AD7452 Analog Devices, AD7452 Datasheet - Page 18

• Manufacturer Part Number: AD7452
• Description: Differential Input, 555 kSPS, 12-Bit A/D Converter in 8-Lead SOT-23
• Manufacturer: Analog Devices

Specifications of AD7452

• Resolution (bits): 12bit
• # Chan: 1
• Sample Rate: 555kSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: (2Vref) p-p
• Adc Architecture: SAR
• Pkg Type: SOT

AD7452
DIGITAL INPUTS
The digital inputs applied to the AD7452 are not limited by the
maximum ratings, which limit the analog limits. Instead the
digital inputs applied, i.e., CS and SCLK, can go to 7 V and are
not restricted by the V
The main advantage of the inputs being unrestricted to the
V
avoided. If CS and SCLK are applied before V
of latch-up as there would be on the analog inputs if a signal
greater than 0.3 V was applied prior to V
REFERENCE
An external reference source is required to supply the reference
to the AD7452. This reference input can range from 100 mV to
3.5 V. With a 5 V power supply, the specified reference is 2.5 V
and the maximum reference is 3.5 V. With a 3 V power supply,
the specified reference is 2 V and the maximum reference is
2.2 V. In both cases, the reference is functional from 100 mV.
It is important to ensure that when choosing the reference value
for a particular application, the maximum analog input range
(V
maximum ratings of the device. The following two examples
calculate the maximum V
operating the AD7452 at a V
Example 1
V
V
If V
Therefore
3 × V
V
Thus, when operating at V
from 100 mV to a maximum value of 3.5 V. When V
V
Example 2
V
V
If V
Therefore
3 × V
V
Thus, when operating at V
from 100 mV to a maximum value of 2.2 V. When V
V
DD
IN
IN
REF
REF
IN
IN
REF
REF
IN
max = V
max = V
max = V
max = V
DD
DD
+ 0.3 V limit is that power supply sequencing issues are
max) is never greater than V
max = 3.5 V
max = 3.17 V.
max = 2.2 V
max = 2 V.
REF
REF
= 5 V, then V
= 3 V, then V
/2 = 5.3 V
/2 = 3.3 V
DD
REF
DD
REF
+ 0.3
+ 0.3
+ V
+ V
REF
REF
IN
IN
/2
max = 5.3 V.
/2
max = 3.3 V.
DD
+ 0.3 V limits as on the analog input.
REF
DD
DD
DD
input that can be used when
= 5 V, the value of V
= 3 V, the value of V
of 5 V and 3 V, respectively.
DD
+ 0.3 V to comply with the
DD
.
DD
, there is no risk
REF
REF
DD
DD
can range
can range
= 4.75 V,
= 2.7 V,
Rev. B | Page 18 of 28
These examples show that the maximum reference applied to
the AD7452 is directly dependent on the value applied to V
The value of the reference sets the analog input span and the
common-mode voltage range. Errors in the reference source
result in gain errors in the AD7452 transfer function and add to
specified full-scale errors on the part. A 0.1 µF capacitor should
be used to decouple the V
Figure 33 shows a typical connection diagram for the V
Table 5. Examples of Suitable Voltage References
Reference
AD780
ADR421
ADR420
SINGLE-ENDED OPERATION
When supplied with a 5 V power supply, the AD7452 can han-
dle a single-ended input. The design of this part is optimized for
differential operation, so with a single-ended input, perfor-
mance degrades. Linearity degrades by 0.2 LSB typically, the
full-scale errors degrade by 1 LSB typically, and ac performance
is not guaranteed.
To operate the AD7452 in single-ended mode, the V
coupled to the signal source, while the V
appropriate voltage corresponding to the midscale code transi-
tion. This voltage is the common mode, which is a fixed dc
voltage (usually the reference). The V
this value and should have a voltage span of 2 × V
use of the full dynamic range of the part. The input signal
therefore has peak-to-peak values of common mode ± V
the analog input is unipolar, an op amp in a noninverting unity
gain configuration can be used to drive the V
the ADC operates from a single supply, it is necessary to level
shift ground-based bipolar signals to comply with the input
requirements. An op amp can be configured to rescale and level
shift the ground-based bipolar signal so it is compatible with
the selected input range of the AD7452 (see Figure 34).
*ADDITIONAL PINS OMITTED FOR CLARITY
V
DD
0.1µF
Figure 33. Typical V
10nF
Output
Voltage (V)
2.5/3
2.5
2.048
0.1µF
NC
REF
REF
1
2
3
4
Connection Diagram for V
NC = NO CONNECT
V
TEMP
GND
pin to GND.
IN
AD780
Initial
Accuracy (%)
0.04
0.04
0.05
OPSEL
V
TRIM
OUT
IN+
8
7
6
5
IN–
input swings around
2.5V
NC
NC
NC
input is biased to the
IN+
pin. Because
DD
Operating
Current (µA)
1000
500
500
REF
AD7452*
= 5 V
IN+
to make
0.1µF
input is
REF
REF
pin.
V
V
DD
. If
REF
DD
.