AD588TQ Analog Devices, AD588TQ Datasheet - Page 4

• Manufacturer Part Number: AD588TQ
• Description: High Precision Voltage Reference
• Manufacturer: Analog Devices

AD588
THEORY OF OPERATION
The AD588 consists of a buried Zener diode reference, amplifiers
used to provide pin programmable output ranges, and associ-
ated thin-film resistors as shown in Figure 1. The temperature
compensation circuitry provides the device with a temperature
coefficient of 1.5 ppm/°C or less.
Amplifier A1 performs several functions. A1 primarily acts to
amplify the Zener voltage from 6.5 V to the required 10 V output.
In addition, A1 also provides for external adjustment of the
10 V output through Pin 5, GAIN ADJ. Using the bias compen-
sation resistor between the Zener output and the noninverting
input to A1, a capacitor can be added at the NOISE REDUCTION
pin (Pin 7) to form a low-pass filter and reduce the noise contri-
bution of the Zener to the circuit. Two matched 10 kΩ nominal
thin-film resistors (R4 and R5) divide the 10 V output in half.
Pin V
span and Pin 12 (BAL ADJ) can be used for fine adjustment
of this division.
Ground sensing for the circuit is provided by amplifier A2. The
noninverting input (Pin 9) senses the system ground, which
will be transferred to the point on the circuit where the invert-
ing input (Pin 10) is connected. This may be Pin 6, 8, or 11.
The output of A2 drives Pin 8 to the appropriate voltage. Thus, if
Pin 10 is connected to Pin 8, the V
voltage as the system ground. Alternatively, if Pin 10 is con-
nected to the V
be +5 V and –5 V, respectively.
Amplifiers A3 and A4 are internally compensated and are used
to buffer the voltages at Pins 6, 8, and 11, as well as to provide a
full Kelvin output. Thus, the AD588 has a full Kelvin capability
by providing the means to sense a system ground and provide
forced and sensed outputs referenced to that ground.
GAIN
ADJ
CT
R3
Figure 1. AD588 Functional Block Diagram
(Pin 11) provides access to the center of the voltage
R
REDUCTION
SENSE
GND
B
+IN
R2
NOISE
A2
CT
SENSE
GND
–IN
A1
pin, it will be ground and Pin 6 and Pin 8 will
R1
V
V
HIGH
LOW
R4
R5
BAL
ADJ
A3 IN
R6
LOW
V
CT
A3 OUT
SENSE
pin will be the same
A4 IN
AD588
A3
A4
A3 OUT
A4 OUT
A4 OUT
FORCE
SENSE
FORCE
+V
–V
S
S
–4–
APPLYING THE AD588
The AD588 can be configured to provide +10 V and –10 V
reference outputs as shown in Figures 2a and 2c, respectively. It
can also be used to provide +5 V, –5 V, or a ± 5 V tracking
reference, as shown in Figure 2b. Table I details the appropriate
pin connections for each output range. In each case, Pin 9 is
connected to system ground and power is applied to Pins 2 and 16.
The architecture of the AD588 provides ground sense and
uncommitted output buffer amplifiers that offer the user a great
deal of functional flexibility. The AD588 is specified and tested
in the configurations shown in Figure 2a. The user may choose
to take advantage of the many other configuration options available
with the AD588. However, performance in these configurations
is not guaranteed to meet the extremely stringent data sheet
specifications.
As indicated in Table I, a +5 V buffered output can be provided
using amplifier A4 in the +10 V configuration (Figure 2a). A –5 V
buffered output can be provided using amplifier A3 in the –10 V
configuration (Figure 2c). Specifications are not guaranteed for
the +5 V or –5 V outputs in these configurations. Performance
will be similar to that specified for the +10 V or –10 V outputs.
As indicated in Table I, unbuffered outputs are available at
Pins 6, 8, and 11. Loading of these unbuffered outputs will
impair circuit performance.
Amplifiers A3 and A4 can be used interchangeably. However,
the AD588 is tested (and the specifications are guaranteed) with
the amplifiers connected as indicated in Figure 2a and Table I.
When either A3 or A4 is unused, its output force and sense pins
should be connected and the input tied to ground.
Two outputs of the same voltage may be obtained by connect-
ing both A3 and A4 to the appropriate unbuffered output on
Pins 6, 8, or 11. Performance in these dual-output configura-
tions will typically meet data sheet specifications.
CALIBRATION
Generally, the AD588 will meet the requirements of a precision
system without additional adjustment. Initial output voltage
error of 1 mV and output noise specs of 10 µV p-p allow for
accuracies of 12 bits to 16 bits. However, in applications where
an even greater level of accuracy is required, additional calibra-
tion may be called for. Provision for trimming has been made
through the use of the GAIN ADJ and BAL ADJ pins (Pins 5 and
12, respectively).
The AD588 provides a precision 10 V span with a center tap
(V
achieve the voltage output configurations in Table I. GAIN
ADJUST and BALANCE ADJUST can be used in any of these
configurations to trim the magnitude of the span voltage and
the position of the center tap within the span. The GAIN
ADJUST should be performed first. Although the trims are not
interactive within the device, the GAIN trim will move the
BALANCE trim point as it changes the magnitude of the span.
CT
) that is used with the buffer and ground sense amplifiers to
REV. D