AD7873ACP datasheet(14/28 Pages) AD

14 / 28 page

AD7873

Rev. D | Page 14 of 28

ANALOG INPUT

Figure 26 shows an equivalent circuit of the analog input

structure of the AD7873, which contains a block diagram of the

input multiplexer, the differential input of the ADC, and the

differential reference.

Table 5 shows the multiplexer address corresponding to each

analog input, both for the SER/DFR bit in the control register

set high and low. The control bits are provided serially to the

device via the DIN pin. For more information on the control

When the converter enters hold mode, the voltage difference

between the +IN and –IN inputs (see Figure 26) is captured on

the internal capacitor array. The input current on the analog

inputs depends on the conversion rate of the device. During the

sample period, the source must charge the internal sampling

capacitor (typically 37 pF). Once the capacitor is fully charged,

there is no further input current. The rate of charge transfer

from the analog source to the converter is a function of

conversion rate.

X+ Y+

REF

INT/

EXT

X– Y– GND

6-TO-1

MUX

3-TO-1

MUX

3-TO-1

MUX

IN+

IN– REF–

REF+

ADC CORE

DATA OUT

VCC

Y–

Y+

X+

X–

ON-CHIP SWITCHES

X+

Y+

Y–

VBAT

AUX

TEMP

Figure 26. Equivalent Analog Input Circuit

Table 5. Analog Input, Reference, and Touch Screen Control

SER/ DFR

Analog Input

X Switches

Y Switches

+REF1

–REF

TEMP0

OFF

VREF

GND

X+

OFF

VREF

GND

VBAT

OFF

VREF

GND

X+ (Z1)

X+ OFF

Y+ ON

VREF

GND

X– ON

Y– OFF

Y– (Z2)

X+ OFF

Y+ ON

VREF

GND

X– ON

Y– OFF

Y+

OFF

VREF

GND

AUX

OFF

VREF

GND

TEMP1

OFF

VREF

GND

Invalid Address. Test Mode: Switches out the Temp0 diode to the PENIRQ pin.

X+

OFF

Y+

Y–

Invalid Address

X+ (Z1)

X+ OFF

Y+ ON

Y+

X–

X– ON

Y– OFF

Y– (Z2)

X+ OFF

Y+ ON

Y+

X–

X– ON

Y– OFF

Y+

OFF

X+

X–

Outputs Identity Code, 1000 0000 0000.

Invalid address. Test mode: Switches out the Temp1 diode to the PENIRQ pin.

1 Internal node, not directly accessible by the user.

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