ADS774 datasheet(13/21 Pages) TI2

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ADS774

where +12V or +15V is supplied on traditional ADC774s.

Pin 11, the –12V or –15V supply input on traditional

ADC774s, is used only as a logic input on the ADS774.

There is a resistor divider internally on pin 11 to reduce that

input to a correct logic level within the ADS774, and this

resistor will add 10mW to 15mW to the power consumption

of the ADS774 when –15V is supplied to pin 11. To

minimize power consumption in a system, pin 11 can be

simply grounded (for Emulation Mode) or tied to +5V (for

Control Mode.)

There are no other modifications required for the ADS774 to

function with a single +5V supply.

CALIBRATION

OPTIONAL EXTERNAL FULL-SCALE

AND OFFSET ADJUSTMENTS

Offset and full-scale errors may be trimmed to zero using

external offset and full-scale trim potentiometers connected

to the ADS774 as shown in Figures 10 and 11 for unipolar

and bipolar operation.

CALIBRATION PROCEDURE—

UNIPOLAR RANGES

If external adjustments of full-scale and offset are not

required, replace R2 in Figure 10 with a 50Ω 1% metal film

resistor and connect pin 12 to pin 9, omitting the other

adjustment components.

If adjustment is required, connect the converter as shown in

Figure 10. Sweep the input through the end-point transition

voltage (0V + 1/2LSB; +1.22mV for the 10V range, +2.44mV

for the 20V range) that causes the output code to be DB0 ON

(HIGH). Adjust potentiometer R1 until DB0 is alternately

toggling ON and OFF with all other bits OFF. Then adjust

full scale by applying an input voltage of nominal full-scale

minus 3/2LSB, the value which should cause all bits to be

ON. This value is +9.9963V for the 10V range and +19.9927V

for the 20V range. Adjust potentiometer R

2 until bits DB1-

DB11 are ON and DB0 is toggling ON and OFF.

CALIBRATION PROCEDURE—BIPOLAR RANGES

If external adjustments of full-scale and bipolar offset are

not required, replace the potentiometers in Figure 11 by

Ω, 1% metal film resistors.

If adjustments are required, connect the converter as shown

in Figure 11. The calibration procedure is similar to that

described above for unipolar operation, except that the offset

adjustment is performed with an input voltage which is

1/2LSB above the minus full-scale value (–4.9988V for the

±5V range, –9.9976V for the ±10V range). Adjust R

1 for

DB0 to toggle ON and OFF with all other bits OFF. To

adjust full-scale, apply a DC input signal which is 3/2LSB

below the nominal plus full-scale value (+4.9963V for

±5V

range, +9.9927V for

±10V range) and adjust R

2 for DB0 to

toggle ON and OFF with all other bits ON.

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