AD7734 Analog Devices, AD7734 Datasheet - Page 27

• Manufacturer Part Number: AD7734
• Manufacturer: Analog Devices

Specifications of AD7734

• Resolution (bits): 24bit
• # Chan: 4
• Sample Rate: 3.05MSPS
• Interface: Ser,SPI
• Analog Input Type: SE-Bip,SE-Uni
• Ain Range: Bip 10V,Bip 5.0V,Uni 10V,Uni 5.0V
• Adc Architecture: Sigma-Delta
• Pkg Type: SOP

Analog Input’s Extended Voltage Range
The AD7734 output data code span corresponds to the nominal
input voltage range. The ADC is functional outside the nominal
input voltage range, but the performance might degrade. The
sigma-delta modulator was designed to fully cover a ±11.6 V
analog input voltage; outside this range, the performance might
degrade more rapidly. The adjacent channels are not affected by
up to ±16.5 V analog input voltage (Figure 8).
When the CLAMP bit in the mode register is set to 1, the
channel data register will be digitally clamped to either all 0s or
all 1s when the analog input voltage goes outside the nominal
input voltage range.
As shown in Table 16 and Table 17, when CLAMP = 0, the data
reflects the analog input voltage outside the nominal voltage
range. In this case, the SIGN and OVR bits in the channel status
register should be considered along with the data register value
to decode the actual conversion result.
Note that the OVR bit in the channel status register is generated
digitally from the conversion result and indicates the sigma-
delta modulator (nominal) overrange. The OVR bit DOES NOT
indicate exceeding the AIN pin’s absolute voltage limits
Table 16. Extended Input Voltage Range, Nominal
Voltage Range ±10 V, 16 Bits, CLAMP = 0
Input (V)
11.60039
10.00061
10.00031
10.00000
0.00031
0.00000
–0.00031
–10.00000
–10.00031
–10.00061
–11.60040
BIASLO
BI ASHI
BI AS
AIN
Data (hex)
147B
0001
0000
FFFF
8001
8000
7FFF
0000
FFFF
FFFE
EB85
MULTIPLEXER
CHOP
BUFFER
f
MCLK
Figure 24. Channel Signal Chain Diagram with Chopping Enabled
/2
SIGN
0
0
0
0
0
0
1
1
1
1
1
MODULATOR
f
MCLK
OVR
1
1
1
0
0
0
0
0
1
1
1
Σ−∆
/2
Rev. 0 | Page 27 of 32
DIGITAL
FILTER
Table 17. Extended Input Voltage Range, Nominal
Voltage Range 0 V to +10 V, 16 Bits, CLAMP = 0
Input (V)
11.60006
10.00031
10.00015
10.00000
0.00015
0.00000
–0.00015
Chopping
With chopping enabled, the multiplexer repeatedly reverses the
ADC inputs. Every output data result is then calculated as an
average of two conversions, the first with the positive and the
second with the negative offset term included. This effectively
removes any offset error of the input buffer and sigma-delta
modulator.
However, chopping is applied only behind the input resistor
divider stage; therefore, chopping does not eliminate the offset
error and drifts caused by the resistors. Figure 24 shows the
channel signal chain with chopping enabled.
CHOP
-
+
(CALIBRATIONS)
ARITHMETIC
SCALING
Data (hex)
28F5
0001
0000
FFFF
0001
0000
0000
INTERFACE
DIGITAL
SIGN
0
0
0
0
0
0
1
OUTPUT DATA
AT THE SELECTED
DATA RATE
AD7734
OVR
1
1
1
0
0
0
1