AD7712 Analog Devices, AD7712 Datasheet - Page 9

• Manufacturer Part Number: AD7712
• Description: CMOS, 24-Bit Sigma-Delta, Signal Conditioning ADC with 2 Analog Input Channels
• Manufacturer: Analog Devices

Specifications of AD7712

• Resolution (bits): 24bit
• # Chan: 2
• Sample Rate: 19.5kSPS
• Interface: Ser
• Analog Input Type: Diff-Bip,Diff-Uni,SE-Bip
• Ain Range: Bip (Vref) x 4,Bip (Vref)/(PGA Gain),Bip 10V,Bip 20V,Uni (Vref) x 4,Uni (Vref)/(PGA Gain),Uni 10V,Uni 20V
• Adc Architecture: Sigma-Delta
• Pkg Type: DIP,SOIC

Control Register (24 Bits)
A write to the device with the A0 input low writes data to the control register. A read to the device with the A0 input low accesses the
contents of the control register. The control register is 24 bits wide and when writing to the register 24 bits of data must be written
otherwise the data will not be loaded to the control register. In other words, it is not possible to write just the first 12 bits of data into
the control register. If more than 24 clock pulses are provided before TFS returns high, then all clock pulses after the 24th clock
pulse are ignored. Similarly, a read operation from the control register should access 24 bits of data.
MD2
0
0
0
0
1
1
1
1
REV. F
Operating Mode
MD1
0
0
1
1
0
0
1
1
MD0
0
1
0
1
0
1
0
1
MSB
MD2
FS11
X = Don’t Care.
Operating Mode
Normal Mode. This is the normal mode of operation of the device whereby a read to the device accesses
data from the data register. This is the default condition of these bits after the internal power-on reset.
Activate Self-Calibration. This activates self-calibration on the channel selected by CH. This is a one-step
calibration sequence, and when complete, the part returns to normal mode (with MD2, MD1, MD0 of
the control registers returning to 0, 0, 0). The DRDY output indicates when this self-calibration is complete.
For this calibration type, the zero-scale calibration is done internally on shorted (zeroed) inputs, and the
full-scale calibration is done on V
Activate System Calibration. This activates system calibration on the channel selected by CH. This is a
two-step calibration sequence, with the zero-scale calibration done first on the selected input channel and
DRDY indicating when this zero-scale calibration is complete. The part returns to normal mode at the
end of this first step in the two-step sequence.
Activate System Calibration. This is the second step of the system calibration sequence with full-scale
calibration being performed on the selected input channel. Once again, DRDY indicates when the full-
scale calibration is complete. When this calibration is complete, the part returns to normal mode.
Activate System Offset Calibration. This activates system offset calibration on the channel selected by
CH. This is a one-step calibration sequence and, when complete, the part returns to normal mode with
DRDY indicating when this system offset calibration is complete. For this calibration type, the zero-scale
calibration is done on the selected input channel, and the full-scale calibration is done internally on V
Activate Background Calibration. This activates background calibration on the channel selected by CH. If
the background calibration mode is on, then the AD7712 provides continuous self-calibration of the
reference and shorted (zeroed) inputs. This calibration takes place as part of the conversion sequence,
extending the conversion time and reducing the word rate by a factor of 6. Its major advantage is that
the user does not have to worry about recalibrating the device when there is a change in the ambient
temperature. In this mode, the shorted (zeroed) inputs and V
continuously monitored, and the calibration registers of the device are automatically updated.
Read/Write Zero-Scale Calibration Coefficients. A read to the device with A0 high accesses the contents
of the zero-scale calibration coefficients of the channel selected by CH. A write to the device with A0 high
writes data to the zero-scale calibration coefficients of the channel selected by CH. The word length for
reading and writing these coefficients is 24 bits, regardless of the status of the WL bit of the control
register. Therefore, when writing to the calibration register, 24 bits of data must be written; otherwise the
new data will not be transferred to the calibration register.
Read/Write Full-Scale Calibration Coefficients. A read to the device with A0 high accesses the contents of
the full-scale calibration coefficients of the channel selected by CH. A write to the device with A0 high
writes data to the full-scale calibration coefficients of the channel selected by CH. The word length for
reading and writing these coefficients is 24 bits, regardless of the status of the WL bit of the control
register. Therefore, when writing to the calibration register, 24 bits of data must be written; otherwise the
new data will not be transferred to the calibration register.
MD1
FS10
MD0
FS9
G2
FS8
G1
FS7
REF
G0
FS6
.
–9–
CH
FS5
PD
FS4
WL
FS3
REF
, as well as the analog input voltage, are
X
FS2
BO
FS1
B/U
FS0
LSB
AD7712
REF
.