AD5940
Data Sheet
When an ECG measurement is required, the AD5940 switch
matrix disconnects the AD5940 AFE from the electrodes and
connects to the AD8233 front end. The AD8233 analog output
is connected to the high performance, 16-bit ADC on the
AD5940 through an AINx pin. The measurement data is stored
in the AD5940 data FIFO to be read by the host controller.
USING THE AD5940, AD8232, AND AD8233 FOR
BIOIMPEDANCE AND ELECTROCARDIOGRAM
(ECG) MEASUREMENTS
The AD5940 can be used in conjunction with the AD8232 and
AD8233 to perform bioimpedance and ECG measurements.
The same electrodes can be used to facilitate both measurements.
For details, see AN-1557.
When a bioimpedance measurement (for example, body
composition, hydration, EDA, and so on) is required, the
AD8232 and AD8233 are put into shutdown (the SDN pin on
the AD8232 and AD8233 is controlled by the AD5940
GPIOx pin) and the AD5940 switch matrix disconnects the
AD8232 and AD8233 from the electrodes.
V
V
ZERO0
BIAS0
AIN1
EXCITATION
BUFFER
VREF2V5
C
ISO
R
LIMIT
HSDAC
CE0
LP DUAL
OUTPUT
DAC
E1
CE0
AIN0
R
R
LIMITECG
RE0
RF = 0Ω
LP
AMP
LPTIA
AIN4
R
TIA = INFΩ
HPDRIVE HPSENSE
AFE2
AFE3
IAOUT
+V
+IN
–IN
LIMITECG
DE0
SE0
+V
S
AD8233
S
SW2_1
E1
E2
REFIN
SW
C
ISO
GND
FR
OPAMP+
REFOUT
OPAMP–
AIN2
AIN4
E2
AIN6
E3
10MΩ
AC/DC
RLD SDN
SDN
+V
S
E4
OUT
RLDFB
TO
HOST/
AD5940
RLD
LOD
C
10MΩ
ISOBIA
AIN3
AIN0
E3
E4
R
LIMIT
ECG
AIN1
ADC
AAF
COARSE
OFFSET
V
BIAS
C
ISO
R
CORRECTION
HSTIA
LIMIT
AIN1
R
C
TIA
BIA
AD5940
TIA
BIA
R
LIMIT
ECG
Figure 53. Body Composition and ECG System Solution Using the AD5940 with the AD8232 and the AD8233
Rev. 0 | Page 128 of 130
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