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PDF AD7818 Data sheet ( Hoja de datos )
| Número de pieza | AD7818 | |
| Descripción | 10-Bit ADC | |
| Fabricantes | Analog Devices | |
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Data Sheet
4-Channel/Single-Channel, 9 μs,
10-Bit ADCs with On-Chip Temperature Sensor
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
device 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
REFIN
VDD
VIN1
VIN2
VIN3
VIN4
AD7817
TEMP
SENSOR
REF
2.5V
MUX
SAMPLING
CAPACITOR
OVERTEMP B
REG
CHARGE
REDISTRIBUTION
DAC
A>B
A
DATA
OUT
CONTROL
LOGIC
REG
CONTROL
VBALANCE
CLOCK
AGND DGND
BUSY
CONVST
Figure 1. AD7817 Functional Block Diagram
VDD
AD7818
TEMP
SENSOR
REF
2.5V
OVERTEMP
REG
B
CHARGE
REDISTRIBUTION
DAC
A>B
A
DATA
OUT
VIN1
MUX
SAMPLING
CAPACITOR
CONTROL
LOGIC
CONTROL
REG
VBALANCE
CLOCK
GENERATOR
AGND
CONVST
Figure 2. AD7818 Functional Block Diagram
OTI
DOUT
DIN
SCLK
RD/WR
CS
OTI
DIN/OUT
SCLK
RD/WR
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. E
Document Feedback
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700 ©2012–2015 Analog Devices, Inc. All rights reserved.
Technical Support
www.analog.com
1 page  
Data Sheet
AD7817/AD7818
Parameter
POWER REQUIREMENTS (AD7818 ONLY)6
VDD
IDD
Normal Operation
Using External Reference
Power-Down (VDD = 5 V)
Power-Down (VDD = 3 V)
Auto Power-Down Mode
10 SPS Throughput Rate
1 kSPS Throughput Rate
10 kSPS Throughput Rate
Power-Down
ANALOG INPUTS (AD7817/AD7818)7
Input Voltage Range
Input Leakage
Input Capacitance
LOGIC INPUTS (AD7817/AD7818)4
Input High Voltage, VINH
Input Low Voltage, VINL
Input High Voltage, VINH
Input Low Voltage, VINL
Input Current, IIN
Input Capacitance, CIN
LOGIC OUTPUTS (AD7817/AD7818)4
Output High Voltage, VOH
Output Low Voltage, VOL
High Impedance Leakage Current
High Impedance Capacitance
A Version1 B Version1 S Version1 Unit
5.5 V max
2.7 V min
2
1.75
10.75
4.5
mA max
mA max
μA max
μA max
6.4 μW typ
48.8 μW typ
434 μW typ
13.5 μW max
VREF VREF VREF V max
0 0 0 V min
±1 ±1 ±1 μA min
10 10 10 pF max
2.4 2.4 2.4 V min
0.8 0.8 0.8 V max
2 2 2 V min
0.4 0.4 0.4 V max
±3 ±3 ±3 μA max
10 10 10 pF max
4 4 4 V min
2.4 2.4 2.4 V min
0.4 0.4 0.4 V max
0.2 0.2 0.2 V max
±1 ±1 ±1 μA max
15 15 15 pF max
Test Conditions/Comments
For specified performance
Logic inputs = 0 V or VDD
1.3 mA typical
2.5 V internal reference connected
6 μA typ
2 μA typ
VDD = 3 V
See the Power vs. Throughput section
for description of power dissipation
in auto power-down mode
Typically 6 μW
VDD = 5 V ±10%
VDD = 5 V ±10%
VDD = 3 V ±10%
VDD = 3 V ±10%
Typically 10 nA, VIN = 0 V to VDD
ISOURCE = 200 μA
VDD = 5 V ± 10%
VDD = 3 V ± 10%
ISINK = 200 μA
VDD = 5 V ± 10%
VDD = 3 V ± 10%
1 The B Version and the S Version only apply to the AD7817. The A Version applies to the AD7817 or the AD7818 (as stated in specification).
2 See Terminology.
3 The accuracy of the temperature sensor is affected by reference tolerance. The relationship between the two is explained in the Temperature Measurement Error Due
to Reference Error section.
4 Sample tested during initial release and after any redesign or process change that may affect this parameter.
5 On-chip reference shuts down when external reference is applied.
6 These specifications are typical for AD7818 at temperatures above 85°C and with VDD greater than 3.6 V.
7 This refers to the input current when the part is not converting. Primarily due to the reverse leakage current in the ESD protection diodes.
Rev. E | Page 5 of 20
5 Page 
Data Sheet
CONTROL BYTE
The AD7817/AD7818 contain two on-chip registers, the
address register and the overtemperature register. These
registers can be accessed by carrying out an 8-bit serial write
operation to the devices. The 8-bit word or control byte written to
the AD7817/AD7818 is transferred to one of the two on-chip
registers as follows.
Address Register
If the five MSBs of the control byte are logic zero, the three LSBs
of the control byte are transferred to the address register (see
Figure 6). The address register is a 3-bit-wide register used to
select the analog input channel on which to carry out a conversion.
It is also used to select the temperature sensor, which has the 000
address. Table 6 shows the channel selection. The internal reference
selection connects the input of the ADC to a band gap reference.
When this selection is made and a conversion is initiated, the ADC
output must be approximately midscale. After power-up, the
default channel selection is DB2 = DB1 = DB0 = 0 (temperature
sensor).
Table 6. Channel Selection
DB2 DB1 DB0 Channel Selection
0 0 0 Temperature sensor
0 0 1 Channel 1
0 1 0 Channel 2
0 1 1 Channel 3
1 0 0 Channel 4
1 1 1 Internal reference (1.23 V)
Device
All
All
AD7817
AD7817
AD7817
All
AD7817/AD7818
Overtemperature Register
If any of the five MSBs of the control byte are logic one, the entire
eight bits of the control byte are transferred to the overtemperature
register (see Figure 6). At the end of a temperature conversion,
a digital comparison is carried out between the 8 MSBs of the
temperature conversion result (10 bits) and the contents of the
overtemperature register (8 bits). If the result of the temperature
conversion is greater than the contents of the overtemperature
register (OTR), the overtemperature indicator (OTI) goes logic
low. The resolution of the OTR is 1°C. The lowest temperature
that can be written to the OTR is −95°C and the highest is
+152°C (see Figure 7). However, the usable temperature range of
the temperature sensor is −55°C to +125°C. Figure 7 shows the
OTR and how to set TALARM (the temperature at which the OTI
goes low).
OTR (Dec) = TALARM (°C) + 103°C
For example, to set TALARM to 50°C, OTR = 50 + 103 = 153 Dec
or 10011001 bin. If the result of a temperature conversion exceeds
50°C, OTI goes logic low. The OTI logic output is reset high at the
end of a serial read operation or if a new temperature measurement
is lower than TALARM. The default power on TALARM is 50°C.
DB2 DB1 DB0 ADDRESS REGISTER
IF ANY BIT DB7 TO DB3 ARE LOGIC 0
THEN DB2 TO DB0 ARE WRITTEN TO
THE ADDRESS REGISTER
MSB
LSB
DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 CONTROL BYTE
DB7
IF ANY BIT DB7 TO DB3 IS SET TO A
LOGIC 1, THEN THE FULL 8 BITS OF THE
CONTROL WORD ARE WRITTEN TO THE
OVERTEMPERATURE REGISTER
DB6 DB5 DB4 DB3 DB2 DB1
DB0
OVERTEMPERATURE
REGISTER (OTR)
Figure 6. Address and Overtemperature Register Selection
OVERTEMPERATURE REGISTER
MSB
LSB
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
00001000
11111111
OVERTEMPERATURE REGISTER (DEC) = TALARM + 103°C
TALARM RESOLUTION = 18/LSB
Figure 7. The Overtemperature Register (OTR)
MINIMUM TEMPERATURE = –95°C
MAXIMUM TEMPERATURE = +152°C
Rev. E | Page 11 of 20
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet AD7818.PDF ] | |
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