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AD7816 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer AD7816
Beschreibung Single- and 4-Channel/ 9 us/ 10-Bit ADCs with On-Chip Temperature Sensor
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 16 Seiten
AD7816 Datasheet, Funktion
a Single- and 4-Channel, 9 s, 10-Bit ADCs
with On-Chip Temperature Sensor
AD7816/AD7817/AD7818
FEATURES
10-Bit ADC with 9 s Conversion Time
One (AD7818) and Four (AD7817) Single-Ended Analog
Input Channels
The AD7816 Is a Temperature Measurement Only Device
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%)
Over-Temperature Indicator
Automatic Power-Down at the End of a Conversion
Low Power Operation
4 W at a Throughput Rate of 10 SPS
40 W at a Throughput Rate of 1 kSPS
400 W at a Throughput Rate of 10 kSPS
Flexible Serial Interface
APPLICATIONS
Ambient Temperature Monitoring (AD7816)
Thermostat and Fan Control
High Speed Microprocessor
Temperature Measurement and Control
Data Acquisition Systems with Ambient Temperature
Monitoring (AD7817 and AD7818)
Industrial Process Control
Automotive
Battery Charging Applications
GENERAL DESCRIPTION
The AD7818 and AD7817 are 10-bit, single- and 4-channel
A/D converters with on-chip temperature sensor that can oper-
ate from a single 2.7 V to 5.5 V power supply. Each part con-
tains a 9 µs successive-approximation converter based around
a capacitor DAC, an on-chip temperature sensor with an accu-
racy of ± 2°C, an on-chip clock oscillator, inherent track-and-
hold functionality and an on-chip reference (2.5 V). The
AD7816 is a temperature monitoring only device in a SOIC/
µSOIC package.
The on-chip temperature sensor of the AD7817 and 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 Measuring Temperature section
of the data sheet.
SPI and QSPI are trademarks of Motorola, Inc.
MICROWIRE is a trademark of National Semiconductor Corporation.
REV. A
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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
FUNCTIONAL BLOCK DIAGRAM
REFIN
VDD
VIN1
VIN2
VIN3
VIN4
AD7817
TEMP
SENSOR
REF
2.5V
MUX
SAMPLING
CAPACITOR
OVER-TEMP
REG
B
CHARGE
REDISTRIBUTION
DAC
A>B
A
DATA
OUT
CONTROL
LOGIC
CONTROL
REG
VBALANCE
CLOCK
AGND DGND
BUSY
CONVST
OTI
DOUT
DIN
SCLK
RD/WR
CS
The AD7816, AD7817 and AD7818 have a flexible serial inter-
face that allows easy interfacing to most microcontrollers.
The interface is compatible with the Intel 8051, Motorola
SPI™ and QSPI™ protocols and National Semiconductors
MICROWIRE™ protocol. For more information refer to the
Serial Interface section of this data sheet.
The AD7817 is available in a narrow body 0.15" 16-lead Small
Outline IC (SOIC), in a 16-lead, Thin Shrink Small Outline
Package (TSSOP), while the AD7816/AD7818 come in an
8-lead Small Outline IC (SOIC) and an 8-lead microsmall
Outline IC (µSOIC).
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 over-temperature 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 over-
temperature register. The over-temperature indicator pin goes
logic low when a predetermined temperature is exceeded.
3. The automatic power-down feature enables the AD7816,
AD7817 and AD7818 to achieve superior power perfor-
mance at slower throughput rates, e.g., 40 µW at 1 kSPS
throughput rate.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 2000






AD7816 Datasheet, Funktion
AD7816/AD7817/AD7818
ABSOLUTE MAXIMUM RATINGS1
(TA = +25°C unless otherwise noted)
VDD to AGND . . . . . . . . . . . . . . . . . . . . . . . . . –0.3␣ V to +7␣ V
VDD to DGND . . . . . . . . . . . . . . . . . . . . . . . . . –0.3␣ V to +7␣ V
Analog Input Voltage to AGND
VIN1 to VIN4 . . . . . . . . . . . . . . . . . . . –0.3 V to VDD + 0.3 V
Reference Input Voltage to AGND2 . . . –0.3 V to VDD + 0.3␣ V
Digital Input Voltage to DGND . . . . . . –0.3 V to VDD + 0.3 V
Digital Output Voltage to DGND . . . . . –0.3 V to VDD + 0.3 V
Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C
Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . +150°C
TSSOP, Power Dissipation . . . . . . . . . . . . . . . . . . . . 450 mW
θJA Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 120°C/W
Lead Temperature, Soldering . . . . . . . . . . . . . . . . . +260°C
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . +215°C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . +220°C
16-Lead SOIC Package, Power Dissipation . . . . . . . . 450 mW
θJA Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 100°C/W
Lead Temperature, Soldering
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . +215°C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . +220°C
8-Lead SOIC Package, Power Dissipation . . . . . . . . . 450 mW
θJA Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 157°C/W
Lead Temperature, Soldering
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . +215°C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . +220°C
µSOIC Package, Power Dissipation . . . . . . . . . . . . . . 450 mW
θJA Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 206°C/W
Lead Temperature, Soldering
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . +215°C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . +220°C
NOTES
1Stresses above those listed under Absolute Maximum Ratings may cause perma-
nent damage to the device. This is a stress rating only; functional operation of the
device at these or any other conditions above those listed in the operational sections
of this specification is not implied. Exposure to absolute maximum rating condi-
tions for extended periods may affect device reliability.
2If the Reference Input Voltage is likely to exceed VDD by more than 0.3 V (e.g.,
during power-up) and the reference is capable of supplying 30 mA or more, it is
recommended to use a clamping diode between the REFIN pin and VDD pin. The
diagram below shows how the diode should be connected.
REFIN
VDD
BAT81
AD7816/AD7817
Model
Temperature
Range
AD7816AR
AD7816ARM
AD7817AR
AD7817BR
AD7817ARU
AD7817BRU
AD7817SR
AD7818AR
AD7818ARM
–55°C to +125°C
–55°C to +125°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–55°C to +125°C
–55°C to +125°C
–55°C to +125°C
ORDERING GUIDE
Temperature Package
Error @ +25°C Description
± 2°C
± 2°C
± 2°C
± 1°C
± 2°C
± 1°C
± 2°C
± 2°C
± 2°C
8-Lead Narrow Body (SOIC)
8-Lead µSOIC
16-Lead Narrow Body (SOIC)
16-Lead Narrow Body (SOIC)
16-Lead (TSSOP)
16-Lead (TSSOP)
16-Lead Narrow Body (SOIC)
8-Lead Narrow Body (SOIC)
8-Lead µSOIC
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection.
Although the AD7816/AD7817/AD7818 feature proprietary ESD protection circuitry, perma-
nent damage may occur on devices subjected to high energy electrostatic discharges. Therefore,
proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
Branding
Information
C4A
C3A
Package
Options
SO-8
RM-8
R-16A
R-16A
RU-16
RU-16
R-16A
SO-8
RM-8
WARNING!
ESD SENSITIVE DEVICE
–6– REV. A

6 Page









AD7816 pdf, datenblatt
AD7816/AD7817/AD7818
For example, if the result of a conversion on Channel 0 was
1000000000 (512 Dec), the ambient temperature is equal to
–103°C + (512/4) = +25°C.
Table II below shows some ADC codes for various temperatures.
Table II. Temperature Sensor Output
ADC Code
00 1100 0000
01 0011 1000
01 1001 1100
10 0000 0000
10 0111 1000
11 1001 0000
Temperature
–55°C
–25°C
0°C
+25°C
+55°C
+125°C
TEMPERATURE MEASUREMENT ERROR DUE TO
REFERENCE ERROR
The AD7816, AD7817 and AD7818 are trimmed using a preci-
sion +2.5 V reference to give the transfer function described
previously. To show the effect of the reference tolerance on a
temperature reading, the temperature sensor transfer function
can be rewritten as a function of the reference voltage and the
temperature.
CODE (Dec) = ([113.3285 × K × T]/[q × VREF] 0.6646) × 1024
where K = Boltzmann’s Constant, 1.38 × 10–23
q = Charge on an electron, 1.6 × 10–19
T = Temperature (K)
So, for example, to calculate the ADC code at 25°C
CODE = ([113.3285 × 298 × 1.38 × 10–23]/[1.6 × 10–19 × 2.5]
– 0.6646) × 1024
= 511.5 (200 Hex)
As can be seen from the expression, a reference error will pro-
duce a gain error. This means that the temperature measure-
ment error due to reference error will be greater at higher
temperatures. For example, with a reference error of –1%, the
measurement error at –55°C would be +2.2 LSBs (0.5°C) and
+16 LSBs (4°C) at +125°C.
SELF-HEATING CONSIDERATIONS
The AD7817 and AD7818 have an analog-to-digital conversion
function capable of a throughput rate of 100 kSPS. At this
throughput rate the AD7817 and AD7818 will consume be-
tween 4 mW and 6.5 mW of power. Because a thermal imped-
ance is associated with the IC package, the temperature of the
die will rise as a result of this power dissipation. The graphs
below show the self-heating effect in a 16-lead SOIC package.
Figures 12 and 13 show the self-heating effect on a two-layer
and four-layer PCB. The plots were generated by assembling a
heater (resistor) and temperature sensor (diode) in the package
being evaluated. In Figure 12, the heater (6 mW) is turned off
after 30 sec. The PCB has little influence on the self-heating
over the first few seconds after the heater is turned on. This can
be more clearly seen in Figure 13 where the heater is switched
off after 2 seconds. Figure 14 shows the relative effects of self-
heating in air, fluid and in thermal contact with a large heat
sink.
These diagrams represent the worst case effects of self-heating.
The heater delivered 6 mW to the interior of the package in all
cases. This power level is equivalent to the ADC continuously
converting at 100 kSPS. The effects of the self-heating can be
reduced at lower ADC throughput rates by operating on Mode
2—see Operating Modes section. When operating in this mode,
the on-chip power dissipation reduces dramatically and, as a
consequence, the self-heating effects.
0.50
2-LAYER PCB
0.45
0.40
0.35
0.30
0.25
0.20
4-LAYER PCB
0.15
0.10
0.05
0.00
–0.05
0
10 20 30 40 50 60
TIME – secs
Figure 12. Self-Heating Effect Two-Layer and
Four-Layer PCB
0.25
0.20
0.15
0.10
0.05
4-LAYER PCB
2-LAYER PCB
0.00
–0.05
0
1
2 3 45
TIME – secs
Figure 13. Self-Heating Effect Two-Layer and
Four-Layer PCB
–12–
REV. A

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