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ADS-917

14-Bit, 1MHz, Low-Power Sampling A/D Converters

DATEL Data Acquisition products  

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-917'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-917, 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 +½ LSB (+305μV).

+15V

ZERO/

OFFSET

ADJUST

20kΩ

–15V

GAIN

ADJUST

SIGNAL

INPUT

50Ω

200kΩ

1.98kΩ

2kΩ

+15V

–15V

Figure 2. ADS-917 Calibration Circuit

To Pin 20

of ADS-917

ADS-917

14-Bit, 1MHz, Low-Power Sampling A/D Converters

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).

Zero/Offset Adjust Procedure

1. Apply a train of pulses to the START CONVERT input (pin 16) so the con-

verter 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.

Table 1. Zero and Gain Adjust

INPUT VOLT-

AGE RANGE

0 to +10V

ZERO ADJUST

+½ LSB

+305μV

GAIN ADJUST

+FS –1½ LSB

+9.999085V

Table 2. Output Coding

INPUT VOLTAGE

(0 TO +10V)

+9.999390

+7.500000

+5.000000

+2.500000

+0.000610

0.000000

UNIPOLAR SCALE

+FS –1LSB

+3/4 FS

+1/2 FS

+1/4 FS

+1LSB

0

DIGITAL OUTPUT

OFFSET BINARY

MSB

LSB

11 1111 1111 1111

11 0000 0000 0000

10 0000 0000 0000

01 0000 0000 0000

00 0000 0000 0001

00 0000 0000 0000

Coding is straight binary; 1LSB = 610μV.

+5V

–12V/–15V

+12V/+15V

+

4.7μF

0.1μF

4.7μF

+

4.7μF

+

0.1μF

0.1μF

0 to +10V

0.1μF

+

4.7μF

13

14

DIGITAL

GROUND

ADS-917

24

19, 23

ANALOG

GROUND

22

20

ANALOG

INPUT

21 +10V REF. OUT

START

CONVERT

16

18 BIT 1 (MSB)

17 BIT 2

12 BIT 3

11 BIT 4

10 BIT 5

9 BIT 6

8 BIT 7

7 BIT 8

6 BIT 9

5 BIT 10

4 BIT 11

3 BIT 12

2 BIT 13

1 BIT 14 (LSB)

15 EOC

Figure 3. Typical ADS-917 Connection Diagram

DATEL, Inc. 11 Cabot Boulevard, Mansfield, MA 02048-1151 USA • Tel: (508) 339-3000 • www.datel.com • e-mail: help@datel.com

MDA_ADS-917.C02 Page 4 of 9

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