UG-1262
Rev. B | Page 57 of 312
ADC CIRCUIT
ADC CIRCUIT OVERVIEW
The SAR ADC circuit is implemented on the analog die. The die operates from a 2.8 V to 3.6 V power supply. The Arm Cortex-M3
processor interfaces to the ADC via an internal die-to-die interface. The ADC uses a precision, low drift, factory calibrated 1.82 V reference.
An external reference can also be connected to the VREF_1.82V pin. ADC conversions can be triggered by writing directly to the
AFECON register.
COMP
SWITCHES CONTROL
BUSY
OUTPUT CODE
CNV
CONTROL
LOGIC
SW+
LSB
SW+
LSB
IN+
VREF_1.82V
AGND
IN–
MSB
MSB
C
C
4C
2C
16,384C
32,768C
C
C
4C
2C
16,384C
32,768C
166
75-
007
Figure 7. ADC Core Block Diagram
ADC
INP
UT
M
UX
THIRD-
ORDER
AAF
PGA
16-BIT ADC
800kSPS/
1600kSPS
GAIN = 1, 1.5, 2, 4, 9
+
+
+
+
–
–
–
–
FRONT-END
BUFFER
ADC
PREBUFFER
POSTPROCESSING
BLOCKS:
OFFSET/GAIN
CALIBRATION,
DIGITAL FILTERS
(SINC3/SINC2)
R
LPF
+
LPTIA1
–
R
TIA
R
LPF
VZERO1
VOLTAGE INPUTS:
AIN0 TO AIN7
VOLTAGE INPUTS:
DE0, SEx, CEx, REx,
VZEROx, VBIASx
VOLTAGE INPUTS:
HIGH SPEED DACs EXCITATION AMP
P AND N NODES
VOLTAGE INPUTS:
INTERNAL CHANNELS:
TEMPERATURE SENSORS,
INTERNAL VOLTAGE REFERENCES
POWER SUPPLY VOLTAGES
+
LPTIA0
–
R
TIA
WE0
VZERO0
+
HSTIA
–
R
TIA
166
75
-108
Figure 8. ADC Input Stages
ADC CIRCUIT FEATURES
The
includes a fast multichannel, 16-bit ADC. The input multiplexer supports a number of external and internal channels.
There are up to 34 user-selectable channels, including the following:
Four low power current measurement channels. These channels are designed to measure the sense, working, and diagnostic
electrode outputs of electrochemical sensors. The current channels feed into a programmable load resistor (R
LOAD
).
Includes two low power TIAs, each containing a programmable gain resistor to convert very small currents to a voltage signal
that the ADC can measure.
The low power current channels can be configured to sample with a low-pass filter in place. Bypassing the low-pass filter can be
useful for diagnostic operations on an electrochemical sensor output.