Datasheet AD581 (Analog Devices) - 9

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AD581 THE AD581 AS A CURRENT LIMITER
The AD581 represents an alternative to current limiter diodes
ANALOG GND
that require factory selection to achieve a desired current. This
+VS
approach often results in temperature coefficients of 1%/°C.
0.1µF AD581 V
The AD581 approach is not limited to a defined set current
OUT
limit; it can be programmed from 0.75 mA to 5 mA with the
GND VREF
insertion of a single external resistor. Of course, the minimum
–10V
voltage required to drive the connection is 13 V. The AD580,
1.2kΩ 5%
3 -01 which is a 2.5 V reference, can be used in this type of circuit 14
–15V
80 0 with compliance voltage down to 4.5 V. Figure 13. 2-Pin −10 V Reference
10 V REFERENCE WITH MULTIPLYING CMOS DACs +V OR ADCs S ~ 10V AD581 i = ___ + 0.75mA 10V = V
The AD581 is ideal for application with the entire AD7533
OUT R
series of 10- and 12-bit multiplying CMOS DACs, especially for
GND R LOAD
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
BOTTOM VIEW OF 10V PRECISION
2 01 to produce a 0 V to −10 V range. If an OP1177 amplifier is used,
REFERENCE CIRCUIT
4-
IN TO-5 CASE
01 08 total quiescent supply current is typically 2 mA. If a 0 V to +10 V Figure 12. A Two-Component Precision Current Limiter full-scale range is desired, the AD581 can be connected to the
NEGATIVE 10 V REFERENCE
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 The AD581 can also be used in a 2-pin Zener mode to provide a CMOS DAC). The AD581 is normally used in the −10 V mode precision −10.00 V reference. As shown in Figure 13, the +VS and with the AD7574 to give a 0 V to +10 V ADC range. This is VOUT pins are connected together to the high supply (in this shown in Figure 15. Bipolar output applications and other case, ground). The ground pin is connected through a resistor operating details can be found in the data sheets for the CMOS to the negative supply. Thus, the output is taken from the products. ground pin instead of VOUT. With 1 mA flowing through the
+15V
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
+10V
that the effective output impedance in this connection increases
AD581
from 0.2 Ω typical to 2 Ω. It is essential to arrange the output
VREF IN
load and the supply resistor, RS, so that the net current through
BIT 1 (MSB) 15 14 RFEEDBACK
the AD581 is always between 1 mA and 5 mA. For operation to
4 16 DIGITAL +15V 5
+125°C, the net current should be between 2 mA and 5 mA. The
INPUT IOUT1 1
temperature characteristics and long-term stability of the device
VOUT 0V TO –10V
are essentially the same as that of a unit used in the standard
IOUT2
3-pin mode.
13 2 –15V BIT 10 (LSB) 3
14 0
GND
4- The AD581 can also be used in a 2-pin mode to develop a 01 08 positive reference. +VS and VOUT are tied together and to the Figure 14. Low Power 10-Bit CMOS DAC Application positive supply through an appropriate supply resistor. The
PRECISION 12-BIT DAC REFERENCE
performance characteristics are similar to those of the negative 2-pin connection. The only advantage of this connection over AD565A, like most DACs, is designed to operate with a +10 V the standard 3-pin connection is that a lower primary supply reference element. In the AD565A, this 10 V reference voltage is can be used, as low as 10.5 V. This type of operation requires con- converted into a reference current of approximately 0.5 mA via siderable attention to load and primary supply regulation to the internal 19.95 kΩ resistor (in series with the external 100 Ω maintain the AD581 within its regulating range of 1 mA to 5 mA trimmer). The gain temperature coefficient of the AD565A is (2 mA to 5 mA for operation beyond +85°C). 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 Rev. C | Page 9 of 12 Document Outline FEATURES FUNCTIONAL BLOCK DIAGRAM GENERAL DESCRIPTION PRODUCT HIGHLIGHTS TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ESD CAUTION APPLYING THE AD581 VOLTAGE VARIATION vs. TEMPERATURE OUTPUT CURRENT CHARACTERISTICS DYNAMIC PERFORMANCE PRECISION HIGH CURRENT SUPPLY CONNECTION FOR REDUCED PRIMARY SUPPLY THE AD581 AS A CURRENT LIMITER NEGATIVE 10 V REFERENCE 10 V REFERENCE WITH MULTIPLYING CMOS DACs OR ADCs PRECISION 12-BIT DAC REFERENCE OUTLINE DIMENSIONS ORDERING GUIDE