REF102AP datasheet(5/19 Pages) TI2

5 / 19 page

REF102

SBVS022B

www.ti.com

TYPICAL CHARACTERISTICS (Cont.)

At TA = +25°C, VS = +15V, unless otherwise noted.

TYPICAL REF102 REFERENCE NOISE

−2

−4

−6

Low Frequency Noise (1s/div)

(See Noise Test Circuit)

–

OPA227

DUT

Noise Test Circuit.

100

µF

15.8k

Ω

µF

Oscilloscope

Gain = 100V/V

= 0.1Hz and 10Hz

−3dB

THEORY OF OPERATION

Refer to the diagram on the first page of this data sheet. The

10V output is derived from a compensated buried zener

diode DZ1, op amp A1, and resistor network R1 – R6.

Approximately 8.2V is applied to the non-inverting input of A1

by DZ1. R1, R2, and R3 are laser-trimmed to produce an exact

10V output. The zener bias current is established from the

regulated output voltage through R4. R5 allows user-trimming

of the output voltage by providing for small external adjust-

ment of the amplifier gain. Because the temperature coeffi-

cient (TCR) of of R5 closely matches the TCR of R1, R2 and

R3 , the voltage trim has minimal effect on the reference drift.

The output voltage noise of the REF102 is dominated by the

noise of the zener diode. A capacitor can be connected

between the Noise Reduction pin and ground to form a low-

pass filter with R6 and roll off the high-frequency noise of the

zener.

DISCUSSION

OF PERFORMANCE

The REF102 is designed for applications requiring a preci-

sion voltage reference where both the initial value at room

temperature and the drift over temperature are of importance

to the user. Two basic methods of specifying voltage refer-

ence drift versus temperature are in common usage in the

industry—the

butterfly method and the box method. The

REF102 is specified by the more commonly-used

box method.

The

box is formed by the high and low specification tempera-

tures and a diagonal, the slope of which is equal to the

maximum specified drift.

Since the shape of the actual drift curve is not known, the

vertical position of the box is not known, either. It is, however,

bounded by VUPPER BOUND and VLOWER BOUND (see Figure 1).

Figure 1 uses the REF102CU as an example. It has a drift

specification of 2.5ppm/

°C maximum and a specification

temperature range of –25

°C to +85°C. The box height,

V1 to V2, is 2.75mV.

REF102CU V

UPPER BOUND

+10.00275

NOMINAL

+10.0000

2.75mV

Worst-case

∆V

OUT for

REF102CU

+9.99725

REF102CU V

LOWER BOUND

−25

+25

+50

+85

Temperature (

°C)

FIGURE 1. REF102CU Output Voltage Drift.

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