Datasheet

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
100± 2.5 V
1010 V to +2.5 V
000± 1.25 V
0010 V to +1.25 V
010± 0.625 V
0110 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.