AD7870LP datasheet(13/28 Pages) AD

13 / 28 page

AD7870/AD7875/AD7876

Rev. C | Page 13 of

10kΩ

500Ω

10kΩ

AGND

VIN

10kΩ

AD7870/

AD7875/

AD78761

1ADDITIONAL PINS OMITTED FOR CLARITY.

Positive Full-Scale Adjust

Apply a voltage of 9.9927 V (FS/2 − 3/2 LSBs) at V1. Adjust R2

until the ADC output code flickers between 0111 1111 1110 and

0111 1111 1111.

Negative Full-Scale Adjust

Apply a voltage of −9.9976 V (FS/2 + 1/2 LSB) at V1 and adjust

R2 until the ADC output code flickers between 1000 0000 0000

and 1000 0000 0001.

OFFSET AND FULL-SCALE ADJUSTMENT—

AD7875

Figure 13. Offset and Full-Scale Adjust Circuit

Similar to the AD7870, most of the DSP applications in which

the AD7875 is used do not require offset and full-scale

adjustment. For applications that do require adjustment, offset

error must be adjusted before full-scale (gain) error. This is

achieved by applying an input voltage of 0.61 mV (1/2 LSB) to

V1 in Figure 13 and adjusting the op amp offset voltage until

the ADC output code flickers between 0000 0000 0000 and

0000 0000 0001. For full-scale adjustment, apply an input

voltage of 4.9982 V (FS − 3/2 LSBs) to V1 and adjust R2 until

the ADC output code flickers between 1111 1111 1110 and

1111 1111 1111.

Positive Full-Scale Adjust

Apply a voltage of 2.9978 V (FS/2 − 3/2 LSBs) at V1. Adjust R2

until the ADC output code flickers between 0111 1111 1110 and

0111 1111 1111.

Negative Full-Scale Adjust

Apply a voltage of −2.9993 V (−FS/2 + 1/2 LSB) at V1 and adjust

R2 until the ADC output code flickers between 1000 0000 0000

and 1000 0000 0001.

OFFSET AND FULL-SCALE ADJUSTMENT—

AD7876

The offset and full-scale adjustment for the AD7876 is similar

to that just outlined for the AD7870. The trim procedure, for

those applications that do require adjustment, is as follows:

apply a voltage of −2.44 mV (−1/2 LSB) at V1 and adjust the op

amp offset voltage until the ADC output code flickers between

1111 1111 1111 and 0000 0000 0000. Full-scale error can be

adjusted at either the first code transition (ADC negative full

scale) or the last code transition (ADC positive full scale). The

trim procedure for both case is as described in the following

sections (see Figure 13).

AD7870LP Folha de dados(PDF) 13 Page - Analog Devices

AD7870LP Folha de dados(HTML) 13 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Folha de dados Download

Ligação URL