LT1031_15 Datasheet, PDF (6/12 Pages) Linear Technology – Precision 10V Reference

LT1031/LH0070
TYPICAL PERFOR A CE CHARACTERISTICS
Output Noise 0.1Hz to 10Hz
FILTERING = 1 ZERO AT 0.1Hz
2 POLES AT 10Hz
10µV (1ppm)
01
2
3
4
TIME (MINUTES)
56
LT1031 • TPC16
APPLICATIO S I FOR ATIO
Trimming Output Voltage
The LT1031 output can be trimmed by driving the ground
pin. The suggested method is shown in the illustration
below. A 5Ω resistor is inserted in series with the ground
pin. The top of the resistor is supplied current from a trim
potentiometer. This technique requires fairly high trim
current of up to 1.5mA from the LT1031 or 3.5mA from the
–15V supply; however it is necessary to maintain low drift
in the reference. Ground pin current changes in the LT1031,
with temperature, could be as high as 4µA/°C. This,
coupled with the 5Ω external resistor, creates up
to 2ppm/°C drift in the reference (5Ω • 4µA/°C = 20µV/°C
= 2ppm/°C). If induced drift higher than this can be
tolerated, all resistor values in the trim circuit can be raised
proportionately to reduce current drain.
Output Voltage Trimming
LT1031
V_IN
IN
OUT
V_OUT
GND
R2*
4.3k
R1**
5Ω
R3
50k
–15V
*CAN BE INCREASED TO 5.6k FOR
LT1031B AND LH0070-2
**INCREASE TO 10Ω FOR LT1031D
LT1031 • TA04
6
Effect of Reference Drift on System Accuracy
A large portion of the temperature drift error budget in
many systems is the system reference voltage. The graph
below indicates the maximum temperature coefficient
allowable if the reference is to contribute no more than
1/2LSB 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 calibration is performed at 25°C, the
temperature span is 40°C. The graph shows that the
temperature coefficient of the reference must be no worse
than 3ppm/°C if it is to contribute less than 1/2LSB error.
For this reason, the LT1031 has been optimized for low
drift.
Maximum Allowable Reference Drift
100
8-BIT
10-BIT
10
12-BIT
14-BIT
1.0
10 20 30 40 50 60 70 80 90 100
TEMPERATURE SPAN (°C)
LT1031 • TA03
1031fb