AD7745_15 Datasheet, PDF (17/28 Pages) Analog Devices – 24-Bit Capacitance-to-Digital Converter with Temperature Sensor

EXC SET-UP REGISTER
Address Pointer 0x09, Default Value 0x03
Capacitive channel excitation setup.
Table 15. EXC Set-Up Bit Map
Bit
Bit 7
Mnemonic
CLKCTRL
Default
0
Bit 6
EXCON
0
Bit 5
EXCB
0
Bit 4
EXCB
0
Bit 3
EXCA
0
Bit 2
EXCA
0
AD7745/AD7746
Bit 1
EXCLVL1
0
Bit 0
EXCLVL0
0
Table 16.
Bit Mnemonic
7
CLKCTRL
6
EXCON
5
EXCB
4
EXCB
3
EXCA
2
EXCA
1
EXCLVL1,
0
EXCLVL0
Description
The CLKCTRL bit should be set to 0 for the specified AD7745/AD7746 performance.
CLKCTRL = 1 decreases the excitation signal frequency and the modulator clock frequency by factor of 2.
This also increases the conversion time on all channels (capacitive, voltage, and temperature) by a factor of 2.
When EXCON = 0, the excitation signal is present on the output only during capacitance channel conversion.
When EXCON = 1, the excitation signal is present on the output during both capacitance and
voltage/temperature conversion.
EXCB = 1 enables EXCB pin as the excitation output.
EXCB = 1 enables EXCB pin as the inverted excitation output.
Only one of the EXCB or the EXCB bits should be set for proper operation.
EXCA = 1 enables EXCA pin as the excitation output.
EXCA = 1 enables EXCA pin as the inverted excitation output.
Only one of the EXCA or the EXCA bits should be set for proper operation.
Excitation Voltage Level.
EXCLVL1
0
0
1
1
EXCLVL0
0
1
0
1
Voltage on Cap
±VDD/8
±VDD/4
±VDD × 3/8
±VDD/2
EXC Pin Low Level
VDD × 3/8
VDD × 1/4
VDD × 1/8
0
EXC Pin High Level
VDD × 5/8
VDD × 3/4
VDD × 7/8
VDD
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