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REF102R Datasheet(PDF) 6 Page - Burr-Brown (TI) |
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REF102R Datasheet(HTML) 6 Page - Burr-Brown (TI) |
6 / 9 page ® REF102 6 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 adjustment of the amplifier gain. Because the TCR 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 with the more commonly used “box method.” The “box” is formed by the high and low specification temperatures 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 exactly known either. It is, however, bounded by V UPPER BOUND and VLOWER BOUND (see Figure 1). Figure 1 uses the REF102CM 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, V 1 to V2, is 2.75mV. FIGURE 1. REF102CM Output Voltage Drift. 2.75mV Worst-case ∆V OUT for REF102CM INSTALLATION AND OPERATING INSTRUCTIONS BASIC CIRCUIT CONNECTION Figure 2 shows the proper connection of the REF102. To achieve the specified performance, pay careful attention to layout. A low resistance star configuration will reduce volt- age errors, noise pickup, and noise coupled from the power supply. Commons should be connected as indicated being sure to minimize interconnection resistances. Minimum range ( ±300mV) and minimal degradation of drift. FIGURE 3. REF102 Optional Output Voltage Adjust. NOTES: (1) Lead resistances here of up to a few ohms have negligible effect on performance. (2) A resistance of 0.1 Ω in series with these leads will cause a 1mV error when the load current is at its maximum of 10mA. This results in a 0.01% error of 10V. FIGURE 2. REF102 Installation. OPTIONAL OUTPUT VOLTAGE ADJUSTMENT Optional output voltage adjustment circuits are shown in Figures 3 and 4. Trimming the output voltage will change the voltage drift by approximately 0.008ppm/ °C per mV of trimmed voltage. In the circuit in Figure 3, any mismatch in TCR between the two sections of the potentiometer will also affect drift, but the effect of the ∆TCR is reduced by a factor of five by the internal resistor divider. A high quality potentiometer, with good mechanical stability, such as a cermet, should be used. The circuit in Figure 3 has a minimum trim range of ±300mV. The circuit in Figure 4 has less range but provides higher resolution. The mismatch in TCR between RS and the internal resistors can introduce some slight drift. This effect is minimized if RS is kept significantly larger than the 50k Ω internal resistor. A TCR of 100ppm/ °C is normally sufficient. REF102BM V UPPER BOUND +10.00275 V1 V NOMINAL +10.0000 V2 +9.99725 REF102BM V LOWER BOUND –25 0 +25 +50 +85 Temperature (°C) REF102 1µF Tantalum + R L 1 R L 2 R L 3 V+ (1) 2 (2) (2) (1) 4 6 REF102 1µF Tantalum + V+ 2 4 20k Output Voltage Adjust Ω +10V 5 V TRIM 6 V OUT |
Similar Part No. - REF102R |
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Similar Description - REF102R |
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