®

®

ADS-916

4

Zero/Offset Adjust Procedure

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

(pin 16) so the converter is continuously converting. If using

LED's on the outputs, a 200kHz conversion rate will reduce

flicker.

2. Apply +305µV to the ANALOG INPUT (pin 20).

3. Adjust the offset potentiometer until the output bits are

all 0's and the LSB flickers between 0 and 1.

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

and the LSB flickers between 1 and 0.

INPUT VOLTAGE

ZERO ADJUST

GAIN ADJUST

RANGE

+½ LSB

+FS –1½ LSB

0 to +10V

+305µV

+9.999085V

Table 1. Zero and Gain Adjust

INPUT VOLTAGE

UNIPOLAR

DIGITAL OUTPUT

(0 to +10V)

SCALE

MSB

LSB

+9.999390

+FS –1LSB

11 1111 1111 1111

+7.500000

+3/4 FS

11 0000 0000 0000

+5.000000

+1/2 FS

10 0000 0000 0000

+2.500000

+1/4 FS

01 0000 0000 0000

+0.000610

+1LSB

00 0000 0000 0001

0.000000

0

00 0000 0000 0000

Table 2. Output Coding

Figure 3. Typical ADS-916 Connection Diagram

Coding is straight binary; 1LSB = 610µV.

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-916'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-916, 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 +½LSB (+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).

Figure 2. ADS-916 Calibration Circuit

13

ADS-916

14

20

16

18

17

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

BIT 13

BIT 14 (LSB)

EOC

ANALOG

INPUT

START

CONVERT

19, 23

22

24

0.1µF

4.7µF

+5V

0.1µF

4.7µF

0.1µF

4.7µF

+

+

–12V/–15V

+12V/+15V

+

0.1µF

+

4.7µF

21 +10V REF. OUT

DIGITAL

GROUND

0 to +10V

ANALOG

GROUND

To Pin 20

of ADS-916

–15V

SIGNAL

INPUT

GAIN

ADJUST

1.98k

Ω

50

Ω

+15V

2k

Ω

200k

Ω

20k

Ω

–15V

+15V

ZERO/

OFFSET

ADJUST