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LM4051AIM3-1.2 Datasheet(PDF) 9 Page - National Semiconductor (TI) |
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LM4051AIM3-1.2 Datasheet(HTML) 9 Page - National Semiconductor (TI) |
9 / 14 page Functional Block Diagram 10122221 *LM4051-ADJ only **LM4051-1.2 only Applications Information The LM4051 is a precision micro-power curvature-corrected bandgap shunt voltage reference. For space critical applica- tions, the LM4051 is available in the sub-miniature SOT-23 surface-mount package. The LM4051 has been designed for stable operation without the need of an external capacitor connected between the “+” pin and the “−” pin. If, however, a bypass capacitor is used, the LM4051 remains stable. De- sign effort is further reduced with the choice of either a fixed 1.2V or an adjustable reverse breakdown voltage. The mini- mum operating current is 60 µA for the LM4051-1.2 and the LM4051-ADJ. Both versions have a maximum operating current of 12 mA. LM4051s using the SOT-23 package have pin 3 connected as the (-) output through the package’s die attach interface. Therefore, the LM4051-1.2’s pin 3 must be left floating or connected to pin 2 and the LM4051-ADJ’s pin 3 is the (-) output. The typical thermal hysteresis specification is defined as the change in +25˚C voltage measured after thermal cycling. The device is thermal cycled to temperature -40˚C and then measured at 25˚C. Next the device is thermal cycled to temperature +125˚C and again measured at 25˚C. The re- sulting V OUT delta shift between the 25˚C measurements is thermal hysteresis. Thermal hysteresis is common in preci- sion references and is induced by thermal-mechanical pack- age stress. Changes in environmental storage temperature, operating temperature and board mounting temperature are all factors that can contribute to thermal hysteresis. In a conventional shunt regulator application (Figure 1), an external series resistor (R S) is connected between the sup- ply voltage and the LM4051. R S determines the current that flows through the load (I L) and the LM4051 (IQ). Since load current and supply voltage may vary, R S should be small enough to supply at least the minimum acceptable I Q to the LM4051 even when the supply voltage is at its minimum and the load current is at its maximum value. When the supply voltage is at its maximum and I L is at its minimum, RS should be large enough so that the current flowing through the LM4051 is less than 12 mA. R S should be selected based on the supply voltage, (VS), the desired load and operating current, (I L and IQ), and the LM4051’s reverse breakdown voltage, V R. The LM4051-ADJ’s output voltage can be adjusted to any value in the range of 1.24V through 10V. It is a function of the internal reference voltage (V REF) and the ratio of the external feedback resistors as shown in Figure 2 . The output voltage is found using the equation V O =VREF[(R2/R1) + 1] (1) (2) where V O is the output voltage. The actual value of the internal V REF is a function of VO. The “corrected” VREF is determined by V REF =VO ( ∆V REF/ ∆V O)+VY (3) where V Y = 1.22V ∆V REF/ ∆V O is found in the Electrical Characteristics and is typically −1.55 mV/V. You can get a more accurate indication of the output voltage by replacing the value of V REF in equation (1) with the value found using equation (3). www.national.com 9 |
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