LTC6655
1
6655fa
Typical applicaTion
DescripTion
0.25ppm Noise, Low Drift
Precision Buffered
Reference Family
The LTC
®
6655 is a complete family of precision bandgap
voltage references, offering exceptional noise and drift
performance. This low noise and drift is ideally suited for
the high resolution measurements required by instrumenta-
tion and test equipment. In addition, the LTC6655 is fully
specified over the temperature range of –40°C to 125°C,
ensuring its suitability for demanding automotive and
industrial applications. Advanced curvature compensation
allows this bandgap reference to achieve a drift of less than
2ppm/°C with a predictable temperature characteristic
and an output voltage accurate to ±0.025%, reducing or
eliminating the need for calibration.
The LTC6655 can be powered from as little as 500mV
above the output voltage to as much as 13.2V. Superior
load regulation with source and sink capability, coupled
with exceptional line rejection, ensures consistent per-
formance over a wide range of operating conditions. A
shutdown mode is provided for low power applications.
Available in a small MSOP package, the LTC6655 family
of references is an excellent choice for demanding preci-
sion applications.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
Basic Connection
FeaTures
applicaTions
n Low Noise: 0.25ppmP-P (0.1Hz to 10Hz)
625nVP-P for the LTC6655-2.5
n Low Drift: 2ppm/°C Max
n High Accuracy: ±0.025% Max
n Fully Specified from –40°C to 125°C
n 100% Tested at –40°C, 25°C and 125°C
n Load Regulation: <10ppm/mA
n Sinks and Sources Current: ±5mA
n Low Dropout: 500mV
n Maximum Supply Voltage: 13.2V
n Low Power Shutdown: <20µA Max
n Available Output Voltages: 1.25V, 2.048V, 2.5V, 3V,
3.3V, 4.096V, 5V
n Available in an 8-Lead MSOP Package
n
Instrumentation and Test Equipment
n
High Resolution Data Acquisition Systems
n
Weigh Scales
n
Precision Battery Monitors
n
High Temperature Applications
n
Precision Regulators
n
Medical Equipment
n
High Output Current Precision Reference
LTC6655-2.5
VIN
SHDN COUT
10µF
VOUT
6655 TA01a
VOUT_F
VOUT_S
3V < VIN ≤ 13.2V
GND
CIN
0.1µF
Low Frequency 0.1Hz to 10Hz Noise (LTC6655-2.5)
500nV/DIV
6655 TA01b
1s/DIV
LTC6655
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Input Voltage
VIN to GND .......................................... 0.3V to 13.2V
SHDN to GND ........................... 0.3V to (VIN + 0.3V)
Output Voltage:
VOUT_F ...................................... 0.3V to (VIN + 0.3V)
VOUT_S ..................................................... 0.3V to 6V
Output Short-Circuit Duration ...................... Indefinite
Operating Temperature Range (Note 2) . 40°C to 125°C
Storage Temperature Range (Note 2) ..... 65°C to 150°C
Lead Temperature Range (Soldering, 10 sec)
(Note 3) .................................................................300°C
(Note 1)
1
2
3
4
SHDN
VIN
GND*
GND
8
7
6
5
GND*
VOUT_F
VOUT_S
GND*
TOP VIEW
MS8 PACKAGE
8-LEAD PLASTIC MSOP
TJMAX = 150°C, θJA = 300°C/W
*CONNECT PINS TO DEVICE GND (PIN 4)
pin conFiguraTionabsoluTe MaxiMuM raTings
orDer inForMaTion
LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION SPECIFIED TEMPERATURE RANGE
LTC6655BHMS8-1.25#PBF LTC6655BHMS8-1.25#TRPBF LTFDG 8-Lead Plastic MSOP –40°C to 125°C
LTC6655CHMS8-1.25#PBF LTC6655CHMS8-1.25#TRPBF LTFDG 8-Lead Plastic MSOP –40°C to 125°C
LTC6655BHMS8-2.048#PBF LTC6655BHMS8-2.048#TRPBF LTFDH 8-Lead Plastic MSOP –40°C to 125°C
LTC6655CHMS8-2.048#PBF LTC6655CHMS8-2.048#TRPBF LTFDH 8-Lead Plastic MSOP –40°C to 125°C
LTC6655BHMS8-2.5#PBF LTC6655BHMS8-2.5#TRPBF LTFCY 8-Lead Plastic MSOP –40°C to 125°C
LTC6655CHMS8-2.5#PBF LTC6655CHMS8-2.5#TRPBF LTFCY 8-Lead Plastic MSOP –40°C to 125°C
LTC6655BHMS8-3#PBF LTC6655BHMS8-3#TRPBF LTFDJ 8-Lead Plastic MSOP –40°C to 125°C
LTC6655CHMS8-3#PBF LTC6655CHMS8-3#TRPBF LTFDJ 8-Lead Plastic MSOP –40°C to 125°C
LTC6655BHMS8-3.3#PBF LTC6655BHMS8-3.3#TRPBF LTFDK 8-Lead Plastic MSOP –40°C to 125°C
LTC6655CHMS8-3.3#PBF LTC6655CHMS8-3.3#TRPBF LTFDK 8-Lead Plastic MSOP –40°C to 125°C
LTC6655BHMS8-4.096#PBF LTC6655BHMS8-4.096#TRPBF LTFDM 8-Lead Plastic MSOP –40°C to 125°C
LTC6655CHMS8-4.096#PBF LTC6655CHMS8-4.096#TRPBF LTFDM 8-Lead Plastic MSOP –40°C to 125°C
LTC6655BHMS8-5#PBF LTC6655BHMS8-5#TRPBF LTFDN 8-Lead Plastic MSOP –40°C to 125°C
LTC6655CHMS8-5#PBF LTC6655CHMS8-5#TRPBF LTFDN 8-Lead Plastic MSOP –40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard 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/
LTC6655
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aVailable opTions
OUTPUT VOLTAGE INITIAL ACCURACY TEMPERATURE COEFFICIENT PART NUMBER
1.250 0.025%
0.05% 2ppm/°C
5ppm/°C LTC6655BHMS8-1.25
LTC6655CHMS8-1.25
2.048 0.025%
0.05% 2ppm/°C
5ppm/°C LTC6655BHMS8-2.048
LTC6655CHMS8-2.048
2.500 0.025%
0.05% 2ppm/°C
5ppm/°C LTC6655BHMS8-2.5
LTC6655CHMS8-2.5
3.000 0.025%
0.05% 2ppm/°C
5ppm/°C LTC6655BHMS8-3.0
LTC6655CHMS8-3.0
3.300 0.025%
0.05% 2ppm/°C
5ppm/°C LTC6655BHMS8-3.3
LTC6655CHMS8-3.3
4.096 0.025%
0.05% 2ppm/°C
5ppm/°C LTC6655BHMS8-4.096
LTC6655CHMS8-4.096
5.000 0.025%
0.05% 2ppm/°C
5ppm/°C LTC6655BHMS8-5
LTC6655CHMS8-5
See Order Information section for complete part number listing.
elecTrical characTerisTics
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = VOUT + 0.5V, VOUT_S connected to VOUT_F, unless otherwise noted.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Output Voltage LTC6655B
LTC6655C –0.025
–0.05 0.025
0.05 %
%
Output Voltage Temperature Coefficient
(Note 4) LTC6655B
LTC6655C
l
l
1
2.5 2
5ppm/°C
ppm/°C
Line Regulation VOUT + 0.5V ≤ VIN ≤ 13.2V, SHDN = VIN
l
5 25
40 ppm/V
ppm/V
Load Regulation (Note 5) ISOURCE = 5mA
l
3
15 ppm/mA
ppm/mA
ISINK = 5mA
l
10
30 ppm/mA
ppm/mA
Operating Voltage (Note 6) LTC6655-1.25, LTC6655-2.048, LTC6655-2.5
ISOURCE = 5mA, VOUT Error ≤ 0.1%
l
3
13.2
V
LTC6655-3, LTC6655-3.3, LTC6655-4.096, LTC6655-5
ISOURCE = ±5mA, VOUT Error ≤ 0.1%
IOUT = 0mA, VOUT Error ≤ 0.1%
l
l
VOUT + 0.5
VOUT + 0.2
13.2
13.2
V
V
Output Short-Circuit Current Short VOUT to GND
Short VOUT to VIN
20
20 mA
mA
Shutdown Pin (SHDN) Logic High Input Voltage
Logic High Input Current, SHDN = 2V
l
l
2.0
12 V
µA
Logic Low Input Voltage
Logic Low Input Current, SHDN = 0.8V
l
l
0.8
15 V
µA
Supply Current No Load
l
5 7
7.5 mA
mA
Shutdown Current SHDN Tied to GND l20 µA
LTC6655
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elecTrical characTerisTics
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = VOUT + 0.5V, VOUT_S connected to VOUT_F, unless otherwise noted.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Output Voltage Noise (Note 7) 0.1Hz ≤ f ≤ 10Hz
10Hz ≤ f ≤ 1kHz 0.25
0.67 ppmP-P
ppmRMS
Turn-On Time 0.1% Settling, COUT = 2.7µF 400 µs
Long-Term Drift of Output Voltage (Note 8) 60 ppm/√kHr
Hysteresis (Note 9) T = –0°C to 70°C
T = –40°C to 85°C
T = –40°C to 125°C
30
35
60
ppm
ppm
ppm
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: Precision may be affected if the parts are stored outside of the
specified temperature range. Large temperature changes may cause
changes in device performance due to thermal hysteresis. For best
performance, extreme temperatures should be avoided whenever possible.
Note 3: The stated temperature is typical for soldering of the leads during
manual rework. For detailed IR reflow recommendations, refer to the
Applications Information section.
Note 4: Temperature coefficient is measured by dividing the maximum
change in output voltage by the specified temperature range.
Note 5: Load regulation is measured on a pulse basis from no load to
the specified load current. Load current does not include the 2mA sense
current. Output changes due to die temperature change must be taken into
account separately.
Note 6: Excludes load regulation errors. Minimum supply for the
LTC6655-1.25, LTC6655-2.048 and LTC6655-2.5 is set by internal circuitry
supply requirements, regardless of load condition. Minimum supply for
the LTC6655-3, LTC6655-3.3, LTC6655-4.096 and LTC6655-5 is specified
by load current.
Note 7: Peak-to-peak noise is measured with a 2-pole highpass filter at
0.1Hz and 3-pole lowpass filter at 10Hz. The unit is enclosed in a still-air
environment to eliminate thermocouple effects on the leads, and the
test time is 10 seconds. Due to the statistical nature of noise, repeating
noise measurements will yield larger and smaller peak values in a given
measurement interval. By repeating the measurement for 1000 intervals,
each 10 seconds long, it is shown that there are time intervals during
which the noise is higher than in a typical single interval, as predicted by
statistical theory. In general, typical values are considered to be those for
which at least 50% of the units may be expected to perform similarly or
better. For the 1000 interval test, a typical unit will exhibit noise that is
less than the typical value listed in the Electrical Characteristics table in
more than 50% of its measurement intervals. See Application Note 124 for
noise testing details. RMS noise is measured with a spectrum analyzer in a
shielded environment.
Note 8: Long-term stability 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 stability is also affected by differential
stresses between the IC and the board material created during board
assembly.
Note 9: Hysteresis in output voltage is created by mechanical stress
that differs depending 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 to the hot or cold temperature limit before successive
measurements. Hysteresis is roughly proportional to the square of the
temperature change. For instruments that are stored at well controlled
temperatures (within 20 or 30 degrees of operational temperature),
hysteresis is usually not a significant error source.
LTC6655
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Typical perForMance characTerisTics
Characteristic curves are similar for most voltage options of the LTC6655. Curves from the LTC6655-1.25, LTC6655-2.5 and the
LTC6655-5 represent the range of performance across the entire family of references. Characteristic curves for other output voltages
fall between these curves and can be estimated based on their voltage output.
1.25V Load Regulation (Sinking)
1.25V Output Voltage Noise
Spectrum
1.25V Sinking Current with a
3.3µF Output Capacitor
1.25V Sourcing Current with a
3.3µF Output Capacitor
1.25V Shutdown Supply Current
vs Input Voltage 1.25V VOUT Distribution
1.25V Low Frequency
0.1Hz to 10Hz Noise
1.25V Output Voltage
Temperature Drift 1.25V Load Regulation (Sourcing)
200nV/
DIV
6655 G01
1s/DIV
TEMPERATURE (°C)
–50 –25
1.2496
OUTPUT VOLTAGE (V)
1.2498
1.2504
050 75
6655 G02
1.2502
1.2500
25 100 125
3 TYPICAL UNITS
OUTPUT CURRENT (mA)
–20
OUTPUT VOLTAGE CHANGE (ppm)
0
20
–30
–10
10
0.001 0.1 1 10
6655 G03
–40
0.01
125°C
25°C
–40°C
OUTPUT CURRENT (mA)
40
OUTPUT VOLTAGE CHANGE (ppm)
80
120
160
200
0.001 0.1 1 10
6655 G04
00.01
125°C
25°C
–40°C
FREQUENCY (kHz)
10
NOISE VOLTAGE (nV/√Hz)
15
25
35
40
0.01 1 10 1000
6655 G05
5
0.1 100
30
20
0
2.7µF
10µF
100µF
IOUT 0mA
5mA
VOUT
10mV/DIV
COUT = 3.3µF 200µs/DIV 6655 G06
IOUT
–5mA
0mA
VOUT
10mV/DIV
COUT = 3.3µF 200µs/DIV 6655 G07
INPUT VOLTAGE (V)
0
8
10
14
6 10
6655 G08
6
4
2 4 8 12 14
2
0
12
SUPPLY CURRENT (µA)
125°C
25°C
–40°C
LTC6655
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2.5V Load Regulation (Sinking)
2.5V Supply Current
vs Input Voltage
2.5V Shutdown Supply Current
vs Input Voltage
2.5V Minimum VIN – VOUT
Differential (Sourcing)
2.5V Minimum VIN – VOUT
Differential (Sinking)
2.5V Output Voltage Noise
Spectrum
2.5V Low Frequency
0.1Hz to 10Hz Noise
2.5V Output Voltage
Temperature Drift 2.5V Load Regulation (Sourcing)
Typical perForMance characTerisTics
Characteristic curves are similar for most voltage options of the LTC6655. Curves from the LTC6655-1.25, LTC6655-2.5 and the
LTC6655-5 represent the range of performance across the entire family of references. Characteristic curves for other output voltages
fall between these curves and can be estimated based on their voltage output.
500nV/
DIV
6655 G10
1s/DIV
TEMPERATURE (°C)
OUTPUT VOLTAGE (V)
6655 G11
2.4990
2.4995
2.5000
2.5005
2.5010
–50 0 50 100 150
3 TYPICAL UNITS
OUTPUT CURRENT (mA)
OUTPUT VOLTAGE CHANGE (ppm)
6655 G12
–50
–40
–30
–20
–10
0
10
0.001 0.01 0.1 1 10
125°C
25°C
–40°C
OUTPUT CURRENT (mA)
OUTPUT VOLTAGE CHANGE (ppm)
6655 G13
–20
0
40
80
120
20
60
100
140
160
0.001 0.01 0.1 1 10
125°C
25°C
–40°C
INPUT VOLTAGE (V)
SUPPLY CURRENT (mA)
6655 G14
0
1
2
3
4
5
6
7
8
0 2 4 6 8 10 12 14
125°C
25°C
–40°C
INPUT VOLTAGE (V)
SUPPLY CURRENT (µA)
6655 G15
0
2
4
6
8
10
12
14
0 2 4 6 8 10 12 14
125°C
25°C
–40°C
INPUT – OUTPUT VOLTAGE (V) 6655 G16
0.01
0.1
1
10
0.01 0.1 1
OUTPUT CURRENT (mA)
125°C
25°C
–40°C
6655 G17
0.01
0.1
1
10
–0.15 –0.05 0.05 0.15
OUTPUT CURRENT (mA)
INPUT – OUTPUT VOLTAGE (V)
125°C
25°C
–40°C
COUT = 100µF
FREQUENCY (kHz)
60
NOISE VOLTAGE (nV√Hz)
100
0.01 10 100 1000
0
20
0.1 1
120
80
40
6655 F01
COUT = 2.7µF
COUT = 10µF
LTC6655
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2.5V Power Supply Rejection
Ratio vs Frequency
2.5V Output Impedance
vs Frequency 2.5V Line Regulation
2.5V VOUT Distribution
2.5V Temperature Drift
Distribution
2.5V SHDN Input Voltage
Thresholds vs VIN
Typical perForMance characTerisTics
Characteristic curves are similar for most voltage options of the LTC6655. Curves from the LTC6655-1.25, LTC6655-2.5 and the
LTC6655-5 represent the range of performance across the entire family of references. Characteristic curves for other output voltages
fall between these curves and can be estimated based on their voltage output.
DRIFT (ppm/C)
0
NUMBER OF PARTS
8
10
12
2.8
6
4
0.8 1.6
0.4 1.2 2 2.4
2
0
14 –40°C TO 125°C
6655 G20
VIN (V)
VTRIP (V)
6655 G21
VTH_UP
VTH_DN
0.0
0.5
1.0
1.5
2.0
2.5
2 4 6 8 10 12 14
FREQUENCY (kHz)
POWER SUPPLY REJECTION RATIO (dB)
40
60
100
80
20
0
120
6655 G22
10.1 10 1000.010.001
COUT = 2.7µF
COUT = 10µF
COUT = 100µF
FREQUENCY (kHz)
OUTPUT IMPEDENCE (Ω)
101 1000.10.001 0.01 1000
6655 G23
0.01
0.1
1
10 COUT = 2.7µF
COUT = 10µF
COUT = 100µF
INPUT VOLTAGE (V)
0
OUTPUT VOLTAGE (V)
2.501
2.500
48
2610 12 14
2.499
2.498
2.502
6655 G24
125°C
25°C
–40°C
LTC6655
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5V Load Regulation (Sinking)
5V Supply Current
vs Input Voltage
5V Output Voltage Noise
Spectrum
5V Minimum VIN-VOUT
Differential (Sourcing)
5V Minimum VIN-VOUT
Differential (Sinking)
5V Start-Up Response with a
3.3µF Output Capacitor
5V Low Frequency
0.1Hz to 10Hz Noise
5V Output Voltage
Temperature Drift 5V Load Regulation (Sourcing)
Typical perForMance characTerisTics
Characteristic curves are similar for most voltage options of the LTC6655. Curves from the LTC6655-1.25, LTC6655-2.5 and the
LTC6655-5 represent the range of performance across the entire family of references. Characteristic curves for other output voltages
fall between these curves and can be estimated based on their voltage output.
TEMPERATURE (°C)
–50
4.9985
OUTPUT VOLTAGE (V)
4.9990
4.9995
5.0000
5.0010
5.0005
–25 0 25 50
6655 G26
75 100 125
3 TYPICAL UNITS
500nV/
DIV
6655 G25
1s/DIV
OUTPUT CURRENT (mA)
OUTPUT VOLTAGE CHANGE (ppm)
0.01
–50
–10
0
10
0.1 1 10
6655 G27
–20
–30
–40 125°C
25°C
–40°C
OUTPUT CURRENT (mA)
OUTPUT VOLTAGE CHANGE (ppm)
0.01
–20
60
80
100
0.1 1 10
6655 G28
40
20
0
125°C
25°C
–40°C
INPUT VOLTAGE (V)
0
SUPPLY CURRENT (mA)
4
5
6
6 10
6655 G29
3
2
2 4 8 12 14
1
0
125°C
25°C
–40°C
FREQUENCY (kHz)
0.01
80
NOISE VOLTAGE (nV/√Hz)
100
120
140
160
0.1 1 10 100 1000
6655 G30
60
40
20
0
180
200
2.7µF
10µF
100µF
INPUT-OUTPUT VOLTAGE (V)
0.01
0.01
OUTPUT CURRENT (mA)
1
10
0.1 1
6655 G31
0.1
125°C
25°C
–40°C
INPUT-OUTPUT VOLTAGE (V)
–0.3
0.01
OUTPUT CURRENT (mA)
0.1
1
10
–0.2 –0.1 0 0.1
6655 G32
125°C
25°C
–40°C
VIN
2V/DIV
VOUT
2V/DIV
COUT = 3.3µF 400µs/DIV 6655 G33
LTC6655
9
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pin FuncTions
SHDN (Pin 1): Shutdown Input. This active low input
powers down the device to <20µA. If left open, an inter-
nal pull-up resistor puts the part in normal operation. It
is recommended to tie this pin high externally for best
performance during normal operation.
VIN (Pin 2): Power Supply. Bypass VIN with a 0.1µF, or
larger, capacitor to GND.
GND (Pin 4): Device Ground. This pin is the main ground
and must be connected to a noise-free ground plane.
VOUT_S (Pin 6): VOUT Sense Pin. Connect this pin at the
load and route with a wide metal trace to minimize load
regulation errors. This pin sinks 2mA. Output error is
RTRACE 2mA, regardless of load current. For load currents
<100µA, tie directly to VOUT_F pin.
VOUT_F (Pin 7): VOUT Force Pin. This pin sources and
sinks current to the load. An output capacitor of 2.7µF to
100µF is required.
GND (Pins 3, 5, 8): Internal Function. Ground these
pins.
blocK DiagraM
+VOUT_F 7
2
VOUT_S
6655 BD
6
BANDGAP
VIN
1
4
SHDN
GND
GND
3,5,8
LTC6655
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applicaTions inForMaTion
Bypass and Load Capacitors
The LTC6655 voltage references require a 0.1µF or larger
input capacitor located close to the part to improve power
supply rejection. An output capacitor with a value between
2.7µF and 100µF is also required.
The output capacitor has a direct effect on the stability,
turn-on time and settling behavior. Choose a capacitor
with low ESR to insure stability. Resistance in series with
the output capacitor (ESR) introduces a zero in the output
buffer transfer function and could cause instability. The
2.7μF to 100μF range includes several types of capacitors
that are readily available as through-hole and surface mount
components. It is recommended to keep ESR less than or
equal to 0.1Ω. Capacitance and ESR are both frequency
dependent. At higher frequencies capacitance drops and
ESR increases. To insure stable operation the output ca-
pacitor should have the required values at 100kHz.
In order to achieve the best performance, caution should
be used when choosing a capacitor. X7R ceramic ca-
pacitors are small, come in appropriate values and are
relatively stable over a wide temperature range. However,
for a low noise application X7R capacitors may not be
suitable since they may exhibit a piezoelectric effect. The
mechanical vibrations cause a charge displacement in the
ceramic dielectric and the resulting perturbation can look
like noise. If X7R capacitors are necessary, a thorough
bench evaluation should be completed to verify proper
performance.
For very low noise applications where every nanovolt
counts, film capacitors should be considered for their
low noise and lack of piezoelectric effects. Film capaci-
tors such as polyester, polystyrene, polycarbonate, and
polypropylene have good temperature stability. Additional
care must be taken as polystyrene and polypropylene have
an upper temperature limit of 85°C to 105°C. Above these
temperatures, the working voltages need to be derated
according to manufacturers specifications. Another type
of film capacitor is polyphenylene sulfide (PPS). These
devices work over a wide temperature range, are stable,
and have large capacitance values beyond 1μF. In general,
film capacitors are found in surface mount and leaded
packages. Table 1 is a partial list of capacitor companies
and some of their available products.
In voltage reference applications, film capacitor lifetime
is affected by temperature and applied voltage. When
polyester capacitors are operated beyond their rated
temperatures (some capacitors are not rated for operation
above 85°C) they need to be derated. Voltage derating is
usually accomplished as a ratio of applied voltage to rated
voltage limit. Contact specific film capacitor manufacturers
to determine exact lifetime and derating information.
The lifetime of X7R capacitors is long, especially for
reference applications. Capacitor lifetime is degraded by
operating near or exceeding the rated voltage, at high
temperature, with AC ripple or some combination of these.
Most reference applications have AC ripple only during
transient events.
Table 1. Film Capacitor Companies
COMPANY DIELECTRIC AVAILABLE CAPACITANCE TEMPERATURE RANGE TYPE
Cornell Dublier Polyester 0.5µF to 10µF –55°C to 125°C DME
Dearborn Electronics Polyester 0.1µF to 12µF –55°C to 125°C 218P, 430P, 431P, 442P, and 410P
Tecate Polyester 0.01µF to 18µF –40°C to 105°C 901, 914, and 914D
Wima Polyester 10µF to 22µF –55°C to 100°C MKS 4, MKS 2-XL
Vishay Polyester 1000pF to 15µF –55°C to 125°C MKT1820
Vishay Polycarbonate 0.01µF to 10µF –55°C to 100°C MKC1862, 632P
Dearborn Electronics Polyphenylene Sulfide (PPS) 0.01µF to 15µF –55°C to 125°C 820P, 832P, 842P, 860P, and 880P
Wima Polyphenylene Sulfide (PPS) 0.01µF to 6.8µF –55°C to 140°C SMD-PPS
LTC6655
11
6655fa
3.5V
3V
VIN
VOUT
50mV/DIV
COUT = 3.3µF 6655 F04
400µs/DIV
applicaTions inForMaTion
The choice of output capacitor also affects the bandwidth
of the reference circuitry and resultant noise peaking. As
shown in Figure 1, the bandwidth is inversely proportional
to the value of the output capacitor.
Noise peaking is related to the phase margin of the output
buffer. Higher peaking generally indicates lower phase mar-
gin. Other factors affecting noise peaking are temperature,
input voltage, and output load current.
Start-Up and Load Transient Response
Results for the transient response plots (Figures 3 to 8)
were produced with the test circuit shown in Figure 2
unless otherwise indicated.
The turn-on time is slew limited and determined by the
short-circuit current, the output capacitor, and output
voltage as shown in the equation:
t V C
I
ON OUT OUT
SC
=
For example, the LTC6655-2.5V, with a 3.3µF output
capacitor and a typical short-circuit current of 20mA, the
start-up time would be approximately:
2 5 3 3 10
0 02 412
6
. .
.
VF
Aµs=
The resulting turn-on time is shown in Figure 3. Here
the output capacitor is 3.3µF and the input capacitor is
0.1µF.
Figure 4 shows the output response to a 500mV step on
VIN. The output response to a current step sourcing and
sinking is shown in Figures 5 and 6, respectively.
Figure 7 shows the output response as the current goes
from sourcing to sinking.
Shutdown Mode
The LTC6655 family of references can be shut down by
tying the SHDN pin to ground. There is an internal pull-up
resistor tied to this pin. If left unconnected this pin rises to
VIN and the part is enabled. Due to the low internal pull-up
current, it is recommended that the SHDN pin be pulled
high externally for normal operation to prevent accidental
LTC6655-2.5
100Ω
VOUT
1,2 7
6
3,4,5,8
CIN
0.1µF
COUT
3.3µF
VGEN
6655 F02
0.5V
VIN
3V
Figure 2. Transient Load Test Circuit
Figure 3. Start-Up Response
Figure 4. Output Response with a 500mV Step On VIN
Figure 1. Output Voltage Noise Spectrum
VIN
2V/DIV
VOUT
1V/DIV
COUT = 3.3µF 6655 F03
200µs/DIV
COUT = 100µF
FREQUENCY (kHz)
60
NOISE VOLTAGE (nV√Hz)
100
0.01 10 100 1000
0
20
0.1 1
120
80
40
6655 F01
COUT = 2.7µF
COUT = 10µF
LTC6655
12
6655fa
COUT = 3.3µF 6655 F08
1ms/DIV
VOUT
1V/DIV
SHDN
2V/DIV
COUT = 3.3µF 6655 F07
200µs/DIV
2mA
–2mA
IOUT
VOUT
10mV/DIV
applicaTions inForMaTion
Figure 8. Shutdown Response with 5mA Source Load
LTC6655-2.5
VIN
GND
SHDN
2N7002
VOUT_F
VOUT_S
TO µC
3V ≤ VIN ≤ 13.2V
VOUT
C1
1µF
C2
10µF
6655 F09
Figure 9. Open-Drain Shutdown Circuit
Figure 7. Output Response Showing a
Sinking to Sourcing Transition
shutdown due to system noise or leakage currents. The
turn-on/turn-off response due to shutdown is shown in
Figure 8.
To control shutdown from a low voltage source, a MOSFET
can be used as a pull-down device as shown in Figure 9.
Note that an external resistor is unnecessary. A MOSFET
with a low drain-to-source leakage over the operating
temperature range should be chosen to avoid inadvertently
pulling down the SHDN pin. A resistor may be added from
SHDN to VIN to overcome excessive MOSFET leakage.
The SHDN thresholds have some dependency on VIN
and temperature as shown in the Typical Performance
Characteristics section. Avoid leaving SHDN at a voltage
between the thresholds as this will cause an increase in
supply current due to shoot-through current.
0mA
–5mA
IOUT
VOUT
10mV/DIV
COUT = 3.3µF 6655 F05
200µs/DIV
5mA
0mA
IOUT
VOUT
10mV/DIV
COUT = 3.3µF 6655 F06
200µs/DIV
Figure 6. Output Response with 5mA Load Step Sinking
Figure 5. Output Response with a 5mA Load Step Sourcing
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 LTC6655 long-term drift data was collected on 80 parts
that were soldered into printed circuit boards similar to a
real world application. The boards were then placed into a
constant temperature oven with a TA = 35°C, their outputs
were scanned regularly and measured with an 8.5 digit
DVM. Typical long-term drift is illustrated in Figure 10.
LTC6655
13
6655fa
Figure 10. Long-Term Drift
applicaTions inForMaTion
Figure 11. Hysteresis Plot –40°C to 125°C
VIN (V)
0
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0
6655 F12
510
NO LOAD
15
POWER (W)
5mA LOAD
Figure 12. LTC6655-2.5 Power Consumption
VIN (V)
0
105
115
125
12
6655 F13
95
85
3 6 9 15
75
65
55
MAXIMUM AMBIENT
OPERATING TEMPERATURE (°C)
NO LOAD
5mA LOAD
Figure 13. LTC6655-2.5 Maximum
Ambient Operating Temperature
Hysteresis
Thermal hysteresis is a measure of change of output
voltage as a result of temperature cycling. Figure 11
illustrates the typical hysteresis based on data taken from
the LTC6655-2.5. A proprietary design technique minimizes
thermal hysteresis.
Power Dissipation
Power dissipation for the LTC6655 depends on VIN and
load current. Figure 12 illustrates the power consump-
tion versus VIN under a no-load and 5mA load condition
at room temperature for the LTC6655-2.5. Other voltage
options display similar behavior.
The MSOP8 package has a thermal resistance (θJA)
equal to 300°C/W. Under the maximum loaded condition,
the increase in die temperature is over 35°C. If operated at
these conditions with an ambient temperature of 125°C,
the absolute maximum junction temperature rating of
the device would be exceeded. Although the maximum
junction temperature is 150°C, for best performance it
is recommended to not exceed a junction temperature
of 125°C. The plot in Figure 13 shows the recommended
maximum ambient temperature limits for differing VIN and
load conditions using a maximum junction temperature
of 125°C.
DISTRIBUTION (ppm)
–90
NUMBER OF UNITS
20
25
50
15
10
–50 –10
–70 90
–30 10 70
30 110
5
0
30
6655 F11
HOURS
0
LONG-TERM DRIFT (ppm)
40
80
120
2000
6655 F10
0
–40
–80 500 1000 1500 2500
4 TYPICAL UNITS
LTC6655-2.5
LTC6655
14
6655fa
applicaTions inForMaTion
LTC6655-2.5
2
7
2mA LOAD
STAR
MINIMIZE RESISTANCE
OF METAL
6
4
6655 F15
+
Figure 15. Kelvin Connection for Good Load Regulation
output current <100µA), VOUT_S should be tied to VOUT_F
by the shortest possible path to reduce errors caused by
resistance in the sense trace.
Careful attention to grounding is also important, espe-
cially when sourcing current. The return load current can
produce an I • R drop causing poor load regulation. Use
a “star” ground connection and minimize the ground to
load metal resistance. Although there are several pins that
are required to be connected to ground, Pin 4 is the actual
ground for return current.
Optimal Noise Performance
The LTC6655 offers extraordinarily low noise for a bandgap
reference—only 0.25ppm in 0.1Hz to 10Hz. As a result,
system noise performance may be dominated by system
design and physical layout.
Some care is required to achieve the best possible noise
performance. The use of dissimilar metals in component
leads and PC board traces creates thermocouples. Varia-
tions in thermal resistance, caused by uneven air flow,
create differential lead temperatures, thereby causing
thermoelectric voltage noise at the output of the refer-
ence. Minimizing the number of thermocouples, as well
as limiting airflow, can substantially reduce these errors.
Additional information can be found in Linear Technology
Application Note 82. Position the input and load capacitors
close to the part. Although the LTC6655 has a DC PSRR
of over 100dB, the power supply should be as stable as
possible to guarantee optimal performance. A plot of the
0.1Hz to 10Hz low frequency noise is shown in the Typical
Performance Characteristic section. Noise performance
can be further improved by wiring several LTC6655s in
parallel as shown in the Typical Applications section. With
this technique the noise is reduced by N, where N is the
number of LTC6655s in parallel.
PC Board Layout
The LTC6655 reference is a precision device that is factory
trimmed to an initial accuracy of ±0.025%, as shown in the
Typical Performance Characteristic section. The mechanical
stress caused by soldering parts to a printed circuit board
may cause the output voltage to shift and the temperature
coefficient to change.
To reduce the effects of stress-related shifts, mount the
reference near the short edge of a printed circuit board
or in a corner. In addition, slots can be cut into the board
on two sides of the device to reduce mechanical stress. A
thicker and smaller board is stiffer and less prone to bend.
Finally, use stress relief, such as flexible standoffs, when
mounting the board.
Additional precautions include making sure the solder
joints are clean and the board is flux free to avoid leakage
paths. A sample PCB layout is shown in Figure 14.
Load Regulation
To take advantage of the VOUT Kelvin force/sense pins,
the VOUT_S pin should be connected separately from the
VOUT_F pin as shown in Figure 15.
The VOUT_S pin sinks 2mA, which is unusual for a Kelvin
connection. However, this is required to achieve the ex-
ceptional low noise performance. The I R drop on the
VOUT_S line directly affects load regulation. The VOUT_S
trace should be as short and wide as practical to minimize
series resistance The VOUT_S trace adds error as RTRACE
2mA, so a 0.1Ω trace adds 200µV error. The VOUT_F pin
is not as important as the VOUT_S pin in this regard. An
I R drop on the VOUT_F pin increases the minimum supply
voltage when sourcing current, but does not directly affect
load regulation. For light loading of the output (maximum
Figure 14. Sample PCB Layout
6655 F14
GND VOUT
VIN
LTC6655
15
6655fa
applicaTions inForMaTion
Noise Specification
Noise in any frequency band is a random function based
on physical properties such as thermal noise, shot noise,
and flicker noise. The most precise way to specify a random
error such as noise is in terms of its statistics, for example
as an RMS value. This allows for relatively simple maximum
error estimation, generally involving assumptions about
noise bandwidth and crest factor. Unlike wideband noise,
low frequency noise, typically specified in a 0.1Hz to 10Hz
band, has traditionally been specified in terms of expected
error, illustrated as peak-to-peak error. Low frequency
noise is generally measured with an oscilloscope over a
10 second time frame. This is a pragmatic approach, given
that it can be difficult to measure noise accurately at low
frequencies, and that it can also be difficult to agree on the
statistical characteristics of the noise, since flicker noise
dominates the spectral density. While practical, a random
sampling of 10 second intervals is an inadequate method
for representation of low frequency noise, especially for
systems where this noise is a dominant limit of system
performance. Given the random nature of noise, the output
voltage may be observed over many time intervals, each
giving different results. Noise specifications that were
determined using this method are prone to subjectivity,
and will tend toward a mean statistical value, rather than
the maximum noise that is likely to be produced by the
device in question.
Because the majority of voltage reference data sheets
express low frequency noise as a typical number, and as
it tends to be illustrated with a repeatable plot near the
mean of a distribution of peak-to-peak values, the LTC6655
data sheet provides a similarly defined typical specification
in order to allow a reasonable direct comparison against
similar products. Data produced with this method gener-
ally suggests that in a series of 10 second output voltage
measurements, at least half the observations should have a
peak-to-peak value that is below this number. For example,
the LTC6655-2.5 measures less than 0.25ppmP-P in at
least 50% of the 10 second observations.
As mentioned above, the statistical distribution of noise
is such that if observed for long periods of time, the
peak error in output voltage due to noise may be much
larger than that observed in a smaller interval. The likely
maximum error due to noise is often estimated using the
RMS value, multiplied by an estimated crest factor, assumed
to be in the range of 6 to 8.4. This maximum possible value
will only be observed if the output voltage is measured
for very long periods of time. Therefore, in addition to the
common method, a more thorough approach to measuring
noise has been used for the LTC6655 (described in detail in
Linear Technologys AN124) that allows more information
to be obtained from the result. In particular, this method
characterizes the noise over a significantly greater length
of time, resulting in a more complete description of low
frequency noise. The peak-to-peak voltage is measured
for 10 second intervals over hundreds of intervals. In ad-
dition, an electronic peak-detect circuit stores an objective
value for each interval. The results are then summarized in
terms of the fraction of measurement intervals for which
observed noise is below a specified level. For example,
the LTC6655-2.5 measures less than 0.27ppmP-P in 80%
of the measurement intervals, and less than 0.295ppmP-P
in 95% of observation intervals. This statistical variation
in noise is illustrated in Table 2 and Figure 17. The test
circuit is shown in Figure 16.
Table 2
Low Frequency Noise (ppmP-P)
50% 0.246
60% 0.252
70% 0.260
80% 0.268
90% 0.292
This method of testing low frequency noise is superior to
more common methods. The results yield a comprehensive
statistical description, rather than a single observation. In
addition, the direct measurement of output voltage over
time gives an actual representation of peak noise, rather
than an estimate based on statistical assumptions such
as crest factor. Additional information can be derived from
a measurement of low frequency noise spectral density,
as shown in Figure 18.
It should be noted from Figure 18 that the LTC6655 has
not only a low wideband noise, but an exceptionally low
flicker noise corner of 1Hz! This substantially reduces
low frequency noise, as well as long-term variation in
peak noise.
LTC6655
16
6655fa
applicaTions inForMaTion
+
100k100k
SHIELD
SHIELDED CAN
1N4697
10V
AC LINE GROUND
1300µF
9V
100k*
10Ω*
+
1k* 200Ω*
2k
450Ω* 900Ω*
15V
15V
–15V
–15V
1µF
1µF A1
LT1012
A2
LT1097
6655 F16
– INPUT
Q1
5
* = 1% METAL FILM
** = 1% WIREWOUND, ULTRONIX105A
= 1N4148
= 2N4393
= 1/4 LTC202
SEE APPENDIX C FOR POWER, SHIELDING
AND GROUNDING SCHEME
= TANTALUM,WET SLUG
ILEAK < 5nA
SEE TEXT/APPENDIX B
= POLYPROPELENE
A4 330µF OUTPUT CAPACITORS = <200nA LEAKAGE
AT 1VDC AT 25°C
Q1, Q2 = THERMALLY MATED
2SK369 (MATCH VGS 10%)
OR LSK389 DUAL
THERMALLY LAG
SEE TEXT
A = 104
LOW NOISE
PRE-AMP
REFERENCE
UNDER TEST
0.15µF
750Ω*
10k
–15V
Q3
2N2907
Q2 0.022µF
1µF
**1.2k
SD
LTC6655
2.5V
IN S
F
+
1µF
0.1µF
124k* 124k*
+
A3
LT1012
1M*
10k*
100Ω*330Ω*
IN OUT
ROOT-SUM-SQUARE
CORRECTION
SEE TEXT
330µF
16V
330µF
16V
+
+
330µF
16V
330µF
16V
+
A4
LT1012
0.1µF
0.1µF
10k
A = 100 AND
0.1Hz TO 10Hz FILTER
1µF
RST
+
A5
1/4 LT1058
+A7
1/4 LT1058
1k
PEAK TO PEAK
NOISE DETECTOR
O TO 1V =
O TO 1µV
+ PEAK
4.7k
P
P
1µF
RST
15
0.1µF
+
A6
1/4 LT1058
+A8
1/4 LT1058
1k
– PEAK
4.7k
10k
100k
100k
P
T
T
+
DVM
TO OSCILLOSCOPE INPUT
VIA ISOLATED PROBE,
1V/DIV = 1µV/DIV,
REFERRED TO INPUT,
SWEEP = 1s/DIV
FROM OSCILLOSCOPE
SWEEP GATE OUTPUT
VIA ISOLATION
PULSE TRANSFORMER
RESET PULSE
GENERATOR
0.22µF
C2 RC2
+15 +15
CLR2
+15
74C221
RST = Q2 +V
+15
A2
B2
10k
BAT-85
BAT-85
10k
+
+
0.005µF
–15 10k
0.005µF
Figure 16. Detailed Noise Test Circuitry. See Application Note 124.
LTC6655
17
6655fa
IR Reflow Shift
The mechanical stress of soldering a part to a board can
cause the output voltage to shift. Moreover, the heat of
an IR reflow or convection soldering oven can also cause
the output voltage to shift. The materials that make up a
semiconductor device and its package have different rates
of expansion and contraction. After a part undergoes the
extreme heat of a lead-free IR reflow profile, like the one
applicaTions inForMaTion
Figure 19. Lead-Free Reflow Profile
Figure 20. Output Voltage Shift Due to IR Reflow
shown in Figure 19, the output voltage shifts. After the
device expands, due to the heat, and then contracts, the
stresses on the die have changed position. This shift is
similar, but more extreme than thermal hysteresis.
Experimental results of IR reflow shift are shown below
in Figure 20. These results show only shift due to reflow
and not mechanical stress.
MINUTES
0
TEMPERATURE (°C)
150
225
8
6655 F19
75
024610
300
T = 150°C
TS = 190°C
TL = 217°C
TP = 260°C
380s
tP
30s
tL
130s
40s
120s
RAMP
DOWN
TS(MAX) = 200°C
RAMP TO
150°C
OUTPUT VOLTAGE SHIFT DUE TO IR REFLOW (%)
–0.029
0
NUMBER OF UNITS
2
4
6
–0.023 –0.017 –0.005–0.011
8
1
3
5
7
6655 F20
Figure 17. Low Frequency Noise Histogram of the LTC6655-2.5
Figure 18. LTC6655-2.5 Low Frequency Noise Spectrum
PEAK-TO-PEAK NOISE (nV)
450
0
NUMBER OF OBSERVATIONS
5
15
20
25
35
6655 F17
10
30
650 950
550 750 850
FREQUENCY (Hz)
0.1
0
NOISE VOLTAGE (nV/√Hz)
120
160
200
1 10 100
6655 F18
80
40
LTC6655
18
6655fa
Typical applicaTions
LTC6655-2.5
GND
SHDN
VIN
VOUT_S
VOUT_F VOUT
C1
0.1µF
R1
BZX84C12
4V TO 30V
C2
10µF
6655 TA02
Extended Supply Range Reference Extended Supply Range Reference
LTC6655-2.5
GND
VIN SHDN
VOUT_S
VOUT_F VOUT
6V TO 80V
ON SEMI
MMBT5551
C1
0.1µF
R1
100k
R2
4.7k
BZX84C12
C2
10µF
0.1µF
6655 TA03
Boosted Output Current
LTC6655-2.5
GND
VIN SHDN
VOUT_S
VOUT + 1.8V TO 13.2V
VOUT_F VOUT
C1
1µF
C3
0.1µF
R1
220Ω
C2
10µF
6655 TA04
2N2905 35mA MAX
R2
1k
C4
1µF
Q1
2N2222
IMAX SET BY NPN
VOUT
6655 TA05
LTC6655-2.5
GND
SHDN
VIN VOUT_S
VOUT_F
C2
4.7µF
C1
0.1µF
4V TO 13.2V
Boosted Output Current
Output Voltage Boost
LTC6655-2.5
GND
SHDN
VIN
VOUT_S
R
R = 0k to 1k
VOUT_F VOUT
2.5V TO 4.5V
C1
1µF
VIN
VOUT + 0.5V TO 13.2V C2
10µF
6655 TA07
VOUT = VOLTAGE OPTION + 0.002 • R
THIS EXAMPLE USES 2.5V AS THE
VOLTAGE OPTION
FOR R USE A POTENTIOMETER THAT
CAN HANDLE 2mA, IS LOW NOISE AND
HAS A LOW TEMPERATURE COEFFICIENT
Low Noise Precision Voltage Boost Circuit
LTC6655-2.5 LT1677
GND
SHDN
VIN
VOUT_S
VOUT_F VOUT
5V
C1
1µF
VIN
VOUT + 0.5V TO 13.2V C2
10µF
R1
10k
R3
5k
VIN
6655 TA08
VOUT = VOLTAGE OPTION • (1 + R1/R2)
THIS EXAMPLE USES 2.5V AS THE
VOLTAGE OPTION
FOR R1 AND R2 USE VISHAY TRIMMED
RESISTOR ARRAY (VSR144 OR MPM).
WITH A PRECISION ARRAY THE
MATCHING AND LOW TC WILL HELP
PRESERVE LOW DRIFT. R3 = R1||R2
+
RLOAD
R2
10k
+
LTC6655
19
6655fa
Typical applicaTions
Low Noise Statistical Averaging Reference
eN = eN/√N; Where N is the Number of LTC6655s in Parallel
6655 TA06a
LTC6655-2.5
R1
32.4Ω
GND
SHDN
VIN
VOUT
VOUT_S
VOUT_F
C2
2.7µF
C1
0.1µF
LTC6655-2.5
R2
32.4Ω
GND
SHDN
VIN VOUT_S
VOUT_F
C4
2.7µF
C3
0.1µF
LTC6655-2.5
R3
32.4Ω
GND
SHDN
VIN VOUT_S
VOUT_F
C6
2.7µF
C5
0.1µF
LTC6655-2.5
R4
32.4Ω
GND
SHDN
VIN VOUT_S
VOUT_F
C8
2.7µF
C7
0.1µF
C9
4.7µF
3V TO
13.2V
200nV/
DIV
6655 TA06b
1s/DIV
320nVP-P
0.1Hz to 10Hz
Low Frequency Noise (0.1Hz to 10Hz)
with Four LTC6655-2.5 in Parallel
LTC6655
20
6655fa
pacKage DescripTion
MS8 Package
8-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1660 Rev F)
MSOP (MS8) 0307 REV F
0.53 p 0.152
(.021 p .006)
SEATING
PLANE
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
0.18
(.007)
0.254
(.010)
1.10
(.043)
MAX
0.22 – 0.38
(.009 – .015)
TYP
0.1016 p 0.0508
(.004 p .002)
0.86
(.034)
REF
0.65
(.0256)
BSC
0o – 6o TYP
DETAIL “A”
DETAIL “A”
GAUGE PLANE
1 2 34
4.90 p 0.152
(.193 p .006)
8765
3.00 p 0.102
(.118 p .004)
(NOTE 3)
3.00 p 0.102
(.118 p .004)
(NOTE 4)
0.52
(.0205)
REF
5.23
(.206)
MIN
3.20 – 3.45
(.126 – .136)
0.889 p 0.127
(.035 p .005)
RECOMMENDED SOLDER PAD LAYOUT
0.42 p 0.038
(.0165 p .0015)
TYP
0.65
(.0256)
BSC
LTC6655
21
6655fa
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 02/10 Voltage Options Added (1.250, 2.048, 3.000, 3.300, 4.096, 5.000), Reflected Throughout the Data Sheet 1 to 22
LTC6655
22
6655fa
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
LINEAR TECHNOLOGY CORPORATION 2009
LT 0210 REV A • PRINTED IN USA
relaTeD parTs
Typical applicaTion
Low Noise Precision 24-Bit Analog-to-Digital Converter Application
–2.5V
7.5V
SPI INTERFACE
THERMOCOUPLE
10µF
0.1µF
LTC6655
VIN
SHDN
VOUT_F
VOUT_S
GND GND
3,5,8 4
1
2
6
7
VCC
5V
6655 TA09
1nF
1nF
0.01µF0.01µF
50Ω
2.5k
50Ω
2.5k
+
+
1/2
LTC6241
1/2
LTC6241
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
CH8
CH9
CH10
CH11
CH12
CH13
CH14
CH15
COM
REF+
REF
GND
GND
GND
GND
GND
GND
GND
MUXOUTN
ADCINN
MUXOUTP
ADCINP
SDI
SCK
SDO
CS
BUSY
EXT
fO
LTC2449
5k
RREF
400Ω
VREF
RTD
VREF
PART NUMBER DESCRIPTION COMMENTS
LT
®
1236 Precision Low Drift Low Noise Reference 0.05% Max, 5ppm/°C Max, 1ppm (Peak-to-Peak) Noise
LT1460 Micropower Series References 0.075% Max, 10ppm/°C Max, 20mA Output Current
LT1461 Micropower Series Low Dropout 0.04% Max, 3ppm/°C Max, 50mA Output Current
LT1790 Micropower Precision Series References 0.05% Max, 10ppm/°C Max, 60mA Supply, SOT23 Package
LT6650 Micropower Reference with Buffer Amplifier 0.5% Max, 5.6µA Supply, SOT23 Package
LTC6652 Precision Low Drift Low Noise Reference 0.05% Max, 5ppm/°C Max, –40°C to 125°C, MSOP8
LT6660 Tiny Micropower Series Reference 0.2% Max, 20ppm/°C Max, 20mA Output Current, 2mm × 2mm DFN