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AD8601 Fiches technique(PDF) 13 Page - Analog Devices |
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AD8601 Fiches technique(HTML) 13 Page - Analog Devices |
13 / 16 page AD8601/AD8602 –13– REV. 0 SETTLING TIME – ns 5 5 3 0 1 3 4 2 1 0 1,000 200 400 600 800 0.1% 0.01% 0.01% 0.1% 2 4 VS = 5V TA = 25 C TPC 49. Output Swing vs. Settling Time THEORY OF OPERATION The AD8601/AD8602 family of amplifiers are rail-to-rail input and output precision CMOS amplifiers specified from 2.7 V to 5.0 V of power supply voltage. These amplifiers use Analog Devices’ propri- etary technology called DigiTrim™ to achieve a higher degree of precision than available from most CMOS amplifiers. DigiTrim technology is a method of trimming the offset voltage of the amplifier after it has already been assembled. The advantage in post-package trimming lies in the fact that it corrects any offset voltages due to the mechanical stresses of assembly. This tech- nology is scalable and utilized with every package option, including SOT23-5, providing lower offset voltages than previously achieved in these small packages. The DigiTrim process is done at the factory and does not add additional pins to the amplifier. All AD860x amplifiers are avail- able in standard op amp pinouts, making DigiTrim completely transparent to the user. The AD860x can be used in any preci- sion op amp application. The input stage of the amplifier is a true rail-to-rail architecture, allowing the input common-mode voltage range of the op amp to extend to both positive and negative supply rails. The voltage swing of the output stage is also rail-to-rail and is achieved by using an NMOS and PMOS transistor pair connected in a common-source configuration. The maximum output voltage swing is proportional to the output current, and larger currents will limit how close the output voltage can get to the supply rail. This is a characteristic of all rail-to-rail output amplifiers. With 1 mA of output current, the output voltage can reach within 20 mV of the positive rail and 15 mV of the negative rail. The open-loop gain of the AD860x is 100 dB, typical, with a load of 2 k Ω. Because of the rail-to-rail output configuration, the gain of the output stage, and thus the open-loop gain of the amplifier, is dependent on the load resistance. Open-loop gain will decrease with smaller load resistances. Again, this is a characteristic inher- ent to all rail-to-rail output amplifiers. Rail-to-Rail Input Stage The input common-mode voltage range of the AD860x extends to both positive and negative supply voltages. This maximizes the usable voltage range of the amplifier, an important feature for single supply and low voltage applications. This rail-to-rail input range is achieved by using two input differential pairs, one NMOS and one PMOS, placed in parallel. The NMOS pair is active at the upper end of the common-mode voltage range, and the PMOS pair is active at the lower end of the common-mode range. The NMOS and PMOS input stage are separately trimmed using DigiTrim to minimize the offset voltage in both differential pairs. Both NMOS and PMOS input differential pairs are active in a 500 mV transition region, when the input common-mode voltage is between approximately 1.5 V and 1 V below the positive supply voltage. Input offset voltage will shift slightly in this transition region, as shown in Figures 5 and 6. Common-mode rejection ratio will also be slightly lower when the input common-mode voltage is within this transition band. Compared to the Burr Brown OPA2340 rail-to-rail input amplifier, shown in Figure 1, the AD860x, shown in Figure 2, exhibits lower offset voltage shift across the entire input common-mode range, including the transi- tion region. VCM – V 0.7 0.4 1.4 0 5 1 23 4 0.2 0.5 0.8 1.1 0.1 Figure 1. Burr Brown OPA2340UR Input Offset Voltage vs. Common-Mode Voltage, 24 SOIC Units @ 25 °C VCM – V 0.7 0.4 1.4 0 5 1 23 4 0.2 0.5 0.8 1.1 0.1 Figure 2. AD8602AR Input Offset Voltage vs. Common-Mode Voltage, 300 SOIC Units @ 25 °C DigiTrim is a trademark of Analog Devices. |
Numéro de pièce similaire - AD8601 |
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Description similaire - AD8601 |
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