ADS-950MC ETC, ADS-950MC Datasheet - Page 4

• Manufacturer Part Number: ADS-950MC
• Description: 18-Bit/ 500kHz/ Low-Power Sampling A/D Converters
• Manufacturer: ETC

ADS-950
CALIBRATION PROCEDURE
Connect the converter per Table 1 for the appropriate input
voltage range. 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-950'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 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-950, offset adjusting is normally accomplished
when the analog input is 0 minus ½LSB (–19µV). See Table 2
for the proper bipolar output coding.
Gain adjusting is accomplished when the analog input is at
nominal full scale minus 1½LSB's (–4.999943V).
+FS –1 LSB
–FS +1 LSB
INPUT VOLTAGE
BIPLOAR
+3/4 FS
+1/2 FS
–1/2 FS
–3/4 FS
SCALE
–FS
RANGE
0
±5V
Table 1. Input Connections
INPUT VOLTAGE
Table 2. Output Coding
+4.999962
+3.750000
+2.500000
+0.000000
–4.999962
–2.500000
–3.750000
–5.000000
COMPLEMENTARY
OFFSET BINARY
ZERO ADJUST
±5V
(–½ LSB)
–19µV
4
Zero/Offset Adjust Procedure
1. Apply a train of pulses to the START CONVERT input
2. For bipolar zero/offset adjust, apply –19µV to the ANALOG
3. Adjust the offset potentiometer until the output code flickers
Gain Adjust Procedure
1. Apply –4.999943V to the ANALOG INPUT (pin 4).
2. Adjust the gain potentiometer until all output bits are 1's
3. To confirm proper operation of the device, vary the applied
(pin 16) so that the converter is continuously converting.
INPUT (pin 4).
equally between 01 1111 1111 1111 1111 and 10 0000
0000 0000 0000.
and the LSB flickers between 1 and 0.
input voltage to obtain the output coding listed in Table 2.
00 0000 0000 0000 0000
00 0111 1111 1111 1111
00 1111 1111 1111 1111
01 1111 1111 1111 1111
10 1111 1111 1111 1111
11 0111 1111 1111 1111
11 1111 1111 1111 1110
11 1111 1111 1111 1111
MSB
OUTPUT CODING
(–FS +1½ LSB)
GAIN ADJUST
–4.999943
LSB
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