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FEATURES 10-Bit Temperature-to-Digital Converter -55 C to +125 C Operating Temperature Range 2 C Accuracy SPI- and DSP-Compatible Serial Interface Shutdown Mode Space-Saving SOT-23 Package APPLICATIONS Hard Disk Drives Personal Computers Electronic Test Equipment Office Equipment Domestic Appliances Process Control
10-Bit Digital Temperature Sensor in 6-Lead SOT-23 AD7814
FUNCTIONAL BLOCK DIAGRAM
BANDGAP TEMPERATURE SENSOR GND 10-BIT ANALOG/DIGITAL CONVERTER VDD
AD7814
TEMPERATURE VALUE REGISTER
SERIAL BUS INTERFACE
CS SCLK DIN DOUT
GENERAL DESCRIPTION
PRODUCT HIGHLIGHTS
The AD7814 is a complete temperature monitoring system in an SOT-23 package or 8-lead SOIC package. It contains a bandgap temperature sensor and 10-bit ADC to monitor and digitize the temperature reading to a resolution of +0.25C. The AD7814 has a flexible serial interface that allows easy interfacing to most microcontrollers. The interface is compatible with SPITM, QSPI and MICROWIRETM protocol and is also compatible with DSPs. The part features a standby mode that is controlled via the serial interface. The AD7814's wide supply voltage range, low supply current and SPI-compatible interface, make it ideal for a variety of applications, including personal computers, office equipment, and domestic appliances.
1. The AD7814 has an on-chip temperature sensor that allows an accurate measurement of the ambient temperature. The measurable temperature range is -55C to +125C, with a 2C temperature accuracy. 2. Supply voltage of +2.7 V to +5.5 V. 3. Space-saving 6-lead SOT-23 package and 8-lead SOIC package. 4. 10-bit temperature reading to +0.25C resolution. 5. The AD7814 features a standby mode that reduces the current consumption to 1 A.
SPI is a trademark of Motorola, Inc. MICROWIRE is a trademark of National Semiconductor, Inc.
REV. B
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. 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 (c) Analog Devices, Inc., 2000
AD7814-SPECIFICATIONS1, 2 (T = T
A
MIN
to TMAX, VDD = +2.7 V to +5.5 V, unless otherwise noted)
Max Units Test Conditions/Comments
Parameter
Min
Typ
TEMPERATURE SENSOR AND ADC Accuracy 2.0 10 400 25 2.7 250 1 80 3 3.3 6 2.4
2.0 2.5 3.5
Resolution Update Rate, tR Temperature Conversion Time SUPPLIES Supply Voltage Supply Current Normal Mode Shutdown Mode Power Dissipation Power Dissipation 1 sps 10 sps 100 sps DIGITAL INPUT Input High Voltage, VIH Input Low Voltage, VIL Input Current, IIN Input Capacitance, CIN DIGITAL OUTPUT Output High Voltage, VOH Output Low Voltage, VOL Output Capacitance, COUT
C C C Bits s s V A A W W W W V V A pF
TA = 0C to +85C. VDD = +3 V to +5.5 V3 TA = -40C to 0C. VDD = +3 V to +5.5 V3 TA = -55C to +125C. VDD = +3 V to +5.5 V
5.5 400 3
For Specified Performance
VDD = +3 V. Using Normal Mode VDD = +3 V. Using Shutdown Mode
0.8 1 10 VDD - 0.3 V 0.4 50
VIN = 0 V to VDD All Digital Inputs ISOURCE = ISINK = 200 A IOL = 200 A
V pF
NOTES 1 All specifications apply for -55C to +125C unless otherwise stated. 2 Guaranteed by design and characterization, not production tested. 3 For VDD = +2.7 V to +3 V and T A = -40C to +85C, the typical temperature error is 2C. Specifications subject to change without notice.
TIMING CHARACTERISTICS1, 2, 3 (T = T
A
MIN
to TMAX, VDD = +2.7 V to +5.5 V, unless otherwise noted)
Parameter t1 t2 t3 t4 4 t5 t6 t7 t8 4
Limit 0 50 50 35 20 0 0 40
Units ns min ns min ns min ns max ns min ns min ns min ns max
Comments CS to SCLK Setup Time SCLK High Pulsewidth SCLK Low Pulsewidth Data Access Time After SCLK Falling Edge Data Setup Time Prior to SCLK Rising Edge Data Hold Time After SCLK Rising Edge CS to SCLK Hold Time CS to DOUT High Impedance
NOTES 1 Guaranteed by design and characterization, not production tested. 2 All input signals are specified with tr = tf = 5 ns (10% to 90% of V DD) and timed from a voltage level of 1.6 V. 3 See Figure 2. 4 Measured with the load circuit of Figure 1.
-2-
REV. B
AD7814
ABSOLUTE MAXIMUM RATINGS*
VDD to GND . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 V to +7 V Digital Input Voltage to GND . . . . . . . -0.3 V to VDD + 0.3 V Digital Output Voltage to GND . . . . . -0.3 V to VDD + 0.3 V Operating Temperature Range . . . . . . . . . . -55C to +125C Storage Temperature Range . . . . . . . . . . . . -65C to +150C Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . +150C SOT-23, Power Dissipation . . . . . . . . . . . . . . . . . . . . 450 mW JA Thermal Impedance . . . . . . . . . . . . . . . . . . . . 240C/W Lead Temperature, Soldering Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . +215C Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . +220C SOIC Package, Power Dissipation . . . . . . . . . . . . . . 450 mW JA Thermal Impedance . . . . . . . . . . . . . . . . . . . . 206C/W Lead Temperature, Soldering Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . +215C Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . +220C
*Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
200 A
IOL
TO OUTPUT PIN
+1.6V CL 50pF
200 A
IOH
Figure 1. Load Circuit for Data Access Time and Bus Relinquish Time
ORDERING GUIDE
Model AD7814ART AD7814ARM
Temperature Range -55C to +125C -55C to +125C
Temperature Error* 2C 2C
Package Description 6-Lead SOT-23 8-Lead SOIC
Branding Information CAA CAA
Package Option RT-6 RM-8
*Temperature error is over 0C to +85C temperature range.
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 AD7814 features proprietary ESD protection circuitry, permanent 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.
WARNING!
ESD SENSITIVE DEVICE
REV. B
-3-
AD7814
PIN FUNCTION DESCRIPTION
Pin Mnemonic GND DIN
SOT-23 Pin No. 1 2
SOIC Pin No. 7 6
Description Analog and Digital Ground. Serial Data Input. Serial data to be loaded to the part's control register is provided on this input. Data is clocked into the control register on the rising edge of SCLK. Positive Supply Voltage, +2.7 V to +5.5 V. Serial Clock Input. This is the clock input for the serial port. The serial clock is used to clock data out of the temperature value register of the AD7814 and also to clock data into the control register on the part. Chip Select Input. Logic Input. The device is selected when this input is low. The SCLK input is disabled when this pin is high. Serial Data Output. Logic output. Data is clocked out of the temperature value register at this pin. Data is clocked out on the falling edge of SCLK. No Connect.
VDD SCLK
3 4
5 4
CS DOUT NC
5 6
3 2 1, 8
PIN CONFIGURATIONS SOT-23
GND 1
6
SOIC
DOUT CS SCLK
NC 1 DOUT 2
8 NC
AD7814
DIN 2 VDD 3
TOP VIEW (Not to Scale)
5 4
7 GND TOP VIEW CS 3 (Not to Scale) 6 DIN 5 VDD
AD7814
SCLK 4
NC = NO CONNECT
-4-
REV. B
AD7814
CIRCUIT INFORMATION Table I. Temperature Data Format
The AD7814 is a 10-bit digital temperature sensor. The part houses an on-chip temperature sensor, a 10-bit A/D converter, a reference and serial interface logic functions in an SOT-23 package. The A/D converter section consists of a conventional successive-approximation converter based around a capacitor DAC. The parts are capable of running on a +2.7 V to +5.5 V power supply. The on-chip temperature sensor allows an accurate measurement of the ambient device temperature to be made. The working measurement range of the AD7814 is -55C to +125C.
CONVERTER DETAILS
Temperature -128C -125C -100C -75C -50C -25C -0.25C 0C +0.25C +10C +25C +50C +75C +100C +125C +127C
SERIAL INTERFACE
Digital Output DB9 . . . DB0 10 0000 0000 10 0000 1100 10 0111 0000 10 1101 0100 11 0011 1000 11 1001 1100 11 1111 1111 00 0000 0000 00 0000 0001 00 0010 1000 00 0110 0100 00 1100 1000 01 0010 1100 01 1001 0000 01 1111 0100 01 1111 1100
The conversion clock for the part is internally generated so no external clock is required except when reading from and writing to the serial port. In normal mode, an internal clock oscillator runs the automatic conversion sequence. A conversion is initiated every 400 s. At this time, the part wakes up and performs a temperature conversion. This temperature conversion typically takes 25 s, at which time the part automatically shuts down. The result of the most recent temperature conversion is available in the serial output register at any time. The AD7814 can be placed in a shutdown mode, via the Control Register, in which case, the on-chip oscillator is shut down and no further conversions are initiated until the AD7814 is taken out of shutdown mode. The conversion result from the last conversion prior to shutdown can still be read from the AD7814 even when it is in shutdown mode. In the automatic conversion mode, every time read or write operation takes place, the internal clock oscillator is restarted at the end of the read or write operation. The result of the conversion is available, typically 25 s later. Similarly, when the part is taken out of shutdown mode, the internal clock oscillator is restarted and the conversion result is available, typically 25 s later. Reading from the device again before conversion is complete will again provide the same set of data.
TEMPERATURE VALUE REGISTER
The serial interface on the AD7814 consists of four wires, CS, SCLK, DIN and DOUT. The interface can be operated in 3-wire mode with DIN tied to Ground, in which case the interface has read-only capability, with data being read from the data register via the DOUT line. The DIN line is used to write the part into standby mode, if required. The CS line is used to select the device when more than one device is connected to the serial clock and data lines. The part operates in a slave mode and requires an externally applied serial clock to the SCLK input to access data from the data register. The serial interface on the AD7814 is designed to allow the part to be interfaced to systems that provide a serial clock that is synchronized to the serial data, such as the 80C51, 87C51, 68HC11, 68HC05 and PIC16Cxx microcontrollers as well as DSP processors. A read operation from the AD7814 accesses data from the Temperature Value Register while a write operation to the part writes data to the Control Register.
The temperature value register is a read-only register that stores the temperature reading from the ADC in 10-bit twos complement format. The temperature data format is shown in Table I. This shows the full theoretical range of the ADC from -128C to +127C, but in practice the temperature measurement range is limited to the operating temperature range of the device (-55C to +125C). A typical performance curve is shown in Figure 7.
REV. B
-5-
AD7814
CS
t1
SCLK 1 2
t2
3 4 11 15 16
t7
t4
DOUT LEADING ZERO DB9
t3
DB8 DB0
t8
t5
DIN DON'T CARE DON'T CARE
t6
POWERDOWN
Figure 2. Serial Interface Timing Diagram
Read Operation
Figure 2 shows the timing diagram for a serial read from the AD7814. The CS line enables the SCLK input. Ten bits of data are transferred during a read operation. Read operations occur during streams of 16 clock pulses. The serial data is accessed in a number of bytes if ten bits of data are being read. At the end of the read operation, the DOUT line remains in the state of the last bit of data clocked out of the AD7814 until CS returns high, at which time the DOUT line goes into three-state.
Write Operation
The serial data transfer to and from the AD7814 requires a 16-bit read operation. Many 8-bit microcontrollers have 8-bit serial ports and this 16-bit data transfer is handled as two 8-bit transfers. Other microcontrollers and DSP processors transfer 16 bits of data in a serial data operation.
AD7814 to MC68HC11 Interface
Figure 2 also shows the timing diagram for a serial write to the AD7814. The write operation takes place at the same time as the read operation. Data is clocked into the Control Register on the part on the rising edge of SCLK. Only the third bit in the data stream provides a user-controlled function. This third bit is the power-down bit which, when set to a 1, puts the AD7814 into shutdown mode. The first two bits of the data stream are don't cares while all other bits in the data stream other, than the power-down bit, should be 0 to ensure correct operation of the AD7814. Data is loaded to the Control Register on the fifteenth falling SCLK edge and the data takes effect at this time i.e., if the part is programmed to go into shutdown, it does so at this point. If the CS is brought high before this fifteenth SCLK edge, the Control Register will not be loaded and the power-down status of the part will not change.
MICROPROCESSOR INTERFACING
Figure 3 shows an interface between the AD7814 and the MC68HC11 microcontroller. The MC68HC11 is configured in the master mode with its CPOL bit set to a logic one and its CPHA bit set to a logic one. When the MC68HC11 is configured like this, its SCLK line idles high between data transfers. Data is transferred to and from the AD7814 in two 8-bit serial data operations. The diagram shows the full (four-wire) interface. PC1 of the MC68HC11 is configured as an output and used to drive the CS input.
AD7814*
SCLK DOUT DIN CS MC68HC11* SCLK MISO MOSI PC1
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 3. AD7814 to MC68HC11 Interface
AD7814 to 8051 Interface
The AD7814's serial interface allows for easy interface to most microcomputers and microprocessors. Figures 3 through 6 show some typical interface circuits. The serial interface on the AD7814 consists of four wires: CS, DIN, DOUT and SCLK. All interface circuits shown utilize all four interface lines. However, it is possible to operate the interface with three wires. If the application does not require the power-down facility offered by the AD7814, the DIN line can be tied permanently low. Thus, the interface can be operated from just three wires, SCLK, CS, and DOUT.
An interface circuit between the AD7814 and the microcontroller is shown in Figure 3. The 8xC51 is configured in its Mode 0 serial interface mode. The serial clock line of the 8xC51 (on P3.1) idles high between data transfers. Data is transferred to and from the AD7814 in two 8-bit serial data operations. The AD7814 outputs the MSB of its data stream as the first valid bit while the 8xC51 expects the LSB first. Thus, the data read into the serial buffer needs to be rearranged before the correct data word from the AD7814 is available in the accumulator.
-6-
REV. B
AD7814
In the example shown, the AD7814 is connected to the serial port of the 8051. Because the serial interface of the 8xC51 contains only one data line, the DIN line of the AD7814 is tied low in the interface example given in Figure 4. For applications that require the use of the power-down feature of the AD7814, the serial interface should be implemented using data port lines on the 8051. This allows a full-duplex serial interface to be implemented. The method involves `bitbanging' a port line to generate a serial clock while using two other port lines to shift data in and out with the fourth port line connecting to CS. Port lines 1.0 through 1.3 (with P1.1 configured as an input) can be used to connect to SCLK, DOUT, DIN and CS, respectively, to implement this scheme.
AD7814*
SCLK DOUT DIN CS P3.1 P3.0 P1.2 P1.3 8051*
The interface requires an inverter between the SCLK line of the ADSP-21xx and the SCLK input of the AD7814. The ADSP21xx has the TFS and RFS of the SPORT tied together with TFS set as an output and RFS set as an input. The DSP operates in Alternate Framing Mode and the SPORT Control Register is set up as described above.
AD7814*
SCLK DOUT DIN CS
ADSP-21xx*
SCK DR DT RFS TFS
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 6. AD7814 to ADSP-21xx Interface
MOUNTING THE AD7814
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 4. AD7814 to 8051 Interface
AD7814 to PIC16C6x/7x Interface
Figure 5 shows an interface circuit between the AD7814 and the PIC16C6x/7x microcontroller. The PIC16C6x/7x Synchronous Serial Port (SSP) is configured as an SPI master with the Clock Polarity bit set to a logic one. In this mode, the serial clock line of the PIC16C6x/7x idles high between data transfers. Data is transferred to and from the AD7814 in two 8-bit serial data operations. In the example shown, port line RA1 is being used to generate the CS for the AD7814.
AD7814*
SCLK DOUT DIN CS PIC16C6x/7x* SCK SDO SDI RA1
The AD7814 can be used for surface or air-temperature sensing applications. If the device is cemented to a surface with thermally conductive adhesive, the die temperature will be within about 0.1C of the surface temperature, thanks to the device's low power consumption. Care should be taken to insulate the back and leads of the device from the air, if the ambient air temperature is different from the surface temperature being measured. The ground pin provides the best thermal path to the die, so the temperature of the die will be close to that of the printed circuit ground track. Care should be taken to ensure that this is in good thermal contact with the surface being measured. As with any IC, the AD7814 and its associated wiring and circuits must be kept free from moisture to prevent leakage and corrosion, particularly in cold conditions where condensation is more likely to occur. Water-resistant varnishes and conformal coatings can be used for protection. The small size of the AD7814 package allows it to be mounted inside sealed metal probes, which provide a safe environment for the device.
SUPPLY DECOUPLING
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 5. AD7814 to PIC16C6x/7x Interface
AD7814 to ADSP-21xx Interface
The AD7814 should be decoupled with a 0.1 F ceramic capacitor between VDD and GND. This is particularly important if the AD7814 is mounted remote from the power supply.
1 0.8
TEMPERATURE ERROR
Figure 6 shows an interface between the AD7814 and the ADSP-21xx DSP processor. To ensure correct operation of the interface the SPORT Control Register should be set up as follows: TFSW = RFSW = 1, Alternate Framing INVRFS = INVTFS = 1, Active Low Framing Signal DTYPE = 00, Right Justify Data SLEN = 1111, 16-Bit Data Words ISCLK = 1, Internal Serial Clock TFSR = RFS = 1, Frame Every Word IRFS = 0, RFS Configured As Input ITFS = 1, TFS Configured As Output
0.6 0.4 0.2 0
-0.2 -0.4 -55
-40
0
25 40 TEMPERATURE - C
85
100
120
Figure 7. Typical AD7814 Temperature Error
REV. B
-7-
AD7814
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
0.122 (3.10) 0.106 (2.70)
0.071 (1.80) 0.059 (1.50) PIN 1
6 1
5 2
4 3
0.118 (3.00) 0.098 (2.50)
0.037 (0.95) BSC 0.075 (1.90) BSC 0.051 (1.30) 0.035 (0.90) 0.059 (0.15) 0.000 (0.00) 0.057 (1.45) 0.035 (0.90) 0.020 (0.50) SEATING 0.010 (0.25) PLANE 10 0.009 (0.23) 0 0.003 (0.08) 0.022 (0.55) 0.014 (0.35)
8-Lead Mini/Micro SOIC (RM-8)
0.122 (3.10) 0.114 (2.90)
8
5
0.122 (3.10) 0.114 (2.90)
1 4
0.199 (5.05) 0.187 (4.75)
PIN 1 0.0256 (0.65) BSC 0.120 (3.05) 0.112 (2.84) 0.006 (0.15) 0.002 (0.05) 0.018 (0.46) SEATING 0.008 (0.20) PLANE 0.043 (1.09) 0.037 (0.94) 0.011 (0.28) 0.003 (0.08) 0.120 (3.05) 0.112 (2.84) 33 27
0.028 (0.71) 0.016 (0.41)
-8-
REV. B
PRINTED IN U.S.A.
C3599a-0-5/00 (rev. B) 01041
6-Lead Plastic Surface Mount SOT-23 (RT-6)

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