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ALD1722ESA Datasheet(PDF) 10 Page - Advanced Linear Devices |
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ALD1722ESA Datasheet(HTML) 10 Page - Advanced Linear Devices |
10 / 10 page 10 Advanced Linear Devices ALD1722E/ALD1722 DEFINITIONS AND DESIGN NOTES: 1. Initial Input Offset Voltage is the offset voltage of the ALD1722E/ALD1722 operational amplifier as shipped from the factory. The device has been pre-programmed and tested for programmability. 2. Offset Voltage Program Range is the range of adjustment of user specified target offset voltage. This is typically an adjust- ment in either the positive or the negative direction of the input offset voltage from an initial offset voltage. The input offset program pins, VE1 or VE2, change the input offset voltage in the negative or positive direction, respectively. User specified target offset voltage can be any offset voltage within this programming range. 3. Programmed Input Offset Voltage Error is the final offset voltage error after programming, when the Input Offset Voltage is at target Offset Voltage. This parameter is sample tested. 4. Total Input Offset Voltage is the same as Programmed Input Offset Voltage, corrected for system offset voltage error. Usu- ally this is an all inclusive system offset voltage, which also includes offset voltage contributions from input offset voltage, PSRR, CMRR, TCVos and noise. It can also include errors introduced by external components, at a system level. Pro- grammed Input Offset Voltage and Total Input Offset Voltage is not necessarily zero offset voltage, but an offset voltage set to compensate for other system errors as well. This parameter is sample tested. 5. The Input Offset and Bias Currents are essentially input protection diode reverse bias leakage currents. This low input bias current assures that the analog signal from the source will not be distorted by it. For applications where source impedance is very high, it may be necessary to limit noise and hum pickup through proper shielding. 6. Input Voltage Range is determined by two parallel comple- mentary input stages that are summed internally, each stage having a separate input offset voltage. While Total Input Offset Voltage can be trimmed to a desired target value, it is essential to note that this trimming occurs at only one selected input bias voltage. Depending on the selected input bias voltage relative to the power supply voltages, offset voltage trimming may affect one or both input stages. For the ALD1722E/ALD1722, the switching point between the two stages occur at approximately 1.5V above the negative supply voltage 7. Input Offset Voltage Drift is the average change in Total Input Offset Voltage as a function of ambient temperature. This parameter is sample tested. 8. Initial PSRR and initial CMRR specifications are provided as reference information. After programming, error contribution to the offset voltage from PSRR and CMRR is set to zero under the specific power supply and common mode conditions, and becomes part of the Programmed Input Offset Voltage Error. 9. Average Long Term Input Offset Voltage Stability is based on input offset voltage shift through operating life test at 125 degrees C extrapolated to Ta = 25 degrees C, assuming activation energy of 1.0eV. This parameter is sample tested. ADDITIONAL DESIGN NOTES: A. The ALD1722E/ALD1722 is internally compensated for unity gain stability using a novel scheme which produces a single pole role off in the gain characteristics while providing more than 70 degrees of phase margin at unity gain frequency. A unity gain buffer using the ALD1722E/ALD1722 will typically drive 400pF of external load capacitance; in the inverting unity gain configu- ration, it can drive up to 800pF of load capacitance. B. The ALD1722E/ALD1722 has complementary p-channel and n-channel input differential stages connected in parallel to accomplish rail to rail input common mode voltage range. The switching point between the two differential stages is 1.5V above negative supply voltage. For applications such as invert- ing amplifier or non-inverting amplifier with a gain larger than 2.5 (5V operation), the common mode voltage does not make excursions below this switching point. However, this switching does take place if the operational amplifier is connected as a rail- to- rail unity gain buffer and the design must allow for input offset voltage variations. C. The output stage consists of class AB complementary output drivers. The oscillation resistant feature, combined with the rail- to-rail input and output feature, makes the ALD1722E/ALD1722 an effective analog signal buffer for high source impedance sensors, transducers, and other circuit networks. D. The ALD1722E/ALD1722 has static discharge protection. However, care must be exercised when handling the device to avoid strong static fields that may degrade a diode junction, causing increased input leakage currents. The user is advised to power up the circuit before, or simultaneously with, any input voltages applied and to limit input voltages to not exceed 0.3V of the power supply voltage levels. E. VE1 and VE2 are high impedance terminals, as the internal bias currents are set very low to a few microamperes to conserve power. For some applications, these terminals may need to be shielded from external coupling sources. For ex- ample, digital signals running nearby may cause unwanted offset voltage fluctuations. Care during the printed circuit board layout to place ground traces around these pins and to isolate them from digital lines would generally eliminate such coupling effects. In addition, optional decoupling capacitors of 1000pF or greater value can be added to VE1 and VE2 terminals. F. The ALD1722E/ALD1722 is designed for use in low voltage, micro-power circuits. The maximum operating voltage during normal operation should remain below 10 Volts at all times. Care should be taken to insure that the application in which the devices are used would not experience any positive or negative transient voltages that cause any of the terminal voltages to exceed this limit. G. All inputs or unused pins except VE1 and VE2 pins should be connected to a supply voltage such as Ground so that they do not become floating pins, since input impedance at these pins is very high. If any of these pins are left undefined, they may cause unwanted oscillation or intermittent excessive current drain. As these devices are built with CMOS technology, normal operating and storage temperature limits, ESD and latchup handling precautions pertaining to CMOS device handling should be observed. |
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