VRE302A ETC [List of Unclassifed Manufacturers], VRE302A Datasheet - Page 9
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VRE302A
Manufacturer Part Number
VRE302A
Description
Low Cost Precision Reference
Manufacturer
ETC [List of Unclassifed Manufacturers]
Datasheet
1.VRE302A.pdf
(41 pages)
VRE302-6
FIGURE 3
THEORY OF OPERATION
figure 2 below. A FET current source is used to bias a
6.3V 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 2.048V output. The
gain is determined by the resistor networks R3 and R4:
G=1 + R4/R3. The 6.3V zener diode is used because it is
the most stable diode over time and temperature.
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
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 adjusting the
slope, Thaler Corporation produces a very stable voltage
over wide temperature ranges.
FIGURE 2
The following discussion refers to the schematic in
The current source provides a closely regulated zener
Corporation
OPTIONAL
NOISE REDUCTION
CAPACITOR
has
DISCUSSION OF PERFORMANCE
developed
C
1µF
EXTERNAL CONNECTIONS
N
a
nonlinear
REF. GND
8
+ V
VRE302-6
2
7
IN
4
V
3
This network is less than 2% of the overall network
resistance so it has a negligible effect on long term
stability.
Figure 3 shows the proper connection of the VRE302-6
series voltage references with the optional trim resistor for
initial error.
terminal brought out on two pins (pin 4 and pin 7) 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 4 to the power supply ground and pin 7 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. Pay careful attention to the circuit layout to
avoid noise pickup and voltage drops in the lines.
TEMP OUT
5
6
The VRE302-6 reference has the ground
10kΩ
+ V
OUT
OPTIONAL
FINE TRIM
ADJUSTMENT
VRE302-6DS REV. B MAY 2001