Reference Manual ADuCM356
PROGRAMMABLE SWITCHES CONNECTING THE EXTERNAL SENSOR TO THE HIGH-SPEED DAC
AND HIGH-SPEED TIA
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The ADuCM356 provides flexibility for connecting external pins to
the high-speed DAC excitation amplifier and to the high-speed TIA
inverting input. The external pin connections provide many options
for impedance measurements to different sensor types and allow
an AC signal to be coupled onto the DC bias voltage of a sensor.
When configuring these switches, the user must account for the
switch settings on the output of the low-power amplifiers. See
Figure 16. On power-up, all switches are open to disconnect the
sensor. For details on the recommended configuration in hibernate
mode, see the Recommended Configuration in Hibernate Mode
section.
DX SWITCHES
These switches select the pin to connect to the high-speed DAC
excitation amplifier output. For an electrochemical gas sensor im-
pedance measurement, this pin is the CE0 or CE1 pin. The Dx
switches can be connected to an external calibration resistor via the
RCAL0 pin if the DR0 switch is closed.
PX SWITCHES
These switches select the pin to connect to the high-speed DAC
excitation amplifier P input. For an electrochemical gas sensor, this
pin is typically RE0 or RE1. The Px switches can be connected to
an external R
CAL
via the RCAL0 pin if the PR0 switch is closed.
NX SWITCHES
These switches select the pin to connect to the high-speed DAC
excitation amplifier N input. The Nx switches can be connected to
an external R
CAL
via the RCAL1 pin if the NR1 switch is closed.
TX SWITCHES
These switches select the pin to connect to the high-speed TIA
inverting input. The Tx switches can be connected to an external
R
CAL
via the RCAL1 pin if the TR1 switch is closed.
OPTIONS FOR CONTROLLING ALL SWITCHES
Figure 27 shows all of the switches connected to the high-speed
DAC excitation amplifier and to the inverting input of the high-speed
TIA.
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