Rainbow Electronics MX7576 - Manual (Page 10)

MX7575/MX7576
______________ Typical Applications
Unipolar Operation
Figure 16a shows the analog circuit connections for
unipolar operation, and Figure 16b shows the nominal
transfer characteristic for unipolar operation. Since the
offset and full-scale errors of the MX7575/MX7576 are
very small, it is not necessary to null these errors in
most cases. If calibration is required, follow the steps in
the sections below.
Offset Adjust
The offset error can be adjusted by using the offset trim
capability of an op amp (when it is used as a voltage fol-
lower) to drive the analog input, AIN. The op amp should
have a common-mode input range that includes 0V. Set
its initial input to 4.8mV (1/2LSB), while varying its offset
until the ADC output code flickers between 0000 0000
and 0000 0001.
Full-Scale Adjustment
Make the full-scale adjustment by forcing the analog
input, AIN, to 2.445V (FS - 3/2LSB). Then vary the refer-
ence input voltage until the ADC output code flickers
between 1111 1110 and 1111 1111.
Bipolar Operation
Figure 18a shows an example of the circuit connection
for bipolar operation, and Figure 18b shows the nominal
transfer characteristic for bipolar operation. The output
code provided by the MX7575 is offset binary. The ana-
log input range for this circuit is ±2.46V (1LSB =
19.22mV), even though the voltage appearing at AIN is
in the 0V to 2.46V range. In most cases, the MX7575 is
accurate enough that calibration will not be necessary. If
calibration is not needed, resistors R1–R7 should have a
0.1% tolerance, with R4 and R5 replaced by one 10k
Ω
resistor, and R2 and R3 with one 1k
Ω
resistor. If calibra-
tion is required, follow the steps in the sections below.
Offset Adjust
Adjust the offset error by applying an analog input volt-
age of 2.43V (+FS - 3/2LSB). Then adjust resistor R5
until the output code flickers between 1111 1110 and
1111 1111.
Full-Scale Adjust
Null the full-scale error by applying an analog input
voltage of -2.45V (-FS + 1/2LSB). Then adjust resistor
R3 until the output code flickers between 0000 0000
and 0000 0001.
CMOS, µP-Compatible, 5µs/10µs, 8-Bit ADCs
10 ______________________________________________________________________________________
16
17
15
5
4
1
2
3
9
18
+5V
+5V
47 µ F
47 µ F
0.1 µ F
3.3k
+1.23V
0.1 µ F
+5V
2.46V(max)
+
-
D7–D0
DATA OUT
CONTROL INPUTS
C CLK
100pF, 1%
R CLK
100k, 2%
AIN
REF
AGND
CLK
BUSY
CS
RD
TP/
MODE
V DD
MX7575
MX7576
0000 0011
0000 0010
0000 0001
0000 0000
1111 1111
1111 1110
1111 1101
1LSB
2LSBs
3LSBs 0
AIN, INPUT VOLTAGE (IN TERMS OF LSBs)
FS - 1LSB
FULL-SCALE
TRANSITION
(FS - 3/2LSB)
OUTPUT
CODE
FS = 2V REF
1LSB = –––
2FS
256
11
12
13
14
7
-55 -25 25 75
8
10
AMBIENT TEMPERATURE (°C)
CONVERSION TIME (
µ s)
0 125 100 50
9
MX7576
MX7575
R CLK = 100k Ω
C CLK = 100pF
Figure 16a. Unipolar Configuration Figure 16b. Nominal Transfer Characteristic for Unipolar
Operation
Figure 17. Typical Conversion Times vs. Temperature Using
Internal Clock