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
)
4. The specified values are without the external noise reduction capacitor.
5. The specified values are unloaded.
2
VRE302DS
VRE302
2. TYPICAL PERFORMANCE CURVES
V
OUT
vs. TEMPERATURE
V
OUT
vs. TEMPERATURE
Temperature
o
C
VRE302J
POSITIVE OUTPUT (TYP)
Temperature
o
C
VRE302L
QUIESCENT CURRENT VS. TEMP JUNCTION TEMP. RISE VS. OUTPUT CURRENT
PSRR VS. FREQUENCY
Temperature, °C
Output Current, (mA)
Frequency, (Hz)
3. THEORY OF OPERATION
The following discussion refers to the schematic in Figure 1. A FET current source is used to bias a 6.3 V zener
diode. The zener voltage is divided by the resistor network R1 and R2. This voltage is then applied to the non-invert-
ing input of the operational amplifier which amplifies the voltage to produce a 2.5 V output. The gain is determined
by the resistor networks R3 and R4: G=1 + R4/R3. The 6.3 V 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’ volt-
age 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 tem-
perature ranges.
A nonlinear compensation network of thermistors and resistors 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, a very stable voltage is produced 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.
VRE302DS
3
VRE302
The proper connection of the VRE302 series voltage references with the optional trim resistor for initial error is
shown below. 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 20 ppm. By con-
necting 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
+ V
IN
2
3
6
PIN CONFIGURATION
V
TEMP OUT
OPTIONAL
NOISE REDUCTION
CAPACITOR
C
N
1µF
8
+ V
OUT
10k
Ω
OPTIONAL
FINE TRIM
ADJUSTMENT
N.C.
+V
IN
1
2
3
4
VRE302
5
7
4
VRE302
8
7
6
5
NOISE
REF. GND
V
OUT
TRIM
TEMP
GND
TOP
VIEW
REF. GND
NEED TECHNICAL HELP? CONTACT APEX SUPPORT!
For all Apex Microtechnology product questions and inquiries, call toll free 800-546-2739 in North America.
For inquiries via email, please contact apex.support@apexanalog.com.
International customers can also request support by contacting their local Apex Microtechnology Sales Representative.
To find the one nearest to you, go to www.apexanalog.com
IMPORTANT NOTICE
Apex Microtechnology, Inc. has made every effort to insure the accuracy of the content contained in this document. However, the information is subject to change
without notice and is provided "AS IS" without warranty of any kind (expressed or implied). Apex Microtechnology reserves the right to make changes without further
notice to any specifications or products mentioned herein to improve reliability. This document is the property of Apex Microtechnology and by furnishing this informa-
tion, Apex Microtechnology grants no license, expressed or implied under any patents, mask work rights, copyrights, trademarks, trade secrets or other intellectual
property rights. Apex Microtechnology owns the copyrights associated with the information contained herein and gives consent for copies to be made of the informa-
tion only for use within your organization with respect to Apex Microtechnology integrated circuits or other products of Apex Microtechnology. This consent does not
extend to other copying such as copying for general distribution, advertising or promotional purposes, or for creating any work for resale.
APEX MICROTECHNOLOGY PRODUCTS ARE NOT DESIGNED, AUTHORIZED OR WARRANTED TO BE SUITABLE FOR USE IN PRODUCTS USED FOR
LIFE SUPPORT, AUTOMOTIVE SAFETY, SECURITY DEVICES, OR OTHER CRITICAL APPLICATIONS. PRODUCTS IN SUCH APPLICATIONS ARE UNDER-
STOOD TO BE FULLY AT THE CUSTOMER OR THE CUSTOMER’S RISK.
Apex Microtechnology, Apex and Apex Precision Power are trademarks of Apex Microtechnolgy, Inc. All other corporate names noted herein may be trademarks
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