MAX1329 Datasheet, PDF (66/78 Pages) Maxim Integrated Products – 12-/16-Bit DASs with ADC, DACs, DPIOs, APIOs, Reference, Voltage Monitors, and Temp Sensor

12-/16-Bit DASs with ADC, DACs, DPIOs, APIOs,
Reference, Voltage Monitors, and Temp Sensor
the two LEDs. The LEDs can be powered directly from
V_BAT or from AV_DD powered by the internal charge
pump if the V_D of the LEDs require a higher or regulat-
ed voltage. Ambient light rejection is performed in the
digital domain in this configuration by digitizing the
photodiode current with the internal ADC while both
LEDs are off and subtracting this from the result when
the LEDs are turned on.
Three-Electrode Potentiostat with
Software-Switchable Single- or Dual-
Channel Connection
The MAX1329 is used in a software switchable single-
or dual-channel three-electrode potentiostat application
(see Figure 29). In both configurations, the DAC buffer
feedback switches, DSWA and DSWB, are normally
open but can be closed during high sensor current to
keep the DAC buffer outputs compliant. In the dual-
channel configuration, the SPDT1 switch is open and
the OSW1 switch is closed. DACA biases the working
electrode (WE) and DACB biases the reference elec-
trode (RE) both relative to the counter electrode (CE).
The CE is shared by the two channels. In this configura-
tion, RE is really a second working electrode and I_A
and I_B are the two sensor currents being measured. I_A
and I_B are converted to voltages through R_A and R_B
and measured by the internal ADC. In the single-chan-
nel configuration, the SPDT1 switch is closed and the
OSW1 switch is open. DACA biases the WE relative to
the RE and the RE is set by IN1-. Op amp 1’s force-
sense configuration holds RE constant while the CE
swings up and down depending on the sensor current
and the sensor impedance. In this configuration, I_A is
the sensor current being measured. The R₁ resistor is
typically a large value to keep op amp 1 stable when
the sensor is not present or not active.
Two-Electrode Potentiostat with AC and
DC Excitation
The circuit in Figure 30 shows the MAX1330 in a two-
electrode potentiostat application with both AC and DC
excitation to the sensor. The DSWA can be open or
closed and OSW1 and OSW2 should be normally open
although OSW1 can be closed during high sensor
current to keep op amp 1 in compliance. REFADC is
analog ground and the working electrode (WE) is con-
nected to analog ground through op amp 1. The sensor
current to be measured is converted to a voltage
through R_F and measured by the internal ADC. For DC
operation, the bias voltage between WE and the
counter electrode (CE) is set by DACA. For AC opera-
tion, DACA is configured to generate a waveform by
programming the FIFOA Control and FIFOA Data regis-
ters for the desired operation. Op amp 2 is configured
as a 2nd-order Sallen Key lowpass filter to smooth the
steps in the AC waveform going to the sensor. The
DACA can be sequenced to create an AC waveform
through the SPI interface or by configuring one of the
DPIOs and driving it with a clock. The internal ADC
includes a 16-word FIFO to facilitate data gathering
during this mode of operation.
Temperature Measurement with Two
Remote Sensors
For external measurements, select single-ended AIN1
and AIN2 temperature measurement relative to AGND
in the lower multiplexer. Two diode-connected 2N3904
transistors are used as external temperature sensing
diodes in Figure 31. For internal temperature sensor
measurements, select internal temperature measure-
ment in the lower multiplexer. During all temperature
measurements, autoconvert and burst modes are
unavailable. Divide the ADC result by eight to obtain
the measured temperature.
When using an external reference at REFADJ, disable the
internal reference and use the temperature correction
equation in the Temperature Measurement section.
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