Datasheet AD588 (Analog Devices) - 6

link to page 6
AD588 Data Sheet THEORY OF OPERATION
The AD588 consists of a buried Zener diode reference, Ground sensing for the circuit is provided by Amplifier A2. The amplifiers used to provide pin programmable output ranges, noninverting input (Pin 9) senses the system ground, which is and associated thin-film resistors, as shown in Figure 3. The transferred to the point on the circuit where the inverting input temperature compensation circuitry provides the device with a (Pin 10) is connected. This can be Pin 6, Pin 8, or Pin 11. The temperature coefficient of 1.5 ppm/°C or less. output of A2 drives Pin 8 to the appropriate voltage. Thus, if Pin 10 is connected to Pin 8, the VLOW pin is the same voltage as Amplifier A1 performs several functions. A1 primarily acts to the system ground. Alternatively, if Pin 10 is connected to the amplify the Zener voltage from 6.5 V to the required 10 V output. VCT pin, it is a ground; and Pin 6 and Pin 8 are +5 V and −5 V, In addition, A1 provides for external adjustment of the 10 V output respectively. through Pin 5, GAIN ADJ. Using the bias compensation resistor between the Zener output and the noninverting input to A1, a Amplifier A3 and Amplifier A4 are internally compensated and capacitor can be added at the NOISE REDUCTION pin (Pin 7) are used to buffer the voltages at Pin 6, Pin 8, and Pin 11, as well to form a low-pass filter and reduce the noise contribution of the as to provide a full Kelvin output. Thus, the AD588 has a full Zener to the circuit. Two matched 10 kΩ nominal thin-film Kelvin capability by providing the means to sense a system resistors (R4 and R5) divide the 10 V output in half. Pin VCT ground and provide forced and sensed outputs referenced to (Pin 11) provides access to the center of the voltage span and that ground. BAL ADJ (Pin 12) can be used for fine adjustment of this division. Note that both positive and negative supplies are required for operation of the AD588.
NOISE A3 OUT V REDUCTION HIGH A3 IN SENSE 7 6 4 3 A3 OUT A3 1 R FORCE B A1 A4 OUT 14 R1 R4 SENSE A4 OUT R2 A4 15 FORCE R5 R6 2 +VS R3 A2 AD588 16 –VS 5 9 10 8 12 11 13 GAIN GND GND VLOW BAL VCT A4 IN
003
ADJ SENSE SENSE ADJ +IN –IN
00531- Figure 3. AD588 Functional Block Diagram Rev. M | Page 6 of 20 Document Outline FEATURES GENERAL DESCRIPTION FUNCTIONAL BLOCK DIAGRAM PRODUCT HIGHLIGHTS TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS THEORY OF OPERATION APPLICATIONS INFORMATION CALIBRATION NOISE PERFORMANCE AND REDUCTION TURN-ON TIME TEMPERATURE PERFORMANCE KELVIN CONNECTIONS DYNAMIC PERFORMANCE USING THE AD588 WITH CONVERTERS AD7535 14-BIT DIGITAL-TO-ANALOG CONVERTER AD569 16-BIT DIGITAL-TO-ANALOG CONVERTER SUBSTITUTING FOR INTERNAL REFERENCES AD574A 12-BIT ANALOG-TO-DIGITAL CONVERTER RESISTANCE TEMPERATURE DETECTOR (RTD) EXCITATION BOOSTED PRECISION CURRENT SOURCE BRIDGE DRIVER CIRCUITS OUTLINE DIMENSIONS ORDERING GUIDE