VRE310 datasheet(4/5 Pages) ETC

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THEORY OF OPERATION

The following discussion refers to the schematic in

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.

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. 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

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 then adjusting

the slope, Thaler Corporation produces a very stable

voltage over wide temperature ranges.

DISCUSSION OF PERFORMANCE

VRE310DS REV. D MAY 2001

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.

VRE310

FIGURE 2

EXTERNAL CONNECTIONS

FIGURE 3

+ V

OUT

+ V

VRE310

10kΩ

1µF

OPTIONAL

NOISE REDUCTION

CAPACITOR

OPTIONAL

FINE TRIM

ADJUSTMENT

V TEMP OUT

REF. GND

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