VRE202MA datasheet(4/5 Pages) ETC

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DISCUSSION OF PERFORMANCE

THEORY OF OPERATION

The following discussion refers to the schematic

below. A FET current source is used to bias a 6.3

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

2.5000V output. The gain is determined by the

resistor networks R3 and R4: G=1 + R4/R3. The 6.3

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.

trimming the zener current a lower drift over

temperature can be achieved. But since the voltage

vs.

temperature

function

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 then adjusting the slope, Thaler Corporation

produces

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. By using highly stable

resistors in our network, we produce a voltage

reference that also has very good long term stability.

VRE202

FIGURE 1

APPLICATION INFORMATION

Figure 2 shows the proper connection of the

VRE202 series voltage references with the optional

trim resistors. Pay careful attention to the circuit

layout to avoid noise pickup and voltage drops in the

lines.

The VRE202 series voltage references have the

ground terminal brought out on two pins (pin 9 and

pin 10) 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 10 to the power supply ground and

pin 9 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.

VRE202DS REV. D NOV 2000

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