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UG-1262
Hardware Reference Manual
Rev. B | Page 160 of 312
LOW POWER
LOOP:
LPTIASWx =
0x302C
D
EXCITATION
AMPLIFIER
LOOP
CE0
R
C
R
E
C
C
SE0
R
W
R
E
C
W
RE0
C = 0.1µF
CE0
RE0
SE0
RC0_0
RC1_0
VBIAS0
C = 0.1µF
RC0_2
RCAL0
RCAL1
R
CAL
= 200Ω
HPTIA
+
–
HPTIACON[1:0] = 01
VZERO0
VZERO0
VZERO1
ADCVBIAS_CAP 1.1V
LPTIASWx[12] = 1
C = 0.1µF
LPTIASWx[2] = 0
Px SWITCHES:
CLOSE PR0
OPEN OTHER
Px SWITCHES
SWCON[7:4] = 0001
PGA
12-BIT
DAC
RCF
DACP
DACN
V
ZERO0
V
BIAS0
DIG
WAVE
GEN
P
Nx SWITCHES:
CLOSE N5
OPEN OTHER
Nx SWITCHES
SWCON[11:8] = 0101
DUAL
OUTPUTS
12-BIT
VDAC
VBIAS0
VZERO0
C = 0.1µF
VZERO0
LPTIASWx[13] = 1
+
–
LPTIA
V
ZERO
R
LOAD02
AMP
–
+
V
BIAS0
MU
X
ADCCON[12:0]
SENSOR IS BIASED
VIA HIGH POWER LOOP
P
N
N
Tx SWITCHES:
CLOSE T5, T9
OPEN OTHER
Tx SWITCHES
SWCON[15:12] = 0101
SWCON[17] = 1
Dx SWITCHES:
CLOSE D5
OPEN OTHER
Dx SWITCHES
SWCON[3:0] = 0101
LPTIASWx[3] = 0
LPTIASWx[8] = 1
LPTIASW[13] = 1
V
ZERO
10mV p-p
V
BIAS
16675
-030
16-BIT
ADC
160kSPS
PGA
BUFFER
BUFFER
AAF
DFT
MUXSELP_HPTIA_P
MUXSELP_HPTIA_N
Figure 42. R
LOAD02
Measurement
Step 4: Measure R
CAL
via the Impedance Measurement Engine
R
CAL
is a known external fixed resistor, typically 200 Ω, but can be other values. The electrochemical sensor dc bias voltage is set by the
low power potentiostat loop.
Configure the Tx, Dx, Nx, and Px switches appropriately, as per the following example code:
AfeSwitchDPNT(SWID_D7_WE0,SWID_P7_WE0,SWID_N5_SE0RLOAD,SWID_T5_SE0RLOAD|SWID_T9);
// Connect Excitation Amplifier D to RCAL0
// Connect Excitation Amplifier P to RCAL0
// Connect Excitation Amplifier N to RCAL1
// Connect HSTIA to RCAL1. Close T9