1
LT1021
1021fc
APPLICATIO S
U
FEATURES
TYPICAL APPLICATIO
U
DESCRIPTIO
U
Precision Reference
Typical Distribution of Temperature Drift
OUTPUT DRIFT (ppm/°C)
–5
UNITS (%)
24
21
18
15
12
9
6
3
– 0
3
1021 TA01
–3 –1 1 52–4 –2 0 4
DISTRIBUTION
OF THREE RUNS
Basic Positive and Negative Connections
LT1021
OUT
IN
GND
LT1021
(7 AND 10 ONLY)
OUT
IN
GND
VOUT
–VOUT
VIN NC
R1 = VOUT – (V –)
ILOAD + 1.5mA
–15V
(V–)
R1
1021 TA01
■
Ultralow Drift: 5ppm/
°
C Max Slope
■
Very Low Noise: <1ppm
P-P
(0.1Hz to 10Hz)
■
100% Noise Tested
■
Pin Compatible with Most Bandgap Reference
Applications, Including Ref 01, Ref 02, LM368,
MC1400 and MC1404 with Greatly Improved
Stability, Noise and Drift
■
Trimmed Output Voltage
■
Operates in Series or Shunt Mode
■
Output Sinks and Sources in Series Mode
■
>100dB Ripple Rejection
■
Minimum Input/Output Differential of 1V
■
Available in 5-Lead Can, N8 and S8 Packages
■
A/D and D/A Converters
■
Precision Regulators
■
Digital Voltmeters
■
Inertial Navigation Systems
■
Precision Scales
■
Portable Reference Standard
The LT
®
1021 is a precision reference with ultralow drift
and noise, extremely good long term stability and almost
total immunity to input voltage variations. The reference
output will both source and sink up to 10mA. Three
voltages are available: 5V, 7V and 10V. The 7V and 10V
units can be used as shunt regulators (two-terminal zeners)
with the same precision characteristics as the three-
terminal connection. Special care has been taken to mini-
mize thermal regulation effects and temperature
induced hysteresis.
The LT1021 references are based on a buried zener diode
structure that eliminates noise and stability problems
associated with surface breakdown devices. Further, a
subsurface zener exhibits better temperature drift and
time stability than even the best bandgap references.
Unique circuit design makes the LT1021 the first IC
reference to offer ultralow drift without the use of high
power on-chip heaters.
The LT1021-7 uses no resistive divider to set output
voltage, and therefore exhibits the best long term stability
and temperature hysteresis. The LT1021-5 and LT1021-
10 are intended for systems requiring a precise 5V or 10V
reference with an initial tolerance as low as ±0.05%.
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
2
LT1021
1021fc
A
U
G
W
A
W
U
W
ARBSOLUTEXI T
IS
Input Voltage .......................................................... 40V
Input/Output Voltage Differential ............................ 35V
Output-to-Ground Voltage (Shunt Mode Current Limit)
LT1021-5............................................................. 10V
LT1021-7............................................................. 10V
LT1021-10........................................................... 16V
Trim Pin-to-Ground Voltage
Positive ............................................... Equal to V
OUT
Negative ........................................................... – 20V
Output Short-Circuit Duration
V
IN
= 35V ......................................................... 10 sec
V
IN
≤ 20V ................................................... Indefinite
Operating Temperature Range
Commercial ............................................ 0°C to 70°C
Industrial ........................................... –40°C to 85°C
Military ............................................ – 55°C to 125°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................ 300°C
WU
U
PACKAGE/ORDER I FOR ATIO
T
JMAX
= 150°C, θ
JA
= 150°C/W,θ
JC
= 45°C/W
TOP VIEW
NC*
NC*
NC*
V
IN
V
OUT
TRIM**
NC*
GND
8
7
6
5
3
2
1
4
H PACKAGE
8-LEAD TO-5 METAL CAN
T
JMAX
= 130°C, θ
JA
= 130°C/W (N)
T
JMAX
= 130°C, θ
JA
= 150°C/W (S)
(Note 1)
1
2
3
4
8
7
6
5
TOP VIEW
DNC*
VIN
DNC*
GND
DNC*
DNC*
V0UT
TRIM**
N8 PACKAGE
8-LEAD PDIP
S8 PACKAGE
8-LEAD PLASTIC SO
*CONNECTED INTERNALLY. DO NOT CONNECT EXTERNAL CIRCUITRY TO THESE PINS.
**NO TRIM PIN ON LT1021-7. DO NOT CONNECT EXTERNAL CIRCUITRY TO PIN 5 ON LT1021-7
ORDER PART NUMBER
*CONNECTED INTERNALLY. DO NOT CONNECT EXTERNAL CIRCUITRY TO THESE PINS.
**NO TRIM PIN ON LT1021-7. DO NOT CONNECT EXTERNAL CIRCUITRY TO PIN 5 ON LT1021-7
OBSOLETE
LT1021BCH-5
LT1021BMH-5
LT1021CCH-5
LT1021CMH-5
LT1021BMH-10
LT1021DCH-5
LT1021DMH-5
LT1021BCH-7
LT1021BMH-7
LT1021DCH-7
LT1021DMH-7
LT1021BCH-10
LT1021CMH-10
LT1021DCH-10
LT1021DMH-10
LT1021BCN8-5
LT1021CCN8-5
LT1021CIN8-5
LT1021DCN8-5
LT1021DIN8-5
LT1021BCN8-7
LT1021DCN8-7
LT1021BCN8-10
LT1021CCN8-10
LT1021CIN8-10
LT1021DCN8-10
LT1021DIN8-10
2105
2107
2110
N8 ORDER PART NUMBER
LT1021DCS8-5
LT1021DCS8-7
LT1021DCS8-10
S8 ORDER PART NUMBER S8 PART MARKING
Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
3
LT1021
1021fc
ELECTRICAL C CHARA TERISTICS
LT1021-5
PARAMETER CONDITIONS MIN TYP MAX UNITS
Output Voltage (Note 2) LT1021C-5 4.9975 5.000 5.0025 V
LT1021B-5/LT1021D-5 4.9500 5.000 5.0500 V
Output Voltage Temperature Coefficient (Note 3) T
MIN
≤ T
J
≤ T
MAX
LT1021B-5 ●2 5 ppm/°C
LT1021C-5/LT1021D-5 ●3 20 ppm/°C
Line Regulation (Note 4) 7.2V ≤ V
IN
≤ 10V 4 12 ppm/V
●20 ppm/V
10V ≤ V
IN
≤ 40V 2 6 ppm/V
●10 ppm/V
Load Regulation (Sourcing Current) 0 ≤ I
OUT
≤ 10mA 10 20 ppm/mA
(Note 4) ●35 ppm/mA
Load Regulation (Sinking Current) 0 ≤ I
OUT
≤ 10mA 60 100 ppm/mA
(Note 4) ●150 ppm/mA
Supply Current 0.8 1.2 mA
●1.5 mA
Output Voltage Noise (Note 6) 0.1Hz ≤ f ≤ 10Hz 3.0 µV
P-P
10Hz ≤ f ≤ 1kHz 2.2 3.5 µV
RMS
Long Term Stability of Output Voltage (Note 7) ∆t = 1000Hrs Noncumulative 15 ppm
Temperature Hysteresis of Output ∆T = ±25°C 10 ppm
LT1021-7
PARAMETER CONDITIONS MIN TYP MAX UNITS
Output Voltage (Note 2) 6.95 7.00 7.05 V
Output Voltage Temperature Coefficient (Note 3) T
MIN
≤ T
J
≤ T
MAX
LT1021B-7 ●2 5 ppm/°C
LT1021D-7 ●3 20 ppm/°C
Line Regulation (Note 4) 8.5V ≤ V
IN
≤ 12V 1.0 4 ppm/V
●2.0 8 ppm/V
12V ≤ V
IN
≤ 40V 0.5 2 ppm/V
●1.0 4 ppm/V
Load Regulation (Sourcing Current) 0 ≤ I
OUT
≤ 10mA 12 25 ppm/mA
(Note 4) ●40 ppm/mA
Load Regulation (Shunt Mode) 1.2mA ≤ I
SHUNT
≤ 10mA 50 100 ppm/mA
(Notes 4, 5) ●150 ppm/mA
Supply Current (Series Mode) 0.75 1.2 mA
●1.5 mA
Minimum Current (Shunt Mode) V
IN
is Open 0.7 1.0 mA
●1.2 mA
Output Voltage Noise (Note 6) 0.1Hz ≤ f ≤ 10Hz 4.0 µV
P-P
10Hz ≤ f ≤ 1kHz 2.5 4.0 µV
RMS
Long Term Stability of Output Voltage (Note 7) ∆t = 1000Hrs Noncumulative 7 ppm
Temperature Hysteresis of Output ∆T = ±25°C 3 ppm
The ● denotes specifications that apply over the full operating temperature
range, otherwise specifications are TA = 25°C. VIN = 10V, IOUT = 0, unless otherwise noted.
The ● denotes specifications that apply over the full operating temperature range, otherwise specifications are TA = 25°C.
VIN = 12V, IOUT = 0, unless otherwise noted.
4
LT1021
1021fc
ELECTRICAL C CHARA TERISTICS
LT1021-10
PARAMETER CONDITIONS MIN TYP MAX UNITS
Output Voltage (Note 2) LT1021C-10 9.995 10.00 10.005 V
LT1021B-10/LT1021D-10 9.950 10.00 10.050 V
Output Voltage Temperature Coefficient (Note 3) T
MIN
≤ T
J
≤ T
MAX
LT1021B-10 ●2 5 ppm/°C
LT1021C-10/LT1021D-10 ●5 20 ppm/°C
Line Regulation (Note 4) 11.5V ≤ V
IN
≤ 14.5V 1.0 4 ppm/V
●6 ppm/V
14.5V ≤ V
IN
≤ 40V 0.5 2 ppm/V
●4 ppm/V
Load Regulation (Sourcing Current) 0 ≤ I
OUT
≤ 10mA 12 25 ppm/mA
(Note 4) ●40 ppm/mA
Load Regulation (Shunt Mode) 1.7mA ≤ I
SHUNT
≤ 10mA 50 100 ppm/mA
(Notes 4, 5) ●150 ppm/mA
Supply Current (Series Mode) 1.2 1.7 mA
●2.0 mA
Minimum Current (Shunt Mode) V
IN
is Open 1.1 1.5 mA
●1.7 mA
Output Voltage Noise (Note 6) 0.1Hz ≤ f ≤ 10Hz 6.0 µV
P-P
10Hz ≤ f ≤ 1kHz 3.5 6 µV
RMS
Long Term Stability of Output Voltage (Note 7) ∆t = 1000Hrs Noncumulative 15 ppm
Temperature Hysteresis of Output ∆T = ±25°C 5 ppm
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: Output voltage is measured immediately after turn-on. Changes
due to chip warm-up are typically less than 0.005%.
Note 3: Temperature coefficient is measured by dividing the change in
output voltage over the temperature range by the change in temperature.
Separate tests are done for hot and cold; T
MIN
to 25°C and 25°C to T
MAX
.
Incremental slope is also measured at 25°C.
Note 4: Line and load regulation are measured on a pulse basis. Output
changes due to die temperature change must be taken into account
separately. Package thermal resistance is 150°C/W for TO-5 (H), 130°C/W
for N and 150°C/W for the SO-8.
Note 5: Shunt mode regulation is measured with the input open. With the
input connected, shunt mode current can be reduced to 0mA. Load
regulation will remain the same.
Note 6: RMS noise is measured with a 2-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. Correction factors are used to convert from average to
RMS and correct for the non-ideal bandpass of the filters.
Peak-to-peak noise is measured with a single 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. Test time is 10 seconds.
Note 7: Consult factory for units with long term stability data.
The ● denotes specifications that apply over the full operating temperature
range, otherwise specifications are TA = 25°C. VIN = 15V, IOUT = 0, unless otherwise noted.
5
LT1021
1021fc
CCHARA TERISTICS
UW
ATYPICALPER
FORCE
Start-Up (Series Mode)
Ripple Rejection
INPUT VOLTAGE (V)
0
85
REJECTION (dB)
90
95
100
105
10 20 30 40
LT1021 G01
110
115
51525 35
f = 150Hz
LT1021-5
LT1021-10
LT1021-7
TIME (µs)
3
OUTPUT VOLTAGE (V)
4
6
7
8
13
10
268
LT1021 G04
5
11
12
9
04 10 12 14
LT1021-10
LT1021-5
LT1021-7
VIN = 0V TO 12V
Output Voltage Noise Spectrum
OUTPUT CURRENT (mA)
0
INPUT/OUTPUT VOLTAGE (V)
1.2
1.6
16
1021 G03
0.8
0.4
04812 20
1.0
1.4
0.6
0.2
14
2610 18
T
J
= 125 °C
T
J
= –55 °C
T
J
= 25 °C
FREQUENCY (Hz)
100
NOISE VOLTAGE (nV/√Hz)
200
250
350
400
10 1k 10k
LT1021 G06
0
100
300
150
50
LT1021-10
LT1021-5
LT1021-7
Ripple Rejection
FREQUENCY (Hz)
10
90
REJECTION (dB)
110
130
120
100
80
60
100 1k 10k
LT1021 G02
70
50
V
IN
= 15V
C
OUT
= 0
LT1021-5
LT1021-10
LT1021-7
Start-Up (Shunt Mode)
LT1021-7, LT1021-10
TIME (µs)
OUTPUT VOLTAGE (V)
9
10
11
48
LT1021 G05
8
7
02 61012
6
5
LT1021-10
LT1021-7
IN
GND
OUT
NC
1k
VOUT
0V
VOUT + 2V
BANDWIDTH (Hz)
10
8
RMS NOISE (µV)
12
16
14
10
6
2
100 1k 10k
LT1021 G07
4
0
C
OUT
= 0
FILTER = 1 POLE
f
LOW
= 0.1Hz
LT1021-10
LT1021-5
LT1021-7
Output Voltage Temperature Drift
LT1021-5
Output Voltage Noise
TEMPERATURE (°C)
–50
4.994
4.996
OUTPUT VOLTAGE (V)
5.000
5.006
050 75
LT1021 G08
4.998
5.004
5.002
–25 25 100 125
Load Regulation LT1021-5
OUTPUT CURRENT
(
mA
)
–10
OUTPUT CHANGE (mV)
1
3
5
4
2
0
–2
–4
6
LT1021 G09
–1
–3
–5 –6–8 –4 0 4 8
–2 210
V
IN
= 8V
SOURCING SINKING
Minimum Input/Output Differential
LT1021-7, LT1021-10
6
LT1021
1021fc
CCHARA TERISTICS
UW
ATYPICALPER
FORCE
Quiescent Current LT1021-5
INPUT VOLTAGE (V)
0
0
INPUT CURRENT (mA)
0.2
0.6
0.8
1.0
3530
1.8
LT1021 G10
0.4
5 10152025 40
1.2
1.4
1.6
T
J
= – 55°C
T
J
= 25°C
T
J
= 125°C
I
OUT
= 0
Sink Mode* Current Limit
LT1021-5
OUTPUT VOLTAGE (V)
0
0
CURRENT INTO OUTPUT (mA)
10
30
40
50
4810 18
LT1021 G11
20
26 12 14 16
60 V
IN
= 8V
*NOTE THAT AN INPUT VOLTAGE IS REQUIRED
FOR 5V UNITS.
Thermal Regulation LT1021-5
TIME (ms)
OUTPUT CHANGE (mV)
–1.0
– 0.5
140
LT1021 G12
20 60 100
0
040 80 120
LOAD
REGULATION
THERMAL
REGULATION
I
LOAD
= 10mA
V
IN
= 25V
∆POWER = 200mW
Load Transient Response
LT1021-5, CLOAD = 1000pF
Load Transient Response
LT1021-5, CLOAD = 0
TIME (µs)
OUTPUT CHANGE (50mV/DIV)
2
LT1021 G13
102413
304
I
SOURCE
= 2-10mA
I
SOURCE
= 0.5mA
I
SINK
= 0
I
SINK
= 0.2mA
I
SINK
= 2-10mA
50mV 50mV
∆I
SINK
= 100µA
P-P
∆I
SOURCE
= 100µA
P-P
I
SOURCE
= 0
Output Noise 0.1Hz to 10Hz
LT1021-5
TIME (µs)
OUTPUT CHANGE (20mV/DIV)
10
LT1021 G14
501020515
15 020
I
SOURCE
= 2-10mA
I
SOURCE
= 0.2mA
I
SINK
= 0
I
SINK
= 0.2mA
I
SINK
= 2-10mA
20mV 20mV
∆I
SINK
= 100µA
P-P
∆I
SOURCE
= 100µA
P-P
I
SOURCE
= 0
TIME (MINUTES)
035
LT1021 G15
12 46
OUTPUT VOLTAGE NOISE (5µV/DIV)
5µV (1ppm)
FILTERING = 1 ZERO AT 0.1Hz
2 POLES AT 10Hz
Load Regulation
LT1021-7, LT1021-10
Output Voltage Temperature
Drift LT1021-7
TEMPERATURE (°C)
–50
6.997
6.998
OUTPUT VOLTAGE (V)
7.000
7.003
050 75
LT1021 G16
6.999
7.002
7.001
–25 25 100 125
OUTPUT CURRENT
(
mA
)
–10
OUTPUT CHANGE (mV)
1
3
5
4
2
0
–2
–4
6
LT1021 G17
–1
–3
–5 –6–8 –4 0 4 8
–2 210
V
IN
= 12V
SOURCING SINKING
Quiescent Current LT1021-7
INPUT VOLTAGE (V)
0
0
INPUT CURRENT (mA)
0.2
0.6
0.8
1.0
3530
1.8
LT1021 G18
0.4
5 10152025 40
1.2
1.4
1.6
T
J
= – 55°C
T
J
= 25°C
T
J
= 125°C
I
OUT
= 0
7
LT1021
1021fc
CCHARA TERISTICS
UW
ATYPICALPER
FORCE
Shunt Characteristics LT1021-7
Shunt Mode Current Limit
LT1021-7 Thermal Regulation LT1021-7
OUTPUT TO GROUND VOLTAGE (V)
0
0
CURRENT INTO OUTPUT (mA)
0.2
0.6
0.8
1.0
2459
1021 G19
0.4
13 678
1.2 INPUT PIN OPEN
T
J
= 125°C
T
J
= –55°C
T
J
= 25°C
OUTPUT VOLTAGE (V)
0
0
CURRENT INTO OUTPUT (mA)
10
30
40
50
4810 18
LT1021 G20
20
26 12 14 16
60 INPUT PIN OPEN
TIME (ms)
OUTPUT CHANGE (mV)
–1.0
–0.5
0
140
LT1021 G21
–1.5
20 60 100
040 80 120
LOAD
REGULATION
THERMAL
REGULATION*
I
LOAD
= 10mA
*INDEPENDENT OF TEMPERATURE COEFFICIENT
V
IN
= 27V
∆POWER = 200mW
Load Regulation
LT1021-7, LT1021-10
TEMPERATURE (°C)
–50
9.994
9.996
OUTPUT VOLTAGE (V)
10.000
10.006
050 75
LT1021 G25
9.998
10.004
10.002
–25 25 100 125
Output Voltage Temperature
Drift LT1021-10
OUTPUT CURRENT
(
mA
)
–10
OUTPUT CHANGE (mV)
1
3
5
4
2
0
–2
–4
6
1021 G26
–1
–3
–5 –6–8 –4 0 4 8
–2 210
V
IN
= 12V
SOURCING SINKING
Input Supply Current LT1021-10
INPUT VOLTAGE (V)
0
0
INPUT CURRENT (mA)
0.2
0.6
0.8
1.0
3530
1.8
1021 G27
0.4
5 10152025 40
1.2
1.4
1.6 TJ = – 55°C
TJ = 25°C
TJ = 125°C
IOUT = 0
Load Transient Response
LT1021-7, CLOAD = 0
TIME (µs)
OUTPUT VOLTAGE CHANGE
2
LT1021 G22
102413
304
ISOURCE = 2-10mA
ISOURCE = 0.5mA
ISINK = 0.8mA
ISINK = 1.2mA
ISINK = 1.4mA
ISINK = 2-10mA
5mV
50mV
∆ISINK = 100µAP-P
∆ISOURCE = 100µAP-P
ISOURCE = 0
NOTE VERTICAL SCALE CHANGE
BETWEEN SOURCING AND SINKING
Load Transient Response
LT1021-7, CLOAD = 1000pF
Output Noise 0.1Hz to 10Hz
LT1021-7
5µs/DIV
OUTPUT VOLTAGE CHANGE
10
LT1021 G23
501020515
15 020
ISOURCE = 2-10mA
ISOURCE = 0.5mA
ISINK = 0.6mA
ISINK = 0.8mA
ISINK = 1mA
ISINK = 2-10mA
5mV 20mV
∆ISINK = 100µAP-P
∆ISOURCE = 100µAP-P
ISOURCE = 0
NOTE VERTICAL SCALE CHANGE
BETWEEN SOURCING AND SINKING
TIME (MINUTES)
035
LT1021 G24
12 46
OUTPUT VOLTAGE NOISE (5µV/DIV)
5µV (0.7ppm)
FILTERING = 1 ZERO AT 0.1Hz
2 POLES AT 10Hz
8
LT1021
1021fc
CCHARA TERISTICS
UW
ATYPICALPER
FORCE
Shunt Characteristics LT1021-10
Shunt Mode Current Limit
LT1021-10 Thermal Regulation LT1021-10
OUTPUT TO GROUND VOLTAGE (V)
0
0
CURRENT INTO OUTPUT (mA)
0.2
0.6
0.8
1.0
8
1.8
1021 G28
0.4
42 6 10 12
1.2
1.4
1.6
TJ = – 55°C
TJ = 25°C
INPUT PIN OPEN
TJ = 125°C
OUTPUT VOLTAGE (V)
0
0
CURRENT INTO OUTPUT (mA)
10
30
40
50
4810 18
1021 G29
20
26 12 14 16
60 INPUT PIN OPEN
TIME (ms)
OUTPUT CHANGE (mV)
–1.0
–0.5
0
140
1021 G30
–1.5
20 60 100
040 80 120
LOAD
REGULATION
THERMAL
REGULATION*
ILOAD = 10mA
*INDEPENDENT OF TEMPERATURE COEFFICIENT
VIN = 30V
∆POWER = 200mW
Load Transient Response
LT1021-10, CLOAD = 0
TIME (µs)
OUTPUT VOLTAGE CHANGE
2
1021 G31
102413
304
ISOURCE = 2-10mA
ISOURCE = 0.2mA
ISINK = 0.6mA
ISINK = 0.8mA
ISINK = 1mA
ISINK = 2-10mA
10mV
50mV
∆ISINK = 100µAP-P
∆ISOURCE = 100µAP-P
ISOURCE = 0
NOTE VERTICAL SCALE CHANGE
BETWEEN SOURCING AND SINKING
Load Transient Response
LT1021-10, CLOAD = 1000pF
TIME (µs)
OUTPUT VOLTAGE CHANGE
2
1021 G32
102413
304
ISOURCE = 2-10mA
ISOURCE = 0.5mA
ISINK = 0.8mA
ISINK = 1.2mA
ISINK = 1.4mA
ISINK = 2-10mA
5mV
20mV
∆ISINK = 100µAP-P
∆ISOURCE = 100µAP-P
ISOURCE = 0
NOTE VERTICAL SCALE CHANGE
BETWEEN SOURCING AND SINKING
Output Noise 0.1Hz to 10Hz
LT1021-10
TIME (MINUTES)
035
1021 G33
12 46
OUTPUT VOLTAGE NOISE (10µV/DIV)
10µV (1ppm)
FILTERING = 1 ZERO AT 0.1Hz
2 POLES AT 10Hz
9
LT1021
1021fc
APPLICATIONS INFORMATION
WUUU
Maximum Allowable Reference Drift
Trimming Output Voltage
LT1021-10
The LT1021-10 has a trim pin for adjusting output voltage.
The impedance of the trim pin is about 12kΩ with a
nominal open-circuit voltage of 5V. It is designed to be
driven from a source impedance of 3kΩ or less to mini-
mize changes in the LT1021 TC with output trimming.
Attenuation between the trim pin and the output is 70:1.
This allows ±70mV trim range when the trim pin is tied to
the wiper of a potentiometer connected between the
output and ground. A 10kΩ potentiometer is recom-
mended, preferably a 20 turn cermet type with stable
characteristics over time and temperature.
Effect of Reference Drift on System Accuracy
A large portion of the temperature drift error budget in
many systems is the system reference voltage. This graph
indicates the maximum temperature coefficient allowable
if the reference is to contribute no more than 0.5LSB error
to the overall system performance. The example shown is
a 12-bit system designed to operate over a temperature
range from 25°C to 65°C. Assuming the system calibra-
tion is performed at 25°C, the temperature span is 40°C.
It can be seen from the graph that the temperature coeffi-
cient of the reference must be no worse than 3ppm/°C if
it is to contribute less than 0.5LSB error. For this reason,
the LT1021 family has been optimized for low drift.
The LT1021-10 “C” version is pre-trimmed to ±5mV and
therefore can utilize a restricted trim range. A 75k resistor
in series with a 20kΩ potentiometer will give ±10mV trim
range. Effect on the output TC will be only 1ppm/°C for the
±5mV trim needed to set the “C” device to 10.000V.
LT1021-5
The LT1021-5 does have an output voltage trim pin, but
the TC of the nominal 4V open-circuit voltage at this pin is
about –1.7mV/°C. For the voltage trimming not to affect
reference output TC, the external trim voltage must track
the voltage on the trim pin. Input impedance of the trim pin
is about 100kΩ and attenuation to the output is 13:1. The
technique shown below is suggested for trimming the
output of the LT1021-5 while maintaining minimum shift
in output temperature coefficient. The R1/R2 ratio is
chosen to minimize interaction of trimming and TC shifts,
so the exact values shown should be used.
LT1021-5
OUT
IN
GND TRIM R1
27k
R2
50k
1N4148
VOUT
1021 AI02
TEMPERATURE SPAN (°C)
100
MAXIMUM TEMPERATURE COEFFICIENT FOR
0.5LSB ERROR (ppm/°C)
30
100
LT1021 AI01
1.0
10
20 100
90
807060
50
40
8-BIT
10-BIT
12-BIT
14-BIT
LT1021-7
The 7V version of the LT1021 has no trim pin because the
internal architecture does not have a point which could be
driven conveniently from the output. Trimming must
therefore be done externally, as is the case with ordinary
reference diodes. Unlike these diodes, however, the out-
put of the LT1021 can be loaded with a trim potentiometer.
The following trim techniques are suggested; one for
voltage output and one for current output. The voltage
output is trimmed for 6.95V. Current output is 1mA, as
shown, into a summing junction, but all resistors may be
scaled for currents up to 10mA.
Both of these circuits use the trimmers in a true potentio-
metric mode to reduce the effects of trimmer TC. The
voltage output has a 200Ω impedance, so loading must be
10
LT1021
1021fc
APPLICATIONS INFORMATION
WUUU
minimized. In the current output circuit, R1 determines
output current. It should have a TC commensurate with the
LT1021 or track closely with the feedback resistor around
the op amp.
Kelvin Connections
Although the LT1021 does not have true force/sense
capability at its outputs, significant improvements in ground
loop and line loss problems can be achieved with proper
hook-up. In series mode operation, the ground pin of the
LT1021 carries only ≈1mA and can be used as a sense
line, greatly reducing ground loop and loss problems on
the low side of the reference. The high side supplies load
current so line resistance must be kept low. Twelve feet of
#22 gauge hook-up wire or 1 foot of 0.025 inch printed
circuit trace will create 2mV loss at 10mA output current.
This is equivalent to 1LSB in a 10V, 12-bit system.
The following circuits show proper hook-up to minimize
errors due to ground loops and line losses. Losses in the
output lead can be greatly reduced by adding a PNP boost
transistor if load currents are 5mA or higher. R2 can be
added to further reduce current in the output sense lead.
Capacitive Loading and Transient Response
The LT1021 is stable with all capacitive loads, but for
optimum settling with load transients, output capacitance
should be under 1000pF. The output stage of the reference
is class AB with a fairly low idling current. This makes
transient response worst-case at light load currents. Be-
cause of internal current drain on the output, actual worst-
case occurs at I
LOAD
= 0 on LT1021-5, I
LOAD
=
–0.8mA (sinking) on LT1021-7 and I
LOAD
= 1.4mA (sink-
ing) on LT1021-10. Significantly better load transient
response is obtained by moving slightly away from these
points. See Load Transient Response curves for details. In
general, best transient response is obtained when the
output is sourcing current. In critical applications, a 10µF
solid tantalum capacitor with several ohms in series
provides optimum output bypass.
Standard Series Mode
LT1021
OUT
IN
GND
KEEP THIS LINE RESISTANCE LOW
LOAD
+
INPUT
GROUND
RETURN 1021 AI05
Series Mode with Boost Transistor
LT1021-7
OUT
IN
GND
R3
50k
RESISTOR TC DETERMINES IOUT TC
TC ≤ (10 • R1) TC. R2 AND R3 SCALE
WITH R1 FOR DIFFERENT OUTPUT CURRENTS
*
**
R1*
7.15k
1.000mA
R2**
182k
1021 AI04
–
+
OP AMP
LT1021-7
OUT
IN
TC TRACKING TO 50ppm/°C
GND
R3
10k
R1*
200Ω
1% V
OUT
6.950V
R2*
14k
1%
1021 AI03
LT1021
OUT
GND
IN
LOAD
R1
220Ω
2N3906
R2*
INPUT
GROUND
RETURN
*OPTIONAL—REDUCES CURRENT IN OUTPUT SENSE LEAD
R2 = 2.4k (LT1021-5), 3k (LT1021-7), 5.6k (LT1021-10)
1021 AI06
11
LT1021
1021fc
APPLICATIONS INFORMATION
WUUU
Effects of Air Movement on Low Frequency Noise
The LT1021 has very low noise because of the buried zener
used in its design. In the 0.1Hz to 10Hz band, peak-to-peak
noise is about 0.5ppm of the DC output. To achieve this
low noise, however, care must be taken to shield the
reference from ambient air turbulence. Air movement can
create noise because of thermoelectric differences
between IC package leads (especially kovar lead TO-5) and
printed circuit board materials and/or sockets. Power
dissipation in the reference, even though it rarely exceeds
20mW, is enough to cause small temperature gradients in
the package leads. Variations in thermal resistance, caused
by uneven air flow, create differential lead temperatures,
thereby causing thermoelectric voltage noise at the output
of the reference. The following XY plotter trace dramati-
cally illustrates this effect. The first half of the plot was
done with the LT1021 shielded from ambient air with a
small foam cup. The cup was then removed for the second
half of the trace. Ambient in both cases was a lab environ-
ment with no excessive air turbulence from air condition-
ers, opening/closing doors, etc. Removing the foam cup
increases the output noise by almost an order of magni-
tude in the 0.01Hz to 1Hz band! The kovar leads of the
TO-5 (H) package are the primary culprit. Alloy 42 and
copper lead frames used on dual-in-line packages are not
nearly as sensitive to thermally generated noise because
they are intrinsically matched.
There is nothing magical about foam cups—any enclo-
sure which blocks air flow from the reference will do.
Smaller enclosures are better since they do not allow the
build-up of internally generated air movement. Naturally,
heat generating components external to the reference
itself should not be included inside the enclosure.
Noise Induced By Air Turbulence (TO-5 Package)
TIME (MINUTES)
0610
1021 AI07
24 812
OUTPUT VOLTAGE NOISE (20µV/DIV)
20µVFOAM CUP
REMOVED
LT1021-7 (TO-5 PACKAGE)
f = 0.01Hz TO 10Hz
TYPICAL APPLICATIONS
U
Restricted Trim Range for Improved
Resolution, 10V, “C” Version Only
LT1021C-10
OUT VIN IN 10.000V
TRIM RANGE ≈ ±10mV
GND TRIM
R2
50k
1021 TA11
R1
75k
1021 TA03
LT1021-10
OUT
IN
GND TRIM
R1*
10k
VOUT
*CAN BE RAISED TO 20k FOR
LESS CRITICAL APPLICATIONS
VIN
LT1021-10
OUT
IN
GND
LT1021 TA04
D1
15V
R1
4.7k
–10V AT 50mA
R2
4.7k
–15V
15V
Q1
2N2905
Negative Series Reference
LT1021-10 Full Trim Range (±0.7%)
12
LT1021
1021fc
TYPICAL APPLICATIONS
U
Boosted Output Current
with No Current Limit
Boosted Output Current
with Current Limit Ultraprecise Current Source
LT1021-10
OUT
IN
TRIM GND
4.32k
V
OUT
= 10.24V
V
IN
5k
V
–
= –15V*
*MUST BE WELL REGULATED
dV
OUT
dV
–
=15mV
V1021 TA12
Trimming 10V Units to 10.24V
CMOS DAC with Low Drift Full-Scale Trimming**
LT1021-10
TRIM
GND
OUT
LT1236 TA15
–
+
1.2k
R2
40.2Ω
1%
R1
4.99k
1%
REF
CMOS
DAC
7520, ETC
IOUT
FB
30pF
LT1007C
R4*
100Ω
FULL-SCALE
ADJUST
R3
4.02K
1%
10V
F.S.
–15V
TC LESS THAN 200ppm/°C
NO ZERO ADJUST REQUIRED
WITH LT1007 (V0S ≤ 60µV)
*
**
LT1021-7
OUT
IN
2*LOW TC
3
4
7
GND
–15V
15V
TRIM
100Ω
15V
6
6.98k*
0.1%
17.4k
1%
1021 TA07
–
+
LT1001
I
OUT
= 1mA
REGULATION < 1ppm/V
COMPLIANCE = –13V TO 7V
LT1021
OUT
V+ ≥ (VOUT + 1.8V)
GND
IN
1021 TA05
2N2905
10V AT
100mA
2µF
SOLID
TANT
R1
220Ω
+
LT1021
OUT
GND
IN
1021 TA06
2N2905
10V AT
100mA
2µF
SOLID
TANT
D1*
LED
V
+
≥ V
OUT
+ 2.8V
8.2Ω
R1
220Ω
*GLOWS IN CURRENT LIMIT,
DO NOT OMIT
+
Operating 5V Reference from 5V Supply
2-Pole Lowpass Filtered Reference
LT1021-5
OUT
IN
GND
1021 TA16
1N914
1N914
≈8.5V
C2*
5µF
C1*
5µF
5V
REFERENCE
5V LOGIC
SUPPLY
CMOS LOGIC GATE**
fIN ≥ 2kHz*
FOR HIGHER FREQUENCIES C1 AND C2 MAY BE DECREASED
PARALLEL GATES FOR HIGHER REFERENCE CURRENT LOADING
*
**
+
+
LT1021
OUT
IN
GND
1021 TA13
–
+
R1
36k
1µF
MYLAR
0.5µF
MYLAR
R2
36k
LT1001
V
IN
V
IN
V
REF
–V
REF
f = 10Hz
TOTAL NOISE
≤2µV
RMS
1Hz ≤ f ≤ 10kHz
13
LT1021
1021fc
TYPICAL APPLICATIONS
U
Precision DAC Reference with System TC Trim
Strain Gauge Conditioner for 350Ω Bridge Negative Shunt Reference Driven
by Current Source
LT1021-10
OUT
IN
GND
1021 TA17
15V
8.87k
1%
1.24k
1%
10k
1%
D1
1N457
50k
TC TRIM*
10k
1%
D2
1N457
50k
200k
1%
50k
ROOM TEMP
TRIM 10.36k
1%
8.45k
1mA
TRIMS 1mA REFERENCE CURRENT
TC BY ±40ppm/°C. THIS TRIM SCHEME HAS
VERY LITTLE EFFECT ON ROOM TEMPERATURE
CURRENT TO MINIMIZE ITERATIVE TRIMMING
*DAC
Handling Higher Load Currents
LT1021-10
OUT
GND
IN
1021 TA08
R
L
30mA
15V
R1*
169Ω
V
OUT
10V
TYPICAL LOAD
CURRENT = 30mA
SELECT R1 TO DELIVER TYPICAL LOAD CURRENT.
LT1021 WILL THEN SOURCE OR SINK AS NECESSARY
TO MAINTAIN PROPER OUTPUT. DO NOT REMOVE LOAD
AS OUTPUT WILL BE DRIVEN UNREGULATED HIGH. LINE
REGULATION IS DEGRADED IN THIS APPLICATION
*
LT1021-10
OUT
IN
GND
1021 TA09
–
+
–
+
LM301A
†
100pF 8
1
6 6
3
2
–5V
357Ω
1/2W
–15V
R5
2M
R6*
2M
LT1012C
2
3
R4
20k
R2
20k
5V
R3
2M
VOUT
×100
350Ω STRAIN
GAUGE BRIDGE**
28mA
28.5mA
R1
357Ω
1/2W
15V
THIS RESISTOR PROVIDES POSITIVE FEEDBACK TO
THE BRIDGE TO ELIMINATE LOADING EFFECT OF
THE AMPLIFIER. EFFECTIVE ZIN OF AMPLIFIER
STAGE IS ≥1MΩ. IF R2 TO R5 ARE CHANGED,
SET R6 = R3
*BRIDGE IS ULTRALINEAR WHEN ALL LEGS ARE
ACTIVE, TWO IN COMPRESSION AND TWO IN TENSION,
OR WHEN ONE SIDE IS ACTIVE WITH ONE COMPRESSED
AND ONE TENSIONED LEG
OFFSET AND DRIFT OF LM301A ARE VIRTUALLY
ELIMINATED BY DIFFERENTIAL CONNECTION OF LT1012C
**
†
LT1021-10
OUT
GND
1021 TA14
2.5mA
–10V (ILOAD ≤ 1mA)
–11V TO – 40V
27Ω
LM334
14
LT1021
1021fc
TYPICAL APPLICATIONS
U
Ultralinear Platinum Temperature Sensor*
EQUIVALE T SCHE ATIC
UW
LT1021-10
OUT IN
GND
1021 TA10
–
+
R
S†
100Ω AT
0°C
R4
4.75k
1%
R5
200k
1%
R6
619k
1%
7
4
6
2
3
LT1001
–15V
20V
R13
24.3k
R12
1k
R15
10k
R14
5k
R
F
**
654k
R11
6.65M
1%
R10
182k
1%
R2*
5k
R1**
253k
R3**
5k
R9
100k
R8
10M
–15V
V
OUT
=100mV/°C
–50°C ≤ T ≤ 150°C
R7
392k
1%
20V
STANDARD INDUSTRIAL 100Ω PLATINUM 4-WIRE SENSOR,
ROSEMOUNT 78S OR EQUIVALENT. α = 0.00385
TRIM R9 FOR V
OUT
= 0V AT 0°C
TRIM R12 FOR V
OUT
= 10V AT 100°C
TRIM R14 FOR V
OUT
= 5V AT 50°C
USE TRIM SEQUENCE AS SHOWN. TRIMS ARE NONINTERACTIVE
SO THAT ONLY ONE TRIM SEQUENCE IS NORMALLY REQUIRED.
FEEDBACK LINEARIZES OUTPUT TO ±0.005°C FROM
–50°C TO 150°C
WIREWOUND RESISTORS WITH LOW TC
†
*
**
D1
D2
D3 R1
R2
GND
LT1021 ES
Q1
Q2
D4
6.3V
OUTPUT
–+
A1
INPUT
Q3
15
LT1021
1021fc
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 represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
PACKAGE DESCRIPTION
U
N8 1002
.065
(1.651)
TYP
.045 – .065
(1.143 – 1.651)
.130 ± .005
(3.302 ± 0.127)
.020
(0.508)
MIN
.018 ± .003
(0.457 ± 0.076)
.120
(3.048)
MIN
12 34
87 65
.255 ± .015*
(6.477 ± 0.381)
.400*
(10.160)
MAX
.008 – .015
(0.203 – 0.381)
.300 – .325
(7.620 – 8.255)
.325 +.035
–.015
+0.889
–0.381
8.255
()
NOTE:
1. DIMENSIONS ARE INCHES
MILLIMETERS
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm)
.100
(2.54)
BSC
.050
(1.270)
MAX
.016 – .021**
(0.406 – 0.533)
.010 – .045*
(0.254 – 1.143)
SEATING
PLANE
.040
(1.016)
MAX .165 – .185
(4.191 – 4.699)
GAUGE
PLANE
REFERENCE
PLANE
.500 – .750
(12.700 – 19.050)
.305 – .335
(7.747 – 8.509)
.335 – .370
(8.509 – 9.398)
DIA
.200
(5.080)
TYP
.027 – .045
(0.686 – 1.143)
.028 – .034
(0.711 – 0.864)
.110 – .160
(2.794 – 4.064)
INSULATING
STANDOFF
45°
H8(TO-5) 0.200 PCD 0204
LEAD DIAMETER IS UNCONTROLLED BETWEEN THE REFERENCE PLANE
AND THE SEATING PLANE
FOR SOLDER DIP LEAD FINISH, LEAD DIAMETER IS .016 – .024
(0.406 – 0.610)
*
**
PIN 1
H Package
8-Lead TO-5 Metal Can (.200 Inch PCD)
(Reference LTC DWG # 05-08-1320)
N8 Package
8-Lead PDIP (Narrow .300 Inch)
(Reference LTC DWG # 05-08-1510)
16
LT1021
1021fc
© LINEAR TECHNOLOGY CORPORATION 1995
LT 1005 REV C • PRINTED IN USA
PACKAGE DESCRIPTION
U
.016 – .050
(0.406 – 1.270)
.010 – .020
(0.254 – 0.508)× 45°
0°– 8° TYP
.008 – .010
(0.203 – 0.254)
SO8 0303
.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)
RELATED PARTS
PART NUMBER DESCRIPTION COMMENTS
LT1019 Precision Bandgap Reference 0.05%, 5ppm/°C
LT1027 Precision 5V Reference 0.02%, 2ppm/°C
LT1236 Precision Reference SO-8, 5V and 10V, 0.05%, 5ppm/°C
LTC®1258 Micropower Reference 200mV Dropout, MSOP
LT1389 Nanopower Shunt Reference 800nA Operating Current
LT1460 Micropower Reference SOT-23, 2.5V, 5V, 10V
LT1634 Micropower Shunt Reference 0.05%, 10ppm/°C, MSOP
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear.com
S8 Package
8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
