VRE302
Low Cost
Precision Reference
DESCRIPTION
FEATURES
The VRE302 is a low cost, high precision 2.5V
reference. Packaged in the industry standard 8
pin DIP, the device is ideal for upgrading systems
that use lower performance references.
The device provides ultrastable +2.500V output
with 0.2500 mV (.01%) initial accuracy and a
temperature coefficient of 0.6 ppm/C. This
improvement in accuracy is made possible by a
unique, patented 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 VRE302 series the
most accurate reference available in the standard
8 pin DIP package.
For enhanced performance, the VRE302 has an
external trim option for users who want less than
0.01% initial error. A reference ground pin is
provided to eliminate socket contact resistance
errors.
PIN CONFIGURATION
The VRE302 is recommended for use as a
reference for 14, 16, or 18 bit D/A converters
which require an external precision reference.
The device is also ideal for calibrating scale factor
on high resolution A/D converters. The VRE302
offers superior performance over monolithic
references.
2.500 V OUTPUT 0.250 mV (.01%)
TEMPERATURE DRIFT: 0.6 ppm/C
LOW NOISE: 1.5
V
p-p
(0.1-10Hz)
INDUSTRY STD PINOUT- 8 PIN DIP OR
SURFACE MOUNT PACKAGE
EXCELLENT LINE REGULATION: 6ppm/V Typ.
OUTPUT TRIM CAPABILITY
FIGURE 1
VRE302DS REV. F MAY 2001
SELECTION GUIDE
Model
Temp.
Range
C
Temp.
Coeff.
ppm/C
VRE302A
0.25
0.6
0C to +70C
VRE302B
0.40
1.0
0C to +70C
VRE302C
0.50
2.0
0C to +70C
VRE302J
0.25
0.6
-40C to +85C
VRE302K
0.40
1.0
-40C to +85C
VRE302L
0.50
2.0
-40C to +85C
For package option add D for DIP or S for Surface Mount
to end of model number.
Initial
Error
mV
THALER CORPORATION 2015 N. FORBES BOULEVARD TUCSON, AZ. 85745 (520) 882-4000
5
6
7
8
VRE302
TOP
VIEW
1
2
3
4
N.C.
+V
IN
TEMP
GND
NOISE
REF. GND
V
OUT
TRIM
MODEL
A/J
B/K
C/L
PARAMETER
MIN
TYP
MAX
MIN
TYP
MAX
MIN TYP
MAX
UNITS
ABSOLUTE RATINGS
Power Supply
+13.5
+15
+22
*
*
*
*
*
*
V
Operating Temp. (
A,B,C
)
0
+70
*
*
*
*
C
Operating Temp. (
J,K,L
)
-40
+85
*
*
*
*
C
Storage Temperature
-65
+150
*
*
*
*
C
Short Circuit Protection
Continuous
*
*
OUTPUT VOLTAGE
VRE302
2.500
*
*
V
Temp. Sensor Voltage
630
*
*
mV
OUTPUT VOLTAGE ERRORS
Initial Error
0.25
0.40
0.50
mV
Warmup Drift
1
2
3
ppm
T
min
- T
max
0.6
1.0
2.0
ppm/C
Long-Term Stability
6
*
*
ppm/1000hrs
Noise (.1-10Hz)
1.5
*
*
Vpp
OUTPUT CURRENT
Range
10
*
*
mA
REGULATION
Line
6
10
*
*
*
*
ppm/V
Load
3
*
*
ppm/mA
OUTPUT ADJUSTMENT
Range
10
*
*
mV
POWER SUPPLY CURRENTS
VRE302 +PS
5
7
*
*
*
*
mA
VRE302
NOTES: *Same as A/J Models.
1. The temp. reference TC is 2.1mV/ C
2. The specified values are without external trim.
3. The temperature coefficient is determined by the box
method using the following formula:
V
max
- V
min
T.C. =
x 10
6
V
nominal
x (T
max
-T
min
)
(1)
(5)
(2)
(3)
VRE302DS REV. F MAY 2001
Vps =
+
15V, T = 25C, RL = 10K unless otherwise noted.
ELECTRICAL SPECIFICATIONS
4. The specified values are without the external
noise reduction capacitor.
5. The specified values are unloaded.
(4)
TYPICAL PERFORMANCE CURVES
VRE302DS REV. F MAY 2001
Temperature
o
C
VRE302A
V
OUT
vs. TEMPERATURE
Temperature
o
C
VRE302B
V
OUT
vs. TEMPERATURE
V
OUT
vs. TEMPERATURE
Temperature
o
C
VRE302C
Temperature
o
C
VRE302J
V
OUT
vs. TEMPERATURE
Temperature
o
C
VRE302K
V
OUT
vs. TEMPERATURE
Temperature
o
C
VRE302L
V
OUT
vs. TEMPERATURE
QUIESCENT CURRENT VS. TEMP
Temperature
o
C
JUNCTION TEMP. RISE VS. OUTPUT CURRENT
Output Current (mA)
PSRR VS. FREQUENCY
Frequency
(Hz)
POSITIVE OUTPUT (TYP)
DISCUSSION OF PERFORMANCE
THEORY OF OPERATION
The following discussion refers to the schematic in
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 2.500V 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.
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 adjusting the
slope, Thaler Corporation produces a very stable voltage
over wide temperature ranges.
VRE302
FIGURE 2
VRE302DS REV. F MAY 2001
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
series voltage references with the optional trim resistor for
initial error. The VRE302 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.
EXTERNAL CONNECTIONS
FIGURE 3
8
4
6
5
+ V
OUT
2
+ V
IN
VRE302
10k
C
N
1F
OPTIONAL
NOISE REDUCTION
CAPACITOR
OPTIONAL
FINE TRIM
ADJUSTMENT
3
V
TEMP OUT
7
REF. GND
VRE302DS REV. F MAY 2001
MECHANICAL
FIGURE 4
FIGURE 3
INCHES MILLIMETER
DIM
MIN
MAX
MIN
MAX
DIM
MIN
MAX
MIN
MAX
A
.115
.125
2.92
3.17
D2
.018
.023
0.46
0.58
B
.098
.102
2.48
2.59
E
.507
.513
12.8
13.0
B1
.046
.051
1.14
1.29
E1
.397
.403
10.0
10.2
C
.107
.113
2.71
2.89
E2
.264
.270
6.70
6.85
C1
.009
.012
0.22
0.30
P
.085
.095
2.15
2.41
C2
.052
.058
1.32
1.47
Q
.020
.030
.508
.762
D
.397
.403
10.0
10.2
S
.045
.055
1.14
1.39
D1
.372
.380
9.44
9.65
INCHES MILLIMETER
D2
E
E1
E2
PIN 1 IDENTIFIER
D
D1
BASE
SEATING
A
Q
B
B1
S
E1
C1
C
C2
P
DIM
MIN
MAX
MIN
MAX
DIM
MIN
MAX MIN
MAX
A
.115
.125
2.92
3.17 E
.397
.403
10.0
10.2
B
.018
.022
.457
.558
E1
.264
.270
6.70
6.85
B1
.046
.051
1.14 1.29
G1
.290
.310
7.36
7.87
B2
.098
.102
2.48
2.59
L
.195
.215
4.95
5.46
C
.009
.012
0.22
0.30
P
.085
.095
2.15
2.41
D .397
.403
10.0
10.2 Q
.055
.065
1.39
1.65
D 1
.372
.380
9.44
9.65
S
.045
.055
1.14
1.39
INCHES MILLIMETER
INCHES MILLIMETER
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