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LT1021 Precision Reference
FEATURES
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DESCRIPTIO
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Pin Compatible with Most Bandgap Reference Applications, Including Ref 01, Ref 02, LM368, MC1400 and MC1404 with Greatly Improved Stability, Noise and Drift Ultralow Drift: 5ppm/C Max Slope Trimmed Output Voltage Operates in Series or Shunt Mode Output Sinks and Sources in Series Mode Very Low Noise: <1ppm P-P (0.1Hz to 10Hz) >100dB Ripple Rejection Minimum Input/Output Differential of 1V 100% Noise Tested
The LT(R)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 threeterminal connection. Special care has been taken to minimize 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 LT102110 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.
APPLICATI
s s s s s s
S
A/D and D/A Converters Precision Regulators Digital Voltmeters Inertial Navigation Systems Precision Scales Portable Reference Standard
TYPICAL APPLICATI
Typical Distribution of Temperature Drift Basic Positive and Negative Connections
LT1021 VIN IN GND OUT VOUT NC LT1021 (7 AND 10 ONLY) OUT GND -VOUT V - (V - ) R1 = OUT ILOAD + 1.5mA R1 -15V (V - )
24 21 18
UNITS (%)
IN
15 12 9 6 3
1021 TA01
-0 - 5 - 4 - 3 - 2 -1 0 1 2 3 OUTPUT DRIFT (ppm/C) 4 5
U
DISTRIBUTION OF THREE RUNS
1021 TA01
UO
UO
1
LT1021 ABSOLUTE AXI U RATI GS
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 VOUT Negative ........................................................... - 20V
PACKAGE/ORDER I FOR ATIO
ORDER PART NUMBER
LT1021BCH-5 LT1021BMH-5 LT1021CCH-5 LT1021CMH-5 LT1021DCH-5 LT1021DMH-5 LT1021BCH-7 LT1021BMH-7 LT1021DCH-7 LT1021DMH-7 LT1021BCH-10 LT1021BMH-10 LT1021CCH-10 LT1021CMH-10 LT1021DCH-10 LT1021DMH-10
TOP VIEW NC* 8 NC* 1 VIN 2 NC* 3 7 NC* 6 VOUT
5 TRIM** 4
GND H PACKAGE 8-LEAD TO-5 METAL CAN *CONNECTED INTERNALLY. D0 NOT CONNECT EXTERNAL CIRCUITRY TO THESE PINS **NO TRIM PIN ON LT1021-7. DO NOT CONNECT EXTERNAL CIRCUITRY TO PIN 5 ON LT1021-7
TJMAX = 150C, JA = 150C/W,JC = 45C/W
2
U
U
W
WW
U
W
(Note 1)
Output Short-Circuit Duration VIN = 35V ......................................................... 10 sec VIN 20V ................................................... Indefinite Operating Temperature Range Commercial ............................................ 0C to 70C Industrial ........................................... - 40C to 85C Military ............................................ - 55C to 125C Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec)................ 300C
ORDER PART NUMBER
LT1021BCN8-5 LT1021CCN8-5 LT1021CIN8-5 LT1021DCN8-5 LT1021DIN8-5 LT1021DCS8-5 LT1021BCN8-7 LT1021DCN8-7 LT1021DCS8-7 LT1021BCN8-10 LT1021CCN8-10 LT1021CIN8-10 LT1021DCN8-10 LT1021DCS8-10 LT1021DIN8-10
TOP VIEW DNC* 1 VIN 2 DNC* 3 GND 4 N8 PACKAGE 8-LEAD PDIP 8 7 6 5 DNC* DNC* V0UT TRIM**
S8 PACKAGE 8-LEAD PLASTIC SO
*CONNECTED INTERNALLY. D0 NOT CONNECT EXTERNAL CIRCUITRY TO THESE PINS **NO TRIM PIN ON LT1021-7. DO NOT CONNECT EXTERNAL CIRCUITRY TO PIN 5 ON LT1021-7
TJMAX = 130C, JA = 130C/W (N) TJMAX = 130C, JA = 150C/W (S)
S8 PART MARKING
021DC5 021DC7 021DC1
LT1021
The q denotes specifications that apply over the full operating temperature range, otherwise specifications are TA = 25C. VIN = 10V, IOUT = 0, unless otherwise noted.
PARAMETER Output Voltage (Note 2) Output Voltage Temperature Coefficient (Note 3) CONDITIONS LT1021C-5 LT1021B-5/LT1021D-5 TMIN TJ TMAX LT1021B-5 LT1021C-5/LT1021D-5 7.2V VIN 10V
q q q
ELECTRICAL CHARACTERISTICS
MIN 4.9975 4.9500
LT1021-5 TYP 5.000 5.000 2 3 4 2
MAX 5.0025 5.0500 5 20 12 20 6 10 20 35 100 150 1.2 1.5 3.5
UNITS V V ppm/C ppm/C ppm/V ppm/V ppm/V ppm/V ppm/mA ppm/mA ppm/mA ppm/mA mA mA VP-P VRMS ppm ppm
Line Regulation (Note 4)
10V VIN 40V
q
Load Regulation (Sourcing Current) Load Regulation (Sinking Current) Supply Current
0 IOUT 10mA (Note 4) 0 IOUT 10mA (Note 4)
10
q
60
q
0.8
q
Output Voltage Noise (Note 6) Long Term Stability of Output Voltage (Note 7) Temperature Hysteresis of Output
0.1Hz f 10Hz 10Hz f 1kHz t = 1000Hrs Noncumulative T = 25C
3.0 2.2 15 10
The q denotes specifications that apply over the full operating temperature range, otherwise specifications are TA = 25C. VIN = 12V, IOUT = 0, unless otherwise noted.
PARAMETER Output Voltage (Note 2) Output Voltage Temperature Coefficient (Note 3) TMIN TJ TMAX LT1021B-7 LT1021D-7 8.5V VIN 12V
q q q
CONDITIONS
MIN 6.95
LT1021-7 TYP 7.00 2 3 1.0 2.0 0.5 1.0 12
MAX 7.05 5 20 4 8 2 4 25 40 100 150 1.2 1.5 1.0 1.2 4.0
UNITS V ppm/C ppm/C ppm/V ppm/V ppm/V ppm/V ppm/mA ppm/mA ppm/mA ppm/mA mA mA mA mA VP-P VRMS ppm ppm
Line Regulation (Note 4)
12V VIN 40V
q
Load Regulation (Sourcing Current) Load Regulation (Shunt Mode) Supply Current (Series Mode)
0 IOUT 10mA (Note 4) 1.2mA ISHUNT 10mA (Notes 4, 5)
q
50
q
0.75
q
Minimum Current (Shunt Mode) Output Voltage Noise (Note 6) Long Term Stability of Output Voltage (Note 7) Temperature Hysteresis of Output
VIN is Open
q
0.7 4.0 2.5 7 3
0.1Hz f 10Hz 10Hz f 1kHz t = 1000Hrs Noncumulative T = 25C
3
LT1021
The q denotes specifications that apply over the full operating temperature range, otherwise specifications are TA = 25C. VIN = 15V, IOUT = 0, unless otherwise noted.
PARAMETER Output Voltage (Note 2) Output Voltage Temperature Coefficient (Note 3) CONDITIONS LT1021C-10 LT1021B-10/LT1021D-10 TMIN TJ TMAX LT1021B-10 LT1021C-10/LT1021D-10 11.5V VIN 14.5V
q q q
ELECTRICAL CHARACTERISTICS
MIN 9.995 9.950
LT1021-10 TYP 10.00 10.00 2 5 1.0 0.5
MAX 10.005 10.050 5 20 4 6 2 4 25 40 100 150 1.7 2.0 1.5 1.7 6
UNITS V V ppm/C ppm/C ppm/V ppm/V ppm/V ppm/V ppm/mA ppm/mA ppm/mA ppm/mA mA mA mA mA VP-P VRMS ppm ppm
Line Regulation (Note 4)
14.5V VIN 40V
q
Load Regulation (Sourcing Current) Load Regulation (Shunt Mode) Supply Current (Series Mode)
0 IOUT 10mA (Note 4) 1.7mA ISHUNT 10mA (Notes 4, 5)
12
q
50
q
1.2
q
Minimum Current (Shunt Mode) Output Voltage Noise (Note 6) Long Term Stability of Output Voltage (Note 7) Temperature Hysteresis of Output
VIN is Open
q
1.1 6.0 3.5 15 5
0.1Hz f 10Hz 10Hz f 1kHz t = 1000Hrs Noncumulative T = 25C
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; TMIN to 25C and 25C to TMAX. Incremental slope is also measured at 25C. 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 150C/W for TO-5 (H), 130C/W for N and 150C/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.
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LT1021
TYPICAL PERFOR A CE CHARACTERISTICS
Ripple Rejection
115 110
REJECTION (dB)
f = 150Hz
LT1021-7 120 LT1021-10 110
LT1021-7
INPUT/OUTPUT VOLTAGE (V)
REJECTION (dB)
105 100
LT1021-5 95 90 85 0 5 10
15 20 25 30 INPUT VOLTAGE (V)
Start-Up (Series Mode)
13 12 11
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
VIN = 0V TO 12V
10 9 8 7 6 5 4 3 0 2 4
LT1021-10
VOUT + 2V
1k VOUT OUT IN GND
NOISE VOLTAGE (nV/Hz)
LT1021-7
LT1021-5
6 8 TIME (s)
10
Output Voltage Noise
16 14 12
RMS NOISE (V)
COUT = 0 FILTER = 1 POLE fLOW = 0.1Hz
OUTPUT CHANGE (mV)
OUTPUT VOLTAGE (V)
10 8 LT1021-7 6 4 LT1021-5 2 0 10 100 1k BANDWIDTH (Hz) 10k
LT1021 G07
LT1021-10
UW
35 40
LT1021 G01
Ripple Rejection
130
Minimum Input/Output Differential LT1021-7, LT1021-10
1.6 TJ = 125 C TJ = -55 C TJ = 25 C 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0
VIN = 15V COUT = 0
100 LT1021-10 90 LT1021-5 80 70 60 50 10 100 1k FREQUENCY (Hz) 10k
LT1021 G02
0
2
4
6 8 10 12 14 16 18 20 OUTPUT CURRENT (mA)
1021 G03
Start-Up (Shunt Mode) LT1021-7, LT1021-10
11 LT1021-10 10 9 8 7 6 5
12 14
0V NC
Output Voltage Noise Spectrum
400 350 300 250 200 150 100 50 0 LT1021-10 LT1021-7 LT1021-5
LT1021-7
0
2
6 4 TIME (s)
8
10
12
10
100 1k FREQUENCY (Hz)
10k
LT1021 G06
LT1021 G04
LT1021 G05
Output Voltage Temperature Drift LT1021-5
5.006 5.004 5.002 5.000 4.998 4.996 4.994 - 50 -25
Load Regulation LT1021-5
5 4 3 2 1 0 -1 -2 -3 -4 VIN = 8V
50 0 75 25 TEMPERATURE (C)
100
125
-5 -10 - 8 - 6 - 4 - 2 SOURCING
0
2
468 SINKING
10
LT1021 G08
OUTPUT CURRENT (mA)
LT1021 G09
5
LT1021
TYPICAL PERFOR A CE CHARACTERISTICS
Quiescent Current LT1021-5
1.8 1.6 1.4
INPUT CURRENT (mA)
IOUT = 0
CURRENT INTO OUTPUT (mA)
1.2 TJ = - 55C 1.0 0.8 0.6 0.4 0.2 0 0 5 10 15 20 25 30 INPUT VOLTAGE (V) 35 40 TJ = 25C TJ = 125C
40 30 20 10 0 0 2 4 6 8 10 12 14 OUTPUT VOLTAGE (V) 16 18
OUTPUT CHANGE (mV)
Load Transient Response LT1021-5, CLOAD = 0
ISOURCE = 0 ISINK = 0
OUTPUT VOLTAGE NOISE (5V/DIV)
OUTPUT CHANGE (50mV/DIV)
OUTPUT CHANGE (20mV/DIV)
50mV
50mV
ISOURCE = 0.5mA ISOURCE = 2-10mA
ISINK = 0.2mA ISINK = 2-10mA
ISOURCE = 100AP-P 0 1 2
ISINK = 100AP-P 1 2 3 4
340 TIME (s)
Output Voltage Temperature Drift LT1021-7
7.003 7.002
OUTPUT CHANGE (mV)
OUTPUT VOLTAGE (V)
7.001 7.000 6.999 6.998 6.997 - 50 -25
2 1 0 -1 -2 -3 -4
INPUT CURRENT (mA)
50 0 75 25 TEMPERATURE (C)
6
UW
LT1021 G10
LT1021 G13
Sink Mode* Current Limit LT1021-5
60 50 VIN = 8V
Thermal Regulation LT1021-5
VIN = 25V POWER = 200mW 0 - 0.5 - 1.0 LOAD REGULATION THERMAL REGULATION
ILOAD = 10mA
0
20
40 60 80 TIME (ms)
100 120 140
LT1021 G12
*NOTE THAT AN INPUT VOLTAGE IS REQUIRED FOR 5V UNITS. LT1021 G11
Load Transient Response LT1021-5, CLOAD = 1000pF
ISOURCE = 0 ISINK = 0
Output Noise 0.1Hz to 10Hz LT1021-5
FILTERING = 1 ZERO AT 0.1Hz 2 POLES AT 10Hz 5V (1ppm)
20mV
20mV
ISOURCE = 0.2mA ISOURCE = 2-10mA
ISINK = 0.2mA ISINK = 2-10mA
ISOURCE = 100AP-P 0 5
ISINK = 100AP-P 5 10 15 20
LT1021 G14
10 15 20 0 TIME (s)
0
1
4 3 2 TIME (MINUTES)
5
6
LT1021 G15
Load Regulation LT1021-7, LT1021-10
5 4 3 VIN = 12V
1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2
Quiescent Current LT1021-7
IOUT = 0
TJ = - 55C TJ = 25C TJ = 125C
100
125
-5 -10 - 8 - 6 - 4 - 2 SOURCING
0
2
468 SINKING
10
0 0 5 10 15 20 25 30 INPUT VOLTAGE (V) 35 40
LT1021 G16
OUTPUT CURRENT (mA)
LT1021 G17
LT1021 G18
LT1021
TYPICAL PERFOR A CE CHARACTERISTICS
Shunt Characteristics LT1021-7
1.2 1.0 0.8 0.6 0.4 0.2 0 0 7 1 3 8 2 5 6 4 OUTPUT TO GROUND VOLTAGE (V) 9 TJ = 125C TJ = - 55C TJ = 25C INPUT PIN OPEN
CURRENT INTO OUTPUT (mA)
60 50 40 30 20 10 0 0 2 4 6 8 10 12 14 OUTPUT VOLTAGE (V) 16 18
CURRENT INTO OUTPUT (mA)
OUTPUT CHANGE (mV)
Load Transient Response LT1021-7, CLOAD = 0
ISINK = 0.8mA ISOURCE = 0
ISINK = 1.2mA 5mV 50mV ISOURCE = 0.5mA ISINK = 1.4mA ISOURCE = 2-10mA ISOURCE = 100AP-P 0 1 2 ISINK = 2-10mA ISINK = 100AP-P 1 2 3 4
5mV
20mV
OUTPUT VOLTAGE NOISE (5V/DIV)
OUTPUT VOLTAGE CHANGE
OUTPUT VOLTAGE CHANGE
340 TIME (s)
NOTE VERTICAL SCALE CHANGE BETWEEN SOURCING AND SINKING
LT1021 G22
Output Voltage Temperature Drift LT1021-10
10.006 10.004
OUTPUT CHANGE (mV)
OUTPUT VOLTAGE (V)
10.002 10.000 9.998 9.996 9.994 - 50 -25
2 1 0 -1 -2 -3 -4
INPUT CURRENT (mA)
50 0 75 25 TEMPERATURE (C)
UW
1021 G19
Shunt Mode Current Limit LT1021-7
INPUT PIN OPEN
Thermal Regulation LT1021-7
VIN = 27V POWER = 200mW 0 - 0.5 -1.0 -1.5 ILOAD = 10mA THERMAL REGULATION* LOAD REGULATION
0
20
40 60 80 TIME (ms)
100 120 140
LT1021 G20
*INDEPENDENT OF TEMPERATURE COEFFICIENT
LT1021 G21
Load Transient Response LT1021-7, CLOAD = 1000pF
ISOURCE = 0 ISINK = 0.6mA
Output Noise 0.1Hz to 10Hz LT1021-7
FILTERING = 1 ZERO AT 0.1Hz 2 POLES AT 10Hz 5V (0.7ppm)
ISINK = 0.8mA ISOURCE = 0.5mA ISINK = 1mA ISOURCE = 2-10mA ISOURCE = 100AP-P 0 5 ISINK = 2-10mA ISINK = 100AP-P 5 10 15 20
10 15 20 0 5s/DIV
0
1
4 3 2 TIME (MINUTES)
5
6
NOTE VERTICAL SCALE CHANGE BETWEEN SOURCING AND SINKING
LT1021 G23
LT1021 G24
Load Regulation LT1021-7, LT1021-10
5 4 3 VIN = 12V
1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2
Input Supply Current LT1021-10
IOUT = 0 TJ = - 55C TJ = 25C TJ = 125C
100
125
-5 -10 - 8 - 6 - 4 - 2 SOURCING
0
2
468 SINKING
10
0 0 5 10 15 20 25 30 INPUT VOLTAGE (V) 35 40
LT1021 G25
OUTPUT CURRENT (mA)
1021 G26
1021 G27
7
LT1021
TYPICAL PERFOR A CE CHARACTERISTICS
Shunt Characteristics LT1021-10
1.8 1.6
CURRENT INTO OUTPUT (mA) CURRENT INTO OUTPUT (mA)
INPUT PIN OPEN
1.2 1.0 0.8 0.6 0.4 0.2 0 0 2 4 6 10 8 OUTPUT TO GROUND VOLTAGE (V) 12 TJ = 125C TJ = 25C TJ = - 55C
40 30 20 10 0 0 2 4 6 8 10 12 14 OUTPUT VOLTAGE (V) 16 18
OUTPUT CHANGE (mV)
1.4
Load Transient Response LT1021-10, CLOAD = 0
ISINK = 0.6mA ISOURCE = 0
ISOURCE = 0
OUTPUT VOLTAGE CHANGE
50mV 10mV ISINK = 0.8mA ISOURCE = 0.2mA
20mV 5mV ISINK = 1.2mA
OUTPUT VOLTAGE NOISE (10V/DIV)
OUTPUT VOLTAGE CHANGE
ISINK = 1mA ISINK = 2-10mA ISINK = 100AP-P 1 2 3 4
ISOURCE = 2-10mA ISOURCE = 100AP-P 0 1 2
340 TIME (s)
NOTE VERTICAL SCALE CHANGE BETWEEN SOURCING AND SINKING
1021 G31
8
UW
1021 G28
Shunt Mode Current Limit LT1021-10
60 50
0 - 0.5 -1.0 -1.5
Thermal Regulation LT1021-10
VIN = 30V POWER = 200mW LOAD REGULATION
INPUT PIN OPEN
THERMAL REGULATION*
ILOAD = 10mA
0
20
40 60 80 TIME (ms)
100 120 140
1021 G29
*INDEPENDENT OF TEMPERATURE COEFFICIENT
1021 G30
Load Transient Response LT1021-10, CLOAD = 1000pF
ISINK = 0.8mA
Output Noise 0.1Hz to 10Hz LT1021-10
FILTERING = 1 ZERO AT 0.1Hz 2 POLES AT 10Hz 10V (1ppm)
ISOURCE = 0.5mA
ISINK = 1.4mA
ISOURCE = 2-10mA ISOURCE = 100AP-P 0 1 2
ISINK = 2-10mA ISINK = 100AP-P 1 2 3 4
340 TIME (s)
0
1
4 3 2 TIME (MINUTES)
5
6
1021 G33
NOTE VERTICAL SCALE CHANGE BETWEEN SOURCING AND SINKING
1021 G32
LT1021
APPLICATIONS INFORMATION
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 25C to 65C. Assuming the system calibration is performed at 25C, the temperature span is 40C. It can be seen from the graph that the temperature coefficient 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.
Maximum Allowable Reference Drift
MAXIMUM TEMPERATURE COEFFICIENT FOR 0.5LSB ERROR (ppm/C)
100 8-BIT
10-BIT 10
IN LT1021-5 OUT TRIM R1 27k R2 50k 1N4148 VOUT
12-BIT 14-BIT 1.0
0
10 20 30 40 50 60 70 80 90 100 TEMPERATURE SPAN (C)
LT1021 AI01
Trimming Output Voltage LT1021-10 The LT1021-10 has a trim pin for adjusting output voltage. The impedance of the trim pin is about 12k with a nominal open-circuit voltage of 5V. It is designed to be driven from a source impedance of 3k or less to minimize 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 10k potentiometer is recommended, preferably a 20 turn cermet type with stable characteristics over time and temperature.
U
W
U
U
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 20k 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 100k 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.
GND
1021 AI02
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 output 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 potentiometric mode to reduce the effects of trimmer TC. The voltage output has a 200 impedance, so loading must be
9
LT1021
APPLICATIONS INFORMATION
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.
LT1021-7 IN GND R3 10k OUT R2* 14k 1% R1* 200 1%
VOUT 6.950V
TC TRACKING TO 50ppm/C
1021 AI03
LT1021-7 IN GND R3 50k R2** 182k OUT R1* 7.15k
1.000mA
-
OP AMP
+
1021 AI04
*RESISTOR TC DETERMINES IOUT TC **TC (10 * R1) TC. R2 AND R3 SCALE WITH R1 FOR DIFFERENT OUTPUT CURRENTS
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. Because of internal current drain on the output, actual worstcase occurs at I LOAD = 0 on LT1021-5, I LOAD = - 0.8mA (sinking) on LT1021-7 and ILOAD = 1.4mA (sinking) 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 10F solid tantalum capacitor with several ohms in series provides optimum output bypass.
Series Mode with Boost Transistor
INPUT R1 220 2N3906
10
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W
U
U
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.
Standard Series Mode
LT1021 INPUT IN GND OUT
KEEP THIS LINE RESISTANCE LOW
+
LOAD
GROUND RETURN
1021 AI05
IN LT1021 OUT GND R2* LOAD
GROUND RETURN
1021 AI06
*OPTIONAL--REDUCES CURRENT IN OUTPUT SENSE LEAD R2 = 2.4k (LT1021-5), 3k (LT1021-7), 5.6k (LT1021-10)
LT1021
APPLICATIONS INFORMATION
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 dramatically 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 environment with no excessive air turbulence from air conditioners, opening/closing doors, etc. Removing the foam cup increases the output noise by almost an order of magnitude 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 enclosure 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)
LT1021-7 (TO-5 PACKAGE) f = 0.01Hz TO 10Hz
OUTPUT VOLTAGE NOISE (20V/DIV)
TYPICAL APPLICATIONS
Restricted Trim Range for Improved Resolution, 10V, "C" Version Only LT1021-10 Full Trim Range (0.7%) Negative Series Reference
15V
LT1021C-10 VIN IN GND OUT TRIM R1 75k R2 50k 10.000V
VIN LT1021-10 IN GND OUT TRIM R1* 10k VOUT
1021 TA11
TRIM RANGE 10mV
U
W
U
U
U
20V
FOAM CUP REMOVED
0
2
8 6 4 TIME (MINUTES)
10
12
1021 AI07
R1 4.7k D1 15V
LT1021-10 IN OUT GND
R2 4.7k
1021 TA03
-15V
*CAN BE RAISED TO 20k FOR LESS CRITICAL APPLICATIONS
Q1 2N2905
-10V AT 50mA
LT1021 TA04
11
LT1021 TYPICAL APPLICATIONS
Boosted Output Current with No Current Limit
V + (VOUT + 1.8V) R1 220 2N2905 IN LT1021 OUT GND 10V AT 100mA
+
6
LT1001 3
1021 TA06
4 -15V IOUT = 1mA REGULATION < 1ppm/V COMPLIANCE = -13V TO 7V
1021 TA07
*GLOWS IN CURRENT LIMIT, DO NOT OMIT
2-Pole Lowpass Filtered Reference
Operating 5V Reference from 5V Supply
5V LOGIC SUPPLY
1F MYLAR
VIN
1N914 CMOS LOGIC GATE** fIN 2kHz* 1N914 8.5V C2* 5F LT1021-5 IN GND OUT 5V REFERENCE
-
LT1021 VIN IN GND OUT R1 36k f = 10Hz R2 36k LT1001 VREF
+
0.5F MYLAR TOTAL NOISE 2VRMS 1Hz f 10kHz
C1* 5F
+
*FOR HIGHER FREQUENCIES C1 AND C2 MAY BE DECREASED **PARALLEL GATES FOR HIGHER REFERENCE CURRENT LOADING
-VREF
1021 TA13
Trimming 10V Units to 10.24V CMOS DAC with Low Drift Full-Scale Trimming**
LT1021-10
OUT LT1021-10 TRIM GND R1 4.99k 1% REF R2 40.2 1% 1.2k -15V *TC LESS THAN 200ppm/C **NO ZERO ADJUST REQUIRED WITH LT1007 (V0S 60V) CMOS DAC 7520, ETC FB 30pF IOUT R3 4.02K 1%
VIN
R4* 100 FULL-SCALE ADJUST 10V F.S.
IN TRIM
OUT GND
-
LT1007C
+
V - = -15V* *MUST BE WELL REGULATED dVOUT 15mV = V dV - 1021 TA12
LT1236 TA15
12
+
1021 TA05
-
2F SOLID TANT
+
U
Boosted Output Current with Current Limit
V + VOUT + 2.8V D1* LED R1 220 8.2
15V IN
Ultraprecise Current Source
LT1021-7 OUT GND TRIM 100 17.4k 1%
2N2905 IN LT1021 OUT GND 10V AT 100mA
15V 7 2
6.98k* 0.1% *LOW TC
+
2F SOLID TANT
1021 TA16
VOUT = 10.24V
4.32k 5k
LT1021 TYPICAL APPLICATIONS
Strain Gauge Conditioner for 350 Bridge
R1 357 1/2W
LT1021-10 15V IN GND OUT
28mA 28.5mA 5V 350 STRAIN GAUGE BRIDGE** R2 20k R4 20k R3 2M
3
6 1
LM301A
2
100pF
8
*THIS RESISTOR PROVIDES POSITIVE FEEDBACK TO THE BRIDGE TO ELIMINATE LOADING EFFECT OF THE AMPLIFIER. EFFECTIVE ZIN OF AMPLIFIER STAGE IS 1M. IF R2 TO R5 ARE CHANGED, SET R6 = R3
Precision DAC Reference with System TC Trim
LT1021-10 15V IN GND OUT 8.87k 1% D1 1N457 1.24k 1% 50k TC TRIM* 10k 1% 50k ROOM TEMP TRIM
*TRIMS 1mA REFERENCE CURRENT TC BY 40ppm/C. THIS TRIM SCHEME HAS VERY LITTLE EFFECT ON ROOM TEMPERATURE CURRENT TO MINIMIZE ITERATIVE TRIMMING
U
Negative Shunt Reference Driven by Current Source
LT1021-10 OUT GND -10V (ILOAD 1mA) 2.5mA
2
-
+
-
LT1012C 6
LM334 VOUT x 100 27
3 R5 2M
+
R6* 2M -5V 357 1/2W -15V **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
1021 TA09
-11V TO - 40V
1021 TA14
Handling Higher Load Currents
15V
30mA
IN LT1021-10 OUT GND
10.36k 1%
R1* 169 VOUT 10V RL TYPICAL LOAD CURRENT = 30mA
10k 1%
D2 1N457 50k
200k 1% 1mA 8.45k
1021 TA08
*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
DAC
1021 TA17
13
LT1021 TYPICAL APPLICATIONS
Ultralinear Platinum Temperature Sensor*
LT1021-10 OUT R2* 5k R1** 253k R11 6.65M 1% R15 10k R12 1k R13 24.3k 6 R10 182k 1% GND IN 20V
R9 100k
R8 10M
R3** 5k RS 100 AT 0C R7 392k 1% -15V
EQUIVALE T SCHE ATIC
INPUT Q3 D1 D2 OUTPUT D3 Q1 R1
14
U
R14 5k
RF** 654k
20V R4 4.75k 1% R5 200k 1% 2
- +
7 LT1001 VOUT =100mV/C - 50C T 150C
3
4 -15V
R6 619k 1%
STANDARD INDUSTRIAL 100 PLATINUM 4-WIRE SENSOR, ROSEMOUNT 78S OR EQUIVALENT. = 0.00385 TRIM R9 FOR VOUT = 0V AT 0C TRIM R12 FOR VOUT = 10V AT 100C TRIM R14 FOR VOUT = 5V AT 50C USE TRIM SEQUENCE AS SHOWN. TRIMS ARE NONINTERACTIVE SO THAT ONLY ONE TRIM SEQUENCE IS NORMALLY REQUIRED. *FEEDBACK LINEARIZES OUTPUT TO 0.005C FROM - 50C TO 150C **WIREWOUND RESISTORS WITH LOW TC 1021 TA10
W
U
-
A1 D4 6.3V
+
R2
Q2 GND
LT1021 ES
LT1021
PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted.
H Package 8-Lead TO-5 Metal Can (0.200 PCD)
(LTC DWG # 05-08-1320)
0.335 - 0.370 (8.509 - 9.398) DIA 0.305 - 0.335 (7.747 - 8.509) 0.040 (1.016) MAX 0.050 (1.270) MAX GAUGE PLANE 0.010 - 0.045* (0.254 - 1.143) 0.016 - 0.021** (0.406 - 0.533) 0.165 - 0.185 (4.191 - 4.699) REFERENCE PLANE 0.500 - 0.750 (12.700 - 19.050)
SEATING PLANE
45TYP 0.028 - 0.034 (0.711 - 0.864)
0.300 - 0.325 (7.620 - 8.255)
0.009 - 0.015 (0.229 - 0.381)
(
+0.035 0.325 -0.015 8.255 +0.889 -0.381
)
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
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.
U
0.027 - 0.045 (0.686 - 1.143) PIN 1
0.200 (5.080) TYP
0.110 - 0.160 (2.794 - 4.064) INSULATING STANDOFF
*LEAD DIAMETER IS UNCONTROLLED BETWEEN THE REFERENCE PLANE AND 0.045" BELOW THE REFERENCE PLANE 0.016 - 0.024 **FOR SOLDER DIP LEAD FINISH, LEAD DIAMETER IS (0.406 - 0.610)
H8(TO-5) 0.200 PCD 1197
N8 Package 8-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
0.400* (10.160) MAX 8 7 6 5
0.255 0.015* (6.477 0.381)
1
2
3
4 0.130 0.005 (3.302 0.127)
0.045 - 0.065 (1.143 - 1.651)
0.065 (1.651) TYP 0.125 (3.175) 0.020 MIN (0.508) MIN 0.018 0.003 (0.457 0.076)
N8 1098
0.100 (2.54) BSC
15
LT1021
PACKAGE DESCRIPTION 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
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP
0.016 - 0.050 0.406 - 1.270
*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
RELATED PARTS
PART NUMBER LT1019 LT1027 LT1236 LTC 1258 LT1389 LT1460 LT1634
(R)
DESCRIPTION Precision Bandgap Reference Precision 5V Reference Precision Reference Micropower Reference Nanopower Shunt Reference Micropower Reference Micropower Shunt Reference
16
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com
U
0.228 - 0.244 (5.791 - 6.197)
0.150 - 0.157** (3.810 - 3.988)
1
2
3
4
0.053 - 0.069 (1.346 - 1.752)
0.004 - 0.010 (0.101 - 0.254)
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) TYP
SO8 0996
COMMENTS 0.05%, 5ppm/C 0.02%, 2ppm/C SO-8, 5V and 10V, 0.05%, 5ppm/C 200mV Dropout, MSOP 800nA Operating Current SOT-23, 2.5V, 5V, 10V 0.05%, 10ppm/C, MSOP
1021fa LT/GP 0399 2K REV A * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1995

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