datasheet for LT1461 by Linear Technology

datasheet for LT1461 by Linear Technology
LT1461
Micropower Precision
Low Dropout Series
Voltage Reference Family
FEATURES
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DESCRIPTIO
Trimmed to High Accuracy: 0.04% Max
Low Drift: 3ppm/°C Max
Low Supply Current: 50µA Max
Temperature Coefficient Guaranteed to 125°C
High Output Current: 50mA Min
Low Dropout Voltage: 300mV Max
Excellent Thermal Regulation
Power Shutdown
Thermal Limiting
Operating Temperature Range: – 40°C to 125°C
Voltage Options: 2.5V, 3V, 3.3V, 4.096V and 5V
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APPLICATIO S
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A/D and D/A Converters
Precision Regulators
Handheld Instruments
Power Supplies
The LT ®1461 is a family of low dropout micropower bandgap
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 immeasurable, while the exceedingly good load and thermal 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 conditions. The LT1461 is
available in 2.5V, 3V, 3.3V 4.096V and 5V options.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATIO
LT1461-2.5 Load Regulation, PDISS = 200mW
Basic Connection
(VOUT + 0.3V) ≤ VIN ≤ 20V
VOUT
LT1461
CIN
1µF
CL
2µF
1461 TA01
0mA
IOUT
20mA
VOUT LOAD REG
1mV/DIV
10ms/DIV
1461 TA02
1
LT1461
W W
W
AXI U
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ABSOLUTE
RATI GS
(Note 1)
Input Voltage ........................................................... 20V
Output Short-Circuit Duration ......................... Indefinite
Operating Temperature Range
(Note 2) ........................................... – 40°C to 125°C
Storage Temperature Range (Note 3) ... – 65°C to 150°C
Specified Temperature Range
Commercial ............................................ 0°C to 70°C
Industrial ........................................... – 40°C to 85°C
High ................................................. – 40°C to 125°C
Lead Temperature (Soldering, 10 sec).................. 300°C
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PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
TOP VIEW
DNC* 1
8
DNC*
VIN 2
7
DNC*
SHDN 3
6
VOUT
GND 4
5
DNC*
S8 PACKAGE
8-LEAD PLASTIC SO
*DNC: DO NOT CONNECT
TJMAX = 150°C, θJA = 190°C/ W
(Note 3)
LT1461ACS8-2.5
LT1461BCS8-2.5
LT1461CCS8-2.5
LT1461AIS8-2.5
LT1461BIS8-2.5
LT1461CIS8-2.5
LT1461DHS8-2.5
LT1461ACS8-3
LT1461BCS8-3
LT1461CCS8-3
LT1461AIS8-3
LT1461BIS8-3
LT1461CIS8-3
LT1461DHS8-3
LT1461ACS8-3.3
LT1461BCS8-3.3
LT1461CCS8-3.3
LT1461AIS8-3.3
LT1461BIS8-3.3
LT1461CIS8-3.3
LT1461DHS8-3.3
LT1461ACS8-4
LT1461BCS8-4
LT1461CCS8-4
LT1461AIS8-4
LT1461BIS8-4
LT1461CIS8-4
LT1461DHS8-4
S8 PART MARKING
LT1461ACS8-5
LT1461BCS8-5
LT1461CCS8-5
LT1461AIS8-5
LT1461BIS8-5
LT1461CIS8-5
LT1461DHS8-5
461A25
461B25
461C25
61AI25
61BI25
61CI25
61DH25
1461A3
1461B3
1461C3
461AI3
461BI3
461CI3
461DH3
461A33
461B33
461C33
61AI33
61BI33
61CI33
61DH33
1461A4
1461B4
1461C4
461AI4
461BI4
461CI4
461DH4
1461A5
1461B5
1461C5
461AI5
461BI5
461CI5
461DH5
Consult factory for Military grade parts.
AVAILABLE OPTIO S
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OUTPUT VOLTAGE
INITIAL
ACCURACY
TEMPERATURE
COEFFICIENT
TEMPERATURE
RANGE
2.5V
3.0V
3.3V
4.096V
5.0V
0.04% Max
0.04% Max
3ppm/°C Max
3ppm/°C Max
0°C to 70°C
– 40°C to 85°C
LT1461ACS8-2.5
LT1461AIS8-2.5
LT1461ACS8-3
LT1461AIS8-3
LT1461ACS8-3.3
LT1461AIS8-3.3
LT1461ACS8-4
LT1461AIS8-4
LT1461ACS8-5
LT1461AIS8-5
0.06% Max
0.06% Max
7ppm/°C Max
7ppm/°C Max
0°C to 70°C
– 40°C to 85°C
LT1461BCS8-2.5
LT1461BIS8-2.5
LT1461BCS8-3
LT1461BIS8-3
LT1461BCS8-3.3
LT1461BIS8-3.3
LT1461BCS8-4
LT1461BIS8-4
LT1461BCS8-5
LT1461BIS8-5
0.08% Max
0.08% Max
12ppm/°C Max
12ppm/°C Max
0°C to 70°C
– 40°C to 85°C
LT1461CCS8-2.5
LT1461CIS8-2.5
LT1461CCS8-3
LT1461CIS8-3
LT1461CCS8-3.3
LT1461CIS8-3.3
LT1461CCS8-4
LT1461CIS8-4
LT1461CCS8-5
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
2
LT1461
ELECTRICAL CHARACTERISTICS
The ● denotes 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.
PARAMETER
CONDITIONS
Output Voltage (Note 4)
LT1461ACS8/LT1461AIS8
LT1461BCS8/LT1461BIS8
LT1461CCS8/LT1461CIS8
LT1461DHS8
MIN
Output Voltage Temperature Coefficient (Note 5)
LT1461ACS8/LT1461AIS8
LT1461BCS8/LT1461BIS8
LT1461CCS8/LT1461CIS8
LT1461DHS8
Line Regulation
(VOUT + 0.5V) ≤ VIN ≤ 20V
TYP
– 0.04
– 0.06
– 0.08
– 0.15
ppm/°C
ppm/°C
ppm/°C
ppm/°C
2
8
12
ppm/V
ppm/V
15
50
ppm/V
12
●
30
40
ppm/mA
ppm/mA
LT1461DHS8, 0 ≤ IOUT ≤ 10mA
●
50
ppm/mA
VIN – VOUT, VOUT Error = 0.1%
IOUT = 0mA
IOUT = 1mA
IOUT = 10mA
IOUT = 50mA, I and C Grades Only
●
●
●
0.3
0.4
2.0
V
V
V
V
●
VIN = VOUT + 2.5V
0 ≤ IOUT ≤ 50mA
Output Current
Short VOUT to GND
Shutdown Pin
Logic High Input Voltage
Logic High Input Current, Pin 3 = 2.4V
●
●
Logic Low Input Voltage
Logic Low Input Current, Pin 3 = 0.8V
●
●
Supply Current
0.06
0.13
0.20
1.50
100
No Load
RL = 1k
mA
2.4
2
15
V
µA
0.5
0.8
4
V
µA
35
50
70
µA
µA
25
35
55
µA
µA
●
Shutdown Current
%
%
%
%
3
7
12
20
LT1461DHS8
Dropout Voltage
UNITS
0.04
0.06
0.08
0.15
1
3
5
7
●
●
●
●
●
Load Regulation Sourcing (Note 6)
MAX
●
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
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LT1461 is guaranteed functional over the operating
temperature range of – 40°C to 125°C.
Note 3: If the part is stored outside of the specified temperature range, or
the junction temperature exceeds the specified temperature range, the
output may shift due to hysteresis.
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 stillair 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.
3
LT1461
ELECTRICAL CHARACTERISTICS
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.
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TYPICAL PERFOR A CE 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.
2.5V Reference Voltage
vs Temperature
2.5010
2.5005
2.5000
2.4995
2.4990
2.4985
2.4980
– 60 – 40 – 20
0
VIN = 7.5V
–1
1200
125°C
25°C
800
400
–2
–3
–4
–5
–6
– 55°C
–7
0
0.1
0 20 40 60 80 100 120
TEMPERATURE (°C)
1
10
OUTPUT CURRENT (mA)
SUPPLY ∆ = 15V
5V – 20V
–8
–40 – 20
100
0
20 40 60 80
TEMPERATURE (°C)
100 120
1461 G02
1461 G01
1461 G03
2.5V Ripple Rejection Ratio
vs Frequency
2.5V Supply Current
vs Input Voltage
2.5V Minimum Input/Output
Voltage Differential vs Load Current
10
LINE REGULATION (ppm/V)
REFERENCE VOLTAGE (V)
2.5015
1600
TEMPCO –60°C TO 120°C
3 TYPICAL PARTS
OUTPUT VOLTAGE CHANGE (ppm)
2.5020
2.5V Line Regulation
vs Temperature
2.5V Load Regulation
100
1000
125°C
RIPPLE REJECTION RATIO (dB)
1
SUPPLY CURRENT (µA)
INPUT/OUTPUT VOLTAGE (V)
90
100
125°C
25°C
– 55°C
25°C
0.1
1
10
OUTPUT CURRENT (mA)
100
1461 G04
4
70
60
50
40
30
20
10
– 55°C
0.1
80
10
0
5
10
15
20
INPUT VOLTAGE (V)
25
1461 G05
0
0.01
0.1
1
10
FREQUENCY (kHz)
100
1000
1641 G06
LT1461
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TYPICAL PERFOR A CE 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.
2.5V Output Impedance
vs Frequency
2.5V Turn-On Time
2.5V Turn-On Time
1000
10
10
10
0
0
2
2
VOUT
VOUT
1
1
CIN = 1µF
CL = 2µF
RL = ∞
0
1
0.01
0.1
1
FREQUENCY (kHz)
VIN
20
VOLTAGE (V)
COUT = 1µF
100
VIN
20
VOLTAGE (V)
OUTPUT IMPEDANCE (Ω)
COUT = 2µF
10
CIN = 1µF
CL = 2µF
RL = 50Ω
0
TIME (100µs/DIV)
TIME (100µs/DIV)
1461 G08
1461 G09
1461 G07
2.5V Transient Response to 10mA
Load Step
VIN
VOUT
50mV/DIV
5V
OUTPUT NOISE (10µV/DIV)
IOUT
0mA
10mA/DIV
2.5V Output Noise
0.1Hz ≤ f ≤ 10Hz
2.5V Line Transient Response
4V
VOUT
50mV/DIV
CL = 2µF
1461 G10
CIN = 0.1µF
1461 G11
TIME (2SEC/DIV)
1461 G12
5
LT1461
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TYPICAL PERFOR A CE 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.
5V Reference Voltage
vs Temperature
2000
5.0040
TEMPCO –60°C TO 120°C
5.0030 3 TYPICAL PARTS
5.0020
VIN = 10V
0
125°C
25°C
5.0010
5.0000
4.9990
4.9980
4.9970
4.9960
4.9950
1600
–1
LINE REGULATION (ppm/V)
LOAD REGULATION (ppm)
REFERENCE VOLTAGE (V)
5V Line Regulation
vs Temperature
5V Load Regulation
–55°C
1200
800
25°C
400
125°C
–55°C
0
0.1
0 20 40 60 80 100 120
TEMPERATURE (°C)
1
10
OUTPUT CURRENT (mA)
–4
–5
–6
SUPPLY ∆ = 14V
6V TO 20V
–8
–40 –20 0
20 40 60 80
TEMPERATURE (°C)
100
100 120
1461 G14
1461 G13
1461 G15
5V Ripple Rejection Ratio
vs Frequency
5V Supply Current
vs Input Voltage
5V Minimum Input/Output Voltage
Differential vs Load Current
10000
10
–3
–7
4.9940
4.9930
–60 –40 –20
–2
100
1
25°C
125°C
–55°C
0.1
RIPPLE REJECTION RATIO (dB)
SUPPLY CURRENT (µA)
INPUT/OUTPUT VOLTAGE (V)
90
1000
100
125°C
–55°C
25°C
10
80
70
60
50
40
30
20
10
0.01
0
0.01
1
0.1
1
10
OUTPUT CURRENT (mA)
100
0
5
10
15
INPUT VOLTAGE (V)
20
1461 G16
25
0.1
1
10
FREQUENCY (kHz)
100
1461 G17
5V Output Impedance vs Frequency
1000
1461 G18
5V Turn-On Time
5V Turn-On Time
1000
COUT = 2µF
COUT = 1µF
VIN
4
4
2
2
0
VOUT
4
10
2
1
0.01
0.1
1
FREQUENCY (kHz)
10
0
VOUT
2
CIN = 1µF
COUT = 2µF
IOUT = 0
CIN = 1µF
COUT = 2µF
IOUT = 50mA
0
200µs/DIV
200µs/DIV
1461 G20
1461 G19
VIN
4
0
6
6
2V/DIV
100
2V/DIV
OUTPUT IMPEDANCE (Ω)
6
1461 G21
LT1461
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TYPICAL PERFOR A CE 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.
5V Transient Response to 10mA
Load Step
7V
VIN
6V
OUTPUT NOISE (10µV/DIV)
IOUT
5V Output Noise
0.1Hz ≤ f ≤ 10Hz
5V Line Transient Response
0mA
10mA
VOUT
50mV/DIV
VOUT
50mV/DIV
1461 G22
CL = 2µF
1461 G23
CIN = 0.1µF
TIME (2SEC/DIV)
1461 G24
Supply Current
vs Temperature
SHDN Pin Current
vs SHDN Input Voltage
Current Limit vs Temperature
200
140
50
180
IS
30
20
SHDN PIN CURRENT (µA)
120
IS(SHDN)
CURRENT LIMIT (mA)
SUPPLY CURRENT (µA)
40
100
80
125°C
120
25°C
100
– 55°C
80
60
40
60
10
160
140
20
0
– 40 –20
0
20 40
60 80
TEMPERATURE (°C)
100 120
1461 G25
40
–50
0
–25
50
25
0
75
TEMPERATURE (°C)
100
125
1461 G26
0
15
10
5
SHDN PIN INPUT VOLTAGE (V)
20
1461 G27
7
LT1461
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TYPICAL PERFOR A CE 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.
0°C to 70°C Hysteresis
20
18
WORST-CASE HYSTERESIS
ON 35 UNITS
NUMBER OF UNITS
16
14
70°C TO 25°C
12
0°C TO 25°C
10
8
6
4
2
0
–100
– 80
– 60
– 40
– 20
0
20
HYSTERESIS (ppm)
40
60
80
100
1461 G29
– 40°C to 85°C Hysteresis
20
18
WORST-CASE HYSTERESIS
ON 35 UNITS
NUMBER OF UNITS
16
14
85°C TO 25°C
12
– 40°C TO 25°C
10
8
6
4
2
0
–100
– 80
– 60
– 40
– 20
0
20
HYSTERESIS (ppm)
40
60
80
100
1461 G30
– 40°C to 125°C Hysteresis
16
14
NUMBER OF UNITS
12
WORST-CASE HYSTERESIS
ON 35 UNITS
125°C TO 25°C
– 40°C TO 25°C
10
8
6
4
2
0
–200
–160
–120
–80
–40
0
40
HYSTERESIS (ppm)
80
120
160
200
1461 G31
8
LT1461
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TYPICAL PERFOR A CE 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.
Long-Term Drift (Number of Data Points Reduced at 650 Hours)*
250
LT1461S8
3 TYPICAL PARTS SOLDERED ONTO PCB
TA = 30°C
200
ppm
150
100
50
0
–50
0
200
600
400
800
1000
HOURS
1200
1400
1600
1800
2000
1461 G15
*SEE APPLICATIONS INFORMATION FOR DETAILED EXPLANATION OF LONG-TERM DRIFT
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APPLICATIO S I FOR ATIO
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
should be sufficient. The output capacitor acts as frequency compensation for the reference and cannot be
omitted. For light loads ≤ 1mA, a 1µF nonpolar output
capacitor is usually adequate, but for higher loads (up to
75mA), the output capacitor should be 2µF or greater.
Figures 1 and 2 show the transient response to a 1mA
load step with a 1µF output capacitor and a 50mA load
step with a 2µF output capacitor.
IOUT 0mA
1mA/DIV 1mA
IOUT
50mA/DIV
VOUT
200mV/DIV
VOUT
20mV/DIV
1461 F01
Figure 1. 1mA Load Step with CL = 1µF
1461 F02
Figure 2. 50mA Load Step with CL = 2µF
9
LT1461
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APPLICATIO S I FOR ATIO
Precision Regulator
PC Board Layout
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.
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.
Shutdown
The shutdown (Pin 3 low) serves to shut off load current
when the LT1461 is used as a regulator. The LT1461
operates 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.
5V
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 displacement and finally, flexure #4 is a convex movement.
This motion is repeated for a number of cycles and the
PIN 3
1
0V
2
VOUT
3
0V
4
1461 F03
Figure 3. Shutdown While Delivering 25mA, RL = 100Ω
10
1461 F04
Figure 4. Flexure Numbers
LT1461
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APPLICATIO S I FOR ATIO
relative 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
system has a calibration. In this case, as with temperature
hysteresis, this low level can be important and even more
careful techniques are required.
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.
2
OUTPUT DEVIATION (mV)
OUTPUT DEVIATION (mV)
2
1
LONG DIMENSION
0
0
SLOT
–1
–1
0
10
20
30
FLEXURE NUMBER
0
40
10
20
30
FLEXURE NUMBER
1461 F05a
Figure 5a. Two Typical LT1461S8-2.5s,
Vertical Orientation Without Slots
40
1461 F06a
Figure 6a. Same Two LT1461S8-2.5s in Figure 5a, but with Slots
2
2
OUTPUT DEVIATION (mV)
OUTPUT DEVIATION (mV)
1
1
LONG DIMENSION
0
–1
0
10
20
30
FLEXURE NUMBER
Figure 5b. Two Typical LT1461S8-2.5s,
Horizontal Orientation Without Slots
40
1461 F05b
1
0
SLOT
–1
0
10
20
FLEXURE NUMBER
30
40
1461 F06b
Figure 6b. Same Two LT1461S8-2.5s in Figure 5b, but with Slots
11
LT1461
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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 factor from elevated temperature readings. The
equation is:
AF
EA  1 1 
 – 
= e K  T 1 T 2
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:
AF
 1
0.7
1
–


.
0
0000863
303
403


=e
= 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 longterm 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 a “real world”
application. The boards were then placed into a constant
temperature oven with TA = 30°C, their outputs were
12
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 Characteristics 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.
PCB3
PCB2
PCB1
SCANNER
8.5 DIGIT
DVM
COMPUTER
1461 F07
FLUKE
732A
LABORATORY
REFERENCE
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 different
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
LT1461
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APPLICATIO S I FOR ATIO
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.
12
11
WORST-CASE HYSTERESIS
ON 35 UNITS
10
85°C TO 25°C
9
NUMBER OF UNITS
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
junction temperature of TJ = 25°C + 166°C = 191°C. What
will actually occur is the thermal shutdown will limit the
junction 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.
– 40°C TO 25°C
8
7
6
5
4
3
2
1
0
– 200
–160
–120
– 80
– 40
0
40
HYSTERESIS (ppm)
80
120
160
200
1461 F08
Figure 8. – 40°C to 85°C Hysteresis of 35 Parts Soldered Onto a PC Board
12
NUMBER OF UNITS
10
8
6
4
2
0
–300
200
0
100
–200 –100
OUTPUT VOLTAGE SHIFT (ppm)
300
1461 F09
Figure 9. Typical Distribution of Output Voltage Shift After Soldering Onto PC Board
13
LT1461
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SI PLIFIED SCHE ATIC
2 VIN
6 VOUT
100k
SHDN 3
4 GND
1461 SS
14
LT1461
U
PACKAGE DESCRIPTIO
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)
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
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.
SO8 1298
15
LT1461
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TYPICAL APPLICATIO
Low Power 16-Bit A/D
VCC
35µA
200µA
VCC
1µF
VCC
FO
LTC2400
VREF
SCK
SD0
CS
VIN
LT1461-2.5
VOUT
1µF
INPUT
0.1µF
GND
GND
SPI
INTERFACE
1461 TA03
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
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1019
Precision Reference
Bandgap, 0.05%, 5ppm/°C
LT1027
Precision 5V Reference
Lowest TC, High Accuracy, Low Noise, Zener Based
LT1236
Precision Reference
5V and 10V Zener-Based 5ppm/°C, SO-8 Package
LTC 1798
Micropower Low Dropout Reference
0.15% Max, 6.5µA Supply Current
LT1460
Micropower Precision Series Reference
Bandgap, 130µA Supply Current 10ppm/°C, Available in SOT-23
LT1634
Micropower Precision Shunt Voltage Reference
Bandgap 0.05%, 10ppm/°C, 10µA Supply Current
LT1790
Precision SOT-23 Series Reference
Bandgap 0.05% Max, 10ppm/°C Max
®
16
Linear Technology Corporation
1461f LT/LCG 0800 4K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com
 LINEAR TECHNOLOGY CORPORATION 1999
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