®
®
ADS-933
CALIBRATION PROCEDURE
Connect the converter per Figure 2. Any offset/gain
calibration procedures should not be implemented until the
device is fully warmed up. To avoid interaction, adjust offset
before gain. The ranges of adjustment for the circuits in
Figure 2 are guaranteed to compensate for the ADS-933’s
initial accuracy errors and may not be able to compensate for
additional system errors.
A/D converters are calibrated by positioning their digital
outputs exactly on the transition point between two adjacent
digital output codes. This is accomplished by connecting
20k
Ω
+5V
–5V
+5V
20k
Ω
–5V
LED's to the digital outputs and performing adjustments until
certain LED's "flicker" equally between on and off. Other
approaches employ digital comparators or microcontrollers to
detect when the outputs change from one code to the next.
For the ADS-933, offset adjusting is normally accomplished
when the analog input is 0 minus �½ LSB (–42µV). See Table
2b for the proper bipolar output coding.
Gain adjusting is accomplished when the analog input is at
nominal full scale minus 1�½ LSB's (+2.749874V).
Note: Connect pin 5 to ANALOG GROUND (pin 4) for
operation without zero/offset adjustment. Connect pin 6 to
pin 4 for operation without gain adjustment.
6
GAIN
ADJUST
+5V
4.7µF
0.1µF
31
+5V
DIGITAL
5
OFFSET
ADJUST
DIGITAL
7, 30 GROUND
+
+5V
4.7µF
38
0.1µF
+5V ANALOG
+
ANALOG
2, 4, 36 GROUND
37
–5V
–5V
4.7µF
0.1µF
ADS-933
34
8
10
11
1
0.1µF
4.7µF
ENABLE
FIFO/DIR
FSTAT1
ANALOG INPUT
FSTAT2
FIFO READ
+3.2V
REF. OUT
START CONVERT 12
COMP. BITS 35
9
3
33
32
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
OVERFLOW
EOC
BIT 1 (MSB)
BIT 1 (MSB)
BIT2
BIT 3
BIT 4
BIT 5
BIT 6
BIT 7
BIT 8
BIT 9
BIT 10
BIT 11
BIT 12
BIT 13
BIT 14
BIT 15
BIT 16 (LSB)
Zero/Offset Adjust Procedure
1. Apply a train of pulses to the START CONVERT input (pin
12) so that the converter is continuously converting.
2. For zero/offset adjust, apply –42µV to the ANALOG INPUT
(pin 3).
3. Adjust the offset potentiometer until the code flickers
between 1000 0000 0000 0000 and 0111 1111 1111 1111
with pin 35 tied high (complementary offset binary) or
between 0111 1111 1111 1111 and 1000 0000 0000 0000
with pin 35 tied low (offset binary).
4. Two's complement coding requires using BIT 1 (MSB) (pin
29). With pin 35 tied low, adjust the trimpot until the output
code flickers between all 0’s and all 1’s.
+5V
Gain Adjust Procedure
1. For gain adjust, apply +2.749874V to the ANALOG INPUT
(pin 3).
2. Adjust the gain potentiometer until all output bits are 0’s and
the LSB flickers between a 1 and 0 with pin 35 tied high
(complementary offset binary) or until all output bits are 1’s
and the LSB flickers between a 1 and 0 with pin 35 tied low
(offset binary).
3. Two's complement coding requires using BIT 1 (MSB)
(pin 29). With pin 35 tied low, adjust the gain trimpot until
the output code flickers equally between 0111 1111 1111
1111 and 0111 1111 1111 1110.
4. To confirm proper operation of the device, vary the applied
input voltage to obtain the output coding listed in Table 2b.
Table 2b. Output Coding
Figure 2. Connection Diagram
Table 2a. Setting Output Coding Selection (Pin 35)
OUTPUT FORMAT
Complementary Offset Binary
Offset Binary
PIN 35 LOGIC LEVEL
1
0
1
0
Complementary Two’s Complement
(Using MSB, pin 29)
Two’s Complement
(Using MSB, pin 29)
OUTPUT CODING
MSB
1111 1111 1111
LSB "1" to "0"
1110 0000 0000
1100 0000 0000
1000 0000 0000
0111 1111 1111
0100 0000 0000
0010 0000 0000
0000 0000 0000
LSB "0" to "1"
0000 0000 0000
LSB
1111
0000
0000
0000
1111
0000
0000
0001
0000
MSB
LSB
MSB
LSB
MSB
LSB
INPUT
RANGE
±2.75V
+2.749916
+2.749874
+2.062500
+1.375000
0.000000
–0.000084
–1.375000
–2.062500
–2.749916
–2.749958
–2.750000
BIPOLAR
SCALE
+FS –1 LSB
+FS –1 1/2 LSB
+3/4 FS
+1/2 FS
0
–1 LSB
–1/2 FS
–3/4 FS
–FS +1 LSB
–FS + 1/2 LSB
–FS
0000 0000 0000 0000
LSB "0" to "1"
0001 1111 1111 1111
0011 1111 1111 1111
0111 1111 1111 1111
1000 000 000 0000
1011 1111 1111 1111
1101 1111 1111 1111
1111 1111 1111 1110
LSB "1" to "0"
1111 1111 1111 1111
COMP. OFF. BIN.
0111 1111 1111 1111
LSB "1" to "0"
0110 0000 0000 0000
0100 0000 0000 0000
0000 0000 0000 0000
1111 1111 1111 1111
1100 0000 0000 0000
1010 0000 0000 0000
1000 0000 0000 0001
LSB "0" to "1"
1000 0000 0000 0000
TWO'S COMP.
1000 0000 0000 0000
LSB "0" to "1"
1001 1111 1111 1111
1011 1111 1111 1111
1111 1111 1111 1111
0000 0000 0000 0000
0011 1111 1111 1111
0101 1111 1111 1111
0111 1111 1111 1110
LSB "1" to "0"
0111 1111 1111 1111
COMP. TWO'S COMP.
OFFSET BINARY
5
MURATA-PS [ MURATA POWER SOLUTIONS INC. ]
