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ADR5043ARTZ-REEL Datasheet(PDF) 11 Page - Analog Devices |
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ADR5043ARTZ-REEL Datasheet(HTML) 11 Page - Analog Devices |
11 / 16 page Data Sheet ADR5040/ADR5041/ADR5043/ADR5044/ADR5045 Rev. B | Page 11 of 16 THEORY OF OPERATION The ADR504x family uses the band gap concept to produce a stable, low temperature coefficient voltage reference suitable for high accuracy data acquisition components and systems. The devices use the physical nature of a silicon transistor base-emitter voltage in the forward-biased operating region. All such transistors have approximately a −2 mV/°C temperature coefficient (TC), making them unsuitable for direct use as a low temperature coefficient reference. Extrapolation of the temperature charac- teristic of any one of these devices to absolute zero (with the collector current proportional to the absolute temperature), however, reveals that its VBE approaches approximately the silicon band gap voltage. Therefore, if a voltage develops with an opposing temperature coefficient to sum the VBE, a zero temperature coefficient reference results. APPLICATIONS INFORMATION The ADR5040/ADR5041/ADR5043/ADR5044/ADR5045 are a series of precision shunt voltage references. They are designed to operate without an external capacitor between the positive and negative terminals. If a bypass capacitor is used to filter the supply, the references remain stable. For a stable voltage, all shunt voltage references require an external bias resistor (RBIAS) between the supply voltage and the reference (see Figure 19). The RBIAS sets the current that flows through the load (IL) and the reference (IIN). Because the load and the supply voltage can vary, the RBIAS needs to be chosen based on the following considerations: RBIAS must be small enough to supply the minimum IINcurrent to the ADR5040/ADR5041/ADR5043/ADR5044/ADR5045, even when the supply voltage is at its minimum value and the load current is at its maximum value. RBIAS must be large enough so that IIN does not exceed 15 mA when the supply voltage is at its maximum value and the load current is at its minimum value. Given these conditions, RBIAS is determined by the supply voltage (VS), the ADR5040/ADR5041/ADR5043/ADR5044/ ADR5045 load and operating current (IL and IIN), and the ADR5040/ADR5041/ADR5043/ADR5044/ADR5045 output voltage (VOUT). IN L OUT S BIAS I I V V R (3) IIN + IL RBIAS VS VOUT IL IIN ADR5040/ADR5041/ ADR5043/ADR5044/ ADR5045 Figure 19. Shunt Reference Precision Negative Voltage Reference The ADR5040/ADR5041/ADR5043/ADR5044/ADR5045 are suitable for applications where a precise negative voltage is desired. Figure 20 shows the ADR5045 configured to provide a negative output. Caution should be exercised in using a low temperature sensitive resistor to avoid errors from the resistor. RBIAS VOUT ADR5045 –5V VCC Figure 20. Negative Precision Reference Configuration Stacking the ADR504x for User-Definable Outputs Multiple ADR504x parts can be stacked together to allow the user to obtain a desired higher voltage. Figure 21a shows three ADR5045 devices configured to give 15 V. The bias resistor, RBIAS, is chosen using Equation 3, noting that the same bias current flows through all the shunt references in series. Figure 21b shows three ADR5045 devices stacked together to give −15 V. RBIAS is calculated in the same manner as before. Parts of different voltages can also be added together; that is, an ADR5041 and an ADR5045 can be added together to give an output of +7.5 V or −7.5 V, as desired. Note, however, that the initial accuracy error is the sum of the errors of all the stacked parts, as are the temperature coefficient and output voltage change vs. input current. RBIAS –15V ADR5045 ADR5045 ADR5045 –VDD RBIAS +15V ADR5045 ADR5045 ADR5045 VDD (a) (b) Figure 21. ±15 V Output with Stacked ADR5045 Devices |
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