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REF2933 Datasheet(PDF) 8 Page - Burr-Brown (TI) |
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REF2933 Datasheet(HTML) 8 Page - Burr-Brown (TI) |
8 / 16 page REF2912, 2920, 2925, 2930, 2933, 2940 8 SBVS033A www.ti.com THEORY OF OPERATION The REF29xx is a series, CMOS, precision bandgap voltage reference. It’s 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-emiter 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 REF29xx 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. 1 3 REF29xx 2 0.47 µF V IN V OUT FIGURE 1. Simplified Schematic of Bandgap Reference. FIGURE 2. Typical Connections for Operating REF29xx. 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 The REF29xx does not require a load capacitor, and is stable with any capacitive load. Figure 2 shows typical connections required for operation of the REF29xx. A supply bypass capacitor of 0.47 µF is recommended. SUPPLY VOLTAGE The REF29xx family of references features an extremely low dropout voltage. With the exception of the REF2912, which has a minimum supply requirement of 1.8V, the REF29xx 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. Supply voltages below the specified levels can cause the REF29xx 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. THERMAL HYSTERESIS Thermal hysteresis for the REF29xx 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 REF29xx 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 REF29xx 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 REF29xx family drift increases to a typical value of 50ppm. |
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Similar Description - REF2933 |
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