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AD581LH1 Datasheet(PDF) 9 Page - Analog Devices |
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AD581LH1 Datasheet(HTML) 9 Page - Analog Devices |
9 / 12 page AD581 Rev. C | Page 9 of 12 THE AD581 AS A CURRENT LIMITER The AD581 represents an alternative to current limiter diodes that require factory selection to achieve a desired current. This approach often results in temperature coefficients of 1%/°C. The AD581 approach is not limited to a defined set current limit; it can be programmed from 0.75 mA to 5 mA with the insertion of a single external resistor. Of course, the minimum voltage required to drive the connection is 13 V. The AD580, which is a 2.5 V reference, can be used in this type of circuit with compliance voltage down to 4.5 V. +VS VOUT GND AD581 R LOAD i = R 10V ~ ___ + 0.75mA 10V = BOTTOM VIEW OF 10V PRECISION REFERENCE CIRCUIT IN TO-5 CASE Figure 12. A Two-Component Precision Current Limiter NEGATIVE 10 V REFERENCE The AD581 can also be used in a 2-pin Zener mode to provide a precision −10.00 V reference. As shown in Figure 13, the +VS and VOUT pins are connected together to the high supply (in this case, ground). The ground pin is connected through a resistor to the negative supply. Thus, the output is taken from the ground pin instead of VOUT. With 1 mA flowing through the AD581 in this mode, a typical unit shows a 2 mV increase in output level over that produced in the 3-pin mode. Note also that the effective output impedance in this connection increases from 0.2 Ω typical to 2 Ω. It is essential to arrange the output load and the supply resistor, RS, so that the net current through the AD581 is always between 1 mA and 5 mA. For operation to +125°C, the net current should be between 2 mA and 5 mA. The temperature characteristics and long-term stability of the device are essentially the same as that of a unit used in the standard 3-pin mode. The AD581 can also be used in a 2-pin mode to develop a positive reference. +VS and VOUT are tied together and to the positive supply through an appropriate supply resistor. The performance characteristics are similar to those of the negative 2-pin connection. The only advantage of this connection over the standard 3-pin connection is that a lower primary supply can be used, as low as 10.5 V. This type of operation requires con- siderable attention to load and primary supply regulation to maintain the AD581 within its regulating range of 1 mA to 5 mA (2 mA to 5 mA for operation beyond +85°C). AD581 GND +VS VOUT 0.1µF –15V 1.2k Ω 5% VREF –10V ANALOG GND Figure 13. 2-Pin −10 V Reference 10 V REFERENCE WITH MULTIPLYING CMOS DACs OR ADCs The AD581 is ideal for application with the entire AD7533 series of 10- and 12-bit multiplying CMOS DACs, especially for low power applications. It is equally suitable for the AD7574 8-bit ADC. In the standard hook-up, as shown in Figure 15, the +10 V reference is inverted by the amplifier/DAC configuration to produce a 0 V to −10 V range. If an OP1177 amplifier is used, total quiescent supply current is typically 2 mA. If a 0 V to +10 V full-scale range is desired, the AD581 can be connected to the CMOS DAC in its −10 V Zener mode, as shown in Figure 13 (the −10 VREF output is connected directly to the VREF IN of the CMOS DAC). The AD581 is normally used in the −10 V mode with the AD7574 to give a 0 V to +10 V ADC range. This is shown in Figure 15. Bipolar output applications and other operating details can be found in the data sheets for the CMOS products. AD581 +15V +10V VREF IN BIT 1 (MSB) BIT 10 (LSB) GND DIGITAL INPUT +15V –15V VOUT 0V TO –10V RFEEDBACK IOUT1 IOUT2 15 14 3 4 5 13 16 1 2 Figure 14. Low Power 10-Bit CMOS DAC Application PRECISION 12-BIT DAC REFERENCE AD565A, like most DACs, is designed to operate with a +10 V reference element. In the AD565A, this 10 V reference voltage is converted into a reference current of approximately 0.5 mA via the internal 19.95 kΩ resistor (in series with the external 100 Ω trimmer). The gain temperature coefficient of the AD565A is primarily governed by the temperature tracking of the 19.95 kΩ resistor and the 5 kΩ to10 kΩ span resistors; gain TC is guaran- teed to 3 ppm/°C. Thus, using the AD581L (at 5 ppm/°C) as the |
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