REV. 0

AD7738

–17–

Channel Setup Registers

8 Bits, Read/Write Register, Address 28h–2Fh, Default Value 00h

These registers are used to configure the selected channel, its input voltage range, and set up the corresponding Channel Status

register.

Bit

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Mnemonic

BUF OFF

COM1

COM0

Stat. Opt.

ENABLE

RNG2

RNG1

RNG0

Default

0

0

0

0

0

0

0

0

Bit

Mnemonic

Description

7

BUF OFF

Buffer Off. If reset to 0, then internal buffer is enabled. Only operation with internal buffer enabled

is recommended.

6, 5

COM1, COM0 Analog Input Configuration. See Table XI.

4

Stat. Opt.

Status Option. When this bit is set to 1, the P1 bit in the Status Channel register will reflect the state

of the P1 pin. When this bit is reset to 0, the P1 bit in the Status Channel register bit will reflect

the channel corresponding RDY bit in the ADC Status register.

3

ENABLE

Channel Enable. Set this bit to 1 to enable the channel in the Continuous Conversion mode. A single

conversion will take place regardless of this bit value.

2–0

RNG2–0

The Channel Input Voltage Range. See Table XII.

Table XI.

COM1

COM0

COM1

COM0

Channel

0

0

1

1

0

AIN0–AINCOM

AIN0–AIN1

1

AIN1–AINCOM

AIN2–AIN3

2

AIN2–AINCOM

AIN4–AIN5

3

AIN3–AINCOM

AIN6–AIN7

4

AIN4–AINCOM

AIN0–AIN1

5

AIN5–AINCOM

AIN2–AIN3

6

AIN6–AINCOM

AIN4–AIN5

7

AIN7–AINCOM

AIN6–AIN7

Table XII.

Nominal Input

RNG2

RNG1

RNG0

Voltage Range

10

0

±2.5 V

10

10 V to +2.5 V

00

0

±1.25 V

00

10 V to +1.25 V

01

0

±0.625 V

01

10 V to +0.625 V

Channel Conversion Time Registers

8 Bits, Read/Write Register, Address 30h–37h, Default Value 91h

The Conversion Time registers enable or disable chopping and configure the digital filter for a particular channel.

This register value affects the conversion time, frequency response, and noise performance of the ADC.

Bit

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Mnemonic

CHOP

FW (7-Bit Filter Word)

Default

1

11h

Bit

Mnemonic

Description

7

CHOP

Chop Enable Bit. Set to 1 to apply chopping mode for a particular channel.

6–0

FW

CHOP = 1, Single Conversion or Continuous Conversion with one channel enabled.

Conversion Time (

µs) = (FW

128 + 248)/MCLK Frequency (MHz), the FW in range of 2 to 127.

CHOP = 1, Continuous Conversion with two or more channels enabled.

Conversion Time (

µs) = (FW

128 + 249)/MCLK Frequency (MHz), the FW in range of 2 to 127.

CHOP = 0, Single Conversion or Continuous Conversion with one channel enabled.

Conversion Time (

µs) = (FW

64 + 206)/MCLK Frequency (MHz), the FW in range of 3 to 127.

CHOP = 0, Single Conversion or Continuous Conversion with two or more channels enabled.

Conversion Time (

µs) = (FW

64 + 207)/MCLK Frequency (MHz), the FW in range of 3 to 127.