AD578/AD579
200ns, min
UNIPOLAR CALIBRATION
CONVERT
START
CONVERSION TIME
70ns
100ns
The AD578/AD579 are intended to have a nominal 1/2 LSB
offset so that the exact analog input for a given code will be in
the middle of that code (halfway between the transitions to the
codes above and below it). Thus, when properly calibrated, the
first transition (from 0000 0000 0000 to 0000 0000 0001) will
occur for an input level of +1/2 LSB.
125ns
~15ns
GATED
CLOCK
t1 t2 t3 t4 t5 t6 t7 t8 t9 t10
t0
100ns
CONVERSION IN PROGRESS
PARALLEL DATA VALID
EOC
25ns
75ns
BIT 1
(MSB)
If Pin 26 is connected to Pin 30, the unit will behave in this
manner, within specifications. Refer to Table I, Table II, and
Figure 3 for further clarification. If the offset trim (R1) is used,
it should be trimmed as above, although a different offset can be
set for a particular system requirement. This circuit will give
approximately 25 mV of offset trim range.
BIT 2
BIT 3
BIT 4
BIT 5
BIT 6
BIT 7
BIT 8
BIT 9
BIT 10
The full-scale trim is done by applying a signal 1 1/2 LSB
below the nominal full scale. Trim R2 to give the last transition
(1111 1111 1110 to 1111 1111 11111).
+15V
R1
ZERO ADJ
10k⍀
–15V
0V TO +20V
20V IN
B1 B2 B3 B4 B5 B6 B7 B8 B9 B10
SERIAL
CLOCK
ANALOG INPUTS
BITS 1–12 (AD578)
10V IN
BITS 1–10 (AD579)
0V TO +10V
INTERNAL: CONNECT CLOCK OUT (18) TO CLOCK IN (19)
EXTERNAL: CONNECT EXTERNAL CLOCK TO CLOCK IN (19)
CLOCK SHOULD BE AT LEAST 30% DUTY CYCLE WITH
AD578/AD579
MINIMUM PERIOD,T
OF 100ns.
MIN
BIP OFF
Figure 2b. AD579 Timing Diagram
CLK OUT
CLK IN
REF IN
The temperature-compensated buried Zener reference provides the
primary voltage reference to the DAC and guarantees excellent
stability with both time and temperature. The reference is
trimmed to 10 V 1.0%; it is buffered and can supply up to
1 mA to an external load in addition to the current required to
drive the reference input resistor (0.5 mA) and bipolar offset
resistor (1 mA). The thin-film application resistors are trimmed
to match the full-scale output current of the DAC. Two 5 kΩ
input scaling resistors allow either a 10 V or a 20 V span. The
10 kΩ bipolar offset resistor is grounded for unipolar operation
or connected to the 10 V reference for bipolar operation.
R2
100⍀
REF OUT
+
6.8F
DIG GND
ANA GND
Figure 3. Unipolar Input Connections
Table I. AD578 Digital Output Codes vs. Analog Input for Unipolar and Bipolar Ranges
Digital Output Code
Analog Input—Volts
(Center of Quantization Interval)
(Binary for Unipolar Ranges;
Offset Binary for Bipolar Ranges)
0 V to +10 V
Range
0 V to +20 V
Range
–5 V to +5 V
Range
–10 V to +10 V
Range
B1
(MSB)
B12
(LSB)
+9.9976
+19.9951
+4.9976
+9.9951
1 1 1 1 1 1 1 1 1 1 1 1
+9.9952
+19.9902
+4.9952
+9.9902
1 1 1 1 1 1 1 1 1 1 1 0
•
•
•
•
•
•
•
•
•
•
+5.0024
+5.0000
•
+10.0049
+10.0000
•
+0.0024
+0.0000
•
+0.0049
+0.0000
•
1 0 0 0 0 0 0 0 0 0 0 1
1 0 0 0 0 0 0 0 0 0 0 0
•
•
•
•
•
•
+0.0024
+0.0000
+0.0051
+0.0000
–4.9976
–5.0000
–9.9951
–10.0000
0 0 0 0 0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 0 0 0 0 0
REV. C
–7–
ADI [ ADI ]
