AD7785 Analog Devices, AD7785 Datasheet - Page 19

• Manufacturer Part Number: AD7785
• Description: 3-Channel, Low Noise, Low Power, 20-Bit ?-? ADC with On-Chip In-Amp and Reference
• Manufacturer: Analog Devices

Specifications of AD7785

• Resolution (bits): 20bit
• # Chan: 3
• Sample Rate: n/a
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: ± (Vref/Gain)
• Adc Architecture: Sigma-Delta
• Pkg Type: SOP

Table 16. IO Register Bit Designations
Bit Location
IO7 to IO4
IO3 to IO2
IO1 to IO0
OFFSET REGISTER
RS2, RS1, RS0 = 1, 1, 0; Power-On/Reset = 0x800000
Each analog input channel has a dedicated offset register that
holds the offset calibration coefficient for the channel. This
register is 24 bits wide and its power-on/reset value is
0x8000(00). The offset register is used in conjunction with its
associated full-scale register to form a register pair. The power-
on reset value is automatically overwritten if an internal or
system zero-scale calibration is initiated by the user. The offset
register is a read/write register. However, the AD7785 must be
in idle mode or power-down mode when writing to the
offset register.
Bit Name
0
IEXCDIR1 to
IEXCDIR0
IEXCEN1 to
IEXCEN0
Description
These bits must be programmed with a Logic 0 for correct operation.
Direction of current sources select bits.
IEXCDIR1
0
0
1
1
These bits are used to enable and disable the current sources along with selecting the value of the
excitation currents.
IEXCEN1
0
0
1
1
IEXCDIR0
0
1
0
1
IEXCEN0
0
1
0
1
Rev. 0 | Page 19 of 32
Current Source Direction
Current Source IEXC1 connected to Pin IOUT1, Current Source IEXC2
connected to Pin IOUT2.
Current Source IEXC1 connected to Pin IOUT2, Current Source IEXC2
connected to Pin IOUT1.
Both current sources connected to Pin IOUT1. Permitted when the current
sources are set to 10 μA or 210 μA only.
Both current sources connected to Pin IOUT2. Permitted when the current
sources are set to 10 μA or 210 μA only.
Current Source Value
Excitation Current Disabled
10 μA
210 μA
1 mA
FULL-SCALE REGISTER
RS2, RS1, RS0 = 1, 1, 1; Power-On/Reset = 0x5XXX00
The full-scale register is a 24-bit register that holds the full-scale
calibration coefficient for the ADC. The AD7785 has 3 full-scale
registers, each channel having a dedicated full-scale register.
The full-scale registers are read/write registers; however, when
writing to the full-scale registers, the ADC must be placed in
power-down mode or idle mode. These registers are configured
on power-on with factory-calibrated full-scale calibration coef-
ficients, the calibration being performed at gain = 1. Therefore,
every device has different default coefficients. The coefficients
are different depending on whether the internal reference or an
external reference is selected. The default value is automatically
overwritten if an internal or system full-scale calibration is
initiated by the user, or the full-scale register is written to.
AD7785