®
®
ADS-119
CALIBRATION PROCEDURE
(Refer to Figures 3 and 4, Table 1)
Any offset and/or gain calibration procedures should not be
implemented until devices are fully warmed up. To avoid
interaction, offset must be adjusted before gain. The ranges of
adjustment for the circuits in Figure 3 and 4 are guaranteed to
compensate for the ADS-119'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 can be accomplished by connecting LED's
to the digital outputs and adjusting 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.
Offset adjusting for the ADS-119 is normally accomplished at
the point where the MSB is a 1 and all other output bits are 0's
and the LSB just changes from a 0 to a 1. This digital output
transition ideally occurs when the applied analog input is
+�½ LSB (+366µV).
Gain adjusting is accomplished when all bits are 1's and the
LSB just changes from a 1 to a 0. This transition ideally occurs
when the analog input is at +full scale minus 1 �½ LSB's
(+1.4989V).
Zero/Offset Adjust Procedure
1. Apply a train of pulses to the START CONVERT input
(pin 16) so the converter is continuously converting.
2. Apply +366µV to the ANALOG INPUT (pin 19).
3. Adjust the offset potentiometer until the output bits are
1000 0000 0000 and the LSB flickers between 0 and 1.
–15V
SIGNAL
INPUT
50
Ω
Gain Adjust Procedure
1. Apply +1.4989V to the ANALOG INPUT (pin 19).
2. Adjust the gain potentiometer until all output bits are 1's and
the LSB flickers between 1 and 0.
3. To confirm proper operation of the device, vary the input
signal to obtain the output coding listed in Table 1.
Table 1. Output Coding for Bipolar Operation
BIPOLAR
SCALE
+FS–1 LSB
+3/4 FS
+1/2 FS
0
–1/2 FS
–3/4 FS
–FS +1 LSB
–FS
ADS-119
INPUT VOLTAGE
(±1.5V RANGE)
+1.49927V
+1.12500V
+0.75000V
0.00000V
–0.75000V
–1.12500V
–1.49927V
–1.50000V
OUTPUT CODING
OFFSET BINARY
MSB
LSB
1111 1111
1110 0000
1100 0000
1000 0000
0100 0000
0010 0000
0000 0000
0000 0000
2k
Ω
1111
0000
0000
0000
0000
0000
0001
0000
GAIN
ADJUST
+15V
1.98k
Ω
To Pin 19
of ADS-119
Figure 3. Optional Calibration Circuit, ADS-119
+5V
4.7µF
0.1µF
13, 20
12 BIT 1 (MSB)
11 BIT 2
10 BIT 3
9 BIT 4
8 BIT 5
7 BIT 6
14
–5V
4.7µF
+
0.1µF
20
ADS-119
18, 20
+5V
6 BIT 7
5 BIT 8
4 BIT 9
3 BIT 10
2 BIT 11
1 BIT 12 (LSB)
15 DATA VALID
OFFSET
ADJUST
17
20kΩ
–5V
19 ANALOG INPUT
16 START CONVERT
A single +5V supply should be used for both the +5V analog and +5V digital.
If separate supplies are used, the difference between the two cannot exceed 100mV.
Figure 4. Typical Connection Diagram
4
MURATA-PS [ MURATA POWER SOLUTIONS INC. ]
