VRE202
Precision Surface Mount
Reference Supplies
THALER CORPORATION • 2015 N. FORBES BOULEVARD • TUCSON, AZ. 85745 • (520) 882-4000
FEATURES
•
VERY HIGH ACCURACY: 2.5000 V OUTPUT ±200 µV
•
EXTREMELY LOW DRIFT: 0.6 ppm/°C 55°C to +125°C
•
LOW WARM-UP DRIFT: 1 ppm Typ.
•
EXCELLENT STABILITY: 6 ppm/1000 Hrs. Typ.
APPLICATIONS
•
PRECISION A/D and D/A CONVERTERS
•
TRANSDUCER EXCITATION
•
ACCURATE COMPARATOR THRESHOLD
REFERENCE
•
HIGH RESOLUTION SERVO SYSTEMS
•
EXCELLENT LINE REGULATION: 6ppm/V Typ.
•
DIGITAL VOLTMETERS
•
HERMETIC 20 TERMINAL CERAMIC LCC
•
MILITARY PROCESSING OPTION
•
HIGH PRECISION TEST and
MEASUREMENT INSTRUMENTS
DESCRIPTION
VRE202 Series Precision Voltage References
provide ultrastable +2.5000V outputs with ±200
µV initial accuracy and temperature coefficient as
low as 0.6 ppm/°C over the full military
temperature range. This improvement in accuracy
is made possible by a unique, proprietary
multipoint
laser
compensation
technique
developed by Thaler Corporation. Significant
improvements have been made in other
performance parameters as well, including initial
accuracy, warm-up drift, line regulation, and long-
term stability, making the VRE202 series the most
accurate and stable 2.5V surface mount
references available.
VRE202 devices are available in two operating
temperature ranges, -25°C to +85°C and -55°C to
+125°C, and two electrical performance grades.
All devices are packaged in 20 terminal ceramic
LCC packages for maximum long-term stability.
"M" versions are screened for high reliability and
quality.
VRE202DS REV. D NOV 2000
SELECTION GUIDE
Type
VRE202C
VRE202CA
VRE202M
VRE202MA
Output
+2.5V
+2.5V
+2.5V
+2.5V
Temperature
Operating Range
-25°C to +85°C
-25°C to +85°C
-55°C to +125°C
-55°C to +125°C
Max. Volt
Deviation
200µV
100µV
400µV
200µV
DISCUSSION OF PERFORMANCE
THEORY OF OPERATION
The following discussion refers to the schematic
below. A FET current source is used to bias a 6.3
zener diode. The zener voltage is divided by the
resistor network R1 and R2. This voltage is then
applied to the noninverting input of the operational
amplifier which amplifies the voltage to produce a
2.5000V output. The gain is determined by the
resistor networks R3 and R4: G=1 + R4/R3. The 6.3
zener diode is used because it is the most stable
diode over time and temperature.
The current source provides a closely regulated
zener current, which determines the slope of the
references’ voltage vs. temperature function. By
trimming the zener current a lower drift over
temperature can be achieved. But since the voltage
vs. temperature function is nonlinear this
compensation technique is not well suited for wide
temperature ranges.
Thaler Corporation has developed a nonlinear
compensation network of thermistors and resistors
that is used in the VRE series voltage references.
This proprietary network eliminates most of the
nonlinearity in the voltage vs. temperature function.
By then adjusting the slope, Thaler Corporation
produces a very stable voltage over wide
temperature ranges. This network is less than 2% of
the overall network resistance so it has a negligible
effect on long term stability. By using highly stable
resistors in our network, we produce a voltage
reference that also has very good long term stability.
APPLICATION INFORMATION
Figure 2 shows the proper connection of the
VRE202 series voltage references with the optional
trim resistors. Pay careful attention to the circuit
layout to avoid noise pickup and voltage drops in the
lines.
The VRE202 series voltage references have the
ground terminal brought out on two pins (pin 9 and
pin 10) which are connected together internally. This
allows the user to achieve greater accuracy when
using a socket. Voltage references have a voltage
drop across their power supply ground pin due to
quiescent current flowing through the contact
resistance. If the contact resistance was constant with
time and temperature, this voltage drop could be
trimmed out. When the reference is plugged into a
socket, this source of error can be as high as 20ppm.
By connecting pin 10 to the power supply ground and
pin 9 to a high impedance ground point in the
measurement circuit, the error due to the contact
resistance can be eliminated. If the unit is soldered
into place, the contact resistance is sufficiently small
that it does not effect performance.
VRE202
FIGURE 1
VRE202DS REV. D NOV 2000
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