a SMBus/I2C®-Compatible, 10-Bit Digital Temperature Sensors in SOT-23 AD7414/AD7415 FEATURES 10-Bit Temperature-to-Digital Converter Temperature Range: –40ⴗC to +85ⴗC Accuracy of ⴞ2ⴗC SMBus/I2C-Compatible Serial Interface 3 A Power-Down Current Temperature Conversion Time: 29 s Typ Space-Saving 6-Lead (AD7414) and 5-Lead (AD7415) SOT-23 Packages Pin-Selectable Addressing via AS Overtemperature Indicator (AD7414 Only) SMBus Alert Function (AD7414 Only) Four Versions Allow Eight I2C Addresses (AD7414) Two Versions Allow Six I2C Addresses (AD7415) APPLICATIONS Hard Disk Drives Personal Computers Electronic Test Equipment Office Equipment Domestic Appliances Process Control Cellular Phones FUNCTIONAL BLOCK DIAGRAM GND 10-BIT ANALOG-DIGITAL CONVERTER BANDGAP TEMPERATURE SENSOR +VDD CONFIGURATION REGISTER TEMPERATURE VALUE REGISTER THIGH SETPOINT REGISTER SETPOINT COMPARATOR TLOW SETPOINT REGISTER SM BUS/I2C INTERFACE AS The AD7414/AD7415 provides a 2-wire serial interface that is compatible with SMBus and I2C interfaces. The part comes in four versions, AD7414/AD7415-0, AD7414/AD7415-1, AD7414-2 and the AD7414-3. The AD7414/AD7415-0 and AD7414/ AD7415-1 versions allow for a choice of three different SMBus addresses for each version. All four AD7414 versions give the possibility of eight different I2C addresses while the two AD7415 versions allow up to six I2C addresses to be used. The AD7414/AD7415’s 2.7 V supply voltage, low supply current, serial interface, and small package size, make it ideal for a variety of applications, including personal computers, office equipment, cellular phones, and domestic appliances. In the AD7414, on-chip registers can be programmed with high and low temperature limits, and an open drain Over-Temperature Indicator output (ALERT), which becomes active when a programmed limit is exceeded. A configuration register allows programming of the sense of the ALERT output (active high or active low). This output can be used as an interrupt or as an SMBus alert. SCL SDA AD7414 AD7415 GND 10-BIT ANALOG-DIGITAL CONVERTER BANDGAP TEMPERATURE SENSOR GENERAL DESCRIPTION The AD7414/AD7415 is a complete temperature monitoring system in 6-lead and 5-lead SOT-23 packages. It contains a bandgap temperature sensor and 10-bit ADC to monitor and digitize the temperature reading to a resolution of 0.25°C. ALERT +VDD TEMPERATURE VALUE REGISTER CONFIGURATION REGISTER AS SMBus/I2C INTERFACE SCL SDA PRODUCT HIGHLIGHTS 1. The AD7414/AD7415 has an on-chip temperature sensor that allows an accurate measurement of the ambient temperature to be made. It is capable of ± 2°C temperature accuracy. 2. SMBus/I2C-Compatible Serial Interface with pin-selectable choice of three addresses per version of the AD7414/AD7415, eight address options in total for the AD7414 and six in total for the AD7415. 3. Supply voltage of 2.7 V to 5.5 V. 4. Space-saving 5-lead and 6-lead SOT-23 packages. 5. 10-bit temperature reading to 0.25°C resolution. 6. The AD7414 has an Over Temperature Indicator which can be software disabled. Used as an interrupt of SMBus alert. 7. One-shot and automatic temperature conversion rates. 2 I C is a registered trademark of Philips Corporation. REV. 0 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. 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 www.analog.com Fax: 781/326-8703 © Analog Devices, Inc., 2001 AD7414/AD7415–SPECIFICATIONS1 (T = T A Parameter MIN to TMAX, VDD = 2.7 V to 5.5 V, unless otherwise noted.) A Version Unit Test Conditions/Comments ± 2.0 ± 3.0 10 800 25 °C max °C max Bits ms typ µs typ VDD = 3 V VDD = 5.5 V 1.2 mA typ Peak current during conversion. 169 188 µA typ µA typ Supply current with serial bus inactive. Part not converting and D7 of Configuration Register = 0. 180 214 3 µA typ µA typ µA max Supply current with serial bus active. Part not converting and D7 of Configuration Register = 0. D7 of Configuration Register = 1. Typical values are 0.04 µA at 3 V and 0.5 µA at 5 V. DIGITAL INPUT Input High Voltage, VIH Input Low Voltage, VIL Input Current, IIN Input Capacitance, CIN 2.4 0.8 ±1 10 V min V max µA max pF max VIN = 0 V to VDD All Digital Inputs DIGITAL OUTPUT Output High Voltage, VOH Output Low Voltage, VOL Output High Current, IOH Output Capacitance, COUT ALERT Output Saturation Voltage 2.4 0.4 1 10 0.8 V min V max mA max pF max V max IOL = 1.6 mA VOH = 5 V Typ = 3 pF IOUT = 4 mA 2.5 50 0 µs min ns min ns min See Figure 1 See Figure 1 See Figure 1 50 ns min See Figure 1 50 90 4 ns min ns max µs typ See Figure 1 See Figure 1 TEMPERATURE SENSOR AND ADC Accuracy2 Resolution Update Rate, tR Temperature Conversion Time POWER SUPPLIES Supply Current3 Peak Supply Current4 Inactive Serial Bus5 Normal Mode @ 3 V Normal Mode @ 5 V Active Serial Bus6 Normal Mode @ 3 V Normal Mode @ 5 V Shutdown Mode AC ELECTRICAL CHARACTERISTICS7, 8 Serial Clock Period, t1 Data In Setup Time to SCL High, t2 Data Out Stable after SCL Low, t3 SDA Low Setup Time to SCL Low (Start Condition), t4 SDA High Hold Time after SCL High (Stop Condition), t5 SDA and SCL Fall Time, t6 Power-Up Time NOTES 1 Temperature range as follows: A Version = –40°C to +85°C. 2 Accuracy specifications apply only to voltages listed under Test Conditions. See Temperature Accuracy vs. Supply section for typical accuracy performance over the full VDD supply range. 3 These current values can be used to determine average power consumption at different one-shot conversion rates. Average power consumption at the automatic conversion rate of 1.25 kHz is 940 µW. 4 This peak supply current is required for 29 µs (the conversion time plus power-up time) out of every 800 µs (the conversion rate). 5 These current values are derived by not issuing a stop condition at the end of a write or read, thus preventing the part from going into a conversion. 6 The current is derived assuming a 400 kHz serial clock being active continuously. 7 The SDA and SCL timing is measured with the input filters turned on so as to meet the Fast-Mode I 2C specification. Switching off the input filters improves the transfer rate but has a negative effect on the EMC behavior of the part. 8 Guaranteed by design. Not tested in production. Specifications subject to change without notice. –2– REV. 0 AD7414/AD7415 PIN CONFIGURATIONS PIN FUNCTION DESCRIPTIONS Mnemonic Description AS GND VDD SDA ALERT SCL SOT-23 Logic Input. Address Select Input which selects one of three I2C addresses for the AD7414/ AD7415 (See Table I). Analog and Digital Ground. Positive Supply Voltage, 2.7 V to 5.5 V. Digital I/O. Serial Bus Bidirectional Data. OpenDrain Output. AD7414 Digital Output. Over Temperature Indicator, becomes active when temperature exceeds THIGH. Open-Drain output. Digital Input. Serial Bus Clock. AS 6 SDA 1 AD7414 TOP VIEW (Not to Scale) GND 2 VDD 3 5 ALERT 4 SCL SOIC NC 8 NC 1 AD7414 TOP VIEW (Not to Scale) SDA 2 ABSOLUTE MAXIMUM RATINGS* VDD to GND . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +7 V SDA Input Voltage to GND . . . . . . . . . . . . . . –0.3 V to +7 V SDA Output Voltage to GND . . . . . . . . . . . . . –0.3 V to +7 V SCL Input Voltage to GND . . . . . . . . . . . . . . –0.3 V to +7 V ALERT Output Voltage to GND . . . . . . . . . . –0.3 V to +7 V Operating Temperature Range . . . . . . . . . . . –40°C to +85°C Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . 150°C SOT-23, Power Dissipation . . . . . . . . . . . . . . . . . . . . 450 mW JA Thermal Impedance . . . . . . . . . . . . . . . . . . . . . . 240°C/W Lead Temperature, Soldering Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . . 215°C Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . 220°C ALERT 3 7 AS 6 GND SCL 4 5 VDD NC = NO CONNECT SOT-23 AS 5 SDA 1 AD7415 GND 2 VDD 3 TOP VIEW (Not to Scale) 4 SCL *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. t1 SC t4 t2 t5 SDA DATA IN t3 SDA DATA OUT t6 Figure 1. Diagram for Serial Bus Timing 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 AD7414/AD7415 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. REV. 0 –3– WARNING! ESD SENSITIVE DEVICE AD7414/AD7415 ORDERING GUIDE Model Temperature Range Temperature Error @ 3 V Package Options Package Description Branding Information Min Qtys/ Reel AD7414ART-0REEL7 AD7414ART-0REEL AD7414ART-0500RL7 AD7414ARM-0REEL7 AD7414ARM-0REEL AD7414ARM-02 –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C ± 2°C ± 2°C ± 2°C ± 2°C ± 2°C ± 2°C RT-6 RT-6 RT-6 RM-8 RM-8 RM-8 6-Lead SOT-23 6-Lead SOT-23 6-Lead SOT-23 8-Lead Mini_SO 8-Lead Mini_SO 8-Lead Mini_SO CHA1 CHA1 CHA1 CHA1 CHA1 CHA1 3000 10000 500 3000 10000 AD7414ART-1REEL7 AD7414ART-1REEL –40°C to +85°C –40°C to +85°C ± 2°C ± 2°C RT-6 RT-6 6-Lead SOT-23 6-Lead SOT-23 CHB3 CHB3 3000 10000 AD7414ART-1500RL7 AD7414ARM-1REEL7 AD7414ARM-1REEL AD7414ARM-12 –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C ± 2°C ± 2°C ± 2°C ± 2°C RT-6 RM-8 RM-8 RM-8 6-Lead SOT-23 8-Lead Mini_SO 8-Lead Mini_SO 8-Lead Mini_SO CHB3 CHB3 CHB3 CHB3 500 3000 10000 AD7414ART-2REEL7 AD7414ART-2REEL –40°C to +85°C –40°C to +85°C ± 2°C ± 2°C RT-6 RT-6 6-Lead SOT-23 6-Lead SOT-23 CHC3 CHC3 3000 10000 AD7414ART-3REEL7 AD7414ART-3REEL –40°C to +85°C –40°C to +85°C ± 2°C ± 2°C RT-6 RT-6 6-Lead SOT-23 6-Lead SOT-23 CHD3 CHD3 3000 10000 AD7415ART-0REEL7 AD7415ART-0REEL AD7415ART-0500RL7 –40°C to +85°C –40°C to +85°C –40°C to +85°C ± 2°C ± 2°C ± 2°C RT-5 RT-5 RT-5 5-Lead SOT-23 5-Lead SOT-23 5-Lead SOT-23 CGA1 CGA1 CGA1 3000 10000 500 AD7415ART-1REEL7 AD7415ART-1REEL AD7415ART-1500RL7 –40°C to +85°C –40°C to +85°C –40°C to +85°C ± 2°C ± 2°C ± 2°C RT-5 RT-5 RT-5 5-Lead SOT-23 5-Lead SOT-23 5-Lead SOT-23 CGB3 CGB3 CGB3 3000 10000 500 NOTES 1 Available to order. 2 This model shipped in tubes. 3 Contact factory for availability. Table I. I2C Address Selection Part Number AS Pin I2C Address AD7414-0 AD7414-0 AD7414-0 Float GND VDD 1001 000 1001 001 1001 010 AD7414-1 AD7414-1 AD7414-1 Float GND VDD 1001 100 1001 101 1001 110 AD7414-2 N/A 1001 011 AD7414-3 N/A 1001 111 AD7415-0 AD7415-0 AD7415-0 Float GND VDD 1001 000 1001 001 1001 010 AD7415-1 AD7415-1 AD7415-1 Float GND VDD 1001 100 1001 101 1001 110 –4– REV. 0 AD7414/AD7415 CIRCUIT INFORMATION The AD7414/AD7415 is a stand-alone digital temperature sensor. The on-chip temperature sensor allows an accurate measurement of the ambient device temperature to be made. The 10-bit A/D converter converts the temperature measured into a two’s complement format for storage in the Temperature Register. The A/D converter is made up of a conventional successiveapproximation converter based around a capacitor DAC. The serial interface is I2C and SMBus compatible. The AD7414 AD7415 requires a 2.7 V to 5.5 V power supply. The temperature sensor has a working measurement range of –40°C to +85°C. SUPPLY 2.7 V TO 5.5 V 10F 0.1F VDD SDA AS SCL GND C/P ALERT AD7414 Figure 2. Typical Connection Diagram FUNCTIONAL DESCRIPTION Temperature measurement is initiated by a couple of methods. The first uses an internal clock countdown of 800 ms, and a conversion is performed. The internal oscillator is the only circuit that is powered up between conversions and once it times out, every 800 ms, a wake-up signal is sent to power up the rest of the circuitry. A monostable is activated at the beginning of the wake-up signal to ensure that sufficient time is given to the powerup process. The monostable typically takes 4 µs to time out. It then takes typically 25 µs for each conversion to be completed. The new temperature value is loaded into the Temperature Value Register and ready for reading by the I2C interface. A temperature measurement is also initiated every time the oneshot method is used. This method requires the user to write to the One-Shot Bit in the Configuration Register when a temperature measurement is needed. Setting the One-Shot Bit to a 1 will start a temperature conversion directly after the write operation. The track/hold goes into hold approximately 4 µs (monostable timeout) after the STOP condition and a conversion is then initiated. Typically 25 µs later, the conversion is complete and the Temperature Value Register is loaded with a new temperature value. MEASUREMENT TECHNIQUE A common method of measuring temperature is to exploit the negative temperature coefficient of a diode, or the base-emitter voltage of a transistor, operated at constant current. Unfortunately, this technique requires calibration to null out the effect of the absolute value of VBE, which varies from device to device. The technique used in the AD7414/AD7415 is to measure the change in VBE when the device is operated at two different currents. This is given by: ∆VBE = KT/q × ln (N) where: K is Boltzmann’s constant. q is charge on the electron (1.6 × 10–19 Coulombs). T is absolute temperature in Kelvins. N is the ratio of the two currents. I The measurement modes are compared with a high temperature limit, stored in an 8-bit read/write register. This is applicable only to the AD7414 as the AD7415 does not have an ALERT pin and subsequently does not have an over-temperature monitoring function. If the measurement is greater than the high limit, the ALERT pin is activated (if it has already been enabled in the Configuration Register). There are two ways to deactivate the ALERT pin again, firstly when the Alert Reset bit in the Configuration register is set to a 1 by a write operation; and secondly when the temperature measured is less than the value in the TLOW Register. This ALERT pin is compatible with the SMBus SMBALERT option. REV. 0 VDD VOUT + TO ADC SENSING TRANSISTOR Configuration functions consist of: • Switching between normal operation and full power-down. • Enabling or disabling the SCL and SDA filters. • Enabling or disabling the ALERT function. • Setting ALERT pin polarity. NⴛI SENSING TRANSISTOR VOUT – Figure 3. Temperature Measurement Technique Figure 3 shows the method the AD7414/AD7415 uses to measure the ambient device temperature. To measure ∆VBE, the sensor (substrate transistor) is switched between operating currents of I and N × I. The resulting waveform is passed through a chopperstabilized amplifier that performs the functions of amplification and rectification of the waveform to produce a dc voltage proportional to DVBE. This voltage is measured by the ADC to give a temperature output in 10-bit two’s complement format. –5– AD7414/AD7415 The AD7415 has three internal registers as shown in Figure 5. Two are data registers and one is an Address Pointer Register. TEMPERATURE DATA FORMAT The temperature resolution of the ADC is 0.25°C which corresponds to one LSB of the ADC. The ADC can theoretically measure a temperature span of 255°C; the practical lowest value is limited to –40°C due to device maximum ratings. The A grade can measure a temperature range of –40°C to +85°C. (Temperature data format is shown in Table II.) TEMPERATURE VALUE REGISTER ADDRESS POINTER REGISTER CONFIGURATION REGISTER Table II. A-Grade Temperature Data Format Digital Output Temperature DB9 . . . DB0 –55°C 11 0010 0100 –50°C 11 0011 1000 –25°C 11 1001 1100 –0.25°C 11 1111 1111 0°C 00 0000 0000 +0.25°C 00 0000 0001 +10°C 00 0010 1000 +25°C 00 0110 0100 +50°C 00 1100 1000 +75°C 01 0010 1100 +100°C 01 1001 0000 +125°C 01 1111 0100 D A T A SDA SERIAL BUS INTERFACE SCL Figure 5. AD7415 Register Structure Each data register has an address pointed to by the Address Pointer Register when communicating with it. The Temperature Value Register is the only data register that is read only. ADDRESS POINTER REGISTER The Address Pointer Register is an 8-bit register that stores an address that points to one of the four data registers of the AD7414 and one of the two data registers of the AD7415. The first byte of every serial write operation to the AD7414/AD7415 is the address of one of the data registers, which is stored in the Address Pointer Register, and selects the data register to which subsequent data bytes are written. Only the two LSBs of this register are used to select a data register. A Grade Temperature Conversion Formula: 1. Positive Temperature = ADC Code/4 2. Negative Temperature = (ADC Code* – 512)/4 *DB9 is removed from the ADC Code. Table III. Address Pointer Register INTERNAL REGISTER STRUCTURE P7 P6 P5 P4 P3 P2 P1 The AD7414 has five internal registers as shown in Figure 4. Four are data registers and one is an Address Pointer Register. 0 0 0 0 0 0 Register Select P0 Table IV. AD7414 Register Address TEMPERATURE VALUE REGISTER CONFIGURATION REGISTER ADDRESS POINTER REGISTER THIGH REGISTER P1 P0 Registers 0 0 1 1 0 1 0 1 Temperature Value Register (Read Only) Configuration Register (Read/Write) THIGH Register (Read/Write) TLOW Register (Read/Write) D A T A Table V. AD7415 Register Address TLOW REGISTER P1 P0 Registers 0 0 0 1 Temperature Value Register (Read Only) Configuration Register (Read/Write) SDA SERIAL BUS INTERFACE SCL Figure 4. AD7414 Register Structure –6– REV. 0 AD7414/AD7415 Table VI. AD7414 Configuration Register D7 D6 D5 D4 D3 D2 Table VIII. AD7415 Configuration Register D1 D0 PD FLTR ALERT ALERT ALERT ONE EN POLARITY RESET SHOT MODE 0* 1* 0s* 0* 0* 0* TEST 0* *Default settings at Power-up. D7 D6 D5 PD FLTR 0* 1* D4 D3 D2 TEST MODE 0s* D1 D0 ONE SHOT TEST MODE 0s* 0s* *Default settings at Power-up. In the AD7415, only three of the bits are used (D7, D6 and D2) to set the operating modes, see Table IX. D0, D1 and D3 to D5 are used for factory settings and must have zeros written to them during normal operation. CONFIGURATION REGISTER (ADDRESS 01H) The Configuration Register is an 8-bit read/write register that is used to set the operating modes of the AD7414/AD7415. In the AD7414, six of the MSBs are used (D7 to D2) to set the operating modes, see Table VII. D0 and D1 are used for factory settings and must have zeros written to them during normal operation. Table IX. AD7415 Configuration Register Settings D7 D6 D2 Table VII. AD7414 Configuration Register Settings D7 Full Power-Down if = 1 D6 Bypass SDA and SCL filtering if = 0 D5 Disable ALERT if = 1 D4 ALERT is active low if D4 = 0, ALERT is active high if D4 = 1 D3 Reset the Alert pin if set to 1. The next temperature conversion will have the ability to activate the Alert function. The bit status is not stored, thus this bit will be “0” if read. D2 Initiate a temperature conversion if set to a 1. The bit status is not stored, thus this bit will be “0” if read. 1 Full Power-Down if = 1 Bypass SDA and SCL Filtering if = 0 Initiate a temperature conversion if set to a 1. The bit status is not stored, thus this bit will be “0” if read. If the AD7414/AD7415 is in power-down mode (D7 = 1), a temperature conversion can still be initiated by the one-shot operation. This involves a write operation to the Configuration Register and setting the One-shot Bit to a 1 (D2 = 1) will cause the AD7414/AD7415 to power-up, perform a single conversion and power-down again. This is a very power-efficient mode. 9 9 1 SCL 1 SDA 0 START BY MASTER 0 A2 1 A0 A1 FRAME 1 SERIAL BUS ADDRESS BYTE P6 P7 R/W P5 P3 P4 P1 P2 P0 ACK. BY AD7414/AD7415 FRAME 2 ADDRESS POINTER REGISTER BYTE ACK. BY AD7414/AD7415 STOP BY MASTER Figure 6. Writing to the Address Pointer Register to Select a Register for a Subsequent Read Operation 1 9 1 9 SCL SDA 1 0 0 1 A2 A1 START BY MASTER R/W A0 P7 P6 P5 P4 P3 P2 P1 P0 ACK. BY AD7414/AD7415 FRAME 2 ADDRESS POINTER REGISTER BYTE 9 ACK. BY AD7414/AD7415 FRAME 1 SERIAL BUS ADDRESS BYTE 1 SCL (CONTINUED) SDA (CONTINUED) D7 D6 D5 D4 D3 D2 FRAME 3 DATA BYTE D1 D0 ACK. BY STOP BY AD7414/AD7415 MASTER Figure 7. Writing to the Address Pointer Register followed by a Single Byte of Data to the Selected Register REV. 0 –7– AD7414/AD7415 Table XI. AD7414 Temperature Value Register (Second Read) TEMPERATURE VALUE REGISTER (ADDRESS 00H) The Temperature Value Register is a 10-bit read-only register that stores the temperature reading from the ADC in two’s complement format. Two reads are necessary to read data from this register. Table X shows the contents of the first byte to be read while Table XI and Table XII show the contents of the second byte to be read from AD7414 and AD7415 respectively. In Table XI, D3 to D5 of the second byte are used as flag bits and are obtained from other internal registers. They function as follows: ALERT _Flag: The state of this bit is same as that of the ALERT pin. THIGH_Flag: This flag is set to a 1 when the temperature measured goes above the THIGH limit. It is reset when the second temperature byte (Table XI) is read. If the temperature is still greater than the THIGH limit after the read operation, then the flag will be set again. TLOW_Flag : This flag is set to a 1 when the temperature measured goes below the TLOW limit. It is reset when the second temperature byte (Table XI) is read. If the temperature is still less than the TLOW limit after the read operation, then the flag will be set again. D6 D5 D4 D3 B1 LSB ALERT Flag THIGH TLOW Flag Flag D2 D1 D0 0 0 0 Table XII. AD7415 Temperature Value Register (Second Read) D7 D6 D5 D4 D3 D2 D1 D0 B1 LSB N/A N/A N/A N/A N/A N/A AD7414 THIGH REGISTER (Address 02h) The THIGH Register is an 8-bit read/write register that stores the upper limit that will activate the ALERT output. Therefore, if the value in the Temperature Value Register is greater than the value in the THIGH Register, then the ALERT pin is activated (that is, if ALERT is enabled in the Configuration Register). As it is an 8-bit register the temperature resolution is 1°C. Table XIII. THIGH Register D14 D13 D12 D11 D10 D9 D8 MSB B8 B7 B6 B5 B4 B3 B2 D6 D5 D4 D3 D2 D1 D0 MSB B6 B5 B4 B3 B2 B1 B0 The TLOW Register is an 8-bit read/write register that stores the lower limit that will deactivate the ALERT output. Therefore, if the value in the Temperature Value Register is less than the value in the TLOW Register, the ALERT pin is deactivated (that is, if ALERT is enabled in the Configuration Register). As it is an 8-bit register, the temperature resolution is 1°C. Table X. Temperature Value Register (First Read) D15 D7 AD7414 TLOW REGISTER (Address 03h) The full theoretical span of the ADC is 255°C, but in practice the temperature measurement range is limited to the operating range of the device, –40°C to +85°C for A grade. 1 D7 9 1 9 SCL SDA 1 0 0 1 A2 A1 A0 D7 R/W D6 D5 D4 D3 D2 D1 ACK. BY AD7414/AD7415 START BY MASTER D0 NO ACK. BY MASTER FRAME 1 SERIAL BUS ADDRESS BYTE STOP BY MASTER FRAME 2 SINGLE DATA BYTE FROM AD7414/AD7415 Figure 8. Reading a Single Byte of Data from a Selected Register 1 9 9 1 SCL SDA 1 0 0 1 A2 A1 A0 D15 R/W D14 D13 D12 D10 D11 D9 FRAME 1 SERIAL BUS ADDRESS BYTE D8 ACK. BY MASTER ACK. BY AD7414/AD7415 START BY MASTER FRAME 2 MOST SIGNIFICANT DATA BYTE FROM AD7414/AD7415 9 1 SCL (CONTINUED) SDA (CONTINUED) D6 D7 D5 D4 D3 D2 D1 D0 NO ACK. BY STOP BY MASTER MASTER FRAME 3 LEAST SIGNIFICANT DATA BYTE FROM AD7414/AD7415 –8– REV. 0 AD7414/AD7415 Table XIV. TLOW Register D7 D6 D5 D4 D3 D2 D1 D0 MSB B6 B5 B4 B3 B2 B1 B0 AD7414/AD7415 SERIAL INTERFACE Control of the AD7414/AD7415 is carried out via the I2Ccompatible serial bus. The AD7414/AD7415 is connected to this bus as a slave device, under the control of a master device, e.g., the processor. SERIAL BUS ADDRESS Like all I2C-compatible devices, the AD7414/AD7415 has a 7-bit serial address. The four MSBs of this address for the AD7414/AD7415 are set to 1001. The AD7414/AD7415 comes in four versions, the AD7414/AD7415-0, AD7414/AD7415-1, AD7414-2 and the AD7414-3. The first two versions have three different I2C addresses available which are selected by either tying the AS pin to GND, to VDD or letting the pin float (see Table I). By giving different addresses for the four versions, up to eight AD7414s or six AD7415s can be connected to a single, serial bus, or the addresses can be set to avoid conflicts with other devices on the bus. The serial bus protocol operates as follows: 1. The master initiates data transfer by establishing a START condition, defined as a high to low transition on the serial data line SDA while the serial clock line SCL remains high. This indicates that an address/data stream will follow. All slave peripherals connected to the serial bus respond to the START condition, and shift in the next eight bits, consisting of a 7-bit address (MSB first) plus a R/W bit, which determines the direction of the data transfer, i.e. whether data will be written to or read from the slave device. The peripheral whose address corresponds to the transmitted address responds by pulling the data line low during the low period before the ninth clock pulse, known as the Acknowledge bit. All other devices on the bus now remain idle while the selected device waits for data to be read from or written to it. If the R/W bit is a 0 then the master will write to the slave device. If the R/W bit is a 1 the master will read from the slave device. 2. Data is sent over the serial bus in sequences of nine clock pulses, eight bits of data followed by an Acknowledge Bit from the receiver of data. Transitions on the data line must occur during the low period of the clock signal and remain stable during the high period, as a low to high transition when the clock is high may be interpreted as a STOP signal. 3. When all data bytes have been read or written, stop conditions are established. In WRITE mode, the master will pull the data line high during the 10th clock pulse to assert a STOP condition. In READ mode, the master device will pull the data line high during the low period before the 9th clock pulse. This is known as No Acknowledge. The master will then take the data line low during the low period before the tenth clock pulse, then high during the tenth clock pulse to assert a STOP condition. REV. 0 Any number of bytes of data may be transferred over the serial bus in one operation, but it is not possible to mix read and write in one operation, because the type of operation is determined at the beginning and cannot subsequently be changed without starting a new operation. WRITING TO THE AD7414/AD7415 Depending on the register being written to, there are two different writes for the AD7414/AD7415. Writing to the Address Pointer Register for a Subsequent Read In order to read data from a particular register, the Address Pointer Register must contain the address of that register. If it does not, the correct address must be written to the Address Pointer Register by performing a single-byte write operation, as shown in Figure 6. The write operation consists of the serial bus address followed by the address pointer byte. No data is written to any of the data registers. A read operation is then performed to read the register. Writing a Single Byte of Data to the Configuration Register, THIGH Register or TLOW Register All three registers are 8-bit registers so only one byte of data can be written to each register. Writing a single byte of data to one of these registers consists of the serial bus address, the Data Register address written to the Address Pointer Register, followed by the data byte written to the selected data register. This is illustrated in Figure 7. READING DATA FROM THE AD7414/AD7415 Reading data from the AD7414/AD7415 is a one or two byte operation. Reading back the contents of the Configuration Register, THIGH Register or TLOW Register is a single byte read operation as shown in Figure 8. The register address previously having been set up by a single byte write operation to the Address Pointer Register. Once the register address has been set up, any number of reads can be subsequently done from that register without having to write to the Address Pointer Register again. If you want to read from another register then you will have to write to the Address Pointer Register again to set up the relevant register address. Reading data from the Temperature Value Register is a two byte operation as shown in Figure 9. The same rules apply for a two byte read as a single byte read. SMBus ALERT The AD7414 ALERT output is an SMBus interrupt line for devices that want to trade their ability to master for an extra pin. The AD7414 is a slave only device and uses the SMBus ALERT to signal the host device that it wants to talk. The SMBus ALERT on the AD7414 is used as an over temperature indicator. The ALERT pin has an open-drain configuration which allows the ALERT outputs of several AD7414s to be wired-AND together when the ALERT pin is active low. Use D4 of the Configuration Register to set the active polarity of the ALERT output. The power-up default is active low. The ALERT function can be disabled or enabled by setting D5 of the Configuration Register to 1 or 0 respectively. –9– AD7414/AD7415 When a temperature measurement is required, a write operation can be performed to power-up the part and put it into one-shot mode (setting D2 of the Configuration register to a 1). The power-up takes approximately 4 ms. The part then performs a conversion and is returned to full power-down. The temperature value can be read in the full power-down mode as the serial interface is still powered up. The host device can process the ALERT interrupt and simultaneously access all SMBus ALERT devices through the alert response address. Only the device that pulled the ALERT low will acknowledge the ARA (Alert Response Address). If more than one device pulls the ALERT pin low, the highest priority (lowest address) device will win communication rights via standard I2C arbitration during the slave address transfer. The ALERT output becomes active when the value in the Temperature Value Register exceeds the value in the THIGH Register. It is reset when a write operation to the Configuration register sets D3 to a 1 or when the temperature falls below the value stored in the TLOW Register. The ALERT output requires an external pull-up resistor. This can be connected to a voltage different from VDD provided the maximum voltage rating of the ALERT output pin is not exceeded. The value of the pull-up resistor depends on the application, but should be as large as possible to avoid excessive sink currents at the ALERT output, which can heat the chip and affect the temperature reading. POWER-ON DEFAULTS POWER VS. THROUGHPUT The two modes of operation for the AD7414/AD7415 will produce different power versus throughput performances. Mode 2 is the sleep mode of the part and it achieves the optimum power performance. Mode 1 In this mode continuous conversions are performed at a rate of approximately one every 800 ms. Figure 10 shows the times and the currents involved with this mode of operation for a 5 V supply. At 5 V the current consumption for the part when converting is 1.1 mA typically and the quiescent current is 188 µA typically. The conversion time of 25 µs plus power-up time of typically 4 µs contributes 199.3 nW to the overall power dissipation in the following way: The AD7414/AD7415 always powers up with the following defaults: (29 µs/800 ms) × (5 × 1.1 mA) = 199.3 nW Address Pointer Register pointing to the Temperature Value Register. THIGH Register loaded with 7F Hex. TLOW Register loaded with 80 Hex. Configuration Register loaded with 40 Hex. The contribution to the total power dissipated by the remaining time is 939.96 µW. (799.971 ms/800 ms) × (5 × 188 µA) = 939.96 µW Thus the total power dissipated during each cycle is: 199.3 nW + 939.96 µW = 940.16 µW Note: The AD7415 does not have any T HIGH or TLOW registers. 1.1mA OPERATING MODES Mode 1 IDD 188A This is the power-on default mode of the AD7414/AD7415. In this mode the AD7414/AD7415 does a temperature conversion every 800 ms and then partially powers down until the next conversion occurs. 800ms 29s TIME Figure 10. Mode 1 Power Dissipation If a one-shot operation (setting D2 of the Configuration register to a 1) is performed between automatic conversions, a conversion is initiated right after the write operation. After this conversion, the part returns to performing a conversion every 800 ms Depending on where a serial port access occurs during a conversion, that conversion might or might not be aborted. If the conversion is completed before the part recognizes a serial port access then the Temperature Register will be updated with the new conversion. If the conversion is completed after the part recognizes a serial port access then the internal logic will prevent the Temperature Register from being updated as corrupt data could be read. A temperature conversion can start anytime during a serial port access (other than a one-shot operation), but the result of that conversion will only be loaded into the Temperature Register if serial port access is not active at the end of the conversion. Mode 2 In this mode the part is totally powered down. All circuitry except the serial interface is switched off. The most power efficient way of operating in this mode is to use the one-shot method. Write to the configuration register and set the one-shot bit to a 1. The part will power-up in approximately 4 ms and then perform a conversion. Once the conversion is finished the device will power down again until the PD bit in the configuration register is set to a 0 or the one-shot bit is set to a 1. Figure 11 shows the same timing as Figure 10 in mode 1, a one-shot is initiated every 800 ms. If we take the voltage supply to be 5 V we can work out the power dissipation in the following way. The current consumption for the part when converting is 1.1 mA typically and the quiescent current is 800 nA typically. The conversion time of 25 µs plus power-up time of typically 4 ms contributes 199.3 nW to the overall power dissipation in the following way: (29 µs/800 ms) × (5 V × 1.1 mA) = 199.3 nW Mode 2 The only other mode in which the AD7414/AD7415 operates is the full power-down mode. This mode is usually used when temperature measurements are required at a very slow rate. The power consumption of the part can be greatly reduced in this mode by writing to the part to go to a full power-down. Full power-down is initiated right after D7 of the Configuration Register set to a 1. The contribution to the total power dissipated by the remaining time is 3.9 µW. (799.971 ms/800 ms) × (5 V × 800 nA) = 3.9 µW Thus the total power dissipated during each cycle is: –10– 199.3 nW + 3.9 µW = 4.1 µW REV. 0 AD7414/AD7415 4 1.1mA 3 TEMPERATURE ERROR – ⴗC IDD 800nA 800ms 29s TIME Figure 11. Mode 2 Power Dissipation MOUNTING THE AD7414/AD7415 The AD7414/AD7415 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 0.1°C 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. –40ⴗC 1 0 +40ⴗC –1 +85ⴗC –2 –3 –4 2.7 3.0 SUPPLY VOLTAGE – V 5.5 Figure 12. Typical Temperature Error vs. Supply for Large Sample of Parts 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. 4 TEMPERATURE ERROR – ⴗC 3 As with any IC, the AD7414/AD7415 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 AD7414/ AD7415 packages allows it to be mounted inside sealed metal probes, which provide a safe environment for the device. 2 –40ⴗC 1 0 +40ⴗC –1 +85ⴗC –2 –3 SUPPLY DECOUPLING The AD7414/AD7415 should be at least decoupled with a 0.1 µF ceramic capacitor between VDD and GND. This is particularly important if the AD7414/AD7415 is mounted remote from the power supply. 2 –4 2.7 5.0 3.3 SUPPLY VOLTAGE – V 5.5 Figure 13. Typical Temperature Error vs. Supply for One Part TEMPERATURE ACCURACY VS. SUPPLY The Temperature Accuracy specifications are guaranteed for voltage supplies of 3 V and 5.5 V only. Figure 12 gives the typical performance characteristics of a large sample of parts over the full voltage range of 2.7 V to 5.5 V. Figure 13 gives the typical performance characteristics of one part over the full voltage range of 2.7 V to 5.5 V. TYPICAL TEMPERATURE ERROR GRAPH Figure 14 shows typical temperature error plots for one device with VDD at 3.3 V and at 5.5 V. 4 TEMPERATURE ERROR – ⴗC 3 2 5.5V 1 0 –1 3.3V –2 –3 –4 –40 –30 –20 –10 0 10 20 30 40 50 TEMPERATURE – ⴗC 60 70 80 90 Figure 14. Typical Temperature Error @ 3.3 V and 5.5 V REV. 0 –11– AD7414/AD7415 OUTLINE DIMENSIONS Dimensions shown in inches and (mm). C02463–1–7/01(0) 6-Lead Plastic Surface-Mount SOT-23 (RT-6) 0.122 (3.10) 0.106 (2.70) 0.071 (1.80) 0.059 (1.50) 6 5 4 1 2 3 0.118 (3.00) 0.098 (2.50) PIN 1 0.037 (0.95) BSC 0.075 (1.90) BSC 0.051 (1.30) 0.035 (0.90) 0.057 (1.45) 0.035 (0.90) 0.020 (0.50) SEATING 0.010 (0.25) PLANE 0.006 (0.15) 0.000 (0.00) 10ⴗ 0.009 (0.23) 0ⴗ 0.003 (0.08) 0.022 (0.55) 0.014 (0.35) 8-Lead Mini_SO (RM-8) 0.122 (3.10) 0.114 (2.90) 8 5 0.122 (3.10) 0.114 (2.90) 0.199 (5.05) 0.187 (4.75) 1 4 PIN 1 0.0256 (0.65) BSC 0.120 (3.05) 0.112 (2.84) 0.120 (3.05) 0.112 (2.84) 0.043 (1.09) 0.037 (0.94) 0.006 (0.15) 0.002 (0.05) 0.018 (0.46) SEATING 0.008 (0.20) PLANE 0.011 (0.28) 0.003 (0.08) 33ⴗ 27ⴗ 0.028 (0.71) 0.016 (0.41) 5-Lead Plastic Surface-Mount SOT-23 (RT-5) 0.0669 (1.70) 0.0590 (1.50) 5 1 4 2 PRINTED IN U.S.A. 0.1181 (3.00) 0.1102 (2.80) 0.1181 (3.00) 0.1024 (2.60) 3 PIN 1 0.0374 (0.95) BSC 0.0748 (1.90) BSC 0.0512 (1.30) 0.0354 (0.90) 0.0059 (0.15) 0.0019 (0.05) 0.0079 (0.20) 0.0031 (0.08) 0.0571 (1.45) 0.0374 (0.95) 0.0197 (0.50) 0.0138 (0.35) SEATING PLANE –12– 10ⴗ 0ⴗ 0.0217 (0.55) 0.0138 (0.35) REV. 0