ADS-919MC Murata Power Solutions Inc, ADS-919MC Datasheet - Page 4

• Manufacturer Part Number: ADS-919MC
• Description: Analog To Digital Converter
• Manufacturer: Murata Power Solutions Inc

ADS-919
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-919'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-919, offset adjusting is normally accomplished at
the point where the 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
(+9.999085V).
OFFSET
ADJUST
ZERO/
SIGNAL
INPUT
–15V
+15V
20k
Figure 2. ADS-919 Calibration Circuit
ADJUST
GAIN
50
1.98k
200k
+15V
–15V
2k
Figure 3. Typical ADS-919 Connection Diagram
To Pin 20
of ADS-919
4
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 +9.999085V to the ANALOG INPUT (pin 20).
2. Adjust the gain potentiometer until the output bits are all 1's
INPUT VOLTAGE
Coding is straight binary; 1LSB = 610µV.
INPUT VOLTAGE
(pin 16) so the converter is continuously converting. If
using LED's on the outputs, a 200kHz conversion rate will
reduce flicker.
all 0's and the LSB flickers between 0 and 1.
and the LSB flickers between 1 and 0.
(0 TO +10V)
+9.999390
+7.500000
+5.000000
+2.500000
+0.000610
0 to +10V
RANGE
0.000000
Table 1. Zero and Gain Adjust
Table 2. Output Coding
ZERO ADJUST
+FS – 1LSB
UNIPOLAR
+3/4FS
+1/2FS
+1/4FS
+1LSB
SCALE
+½ LSB
+305µV
0
®
MSB
11 1111 1111 1111
11 0000 0000 0000
10 0000 0000 0000
01 0000 0000 0000
00 0000 0000 0001
00 0000 0000 0000
DIGITAL OUTPUT
GAIN ADJUST
+FS –1½ LSB
+9.999085V
LSB
®