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REF3012 Datasheet(PDF) 8 Page - Texas Instruments |
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REF3012 Datasheet(HTML) 8 Page - Texas Instruments |
8 / 17 page REF3012, 3020, 3025, 3030, 3033, 3040 8 SBVS032F www.ti.com THEORY OF OPERATION The REF30xx is a series, CMOS, precision bandgap voltage reference. Its basic topology is shown in Figure 1. The transistors Q1 and Q2 are biased such that the current density of Q1 is greater than that of Q2. The difference of the two base-emitter voltages, Vbe1 – Vbe2, has a positive temperature coefficient and is forced across resistor R1. This voltage is gained up and added to the base-emitter voltage of Q2, which has a negative coefficient. The resulting output voltage is virtually independent of temperature. The curvature of the bandgap voltage, as seen in the typical curve, “Output Voltage vs Temperature,” is due to the slightly nonlinear temperature coefficient of the base-emitter voltage of Q2. The REF30xx features a low quiescent current, which is extremely stable over changes in both temperature and supply. The typical room temperature quiescent current is 42 µA, and the maximum quiescent current over temperature is just 59 µA. Additionally, the quiescent current typically changes less than 2.5 µA over the entire supply range, as shown in Figure 3. Supply voltages below the specified levels can cause the REF30xx to momentarily draw currents greater than the typical quiescent current. Using a power supply with a fast rising edge and low output impedance easily prevents this. 1 3 REF30xx 2 0.47 µF V IN V OUT FIGURE 1. Simplified Schematic of Bandgap Reference. FIGURE 2. Typical Connections for Operating REF30xx. SUPPLY CURRENT vs INPUT VOLTAGE 42.5 42.0 41.5 41.0 40.5 40.0 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 V IN (V) FIGURE 3. Supply Current vs Supply Voltage. R 1 Q 2 Q 1 + Vbe 1 – + Vbe 2 – APPLICATION INFORMATION For normal operation, the REF30xx does not require a capacitor on the output. If a capacitive load is connected, special care must be taken with the combination of low equivalent series resistance (ESR) capacitors and high capacitance. This caution is especially true for low-output voltage devices; therefore, the REF3012 should only have a low-ESR capacitance of 10 µF or less. Figure 2 shows the typical connections required for operation of the REF30xx. A supply bypass capacitor of 0.47 µF is always recommended. SUPPLY VOLTAGE The REF30xx family of references features an extremely low dropout voltage. With the exception of the REF3012, which has a minimum supply requirement of 1.8V, the REF30xx can be operated with a supply of only 1mV above the output voltage in an unloaded condition. For loaded conditions, a typical dropout voltage versus load is shown on the cover page. THERMAL HYSTERESIS Thermal hysteresis for the REF30xx is defined as the change in output voltage after operating the device at 25 °C, cycling the device through the specified temperature range, and returning to 25 °C, and can be expressed as: V abs V V V ppm HYST PRE POST NOM = • ( ) – 10 6 Where: VHYST = Calculated hysteresis VPRE = Output voltage measured at 25°C pre- temperature cycling VPOST = Output voltage measured when device has been operated at 25 °C, cycled through specified range –40 °C to +125°C and returned to operation at 25 °C. TEMPERATURE DRIFT The REF30xx is designed to exhibit minimal drift error, defined as the change in output voltage over varying temperature. Using the “box” method of drift measurement, the REF30xx features a typical drift coefficient of 20ppm from 0 °C to 70°C— the primary temperature range of use for many applications. For industrial temperature ranges of –40 °C to 125°C, the REF30xx family drift increases to a typical value of 50ppm. |
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