AD7294 Analog Devices, AD7294 Datasheet - Page 20

• Manufacturer Part Number: AD7294
• Description: 12-Bit Monitor and Control System with Multichannel ADC, DACs, Temperature Sensor, and Current Sense
• Manufacturer: Analog Devices

Specifications of AD7294

• Resolution (bits): 12bit
• # Chan: 9
• Sample Rate: 200kSPS
• Interface: I²C/Ser 2-Wire,Ser
• Analog Input Type: Diff-Uni,SE-Uni
• Ain Range: (Vref) p-p,2 V p-p,Uni (Vref),Uni (Vref) x 2
• Adc Architecture: SAR
• Pkg Type: CSP

AD7294
THEORY OF OPERATION
ADC OVERVIEW
The
on-chip track-and-hold, and a successive approximation ADC
based around a capacitive DAC. The analog input range for the
part can be selected as a 0 V to V
configured with either single-ended or differential analog inputs.
The
when an external reference is preferred. If the internal ADC
reference is to be used elsewhere in a system, the output must
first be buffered.
The various monitored and uncommitted input signals are multi-
plexed into the ADC. The
analog input channels, V
single-ended, differential, and pseudo differential mode
measurements of various system signals.
ADC TRANSFER FUNCTIONS
The designed code transitions occur at successive integer LSB
values (1 LSB, 2 LSB, and so on). In single-ended mode, the
LSB size is V
2 × V
transfer characteristic for the ADC when outputting straight
binary coding is shown in Figure 35.
In differential mode, the LSB size is 2 × V
to V
range is used. The ideal transfer characteristic for the ADC when
outputting twos complement coding is shown in Figure 36 (with
the 2 × V
NOTE
1. V
REF
AD7294
AD7294
REF
REF
000...010
000...001
000...000
111...000
111...110
011...111
111...111
range is used, and 4 × V
/4096 when the 0 V to 2 × V
IS EITHER V
REF
range).
Figure 35. Single-Ended Transfer Characteristic
REF
has an on-chip 2.5 V reference that can be disabled
provides the user with a 9-channel multiplexer, an
0V
/4096 when the 0 V to V
1LSB
REF
OR 2 × V
IN
0 to V
AD7294
REF
.
REF
ANALOG INPUT
IN
REF
/4096 when the 0 V to 2 × V
3. These four channels allow
input or a 2 × V
1LSB = V
has four uncommitted
REF
V
range is used. The ideal
REF
REF
REF
REF
range is used and
/4096 when the 0 V
– 1LSB
/4096
REF
input,
Rev. H | Page 20 of 48
REF
For V
straight binary, where
V
In differential mode, the code is twos complement, where
V
V
V
Channel 5 and Channel 6 (current sensor inputs) are twos
complement, where
V
V
V
Channel 7 to Channel 9 (temperature sensor inputs) are twos
complement with the LSB equal to 0.25°C, where
T
T
T
ANALOG INPUTS
The
the configuration register setup, they can be configured as two
single-ended inputs, two pseudo differential channels, or two
fully differential channels. See the Register Setting section for
further details.
Single-Ended Mode
The
In applications where the signal source has high impedance, it is
recommended to buffer the analog input before applying it to the
ADC. The analog input range can be programmed to be either
0 V to V
effectively divided by 2 before the conversion takes place. Note
that the voltage with respect to GND on the ADC analog input
pins cannot exceed AV
If the analog input signal to be sampled is bipolar, the internal
reference of the ADC can be used to externally bias up this
IN
IN
IN
IN
IN+
IN+
IN+
IN+
IN+
IN+
Figure 36. Differential Transfer Characteristic with V
= 0°C, and D
= +255.75°C, and D
= −256°C, and D
= 0 V, D
AD7294
AD7294
− V
− V
− V
− V
− V
− V
IN
000...001
000...000
100...010
100...001
100...000
011...110
011...111
111...111
0 to V
REF
IN−
IN−
IN−
IN−
IN−
IN−
= 0 V, and D
= V
= −V
= 0 mV, and D
= V
= −V
or 0 V to 2 × V
OUT
–V
IN
has a total of four analog inputs. Depending on
can have four single-ended analog input channels.
REF
3 in single-ended mode, the output code is
REF
REF
= x000, V
REF
REF
OUT
/12.5 − 1 LSB, D
+ 1LSB V
− 1 LSB, and D
1LSB = 2 × V
, and D
/12.5, D
= x000
OUT
DD
OUT
OUT
= x800
.
REF
IN
OUT
OUT
REF
OUT
= x7FF
= V
= x00
REF
– 1LSB
. In 2 × V
ANALOG INPUT
= x000
= x800
/4096
= x800
REF
OUT
OUT
− 1 LSB, and D
+V
= x7FF
= x7FF
REF
REF
– 1LSB
mode, the input is
REF
± V
Data Sheet
REF
OUT
Input Range
= xFFF