AD7794/AD7795

Rev. D | Page 22 of 36

CONFIGURATION REGISTER

RS2, RS1, RS0 = 0, 1, 0; Power-On/Reset = 0x0710

The configuration register is a 16-bit read/write register that is

used to configure the ADC for unipolar or bipolar mode, enable

or disable the buffer, enable or disable the burnout currents,

select the gain, and select the analog input channel.

Table 20 outlines the bit designations for the filter register.

CON0 through CON15 indicate the bit locations. CON denotes

that the bits are in the configuration register. CON15 is the first

bit of the data stream. The number in parentheses indicates the

power-on/reset default status of that bit.

CON15

CON14

CON13

CON12

CON11

CON10

CON9

CON8

VBIAS1(0)

VBIAS0(0)

BO(0)

U/B(0)

BOOST(0)

G2(1)

G1(1)

G0(1)

CON7

CON6

CON5

CON4

CON3

CON2

CON1

CON0

REFSEL1(0)

REFSEL0(0)

REF_DET(0)

BUF(1)

CH3(0)

CH2(0)

CH1(0)

CH0(0)

Table 20. Configuration Register Bit Designations

Bit No.

Mnemonic

Description

CON15 to

CON14

VBIAS1 to VBIAS0

These bits are used in conjunction with the BOOST bit.

VBIAS1

VBIAS0

Bias Voltage

0

0

Bias voltage generator disabled

0

1

Bias voltage generator connected to AIN1(−)

1

0

Bias voltage generator connected to AIN2(−)

1

1

Bias voltage generator connected to AIN3(−)

CON13

BO

Burnout Current Enable Bit. This bit must be programmed with a Logic 0 for correct operation. When this

bit is set to 1 by the user, the 100 nA current sources in the signal path are enabled. When BO = 0, the

burnout currents are disabled. The burnout currents can be enabled only when the buffer or in-amp is active.

CON12

U/B

Unipolar/Bipolar Bit. Set by user to enable unipolar coding, that is, zero differential input results in

0x000000 output and a full-scale differential input results in 0xFFFFFF output. Cleared by the user to

enable bipolar coding. Negative full-scale differential input results in an output code of 0x000000, zero

differential input results in an output code of 0x800000, and positive full-scale differential input results in

an output code of 0xFFFFFF.

CON11

BOOST

This bit is used in conjunction with the VBIAS1 and VBIAS0 bits. When set, the current consumed by the

bias voltage generator is increased, which reduces its power-up time.

CON10 to

CON8

G2 to G0

Gain Select Bits.

Written by the user to select the ADC input range as follows:

G2

G1

G0

Gain

ADC Input Range (2.5 V Reference)

0

0

0

1 (in-amp not

used)

2.5 V

0

0

1

2 (in-amp not

used)

1.25 V

0

1

0

4

625 mV

0

1

1

8

312.5 mV

1

0

0

16

156.2 mV

1

0

1

32

78.125 mV

1

1

0

64

39.06 mV

1

1

1

128

19.53 mV

CON7 to

CON6

REFSEL1/REFSEL0

Reference Select Bits.

The reference source for the ADC is selected using these bits.

REFSEL1

REFSEL0

Reference Source

0

0

External reference applied between REFIN1(+) and REFIN1(−)

0

1

External reference applied between REFIN2(+) and REFIN2(−)

1

0

Internal 1.17 V reference

1

1

Reserved