy, 10ppm/°C, 800nA Supply Current, SOT-23 Package
LT6660 Tiny Micropower Series Reference 0.2% Accuracy, 20ppm/°C Drift, 20mA Drive, 2mm × 2mm DFN Package
SCK
SD0
CS
NOISE PERFORMANCE*
VIN = 0V, VNOISE = 1.1ppmRMS = 2.25µVRMS = 16µVP-P
VIN = VREF/2, VNOISE = 1.6ppmRMS = 4µVRMS = 24µVP-P
VIN = VREF, VNOISE = 2.5ppmRMS = 6.25µVRMS = 36µVP-P
*FOR 24-BIT PERFORMANCE USE LT1236 REFERENCE
VREF
VCC
200µA35µA F
1461 TA03
0.1µF
F
FO
LTC2400
VCC
GND
LT1461-2.5
VCC
VOUT
INPUT
GND
VIN
SPI
INTERFACE

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