AD7294 Analog Devices, AD7294 Datasheet - Page 22

• 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
GND
Pseudo Differential Mode
The four uncommitted analog input channels can be configured
as two pseudo differential pairs. Uncommitted input, V
V
mode, V
maximum amplitude of V
range chosen) to make use of the full dynamic range of the part.
A dc input is applied to V
provides an offset from ground or a pseudo ground for the V
input. Which channel is V
allocation. The differential mode must be selected to operate in the
pseudo differential mode. The resulting converted pseudo differen-
tial data is stored in twos complement format in the result register.
The governing equation for the pseudo differential mode, for
V
where V
The benefit of pseudo differential inputs is that they separate
the analog input signal ground from the ADC ground, allowing
dc common-mode voltages to be cancelled. The typical voltage
range for V
Figure 40; Figure 41 shows a connection diagram for pseudo
differential mode.
IN
IN
Figure 39. Dual Op Amp Circuit to Convert a Single-Ended Bipolar Signal
1, are a pseudo differential pair, as are V
0 is
V
Figure 40. V
OUT
–0.5
2.0
1.5
1.0
0.5
IN+
2 × V
0
IN+
0
= 2(V
is the single-ended signal and V
IN−
is connected to the signal source, which can have a
REF
220kΩ
while in pseudo differential mode is shown in
p-p
440Ω
20kΩ
IN+
IN−
A
1
into a Differential Unipolar Signal
Input Range vs. V
− V
220Ω
220Ω
220Ω
IN−
) − V
V+
V–
V+
V–
IN+
IN−
2
REF
1
. The voltage applied to this input
is determined by the ADC channel
10kΩ
ADDITIONAL PINS OMITTED FOR CLARITY.
(or 2 × V
REF_ADC
27Ω
27Ω
V
REF
REF
3
in Pseudo Differential Mode
(V)
REF
, depending on the
3.75V
2.5V
1.25V
3.75V
2.5V
1.25V
4
IN−
AV
V
IN
DRIVE
is a dc voltage.
2 and V
DD
V
V
= DV
IN+
IN–
= 5V
5
REF
DD
AD7294
IN
= 5V
OUT
3. In this
IN
0 and
0.47µF
6
ADC
IN+
1
Rev. H | Page 22 of 48
CURRENT SENSOR
Two bidirectional high-side current sense amplifiers are
provided that can accurately amplify differential current shunt
voltages in the presence of high common-mode voltages from
AV
differential input. Both current sense amplifiers have a fixed
gain of 12.5 and utilize an internal 2.5 V reference.
An analog comparator is also provided with each amplifier for
fault detection. The threshold is defined as
When this limit is reached, the output is latched onto a
dedicated pin. This output remains high until the latch is
cleared by writing to the appropriate register.
The
differential and an instrumentation amplifier. A load current
flowing through the external shunt resistor produces a voltage
at the input terminals of the AD7294. Resistors R1 and R2
connect the input terminals to the differential amplifier (A1).
A1 nulls the voltage appearing across its own input terminals
by adjusting the current through R1 and R2 with Transistor Q1
and Transistor Q2. Common-mode feedback maintains the sum
of these currents at approximately 50 μA. When the input signal
to the
the differential signal is nonzero, the current increases through
one of the resistors and decreases in the other. The current differ-
ence is proportional to the size and polarity of the input signal.
The differential currents through Q1 and Q2 are converted into
a differential voltage by R3 and R4. A2 is configured as an instru-
mentation amplifier, buffering this voltage and providing additional
DD
AD7294
1.2 × Full-Scale Voltage Range
up to 59.4 V. Each amplifier can accept a ±200 mV
AD7294
AV
V
REF
p-p
Figure 41. Pseudo Differential Mode Connection Diagram
DD
TO 54.5V
current sense comprises two main blocks: a
is zero, the currents in R1 and R2 are equal. When
Figure 42. High-Side Current Sense
V
PP
AD7294
1
ADDITIONAL PINS OMITTED FOR CLARITY.
100kΩ
VOLTAGE
DC INPUT
R3
Q1
RS(+)
40kΩ
R1
R
SENSE
A1
A1
RS(–)
R2
40kΩ
Q2
REF
I
V
V
R4
100kΩ
LOAD
IN+
IN–
OUT
A2
/REF
AD7294
Data Sheet
0.47µF
IN
V
TO MUX
OUT
ADC
1