ADS-916MM Murata Power Solutions Inc, ADS-916MM Datasheet - Page 4

• Manufacturer Part Number: ADS-916MM
• Description: Analog To Digital Converter
• Manufacturer: Murata Power Solutions Inc

ADS-926
CALIBRATION PROCEDURE
(Refer to Figures 2 and 3)
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 circuit of Figure 2 are guaranteed to
compensate for the ADS-926's initial accuracy errors and may
not be able to compensate for additional system errors.
All fixed resistors in Figure 2 should be metal-film types, and
multiturn potentiometers should have TCR’s of 100ppm/°C or
less to minimize drift with temperature.
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.
For the ADS-926, offset adjusting 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 (+305µV).
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 1½ LSB's
(+4.999085V).
OFFSET
ADJUST
ZERO/
SIGNAL
INPUT
–15V
+15V
20k
Figure 2. ADS-926 Calibration Circuit
ADJUST
GAIN
50
–12V/–15V
+12V/+15V
1.98k
1.2M
+5V
4.7µF
4.7µF
0.1µF
4.7µF
+15V
–15V
2k
–5V to +5V
+
+
+
Figure 3. Typical ADS-926 Connection Diagram
4.7µF
0.1µF
0.1µF
0.1µF
+
To Pin 20
of ADS-926
13
14
24
19, 23
22
20
21 +10V REF. OUT
DIGITAL
GROUND
ANALOG
INPUT
ANALOG
GROUND
4
ADS-926
Zero/Offset Adjust Procedure
1. Apply a train of pulses to the START CONVERT input
2. Apply +305µV to the ANALOG INPUT (pin 20).
3. Adjust the offset potentiometer until the output bits are
Gain Adjust Procedure
1. Apply +4.999085V to the ANALOG INPUT (pin 20).
2. Adjust the gain potentiometer until the output bits are all 1's
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
Coding is offset binary; 1LSB = 610µV.
INPUT VOLTAGE
OUTPUT CODING
MSB
(pin 16) so the converter is continuously converting. If using
LED's on the outputs, a 200kHz conversion rate will reduce
flicker.
a 1 and all 0's and the LSB flickers between 0 and 1.
and the LSB flickers between 1 and 0.
RANGE
±5V
CONVERT
START
LSB
Table 1. Zero and Gain Adjust
16
Table 2. Output Coding
ZERO ADJUST
INPUT RANGE
18
17
12
11
10
15
9
8
7
6
5
4
3
2
1
+4.99939
+3.75000
+2.50000
–2.50000
–3.75000
–4.99939
–5.00000
+½ LSB
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
+305µV
0.00000
±5V
®
GAIN ADJUST
+FS –1½ LSB
+FS –1 LSB
+3/4 FS
+1/2FS
0
–1/2FS
–3/4FS
–FS +1 LSB
–FS
+4.999085V
BIPOLAR
SCALE
®