MX7575 MAXIM [Maxim Integrated Products], MX7575 Datasheet - Page 10

• Manufacturer Part Number: MX7575
• Description: CMOS, uP-Compatible, 5?s/10?s, 8-Bit ADCs
• Manufacturer: MAXIM [Maxim Integrated Products]

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.
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.
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.
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
CMOS, µP-Compatible, 5µs/10µs, 8-Bit ADCs
Figure 16a. Unipolar Configuration
10
______________ Typical Applications
______________________________________________________________________________________
+
-
+5V
+5V
47 F
47 F
3.3k
2.46V(max)
+1.23V
0.1 F
0.1 F
16
17
15
AIN
REF
AGND
MX7575
MX7576
18
V
9
DD
Unipolar Operation
MODE
BUSY
Full-Scale Adjustment
Bipolar Operation
CLK
TP/
CS
RD
5
4
1
2
3
+5V
D7–D0
DATA OUT
CONTROL INPUTS
Offset Adjust
R
100k, 2%
C
100pF, 1%
CLK
CLK
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 10kΩ
resistor, and R2 and R3 with one 1kΩ resistor. If calibra-
tion is required, follow the steps in the sections below.
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.
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.
Operation
Figure 17. Typical Conversion Times vs. Temperature Using
Internal Clock
Figure 16b. Nominal Transfer Characteristic for Unipolar
1111 1111
1111 1110
1111 1101
0000 0011
0000 0010
0000 0001
0000 0000
14
13
12
11
10
9
8
7
OUTPUT
CODE
-55
0
AIN, INPUT VOLTAGE (IN TERMS OF LSBs)
1LSB
-25
2LSBs
AMBIENT TEMPERATURE (°C)
MX7576
3LSBs
0
(FS - 3/2LSB)
FULL-SCALE
TRANSITION
25
50
MX7575
R
C
FS = 2V
1LSB = –––
FS - 1LSB
75
CLK
CLK
= 100k
= 100pF
Full-Scale Adjust
100
REF
2FS
256
Offset Adjust
125