ADS-CCD1201

®

®

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-CCD1201’s initial accuracy errors and

may not be able to compensate for additional system errors.

Figure 2. ADS-CCD1201 Calibration Circuit

All fixed resistors in Figure 2 should be metal-film types, and

multi-turn potentiometers should have TCR’s of 100ppm/°C or

less to minimize drift with temperature. In many applications,

the CCD will require an offset-adjust (black balance) circuit

near its output and also a gain stage, presumably with adjust

capabilities, to match the output voltage of the CCD to the

input range of the AID. If one is performing a "system I/O

calibration" (from light in to digital out), these circuits can be

used to compensate for the relatively small initial offset and

gain errors of the A/D. This would eliminate the need for the

circuit shown in Figure 2.

Figure 3. Typical ADS-CCD1201 Connection Diagram

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-CCD1201, offset adjusting is normally

accomplished at the point where all 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 +1/2LSB

(+1.2207mV).

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 1/2 LSB’s

(+9.99634V).

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 +1.2207mV to the ANALOG INPUT (pin 20).

3. Adjust the offset potentiometer until the output bits are

0000 0000 00000 and the LSB flickers between 0 and 1.

Gain Adjust Procedure

1. Apply +9.99634V to the ANALOG INPUT (pin 20).

2. Adjust the gain potentiometer until all output bits are 1’s and

the LSB flickers between 1 and 0.

Table 2. ADS-CCD1201 Output Coding

Input Voltage

Unipolar

Digital Output

(0 to +10V)

Scale

MSB LSB

+9.9976

+FS – 1LSB

1111 1111 1111

+7.5000

+3/4 FS

1100 0000 0000

+5.0000

+1/2 FS

1000 0000 0000

+2.5000

+1/4 FS

0100 0000 0000

+0.0024

+1LSB

0000 0000 0001

0

0

0000 0000 0000

Coding is straight binary; 1LSB = 2.44mV

All DATEL sampling A/D converters are fully characterized and

specified over operating temperature (case) ranges of 0 to

production testing is performed without the use of heat sinks or

forced-air cooling. Thermal impedance figures for each device

are listed in their respective specification tables.

These devices do not normally require heat sinks, however,

standard precautionary design and layout procedures should

be used to ensure devices do not overheat. The ground and

power planes beneath the package, as well as all pcb signal

runs to and from the device, should be as heavy as possible to

help conduct heat away from the package. Electrically-

insulating, thermally-conductive "pads" may be installed

underneath the package. Devices should be soldered to boards

rather than "socketed," and of course, minimal air flow over the

surface can greatly help reduce the package temperature.

In more severe ambient conditions, the package/junction

temperature of a given device can be reduced dramatically

(typically 35%) by using one of DATEL’s HS Series heat sinks.

See Ordering Information for the assigned part number. See

page 1-183 of the DATEL Data Acquisition Components

Catalog for more information on the HS Series. Request DATEL

Application Note AN-8, "Heat Sinks for DIP Data Converters,"or

contact DATEL directly, for additional information.

THERMAL REQUIREMENTS

4.

To Pin 20 of

ADS-CCD1201

–15V

SIGNAL

INPUT

GAIN

ADJUST

1.98k

50

+15V

2k

200k

20k

–15V

+15V

ZERO/

OFFSET

ADJUST

Ω

Ω

Ω

Ω

Ω

13

ADS-CCD1201

14

20

15

12

11

10

9

8

7

6

5

4

3

2

1

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)

EOC

ANALOG

INPUT

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

0 to +10V

NO CONNECT

17, 18