VRE310A ETC [List of Unclassifed Manufacturers], VRE310A Datasheet - Page 4

• Manufacturer Part Number: VRE310A
• Description: Low Cost Precision Reference
• Manufacturer: ETC [List of Unclassifed Manufacturers]

VRE310
FIGURE 3
THEORY OF OPERATION
figure 2 below. In operation, approximately 6.3 volts is
applied to the noninverting input of the op amp. The
voltage is amplified by the op amp to produce a 10.000V
output. The gain is determined by the networks R1 and
R2: G=1 + R2/R1. The 6.3V zener diode is used because
it is the most stable diode over time and temperature.
regulated output voltage through R3. This feedback
arrangement provides a closely regulated zener current.
This current 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 then 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 zener operating current is derived from the
Corporation
OPTIONAL
NOISE REDUCTION
CAPACITOR
has
DISCUSSION OF PERFORMANCE
developed
C
1µF
EXTERNAL CONNECTIONS
N
a
nonlinear
REF. GND
8
+ V
VRE310
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. By using highly stable resistors in our network,
we produce a voltage reference that also has very good
long term stability
Figure 3 shows the proper connection of the VRE310
series voltage references with the optional trim resistor.
The VRE310 reference has the ground 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
10k
+ V
Ω
OUT
OPTIONAL
FINE TRIM
ADJUSTMENT
VRE310DS REV. D MAY 2001