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.
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 R
1
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
50Ω, 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.
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 R
2
in Figure 10 with a 50Ω 1% metal film
resistor and connect pin 12 to pin 9, omitting the other
adjustment components.
®
13
ADS774
TI [ TEXAS INSTRUMENTS ]
