®
®
ADS-951
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-951'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-951, 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 1�½LSB's (–4.999943V).
Zero/Offset Adjust Procedure
1. Apply a train of pulses to the START CONVERT input
(pin 16) so that the converter is continuously converting.
2. For bipolar zero/offset adjust, apply –19µV to the ANALOG
INPUT (pin 4).
3. Adjust the offset potentiometer until the output code flickers
equally between 01 1111 1111 1111 1111 and 10 0000
0000 0000 0000.
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
and the LSB flickers between 1 and 0.
3. To confirm proper operation of the device, vary the applied
input voltage to obtain the output coding listed in Table 2.
Table 1. Input Connections
INPUT VOLTAGE
RANGE
±5V
ZERO ADJUST
(–�½ LSB)
–19µV
GAIN ADJUST
(–FS +1�½ LSB)
–4.999943
Table 2. Output Coding
COMPLEMENTARY
OFFSET BINARY
BIPLOAR
SCALE
+FS –1 LSB
+3/4 FS
+1/2 FS
0
–1/2 FS
–3/4 FS
–FS +1 LSB
–FS
INPUT VOLTAGE
±5V
+4.999962
+3.750000
+2.500000
+0.000000
–2.500000
–3.750000
–4.999962
–5.000000
OUTPUT CODING
MSB
00
00
00
01
10
11
11
11
LSB
0000 0000 0000 0000
0111 1111 1111 1111
1111 1111 1111 1111
1111 1111 1111 1111
1111 1111 1111 1111
0111 1111 1111 1111
1111 1111 1111 1110
1111 1111 1111 1111
4
MURATA-PS [ MURATA POWER SOLUTIONS INC. ]
