Datasheet

AD7745/AD7746
Rev. 0| Page 17 of 28
EXC SET-UP REGISTER
Address Pointer 0x09, Default Value 0x03
Capacitive channel excitation setup.
Table 15. EXC Set-Up Bit Map
Bit Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Mnemonic CLKCTRL EXCON EXCB
EXCB
EXCA
EXCA
EXCLVL1 EXCLVL0
Default 0 0 0 0 0 0 0 0
Table 16.
Bit Mnemonic Description
7 CLKCTRL 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.
6 EXCON
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.
5 EXCB EXCB = 1 enables EXCB pin as the excitation output.
4
EXCB
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.
3 EXCA EXCA = 1 enables EXCA pin as the excitation output.
2
EXCA
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 EXCLVL0 Voltage on Cap EXC Pin Low Level EXC Pin High Level
0 0 ±V
DD
/8 V
DD
× 3/8 V
DD
× 5/8
0 1 ±V
DD
/4 V
DD
× 1/4 V
DD
× 3/4
1 0 ±V
DD
× 3/8 V
DD
× 1/8 V
DD
× 7/8
1
0
EXCLVL1,
EXCLVL0
1 1 ±V
DD
/2 0 V
DD