ADC0808/ADC0809
567227
R
A
=R
B
*Ratiometric transducers
FIGURE 13. Symmetrically Centered Reference
3.0 CONVERTER EQUATIONS
The transition between adjacent codes N and N+1 is given
by:
V
REF(+)
÷512)
4.0 ANALOG COMPARATOR INPUTS
The dynamic comparator input current is caused by the peri-
odic switching of on-chip stray capacitances. These are con-
nected alternately to the output of the resistor ladder/switch
tree network and to the comparator input as part of the oper-
ation of the chopper stabilized comparator.
The average value of the comparator input current varies di-
rectly with clock frequency and with V
IN
as shown in
If no filter capacitors are used at the analog inputs and the
signal source impedances are low, the comparator input cur-
rent should not introduce converter errors, as the transient
created by the capacitance discharge will die out before the
comparator output is strobed.
If input filter capacitors are desired for noise reduction and
signal conditioning they will tend to average out the dynamic
comparator input current. It will then take on the characteris-
tics of a DC bias current whose effect can be predicted
conventionally.
(2)
The center of an output code N is given by:
(3)
The output code N for an arbitrary input are the integers within
the range:
(4)
Where:
V
IN
=Voltage at comparator input
V
REF(+)
=Voltage at Ref(+)
V
REF(−)
=Voltage at Ref(−)
V
TUE
=Total unadjusted error voltage (typically
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