Reference Manual ADuCM356
LOW-POWER POTENTIOSTAT AMPLIFIERS AND LOW-POWER TIAS
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External R
TIA
Gain Resistor with Low-Power
TIA Amplifiers
To use an external R
TIA
gain resistor, follow this process:
1. Connect the external R
TIA
across the RC0_0 and RC0_1 pins
for Channel 0. For Channel 1, connect the external R
TIA
across
the RC1_0 and RC1_1 pins.
2. Clear LPTIACONx, Bits[9:5] = 0b00000 to disconnect the inter-
nal R
TIA
from the TIA output terminal.
3. Close the SW9 switch by setting LPTIASWx, Bit 9 = 1. When
using the internal R
TIA
, open the SW9 switch.
LOW-POWER DACS
The low-power DACs are designed to set the sensor bias voltage.
In Figure 15, the sensor bias voltage is the voltage difference
between the reference electrode and sense electrode.
Each low-power DAC has two outputs, an output with 12-bit resolu-
tion (VBIAS0 pin) and an output with 6-bit resolution (VZERO0 pin).
The low-power DACs are made up of two 6-bit string DACs. The
main 6-bit string DAC provides the VZERO0 DAC output, and is
made up of 63 resistors. Each resistor is the same value.
The main 6-bit string with the 6-bit subDAC provides the VBIAS0
DAC output. In 12-bit mode, the MSBs select a resistor from the
main string DAC. The top end of this resistor is selected as the top
of the 6-bit subDAC, and the bottom end of the selected resistor is
connected to the bottom of the 6-bit subDAC string.
The resistor matching between the 12-bit and 6-bit subDAC means
64 LSB 12-bit (VBIAS0 pin) is equal to one LSB 6-bit (VZERO0
pin).
Figure 19 shows the low-power DAC structure. The main DAC
string shows the 64 resistors that make up the six bits of the
VZERO0 output and the six MSBs of the VBIAS output. The main
DAC makes up the 6-bit DAC output (VZERO0 output), and is
controlled by LPDACDATx, Bits[17:12]. The output range is 0.2 V
to 2.36615 V. The right side of the main DAC block shows the
six MSBs of the 12-bit DAC output (VBIAS0 output), which are
controlled by LPDACDATx, Bits[11:0]. The voltage steps of these
bits are equal to the 6-bit VZERO0 output steps. The 12-bit output
is capable of reaching 2.4 V.
The subDAC block shows the 64-resistor string used to generate
the six LSBs of the 12-bit output. The low-power DACs are control-
led by LPDACCONx, Bits[5:0].
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