11

®

ADS804

4V

1V

IN

IN

SEL

V

REF

+2.5V ext.

V

1 +

R

1

R

2

FSR = 2 x V

REF

ADS804

R

1

5k

Ω

+1.5V

R

2

10k

Ω

V

IN

3.5V

1.5V

IN

IN

+1V

SEL

+2.5V ext.

V

IN

ADS804

V

IN

5V

0V

IN

IN

+2.5V

SEL

V

REF

ADS804

SELECTING THE INPUT RANGE AND

REFERENCE

Figures 7 through 9 show a selection of circuits for the most

common input ranges when using the internal reference of

the ADS804. All examples are for single-ended input and

operate with a nominal common-mode voltage of +2.5V.

EXTERNAL REFERENCE OPERATION

Depending on the application requirements, it might be

advantageous to operate the ADS804 with an external

reference. This may improve the DC accuracy if the external

reference circuitry is superior in its drift and accuracy. To

use the ADS804 with an external reference, the user must

disable the internal reference (see Figure 10). By connecting

internal reference. At the same time, the output of the

which now must be driven with the external reference. Note

that a similar bypassing scheme should be maintained as

described for the internal reference operation.

FIGURE 10. External Reference, Input Range 0.5V to 4.5V

(4Vp-p), with +2.5V Common-Mode Voltage.

DIGITAL INPUTS AND OUTPUTS

Over Range (OVR)

One feature of the ADS804 is its ‘Over Range’ digital output

(OVR). This pin can be used to monitor any out-of-range

condition, which occurs every time the applied analog input

output is LOW when the input voltage is within the defined

input range. It becomes HIGH when the input voltage is

beyond the input range. This is the case when the input

voltage is either below the bottom reference voltage or

above the top reference voltage. OVR will remain active

until the analog input returns to its normal signal range and

another conversion is completed. Using the MSB and its

complement in conjunction with OVR a simple clue logic

can be built that detects the overrange and underrange

conditions, (see Figure 11). It should be noted that OVR is

a digital output which is updated along with the bit informa-

tion corresponding to the particular sampling incidence of

the analog signal. Therefore, the OVR data is subject to the

same pipeline delay (latency) as the digital data.

FIGURE 8. Internal Reference with 1.5V to 3.5V Input Range.

FIGURE 9. Internal Reference with 1V to 4V Input Range.

FIGURE 7. Internal Reference with 0V to 5V Input Range.

4.5V

0.5V

IN

IN

+2.5V ext.

+2V

DC

SEL

V

REF

1.24k

Ω

4.99k

Ω

0.1

µF

10

µF

REF1004

+2.5V

+

ADS804

+5V

V

IN