
AD7870/AD7875/AD7876
Rev. C | Page 13 of
28
R1
10k
R2
500
R3
10k
AGND
VIN
R5
10k
R4
10k
AD7870/
AD7875/
AD78761
1ADDITIONAL PINS OMITTED FOR CLARITY.
V1
07
73
0-
01
3
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