Datasheet

Data Sheet AD7739
Rev. A | Page 19 of 32
CHANNEL CONVERSION TIME REGISTERS
8 Bits, Read/Write Registers, Address 0x30 to
Address 0x37, Default Value 0x91
The conversion time registers enable or disable chopping and
configure the digital filter for a particular channel (see Table 25
and Table 26). This register value affects the conversion time,
frequency response, and noise performance of the ADC.
MODE REGISTER
8 Bits, Read/Write Register, Address 0x38 to
Address 0x3F, Default Value 0x00
The mode register configures the part and determines its operating
mode (see Table 27, Table 28, and Table 29). Writing to the
mode register clears the ADC status register, sets the
RDY
pin
to a logic high level, exits all current operations, and starts the
mode specified by the mode bits.
The AD7739 contains only one mode register. The two LSBs of
the address are used for writing to the mode register to specify
the channel selected for the operation determined by the MD2
to MD0 bits. Only the address 0x38 must be used for reading
from the mode register.
Table 25. Channel Conversion Time Registers Bits
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 0x11
Table 26. Channel Conversion Time Registers Bit Descriptions
Bit Mnemonic Description
7 Chop Chopping enable bit. Set to 1 to apply chopping mode for a particular channel.
6 to 0 FW Chop = 1, single conversion or continuous conversion with one channel enabled.
Conversion Time (µs) = (FW × 128 + 262)/MCLK Frequency (MHz), the FW range is 2 to 127.
Chop = 1, continuous conversion with two or more channels enabled.
Conversion Time (µs) = (FW × 128 + 263)/MCLK Frequency (MHz), the FW range is 2 to 127.
Chop = 0, single conversion or continuous conversion with one channel enabled.
Conversion Time (µs) = (FW × 64 + 213)/MCLK Frequency (MHz), the FW range is 3 to 127.
Chop = 0, continuous conversion with two or more channels enabled.
Conversion Time (µs) = (FW × 64 + 214)/MCLK Frequency (MHz), the FW range is 3 to 127.
Table 27. Mode Register Bits
Bit Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Mnemonic
MD2
MD1
MD0
CLKDIS
Dump
Cont RD
24/16 BIT
Clamp
Default
0 0 0 0 0 0 0 0
Table 28. Mode Register Bit Descriptions
Bit Mnemonic Description
7 to 5 MD2 to MD0 Mode bits. These three bits determine the AD7739 operation mode. Writing a new value to the mode bits exit
the part from the mode in which it has been operating and place it in the newly requested mode immediately.
The function of the mode bits follows.
MD2 MD1 MD0 Mode
Address Used for Mode Register Write
Specifies
0 0 0 Idle
0 0 1 Continuous conversion First channel to start converting
0 1 0 Single conversion Channel to convert
0 1 1 Power-down (standby)
1 0 0 ADC zero-scale self-calibration Conversion time for calibration
1 0 1 ADC full-scale self-calibration (for 2.5 V) Conversion time for calibration
1 1 0 Channel zero-scale system calibration Channel to calibrate
1 1 1 Channel full-scale system calibration Channel to calibrate