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SGM8049-2 Datasheet(PDF) 8 Page - SG Micro Corp |
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SGM8049-2 Datasheet(HTML) 8 Page - SG Micro Corp |
8 / 19 page SGM8049-1/SGM8049-2 1.8V, 2.5µA, 120kHz, SGM8049-4 Rail-to-Rail I/O Operational Amplifiers 8 NOVEMBER 2015 SG Micro Corp www.sg-micro.com APPLICATION INFORMATION The SGM8049-1/2/4 operational amplifiers minimize power consumption without compromising bandwidth or noise. Typical values of power supply rejection ratio (PSRR), common mode rejection ratio (CMRR), and open-loop gain (AOL) are 100dB or better. When designing for ultra low power applications, choose system components carefully. To minimize current consumption, select large value resistors. Any resistors will react with stray capacitance in the circuit and the input capacitance of the operational amplifiers. These parasitic RC combinations can affect the stability of the overall system. A feedback capacitor may be required to assure stability and limit overshoot or gain peaking. Good layout practice mandates the use of a 0.1μF bypass capacitor placed closely across the supply pins. Operating Voltage SGM8049-1/2/4 operational amplifiers are fully specified and tested from +1.8V to +5.5V or ±0.9V to ±2.75V. Input Common Mode Voltage Range The input common mode voltage range of the SGM8049-1/2/4 is from (-VS) - 0.1V to (+VS) + 0.1V. This rail-to-rail input is achieved using a complementary input stage. CMRR is specified from the negative rail to 1.2V below the positive rail. Between (-VS) - 0.1V to (+VS) + 0.1V, the amplifier operates with higher offset voltage because of the transition region of the input stage. Protecting Inputs from Over-Voltage Normally, input currents are 1pA. However, a large voltage input (greater than 500mV beyond the supply rails) can cause excessive current to flow in or out of the input pins. Therefore, as well as keeping the input voltage below the maximum rating, it is also important to limit the input current to less than 10mA. This limiting is easily accomplished with an input voltage resistor, as shown in Figure 2. IOVERLOAD 10mA MAX 2k Ω VS VOUT VIN + - SGM8049-1 Figure 2. Input Current Protection for Voltages Exceeding the Supply Voltage Noise Although micro-power amplifiers frequently have high wideband noise, the SGM8049-1/2/4 offer excellent noise performance. Resistors should be chosen carefully because the SGM8049-1/2/4 have only 3.5μVPP of 0.1Hz to 10Hz noise, and 75nV/ Hz of wideband noise; otherwise, they can become the dominant source of noise. Capacitive Load and Stability Follower configurations with load capacitance in excess of 30pF can produce extra overshoot and ringing in the output signal. Increasing the gain enhances the ability of the amplifier to drive greater capacitive loads. In unity-gain configurations, capacitive load drive can be improved by inserting a small (10Ω to 20Ω) resistor, RS, in series with the output, as shown in Figure 3. This resistor significantly reduces ringing while maintaining direct current (DC) performance for purely capacitive loads. However, if there is a resistive load in parallel with the capacitive load, a voltage divider is created, introducing a DC error at the output and slightly reducing the output swing. The error introduced is proportional to the ratio RS/RL, and is generally negligible. VS VOUT VIN RS RL CL 10 Ω to 20Ω + - SGM8049-1 Figure 3. Series Resistor in Unity-Gain Buffer Configuration Improves Capacitive Load Drive |
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