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ADR512 データシート(PDF) 8 Page - Analog Devices |
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ADR512 データシート(HTML) 8 Page - Analog Devices |
8 / 12 page ADR512 Data Sheet Rev. A | Page 8 of 12 APPLICATIONS SECTION The ADR512 is a 1.2 V precision shunt voltage reference. It is designed to operate without an external output capacitor between the positive and negative terminals for stability. An external capacitor can be used for additional filtering of the supply. As with all shunt voltage references, an external bias resistor (RBIAS) is required between the supply voltage and the ADR512 (see Figure 2). RBIAS sets the current that is required to pass through the load (IL) and the ADR512 (IQ). The load and the supply voltage can vary, thus RBIAS is chosen based on • RBIAS must be small enough to supply the minimum IQ current to the ADR512 even when the supply voltage is at its minimum and the load current is at its maximum value. • RBIAS also needs to be large enough so that IQ does not exceed 10 mA when the supply voltage is at its maximum and the load current is at its minimum. Given these conditions, RBIAS is determined by the supply voltage (VS), the load and operating current (IL and IQ) of the ADR512, and the ADR512’s output voltage. RBIAS = (VS − VOUT)/(IL + IQ) (3) ADJUSTABLE PRECISION VOLTAGE SOURCE The ADR512, combined with a precision low input bias op amp such as the AD8610, can be used to output a precise adjustable voltage. Figure 11 illustrates the implementation of this application using the ADR512. The output of the op amp, VOUT, is determined by the gain of the circuit, which is completely dependent on resistors R2 and R1. 1 2 1 R R V OUT + = (4) An additional capacitor in parallel with R2 can be added to filter out high frequency noise. The value of C2 is dependent on the value of R2. ADR512 AD8610 R1 R2 C2 (OPTIONAL) VCC RBIAS 1.2V VOUT = 1.2V (1 + R2/R1) Figure 11. Adjustable Precision Voltage Source OUTPUT VOLTAGE TRIM Using a mechanical or digital potentiometer, the output voltage of the ADR512 can be trimmed ±0.5%. The circuit in Figure 12 illustrates how the output voltage can be trimmed, using a 10 kΩ potentiometer. ADR512 R1 100kΩ VCC RBIAS VOUT POT 50k Ω Figure 12. Output Voltage Trim USING THE ADR512 WITH PRECISION DATA CONVERTERS The compact ADR512 package and the device’s low minimum operating current requirement make it ideal for use in battery powered portable instruments, such as the AD7533 CMOS multiplying DAC, that use precision data converters. Figure 13 shows the ADR512 serving as an external reference to the AD7533, a CMOS multiplying DAC. Such a DAC requires a negative voltage input in order to provide a positive output range. In this application, the ADR512 is supplying a −1.2 V reference to the REF input of the AD7533. ADR512 AD7533 VOUT = 0V TO 1.2V VDD –VDD R2 GN 9 LSB 0 MSB + – + – 1 1 3 2 1 15 Figure 13. ADR512 as a Reference for a 10-Bit CMOS DAC (AD7533) |
同様の部品番号 - ADR512 |
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同様の説明 - ADR512 |
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