ADS950 datasheet(4/6 Pages) ETC

4 / 6 page

ADS-950

®®

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.

BIPLOAR

INPUT VOLTAGE

SCALE

±5V

MSB

LSB

+FS –1 LSB

+4.999962

00 0000 0000 0000 0000

+3/4 FS

+3.750000

00 0111 1111 1111 1111

+1/2 FS

+2.500000

00 1111 1111 1111 1111

+0.000000

01 1111 1111 1111 1111

–1/2 FS

–2.500000

10 1111 1111 1111 1111

–3/4 FS

–3.750000

11 0111 1111 1111 1111

–FS +1 LSB

–4.999962

11 1111 1111 1111 1110

–FS

–5.000000

11 1111 1111 1111 1111

OUTPUT CODING

COMPLEMENTARY

OFFSET BINARY

Table 2. Output Coding

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).

INPUT VOLTAGE

ZERO ADJUST

GAIN ADJUST

RANGE

(–½ LSB)

(–FS +1½ LSB)

±5V

–19µV

–4.999943

Table 1. Input Connections

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