ADC0808/ADC0809
Applications Information
4.0 ANALOG COMPARATOR INPUTS
(Continued)
The dynamic comparator input current is caused by the pe-
riodic switching of on-chip stray capacitances. These are
connected alternately to the output of the resistor ladder/
switch tree network and to the comparator input as part of
the operation 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
Figure 6.
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 con-
ventionally.
Typical Application
DS005672-10
*Address latches needed for 8085 and SC/MP interfacing the ADC0808 to a microprocessor
TABLE 2. Microprocessor Interface Table
PROCESSOR
8080
8085
Z-80
SC/MP
6800
RD
RD
NRDS
VMA
•
φ2
•
R/W
READ
MEMR
WRITE
MEMW
WR
WR
NWDS
VMA
•
φ
•
R/W
INTERRUPT (COMMENT)
INTR (Thru RST Circuit)
INTR (Thru RST Circuit)
INT (Thru RST Circuit, Mode 0)
SA (Thru Sense A)
IRQA or IRQB (Thru PIA)
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