13

LTC1402

FULL-SCALE AND OFFSET ADJUSTMENT

Figure 8 shows the ideal input/output characteristics for

the LTC1402 in bipolar mode and unipolar mode. Figure 9a

shows the components required for full-scale error ad-

justment. Figure 9b includes the components for offset

and full-scale adjustment.

Adjustment in Bipolar Mode with Pin 8 Held High

The code transitions occur midway between successive

integer LSB values (i.e., – FS + 0.5LSB, – FS + 1.5LSB, – FS

is two’s complement binary with 1LSB = FS – (– FS)/4096

= 4.096V/4096 = 1.0mV. In applications where absolute

accuracy is important, offset and full-scale errors can be

adjusted to zero. Offset error must be adjusted before full-

scale error. In Figure 9b, zero offset is achieved by adjust-

flickers between 0000 0000 0000 and 1111 1111 1111.

For full-scale adjustment in Figures 9a and 9b, apply an

R5 until the output code flickers between 0111 1111 1110

and 0111 1111 1111.

Adjustment in Unipolar Mode with Pin 8 Held Low

The code transitions occur midway between successive

integer LSB values (i.e., – FS + 0.5LSB, – FS + 1.5LSB,

– FS + 2.5LSB,...FS – 2.5LSB, FS – 1.5LSB). The output at

Figure 8. LTC1402 Transfer Characteristic

Figure 9a. Full-Scale Adjustment Circuit with

±10LSB Range

Figure 7. CMRR vs Input Frequency

FREQUENCY (MHz)

–40

–30

–20

–10

0

0.1

10

100

1000

1402 F07

–50

–60

–70

1

INPUT VOLTAGE (V)

1402 F08

011...111

011...110

011...101

100...000

100...001

100...010

111...111

111...110

111...101

000...000

000...001

000...010

FS – 1LSB

– (FS – 1LSB)

64k

R1

51

Ω

R3

51

Ω

64k

REFERENCE

AMP

S/H

10

µF

R4

470k

R2

39k

R5

500

Ω

GAIN

BANGAP

REFERENCE

5

ANALOG INPUT

0V TO 4.096V

OR

±2.048V

7

–

4

+

3

AGND2

6

LTC1402

2.048V

1402 F09a

Figure 9b. Offset and Full-Scale Adjustment

Circuits with

±10LSB Range

64k

R1

51

Ω

R3

51

Ω

64k

REFERENCE

AMP

S/H

10

µF

R4

470k

R2

24k

R7

7.5k

R5

500

Ω

GAIN

BANGAP

REFERENCE

5

5V

5V

ANALOG INPUT

0V TO 4.096V

OR

±2.048V

OFFSET

ADJ

FULL-SCALE

ADJ

7

–

4

+

3

AGND2

6

LTC1402

2.048V

1402 F09b

R8

10k

R6

24k