AD7298 Analog Devices, AD7298 Datasheet - Page 15

• Manufacturer Part Number: AD7298
• Description: 8-Channel, 1MSPS, 12-Bit SAR ADC with Temperature Sensor
• Manufacturer: Analog Devices

Specifications of AD7298

• Resolution (bits): 12bit
• # Chan: 8
• Sample Rate: 1MSPS
• Interface: SPI
• Analog Input Type: SE-Uni
• Ain Range: Uni (Vref),Uni 1.0V,Uni 1.25,Uni 2.0V,Uni 2.5V
• Adc Architecture: SAR
• Pkg Type: CSP

Temperature Value Format
One LSB of the ADC corresponds to 0.25°C. The temperature
reading from the ADC is stored in a 12-bit twos complement
format to accommodate both positive and negative temperature
measurements. The temperature data format is provided in
Table 6.
Table 6. Temperature Data Format
Temperature (°C)
−40
−25
−10
−0.25
0
+0.25
+10
+25
+50
+75
+100
+105
+125
The temperature conversion formulas are as follows:
The previous formulas are for a V
If an external reference is used, the temperature sensor requires
an external reference of between 2 V and 2.5 V for correct
operation. When an external reference of less than 2.5 V is
applied, the temperature results are calculated using the
following formula, where V
reference voltage.
Positive Temperature = ADC Code/4
Negative Temperature = (4096 − ADC Code)/4
Temperatur
e
=
V
EXT
_
REF
⎛
⎜
⎝
EXT_REF
ADCCode
10
REF
is the value of the external
Digital Output
1111 0110 0000
1111 1001 1100
1111 1101 1000
1111 1111 1111
0000 0000 0000
0000 0000 0001
0000 0010 1000
0000 0110 0100
0000 1100 1000
0001 0010 1100
0001 1001 0000
0001 1010 0100
0001 1111 0100
of 2.5 V only.
+
109
3 .
⎞
⎟
⎠
−
273
.
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Rev. B | Page 15 of 24
V
The AD7298 also provides the V
voltage at which the serial interface operates. V
ADC to easily interface to both 1.8 V and 3 V processors. For
example, if the AD7298 is operated with a V
V
This enables the AD7298 to operate with a larger dynamic
range with a V
1.8 V processors. Take care to ensure V
V
section).
THE INTERNAL OR EXTERNAL REFERENCE
The AD7298 can operate with either the internal 2.5 V on-chip
reference or an externally applied reference. The EXT_REF bit
in the control register is used to determine whether the internal
reference is used. If the EXT_REF bit is selected in the control
register, an external reference can be supplied through the
V
Suitable external reference sources for the AD7298 include
AD780, AD1582, ADR431, REF193, and ADR391.
The internal reference circuitry consists of a 2.5 V band gap
reference and a reference buffer. When the AD7298 operates in
internal reference mode, the 2.5 V internal reference is available
at the V
capacitor. It is recommended that the internal reference be buffered
before applying it elsewhere in the system.
The internal reference is capable of sourcing up to 2 mA of
current when the converter is static. The reference buffer
requires 5.5 ms to power up and charge the 10 μF decoupling
capacitor during the power-up time.
DRIVE
DRIVE
DD
REF
by more than 0.3 V (see the Absolute Maximum Ratings
pin. On power-up, the internal reference is enabled.
pin can be powered from a 1.8 V supply.
REF
pin, which should be decoupled to GND1 using a 10 μF
DD
of 3.3 V while still being able to interface to
DRIVE
feature. V
DRIVE
does not exceed
DD
of 3.3 V, the
DRIVE
DRIVE
AD7298
allows the
controls the