AD1380

–6–

REV. B

Table II. Transition Values vs. Calibration Codes

Code Under Test

Low Side Transition Value

MSB

LSB

Range

10 V

5 V

2.5 V

0 V to +10 V

0 V to +5 V

000 . . . 000*

+ Full Scale

+10 V

+5 V

+2.5 V

+10 V

+5 V

–3/2 LSB

–3/2 LSB

–3/2 LSB

–3/2 LSB

–3/2 LSB

011 . . . 111

Mid Scale

0–1/2 LSB

0–1/2 LSB

0–1/2 LSB

+5 V–1/2 LSB

+2.5 V–1/2 LSB

111 . . . 110

–Full Scale

–10 V

–5 V

–2.5 V

0 V

0 V

+1/2 LSB

+1/2 LSB

+1/2 LSB

+1/2 LSB

+1/2 LSB

NOTE

For LSB value for range and resolution used, see Table III.

*Voltages given are the nominal value for transition to the code specified.

Table III. Input Voltage Range and LSB Values

Analog Input

Voltage Range

10 V

5 V

2.5 V

0 V to +10 V

0 V to +5 V

Code

COB*

COB*

COB*

Designation

or CTC**

or CTC**

or CTC**

CSB***

CSB***

One Least FSR

FSR

20 V

10 V

5 V

10 V

5 V

Significant

2

n

2

n

2

n

2

n

2

n

2

n

(Bit LSB)

n = 8

78.13 mV

39.06 mV

19.53 mV

39.06 mV

19.53 mV

n = 10

19.53 mV

9.77 mV

4.88 mV

9.77 mV

4.88 mV

n = 12

4.88 mV

2.44 mV

1.22 mV

2.44 mV

1.22 mV

n = 13

2.44 mV

1.22 mV

0.61 mV

1.22 mV

0.61 mV

n = 14

1.22 mV

0.61 mV

0.31 mV

0.61 mV

0.31 mV

n = 15

0.61 mV

0.31 mV

0.15 mV

0.31 mV

0.15 mV

NOTES

MSB).

***CSB = Complementary Straight Binary.

CALIBRATION (14-Bit Resolution Examples)

External ZERO ADJ and GAIN ADJ potentiometers, connected

as shown in Figures 2 and 3, are used for device calibration. To

prevent interaction of these two adjustments, Zero is always

adjusted first and then Gain. Zero is adjusted with the analog

input near the most negative end of the analog range (0 for

unipolar and –FS for bipolar input ranges). Gain is adjusted

with the analog input near the most positive end of the analog

range.

Adjust Zero for digital output = 11111111111110. Zero is

now calibrated. Set analog input to +FSR – 2 LSB =

+9.99878 V. Adjust Gain for 00000000000001 digital output

code; full scale (Gain) is now calibrated. Half-scale calibra-

tion check: set analog input to +5.00000 V; digital output

code should be 01111111111111.

–10 V to +10 V Range: Set analog input to –9.99878 V; adjust

zero for 1111111111110 digital output (complementary offset

binary) code. Set analog input to 9.99756 V; adjust Gain for

00000000000001 digital output (complementary offset binary)

code. Half-scale calibration check: set analog input to

0.00000 V; digital output (complementary offset binary) code

should be 01111111111111.

Figure 9. Analog and Power Connections for Unipolar 0 V

to +10 V Input Range