AD7818_15 Datasheet, PDF (1/20 Pages) Analog Devices – Dual, Low Power CMOS, Analog Front End with DSP Microcomputer

Data Sheet
Dual, Low Power CMOS, Analog Front End
with DSP Microcomputer
AD7817/AD7818
FEATURES
10-bit ADC with 9 µs conversion time
1 AD7818 and 4 AD7817 single-ended analog input channels
On-chip temperature sensor
Resolution of 0.25°C
±2°C error from −40°C to +85°C
−55°C to +125°C operating range
Wide operating supply range: 2.7 V to 5.5 V
Inherent track-and-hold functionality
On-chip reference (2.5 V ± 1%)
Overtemperature indicator
Automatic power-down at the end of a conversion
Low power operation
4 µW at a throughput rate of 10 SPS
40 µW at a throughput rate of 1 kSPS
400 µW at a throughput rate of 10 kSPS
Flexible serial interface
APPLICATIONS
Data acquisition systems with ambient temperature
monitoring
Industrial process control
Automotive
Battery charging applications
GENERAL DESCRIPTION
The AD7817/AD7818 are 10-bit, single- and 4-channel analog-to-
digital converters (ADCs) with an on-chip temperature sensor that
can operate from a single 2.7 V to 5.5 V power supply. Each part
contains a 9 µs successive approximation converter based around
a capacitor digital-to-analog converter (DAC), an on-chip
temperature sensor with an accuracy of ±2°C, an on-chip clock
oscillator, inherent track-and-hold functionality, and an on-chip
reference (2.5 V).
The on-chip temperature sensor of the AD7817/AD7818 can
be accessed via Channel 0. When Channel 0 is selected and a
conversion is initiated, the resulting ADC code at the end of the
conversion gives a measurement of the ambient temperature with a
resolution of ±0.25°C. See the Temperature Measurement section.
The AD7817/AD7818 have a flexible serial interface that allows
easy interfacing to most microcontrollers. The interface is
compatible with the Intel 8051, Motorola SPI and QSPI, and
National Semiconductors MICROWIRE protocols. For more
FUNCTIONAL BLOCK DIAGRAMS
REF_IN
V_DD
AD7817
V_IN1
V_IN2
V_IN3
V_IN4
TEMP
SENSOR
REF
2.5V
MUX
SAMPLING
CAPACITOR
OVERTEMP _B
REG
CHARGE
REDISTRIBUTION
DAC
A>B
A
DATA
OUT
CONTROL
LOGIC
REG
CONTROL
V_BALANCE
CLOCK
OTI
D_OUT
D_IN
SCLK
RD/WR
CS
AGND DGND
BUSY
CONVST
Figure 1. AD7817 Functional Block Diagram
V_DD
AD7818
TEMP
SENSOR
REF
2.5V
OVERTEMP _B
REG
CHARGE
REDISTRIBUTION
DAC
A>B
A
DATA
OUT
V_IN1
MUX
SAMPLING
CAPACITOR
V_BALANCE
CONTROL
LOGIC
CONTROL
REG
CLOCK
GENERATOR
OTI
D_IN/OUT
SCLK
RD/WR
AGND
CONVST
Figure 2. AD7818 Functional Block Diagram
information, refer to the AD7817 Serial Interface section and
the AD7818 Serial Interface Mode section.
The AD7817 is available in a narrow body, 0.15 inch, 16-lead
SOIC and a 16-lead TSSOP, and the AD7818 comes in an 8-lead
SOIC and an 8-lead MSOP.
PRODUCT HIGHLIGHTS
1. The devices have an on-chip temperature sensor that allows
an accurate measurement of the ambient temperature to be
made. The measurable temperature range is −55°C to +125°C.
2. An overtemperature indicator is implemented by carrying out a
digital comparison of the ADC code for Channel 0 (temperature
sensor) with the contents of the on-chip overtemperature
register. The overtemperature indicator pin goes logic low
when a predetermined temperature is exceeded.
3. The automatic power-down feature enables the AD7817 and
AD7818 to achieve superior power performance at slower
throughput rates, that is, 40 µW at 1 kSPS throughput rate.
Rev. D
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