VRE310 データシートの表示（PDF） - Cirrus Logic
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VRE310 Datasheet PDF : 5 Pages
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VRE310
Product Innova tionFrom
3. THEORY OF OPERATION
The following discussion refers to the block diagram in Figure 1. In operation, approximately 6.3 V is applied to
the noninverting input of the op amp. The voltage is amplified by the op amp to produce a 10 V output. The gain is
determined by the networks R1 and R2: G=1 + R2/R1. The 6.3 V zener diode is used because it is the most stable
diode over time and temperature.
The zener operating current is derived from the regulated output voltage through R3. This feedback arrangement
provides a closely regulated zener current. This current determines the slope of the references’ voltage vs. tempera-
ture 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.
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 then 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.
By using highly stable resistors in our network, we produce a voltage reference that also has very good long term
stability.
The proper connection of the VRE310 series voltage references with the optional trim resistor is shown below. 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 volt-
age 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 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
+ VIN
V TEMP OUT
OPTIONAL
NOISE REDUCTION
CAPACITOR
CN
1µF
2
3
8
6
VRE310
5
7
4
+ VOUT
10kΩ
OPTIONAL
FINE TRIM
ADJUSTMENT
REF. GND
PIN CONFIGURATION
N/C 1
8
+VIN 2 VRE310 7
TEMP 3
TOP
VIEW
6
GND 4
5
NOISE
REDUCTION
REF. GND
VOUT
TRIM
VRE310DS
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