ADC0808-N, ADC0809-N

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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 VIN 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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