ance node as compared with traditional ADC574 architec-
tures, where the resistor divider network looks into a com-
parator input node at virtual ground.
CALIBRATION
OPTIONAL EXTERNAL FULL-SCALE
AND OFFSET ADJUSTMENTS
To understand how this circuit works, it is necessary to
know that the input range on the internal sampling capacitor
is from 0V to +3.33V, and the analog input to the ADS574
must be converted to this range. Unipolar 20V range can be
used as an example of how the divider network functions. In
20V operation, the analog input goes into pin 14. Pin 13 is
left unconnected and pin 12 is connected to analog common
pin 9. From Figure 12, it is clear that the input to the
capacitor array will be the analog input voltage on pin 14
divided by the resistor network (68kΩ + 68kΩ || 17kΩ). A
20V input at pin 14 is divided to 3.33V at the capacitor
array, while a 0V input at pin 14 gives 0V at the capacitor
array.
Offset and full-scale errors may be trimmed to zero using
external offset and full-scale trim potentiometers connected
to the ADS574 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, omitting the other adjustment components. Connect
pin 12 to pin 9.
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 R2 until bits DB1-
DB11 are ON and DB0 is toggling ON and OFF.
The main effect of the 10kΩ internal resistor on pin 12 is to
provide offset adjust response the same as that of traditional
ADC574 architectures without needing to change the exter-
nal trimpot values.
SINGLE SUPPLY OPERATION
The ADS574 is designed to operate from a single +5V
supply, and handle all of the unipolar and bipolar input
ranges, in either the Control Mode or the Emulation Mode as
described above. Pin 7 is not connected internally. This is
where +12V or +15V is supplied on traditional ADC574s.
Pin 11, the –12V or –15V supply input on traditional
ADC574s, is used only as a logic input on the ADS574.
There is a resistor divider internally on pin 11 to reduce that
input to a correct logic level within the ADS574, and this
resistor will add 10mW to 15mW to the power consumptionof
the ADS574 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.)
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 R1 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 R2 for DB0 to
toggle ON and OFF with all other bits ON.
There are no other modifications required for the ADS574 to
function with a single +5V supply.
Theinformationprovidedhereinisbelievedtobereliable;however, BURR-BROWNassumesnoresponsibilityforinaccuraciesoromissions. BURR-BROWNassumes
no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change
without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant
any BURR-BROWN product for use in life support devices and/or systems.
®
13
ADS574
BB [ BURR-BROWN CORPORATION ]
