+VCC
Unipolar
Offset
Adjust
Full-Scale
Adjust
Full-Scale Adjust
R1
100kΩ
10 Ref In
R2
100Ω
100Ω
R2
10 Ref In
ADC574A
8
Ref Out
ADC574A
100kΩ
–VCC
8
Ref Out
100Ω
R1
Bipolar
Offset
Adjust
12 Bipolar Offset
100Ω
12 Bipolar Offset
13
14
9
Analog
Input
10V
Range
10V
Range
Comparator
13
14
9
Analog
Input
20V
Range
Comparator
20V
Range
Analog
Common
Analog
Common
FIGURE 3. Bipolar Configuration.
FIGURE 2. Unipolar Configuration.
for the 20V range) that causes the output code to be DB0 ON
(high). Adjust potentiometer R1 until DB0 is alternately
toggling ON and OFF with all other bits OFF. Then adjust
full scale by applying an input voltage of nominal full-scale
value minus 3/2LSB, the value which should cause all bits
to be ON. This value is +9.9963V for the 10V range and
+19.9927V for the 20V range. Adjust potentiometer R2 until
bits DB1-DB11 are ON and DB0 is toggling ON and OFF.
DB0 to toggle ON and OFF with all other bits OFF. To
adjust full-scale, apply a DC input signal which is 3/2LSB
below the nominal plus full-scale value (+4.9963V for ±5V
range, +9.9927V for ±10V range) and adjust R2 for DB0 to
toggle ON and OFF with all other bits ON.
CONTROLLING THE ADC574A
The Burr-Brown ADC574A can be easily interfaced to most
microprocessor systems and other digital systems. The mi-
croprocessor may take full control of each conversion, or the
converter may operate in a stand-alone mode, controlled
only by the R/C input. Full control consists of selecting an
8- or 12-bit conversion cycle, initiating the conversion, and
reading the output data when ready—choosing either 12 bits
all at once, or 8 bits followed by 4 bits in a left-justified
format. The five control inputs (12/8, CS, AO, R/C, and CE)
are all TTL/CMOS-compatible. The functions of the control
inputs are described in Table II. The control function truth
table is listed in Table III.
CALIBRATION PROCEDURE—BIPOLAR RANGES
If external adjustments of full-scale and bipolar offset are
not required, the potentiometers may be replaced by 50Ω,
1% metal-film resistors.
If adjustments are required, connect the converter as shown
in Figure 3. The calibration procedure is similar to that
described above for unipolar operation, except that the offset
adjustment is performed with an input voltage which is
1/2LSB above the minus full-scale value (–4.9988V for the
±5V range, –9.9976V for the ±10V range). Adjust R1 for
PIN
DESIGNATION
DEFINITION
FUNCTION
CE (Pin 6)
Chip Enable
(active high)
Must be high (“1”) to either initiate a conversion or read output data. 0-1 edge may be used to initiate a conversion.
CS (Pin 3)
R/C(Pin 5)
Chip Select
(active low)
Must be low (“0”) to either initiate a conversion or read output data. 1-0 edge may be used to initiate a conversion.
Read/Convert
(“1” = read)
Must be low (“0”) to initiate either 8- or 12-bit conversions. 1-0 edge may be used to initiate a conversion.
Must be high (“1”) to read output data. 0-1 edge may be used to initiate a read operation.
(“0” = convert)
A
O (Pin 4)
Byte Address
Short Cycle
In the start-convert mode, AO selects 8-bit (AO = “1”) or 12-bit (AO = "0") conversion mode. When reading output data
in two 8-bit bytes, AO = “0” accesses 8 MSBs (high byte) and AO = “1” accesses 4 LSBs and trailing “0s” (low byte).
12/8 (Pin 2)
Data Mode Select
(“1” = 12 bits)
(“0” = 8 bits)
When reading output data, 12/8 = “1” enables all 12 output bits simultaneously. 12/8 = “0” will enable the MSBs
or LSBs as determined by the AO line.
TABLE II. ADC574A Control Line Functions.
®
ADC574A
7
BB [ BURR-BROWN CORPORATION ]
