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ISL28166_0808 Folha de dados(PDF) 10 Page - Intersil Corporation |
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ISL28166_0808 Folha de dados(HTML) 10 Page - Intersil Corporation |
10 / 13 page 10 FN6155.4 August 29, 2008 Applications Information Introduction The ISL28166 is a single BiMOS rail-to-rail input, output (RRIO) operational amplifier with an enable feature. The ISL28266 is a dual version without the enable feature. Both devices are designed to operate from single supply (2.4V to 5.0V) or dual supplies (±1.2V to ±2.5V) while drawing only 39µA of supply current per amplifier. This combination of low power and precision performance makes this device suitable for a variety of low power applications including battery powered systems. Rail-to-Rail Input/Output These devices feature bi-polar inputs which have an input common mode range that extends to the rails, and CMOS outputs that can typically swing to within about 4mV of the supply rails with a 100k Ω load. The NMOS sinks current to swing the output in the negative direction. The PMOS sources current to swing the output in the positive direction. Input Protection All input terminals have internal ESD protection diodes to both positive and negative supply rails, limiting the input voltage to within one diode beyond the supply rails. They also contain back-to-back diodes across the input terminals. For applications where the input differential voltage is expected to exceed 0.5V, external series resistors must be used to ensure the input currents never exceed 5mA (Figure 34). Enable/Disable Feature The ISL28166 offers an EN pin that disables the device when pulled up to at least 2.0V. In the disabled state (output in a high impedance state), the part consumes typically 10µA. By disabling the part, multiple ISL28166 parts can be connected together as a MUX. In this configuration, the outputs are tied together in parallel and a channel can be selected by the EN pin. The EN pin also has an internal pull-down. If left open, the EN pin will pull to the negative rail and the device will be enabled by default. The loading effects of the feedback resistors of the disabled amplifier must be considered when multiple amplifier outputs are connected together. Using Only One Channel The ISL28266 is a dual op amp. If the application only requires one channel, the user must configure the unused channel to prevent it from oscillating. The unused channel will oscillate if the input and output pins are floating. This will result in higher than expected supply currents and possible noise injection into the channel being used. The proper way to prevent this oscillation is to short the output to the negative input and ground the positive input (as shown in Figure 35). Current Limiting These devices have no internal current-limiting circuitry. If the output is shorted, it is possible to exceed the Absolute Maximum Rating for output current or power dissipation, potentially resulting in the destruction of the device. Power Dissipation It is possible to exceed the +125°C maximum junction temperatures under certain load and power-supply conditions. It is therefore important to calculate the maximum junction temperature (TJMAX) for all applications to determine if power supply voltages, load conditions, or package type need to be modified to remain in the safe operating area. These parameters are related in Equation 1: where: •PDMAXTOTAL is the sum of the maximum power dissipation of each amplifier in the package (PDMAX) •PDMAX for each amplifier can be calculated using Equation 2: where: •TMAX = Maximum ambient temperature • θJA = Thermal resistance of the package •PDMAX = Maximum power dissipation of 1 amplifier •VS = Supply voltage •IMAX = Maximum supply current of 1 amplifier •VOUTMAX = Maximum output voltage swing of the application •RL = Load resistance FIGURE 34. INPUT CURRENT LIMITING - + RIN RL VIN VOUT FIGURE 35. PREVENTING OSCILLATIONS IN UNUSED CHANNELS - + T JMAX T MAX θ JAxPDMAXTOTAL () + = (EQ. 1) PD MAX 2*V S I SMAX V S ( - V OUTMAX ) V OUTMAX R L ---------------------------- × + × = (EQ. 2) ISL28166, ISL28266 |
Nº de peça semelhante - ISL28166_0808 |
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Descrição semelhante - ISL28166_0808 |
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