VRE302
Low Cost
Precision Reference
THALER CORPORATION • 2015 N. FORBES BOULEVARD • TUCSON, AZ. 85745 • (520) 882-4000
FEATURES
•
2.500 V OUTPUT ± 0.250 mV (.01%)
•
TEMPERATURE DRIFT: 0.6 ppm/°C
•
LOW NOISE: 1.5
µ
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
N.C.
+V
IN
TEMP
GND
1
2
3
4
8
NOISE
REF. GND
V
OUT
TRIM
PIN CONFIGURATION
VRE302
7
6
5
TOP
VIEW
DESCRIPTION
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.
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.
SELECTION GUIDE
Initial
Error
mV
0.25
0.40
0.50
0.25
0.40
0.50
Model
VRE302A
VRE302B
VRE302C
VRE302J
VRE302K
VRE302L
Temp.
Coeff.
ppm/°C
0.6
1.0
2.0
0.6
1.0
2.0
Temp.
Range
°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
For package option add D for DIP or S for Surface Mount
to end of model number.
VRE302DS REV. F MAY 2001
ELECTRICAL SPECIFICATIONS
MODEL
PARAMETER
ABSOLUTE RATINGS
Power Supply
Operating Temp. (
A,B,C
)
Operating Temp. (
J,K,L
)
Storage Temperature
Short Circuit Protection
OUTPUT VOLTAGE
VRE302
(1)
Temp. Sensor Voltage
OUTPUT VOLTAGE ERRORS
Initial Error
Warmup Drift
T
min
- T
max (3)
Long-Term Stability
Noise (.1-10Hz)
(4)
OUTPUT CURRENT
Range
REGULATION
Line
Load
OUTPUT ADJUSTMENT
Range
POWER SUPPLY CURRENTS
VRE302 +PS
(5)
(2)
Vps =
+
15V, T = 25°C, RL = 10KΩ unless otherwise noted.
VRE302
B/K
MAX
MIN
TYP
MAX
MIN
A/J
MIN
TYP
C/L
TYP
MAX
UNITS
+13.5 +15
+22
0
+70
-40
+85
-65
+150
Continuous
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
V
°C
°C
°C
*
*
2.500
630
*
*
*
*
V
mV
0.25
1
0.6
6
1.5
*
*
2
0.40
3
1.0
*
*
0.50
2.0
mV
ppm
ppm/°C
ppm/1000hrs
µVpp
±10
*
*
mA
6
3
10
*
*
*
*
*
*
ppm/V
ppm/mA
10
*
*
mV
5
7
*
*
*
*
mA
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. =
V
nominal
x (T
max
-T
min
)
x 10
6
4. The specified values are without the external
noise reduction capacitor.
5. The specified values are unloaded.
VRE302DS REV. F MAY 2001
TYPICAL PERFORMANCE CURVES
V
OUT
vs. TEMPERATURE
V
OUT
vs. TEMPERATURE
V
OUT
vs. TEMPERATURE
Temperature
o
C
VRE302A
Temperature
o
C
VRE302B
Temperature
o
C
VRE302C
V
OUT
vs. TEMPERATURE
V
OUT
vs. TEMPERATURE
V
OUT
vs. TEMPERATURE
Temperature
o
C
VRE302J
Temperature
o
C
VRE302K
Temperature
o
C
VRE302L
POSITIVE OUTPUT (TYP)
QUIESCENT CURRENT VS. TEMP JUNCTION TEMP. RISE VS. OUTPUT CURRENT
PSRR VS. FREQUENCY
Temperature
o
C
Output Current (mA)
Frequency
(Hz)
VRE302DS REV. F MAY 2001
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.
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.
VRE302
FIGURE 2
EXTERNAL CONNECTIONS
+ V
IN
2
8
V
TEMP OUT
3
6
+ V
OUT
10k
Ω
OPTIONAL
FINE TRIM
ADJUSTMENT
OPTIONAL
NOISE REDUCTION
CAPACITOR
VRE302
C
N
1µF
7
4
5
FIGURE 3
REF. GND
VRE302DS REV. F MAY 2001
FIGURE 3
MECHANICAL
D
D1
D2
INCHES
DIM
A
B
B1
MIN
.115
.098
.046
.107
.009
.052
.397
.372
MAX
.125
.102
.051
.113
.012
.058
.403
.380
MILLIMETER
MIN
2.92
2.48
1.14
2.71
0.22
1.32
10.0
9.44
MAX
3.17
2.59
1.29
2.89
0.30
1.47
10.2
9.65
DIM
D2
E
E1
E2
P
Q
S
INCHES
MIN
.018
.507
.397
.264
.085
.020
.045
MAX
.023
.513
.403
.270
.095
.030
.055
MILLIMETER
MIN
0.46
12.8
10.0
6.70
2.15
.508
1.14
MAX
0.58
13.0
10.2
6.85
2.41
.762
1.39
E2
E1
E
C
C1
C2
D
PIN 1 IDENTIFIER
D1
A
Q
BASE
SEATING
E1
P
C1
C2
C
B
B1
FIGURE 4
S
INCHES
DIM
A
B
B1
B2
C
D
D1
MIN
.115
.018
.046
.098
.009
.397
.372
MAX
.125
.022
.051
.102
.012
.403
.380
MILLIMETER
MIN
2.92
.457
1.14
2.48
0.22
10.0
9.44
MAX
3.17
.558
1.29
2.59
0.30
10.2
9.65
DIM
E
E1
G1
L
P
Q
S
INCHES
MIN
.397
.264
.290
.195
.085
.055
.045
MAX
.403
.270
.310
.215
.095
.065
.055
MILLIMETER
MIN
10.0
6.70
7.36
4.95
2.15
1.39
1.14
MAX
10.2
6.85
7.87
5.46
2.41
1.65
1.39
VRE302DS REV. F MAY 2001
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