P r o d u c t I n n o v a t i o n F r o m

VRE304

VRE304DS

3

2.TYPICalPERFORMaNCECuRVES

VRE304A

VRE304C

QUIESCENT CURRENT VS. TEMP

JUNCTION TEMP. RISE VS. OUTPUT CURRENT

Output Current (mA)

PSRR VS. FREQUENCY

Frequency (Hz)

3.ThEORYOFOPERaTION

The following discussion refers to the block diagram 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 noninvert-

ing input of the operational amplifier which amplifies the voltage to produce a 4.5 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.