AD7298 Analog Devices, AD7298 Datasheet - Page 14

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AD7298

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

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

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AD7298
TEMPERATURE SENSOR OPERATION
The AD7298 contains one local temperature sensor. The
on-chip, band gap temperature sensor measures the temp-
erature of the AD7298 die.
The temperature sensor module on the AD7298 is based on
the three-current principle (see Figure 24), where three currents
are passed through a diode and the forward voltage drop is
measured, allowing the temperature to be calculated free of
errors caused by series resistance.
NOTES
1. V
I
111...111
111...110
TRANSISTOR
111...000
011...111
REF
000...010
000...001
000...000
Figure 24. Top-Level Structure of Internal Temperature Sensor
INTERNAL
IS 2.5V.
SENSE
4 × I
Figure 23. Straight Binary Transfer Characteristic
0V
1LSB
8 × I
I
BIAS
ANALOG INPUT
BIAS
DIODE
1LSB = V
V
DD
+V
REF
REF
/4096
– 1LSB
V
TO ADC
V
OUT+
OUT–
Rev. B | Page 14 of 24
The temperature conversion consists of two phases, the integra-
tion followed by the conversion. The integration is initiated on
the CS falling edge. It takes a period of approximately 100 μs to
complete the integration and conversion of the temperature
result. When the integration is completed, the conversion is
initiated automatically. Once the temperature integration is
initiated, the T
temperature conversion is in progress and remains high until
the conversion is completed.
Theoretically, the temperature measuring circuit can measure
temperatures from –512°C to +511°C with a resolution of
0.25°C. However, temperatures outside T
temperature range for the AD7298) are outside the guaranteed
operating temperature range of the device. The temperature
sensor is selected by setting the T
TEMPERATURE SENSOR AVERAGING
The AD7298 incorporates a temperature sensor averaging
feature to enhance the accuracy of the temperature measure-
ments. To enable the temperature sensor averaging feature, both
the T
control register. In this mode the temperature is internally
averaged to reduce the effect of noise on the temperature result.
The temperature is measured each time a T
performed and a moving average method is used to determine
the result in the T
given by the following equation:
The T
T
The first T
temperature sensor and averaging mode has been selected in
the control register (Bit D1 and Bit D5) is the actual first T
conversion result. If the control register is written to and the
content of the T
reset and the next T
temperature conversion result. If the status of the T
is not changed on successive writes to the control register, the
averaging function is reinitialized and continues calculating the
cumulative average.
The user has the option of disabling the averaging by setting
Bit T
on power-up with the averaging function disabled. The total
time to measure a temperature channel is typically 100 μs.
T
SENSE
SENSE
SENSE
SENSE
AVG
AVG result, a moving average temperature measurement.
SENSE
AVG to 0 in the control register. The AD7298 defaults
AVG bit and the T
=
result read when averaging is enabled is the
SENSE
7
8
(
SENSE_
Previous
conversion result given by the AD7298 after the
SENSE
SENSE
BUSY signal goes high to indicate that a
SENSE
AVG bit changed, the averaging function is
Result Register. The average result is
_
average conversion result is the current
Average
SENSE
bit must be enabled in the
_
SENSE
Result
bit in the control register.
)
A
+
(the specified
SENSE
1
8
(
Current
conversion is
SENSE
_
AVG bit
Result
SENSE
)

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