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EL8178BIWZ-T7 Datasheet(PDF) 6 Page - Intersil Corporation |
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EL8178BIWZ-T7 Datasheet(HTML) 6 Page - Intersil Corporation |
6 / 8 page 6 FN7504.2 October 5, 2005 Applications Information Introduction The EL8178 is a rail-to-rail input and output micro-power precision single supply operational amplifier with an enable feature. The device achieves rail-to-rail input and output operation and eliminates the concerns introduced by a conventional rail-to-rail I/O operational Amplifier. Rail-to-Rail Input The PFET input stage of the EL8178 has an input common- mode voltage range that goes from negative supply to positive supply without introducing offset errors or degrading performance associated with a conventional rail-to-rail input operational amplifier. Many rail-to-rail input stages use two differential input pairs, a long-tail PNP (or PFET) and an NPN (or NFET). Severe penalties have to be paid for this topology. As the input signal moves from one supply rail to another, the operational amplifier switches from one input pair to the other causing drastic changes in input offset voltage and an undesired change in magnitude and polarity of input offset current. The EL8178 achieves input rail-to-rail performance without sacrificing important precision specifications and without degrading distortion performance. The EL8178's input offset voltage exhibits a smooth behavior throughout the entire common-mode input range. Rail-to-Rail Output A pair of complementary MOSFET devices achieves rail-to- rail output swing. The NMOS sinks current to swing the output in the negative direction. The PMOS sources current to swing the output in the positive direction. The EL8178 with a 100k Ω load will swing to within 3mV of the supply rails. Enable/Disable Feature The EL8178 offers an EN pin. The active low enable pin disables the device when pulled up to at least 2.2V. Upon disable the part consumes typically 3µA, while the output is in a high impedance state. The EN also has an internal pull down. If left open, the EN pin will pull to negative rail and the device will be enabled by default. The high impedance at output during disable allows multiple EL8178s to be connected together as a MUX. The outputs are tied together in parallel and a channel can be selected by the EN pin. Typical Applications FIGURE 17. PH PROBE AMPLIFIER A general-purpose combination pH probe has extremely high output impedance typically in the range of 10G Ω to 12G Ω. Low loss and expensive Teflon cables are often used to connect the PH probe to the meter electronics. The above circuit provides a low-cost alternative solution using the EL8178 and a low-cost coax cable. The EL8178 PMOS high impedance input senses the pH probe output signal and buffers it to drive the coax cable. Its rail-to-rail input nature also eliminates the need for a bias resistor network required by other amplifiers in the same application. FIGURE 18. THERMOCOUPLE AMPLIFIER Thermocouples are the most popular temperature-sensing device because of their low cost, interchangeability, and ability to measure a wide range of temperatures. The EL8178 is used to convert the differential thermocouple voltage into single-ended signal with 10X gain. The EL8178's rail-to-rail input characteristic allows the thermocouple to be biased at ground and the converter to run from a single 5V supply. - + 3V + V+ V- EL8178 COAX GENERAL PURPOSE COMBINATION pH PROBE - + 5V + V+ V- EL8178 K TYPE THERMOCOUPLE 10k Ω R3 10k Ω R2 R4 100k Ω R1 100k Ω 410µV/°C EL8178 |
Similar Part No. - EL8178BIWZ-T7 |
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Similar Description - EL8178BIWZ-T7 |
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