®

®

ADS-119

4

Figure 4. Typical Connection Diagram

CALIBRATION PROCEDURE

(Refer to Figures 3 and 4, Table 1)

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 circuits in Figure 3 and 4 are guaranteed to

compensate for the ADS-119'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 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.

Offset adjusting for the ADS-119 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 (+366µV).

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 1 ½ LSB's

(+1.4989V).

Zero/Offset Adjust Procedure

1. Apply a train of pulses to the START CONVERT input

(pin 16) so the converter is continuously converting.

2. Apply +366µV to the ANALOG INPUT (pin 19).

3. Adjust the offset potentiometer until the output bits are

1000 0000 0000 and the LSB flickers between 0 and 1.

Gain Adjust Procedure

1. Apply +1.4989V to the ANALOG INPUT (pin 19).

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 input

signal to obtain the output coding listed in Table 1.

+FS–1 LSB

+1.49927V

1111 1111 1111

+3/4 FS

+1.12500V

1110 0000 0000

+1/2 FS

+0.75000V

1100 0000 0000

0

0.00000V

1000 0000 0000

–1/2 FS

–0.75000V

0100 0000 0000

–3/4 FS

–1.12500V

0010 0000 0000

–FS +1 LSB

–1.49927V

0000 0000 0001

–FS

–1.50000V

0000 0000 0000

BIPOLAR

ADS-119

OUTPUT CODING

SCALE

INPUT VOLTAGE

OFFSET BINARY

(±1.5V RANGE)

MSB

LSB

Table 1. Output Coding for Bipolar Operation

To Pin 19

of ADS-119

–15V

SIGNAL

INPUT

GAIN

ADJUST

1.98k

Ω

50

Ω

+15V

2k

Ω

Figure 3. Optional Calibration Circuit, ADS-119

0.1µF

0.1µF

4.7µF

4.7µF

13, 20

20

18, 20

ADS-119

–5V

20k

Ω

+5V

14

–5V

+5V

19

17

16

12

11

10

9

8

7

6

5

4

3

2

1

15

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 (LSB)

DATA VALID

ANALOG INPUT

START CONVERT

A single +5V supply should be used for both the +5V analog and +5V digital.

If separate supplies are used, the difference between the two cannot exceed 100mV.

Œ

Œ

OFFSET

ADJUST