49

INPUT VOLTAGE RANGE AND LSB VALUES

Input Voltage Range Defined As:

±10V

±5V

Analog Input Connected to Pin

2

3

Pin Connected to AGND

3

2

One Least Significant Bit (LSB)

4.88mV

2.44mV

OUTPUT TRANSITION VALUES

FFEH TO FFFH

+ FULL SCALE

+10V–3/2LSB

+5V–3/2LSB

+9.9927V

+4.9963V

7FFH TO 800H

Mid Scale

0V–1/2LSB

0V–1/2LSB

(Bipolar Zero)

–2.44mV

–1.22mV

000H to 001H

–Full Scale

–10V+1/2LSB

–5V+1/2LSB

-9.9976V

-4.9988V

Table 2. Input Voltages, Transition Voltages and LSB Values

toggles on and off at code 1111 1111 1110

FFE

±10V Range Offset and Gain

Offset — Apply 1.2622V to the

±10V input at

pin 2. Adjust the offset potentiometer until the

LSB toggles on and off at code 1001 0000

0010

Gain — Apply 9.9927V to the

±10V input at pin

2. Adjust the gain potentiometer until the LSB

toggles on and off at code 1111 1111 1110

FFE

Layout Considerations

Because of the high resolution and linearity of

the SP85XX Series, system design problems

such as ground path resistance and contact resis-

tance become very important.

Calibration Procedure

Apply a precision input voltage source to your

chosen input range (

±10V range at pin 2 or ±5V

at pin 3). Set the A/D to convert continuously.

Monitor the output code. Trim the offset first,

then gain. Use the appropriate input voltages

and output target codes for your chosen input

range as follows. The recommended offset cali-

bration voltage values eliminate interaction be-

tween the offset and gain calibration

±5V Range Offset and Gain

Offset — Apply 1.5637V to the

±5V input at pin

3. Adjust the offset potentiometer until the LSB

toggles on and off at code 1010 1000 0000

A80

Gain — Apply 4.9963V to the

±5V input at pin

3. Adjust the gain potentiometer until the LSB

Figure 3. a)

±10V Range b) ±5V Range — With External Trims

a)

b)

SP85XX

1

2

3

4

5

6

7

±10V

Input

GAIN ADJUST

100

Ω

10K

Ω

BIPOLAR ZERO ADJUST

499

Ω

–15V

+5V

SP85XX

1

2

3

4

5

6

7

GAIN ADJUST

±5V

Input

+5V

–15V

1K

Ω

30.1K

Ω

301

Ω