Datasheet

ADC0808-N, ADC0809-N
www.ti.com SNAS535H –OCTOBER 1999–REVISED MARCH 2013
ANALOG COMPARATOR INPUTS
The dynamic comparator input current is caused by the periodic 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 directly with clock frequency and with V
IN
as shown in
Figure 8.
If no filter capacitors are used at the analog inputs and the signal source impedances are low, the comparator
input current 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 characteristics of a DC bias current whose effect can
be predicted conventionally.
Typical Application
*Address latches needed for 8085 and SC/MP interfacing the ADC0808 to a microprocessor
Table 2. Microprocessor Interface Table
PROCESSOR READ WRITE INTERRUPT (COMMENT)
8080 MEMR MEMW INTR (Thru RST Circuit)
8085 RD WR INTR (Thru RST Circuit)
Z-80 RD WR INT (Thru RST Circuit, Mode 0)
SC/MP NRDS NWDS SA (Thru Sense A)
6800 VMA•φ2•R/W VMA•φ•R/W IRQA or IRQB (Thru PIA)
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