®
®
ADS-946
CALIBRATION PROCEDURE
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 Figures 2 and 3 are guaranteed
to compensate for the ADS-946'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-946 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 (+122µV).
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
(+1.99963V).
Zero/Offset Adjust Procedure
1. Apply a train of pulses to the START CONVERT input
(pin 18) so the converter is continuously converting.
2. Apply +122µV to the ANALOG INPUT (pin 21).
3. Adjust the offset potentiometer until the output bits are
10 0000 0000 0000 and the LSB flickers between 0 and 1.
Gain Adjust Procedure
1. Apply +1.99963V to the ANALOG INPUT (pin 21).
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 2.
Table 1. Gain and Zero Adjust
INPUT VOLTAGE
RANGE
±2V
ZERO ADJUST
+�½ LSB
+122µV
GAIN ADJUST
+FS –1�½ LSB
+1.99963V
Table 2. 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
INPUT VOLTAGE
(±2V RANGE)
+1.99976
+1.50000
+1.00000
0.00000
–1.00000
–1.50000
–1.99976
–2.00000
OFFSET BINARY
MSB
LSB
11 1111 1111 1111
11 1000 0000 0000
11 0000 0000 0000
10 0000 0000 0000
01 0000 0000 0000
00 1000 0000 0000
00 0000 0000 0001
00 0000 0000 0000
–5V
+5V
4.7µF
+
4.7µF 4.7µF
+ +
0.1µF
0.1µF 0.1µF
19
ANALOG
INPUT
+5V
ZERO/
OFFSET
ADJUST
–5V
START
CONVERT
18
20
24
22, 13
14
21
23
20k
Ω
ADS-946
1
2
3
4
5
6
7
8
9
10
11
12
15
16
17
BIT 1 (MSB)
BIT 2
BIT 3
BIT 4
BIT 5
BIT 6
BIT 7
BIT 8
BIT 9
BIT 10
BIT 11
BIT 12
BIT 13
BIT 14 (LSB)
EOC
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 3. Typical ADS-946 Connection Diagram
4
MURATA-PS [ MURATA POWER SOLUTIONS INC. ]
