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

0

1

1

0

1

0

EXCLVL1,

EXCLVL0

1

1

0