ADT7481ARMZ-1RL

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It can measure its own ambient temperature or the temperature of two remote thermal diodes. These thermal diodes can be located in a CPU or GPU, or they can be discrete diode connected transistors. The ambient temperature, or the temperature of the remote thermal diode, can be accurately measured to ±1°C. The temperature measurement range defaults to 0°C to +127°C, compatible with ADM1032, but can be switched to a wider measurement range from −64°C to +191°C. The ADT7481 communicates over a 2-wire serial interface compatible with System Management Bus (SMBus) standards. The SMBus address of the ADT7481 is 0x4C. An ADT7481−1 with an SMBus address of 0x4B is also available. An ALERT output signals when the on-chip or remote temperature is outside the programmed limits. The THERM output is a comparator output that allows, for example, on/off control of a cooling fan. The ALERT output can be reconfigured as a second THERM output if required. www.onsemi.com MSOP−10 CASE 846AC PIN ASSIGNMENT • • • • • • • 1 Local and 2 Remote Temperature Sensors 0.25°C Resolution/1°C Accuracy on Remote Channels 1°C Resolution/1°C Accuracy on Local Channel Extended, Switchable Temperature Measurement Range 0°C to 127°C (Default) or −64°C to +191°C 2-wire SMBus Serial Interface with SMBus ALERT Support Programmable Over/Undertemperature Limits Offset Registers for System Calibration Up to 2 Overtemperature Fail-Safe THERM Outputs Small 10-lead MSOP Package 240 mA Operating Current, 5 mA Standby Current These Devices are Pb-Free, Halogen Free and are RoHS Compliant Applications • • • • • • • 1 2 10 SCLK ADT7481 9 SDATA D1− 3 8 ALERT/THERM2 THERM 4 7 D2+ GND 5 6 D2− MARKING DIAGRAM Features • • • • VDD D1+ 10 T0x AYWG G 1 T0x A Y W G = Refer to Ordering Info Table = Assembly Location = Year = Work Week = Pb-Free Package (Note: Microdot may be in either location) ORDERING INFORMATION See detailed ordering and shipping information in the package dimensions section on page 20 of this data sheet. Desktop and Notebook Computers Industrial Controllers Smart Batteries Automotive Embedded Systems Burn-In Applications Instrumentation © Semiconductor Components Industries, LLC, 2014 April, 2019 − Rev. 9 1 Publication Order Number: ADT7481/D ADT7481 ADDRESS POINTER REGISTER 2 D1− 3 D2+ 7 D2− 6 ANALOG MUX ONE-SHOT REGISTER LOCAL TEMPERATURE VALUE REGISTER LOCAL TEMPERATURE THERM LIMIT REGISTER 11-BIT A-TO-D CONVERTER BUSY RUN/STANDBY LOCAL TEMPERATURE LOW LIMIT REGISTER LIMIT COMPARATOR D1+ CONVERSION RATE REGISTER DIGITAL MUX ON-CHIP TEMPERATURE SENSOR REMOTE 1 AND 2 TEMP VALUE REGISTER LOCAL TEMPERATURE HIGH LIMIT REGISTER REMOTE 1 & 2 TEMP. THERM LIMIT REG. REMOTE 1 & 2 TEMP. LOW LIMIT REGISTERS REMOTE 1 AND 2 TEMP OFFSET REGISTER REMOTE 1 & 2 TEMP. HIGH LIMIT REGISTERS CONFIGURATION REGISTER EXTERNAL DIODE OPEN-CIRCUIT INTERRUPT MASKING STATUS REGISTERS ADT7481 SMBUS INTERFACE 1 5 9 10 4 VDD GND SDATA SCLK THERM 8 ALERT/THERM2 Figure 1. Functional Block Diagram Table 1. ABSOLUTE MAXIMUM RATINGS Parameter Positive Supply Voltage (VDD) to GND D+ D− to GND Rating Unit −0.3 to +3.6 V −0.3 to VDD + 0.3 V −0.3 to +0.6 V SCLK, SDATA, ALERT, THERM −0.3 to +3.6 V Input Current, SDATA, THERM −1 to +50 mA Input Current, D− ±1 mA ESD Rating, All Pins (Human Body Model) 1,500 V Maximum Junction Temperature (TJ MAX) 150 °C Storage Temperature Range −65 to +150 °C IR Reflow Peak Temperature 220 °C IR Reflow Peak Temperature for Pb-Free 260 °C Lead Temperature, Soldering (10 sec) 300 °C Stresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality should not be assumed, damage may occur and reliability may be affected. NOTE: This device is ESD sensitive. Use standard ESD precautions when handling. Table 2. THERMAL CHARACTERISTICS Package Type 10-lead MSOP www.onsemi.com 2 qJA qJC Unit 142 43.74 °C/W ADT7481 Table 3. PIN ASSIGNMENT Pin No. Mnemonic Description 1 VDD Positive Supply, 3.0 V to 3.6 V. 2 D1+ Positive Connection to the Remote 1 Temperature Sensor. 3 D1− Negative Connection to the Remote 1 Temperature Sensor. 4 THERM 5 GND Supply Ground Connection. 6 D2− Negative Connection to the Remote 2 Temperature Sensor. 7 D2+ Positive Connection to the Remote 2 Temperature Sensor. 8 ALERT/THERM2 9 SDATA Logic Input/Output, SMBus Serial Data. Open-Drain Output. Requires pullup resistor. 10 SCLK Logic Input, SMBus Serial Clock. Requires pullup resistor. Open-Drain Output. Requires pullup resistor. Signals overtemperature events, could be used to turn a fan on/off, or throttle a CPU clock. Open-Drain Logic Output. Used as interrupt or SMBALERT. This may also be configured as a second THERM output. Requires pullup resistor. Table 4. TIMING SPECIFICATIONS (Note 1) 1. 2. 3. 4. Parameter Limit at TMIN and TMAX Unit fSCLK 400 kHz max Description tLOW 1.3 ms min Clock low period, between 10% points. tHIGH 0.6 ms min Clock high period, between 90% points. tR 300 ns max Clock/data rise time. tF 300 ns max Clock/data fall time. tSU; STA 600 ns min Start condition setup time. tHD; STA (Note 2) 600 ns min Start condition hold time. tSU; DAT (Note 3) 100 ns min Data setup time. tHD; DAT 300 ns min Data hold time. tSU; STO (Note 4) 600 ns min Stop condition setup time. tBUF 1.3 ms min Bus free time between stop and start conditions. Guaranteed by design, not production tested. Time from 10% of SDATA to 90% of SCLK. Time for 10% or 90% of SDATA to 10% of SCLK. Time for 90% of SCLK to 10% of SDATA. t LOW tF t HD; STA tR SCLK t HD; STA t HD; DAT t HIGH t SU; STA t SU; DAT t SU; STO SDATA t BUF STOP START START Figure 2. Serial Bus Timing www.onsemi.com 3 STOP ADT7481 Table 5. ELECTRICAL CHARACTERISTICS (TA = −40°C to +120°C, VDD = 3.0 V to 3.6 V, unless otherwise noted) Parameter Conditions Min Typ Max Unit 3.0 3.30 3.6 V Power Supply Supply Voltage, VDD Average Operating Supply Current, IDD Undervoltage Lockout Threshold 0.0625 Conversions/Sec Rate (Note 1) − 3.0 4.0 mA Standby Mode − 5.0 30 mA VDD Input, Disables ADC, Rising Edge Power-On-Reset Threshold − 2.55 − V 1.0 − 2.5 V − − − − − − ±1 ±1.5 ±2.5 °C − 1.0 − °C − − − − − − ±1 ±1.5 ±2.5 °C Temperature-to-Digital Converter Local Sensor Accuracy (Note 2) 0°C ≤ TA ≤ +70°C 0°C ≤ TA ≤ +85°C −40 ≤ TA ≤ +100°C Resolution Remote Diode Sensor Accuracy (Note 2) 0°C ≤ TA ≤ +70°C, −55°C ≤ TD (Note 3) ≤ +150°C 0°C ≤ TA ≤ +85°C, −55°C ≤ TD (Note 3) ≤ +150°C −40°C ≤ TA ≤ +100°C, −55°C ≤ TD (Note 3) ≤ +150°C Resolution Remote Sensor Source Current Conversion Time − 0.25 − °C High Level (Note 4) − 233 − mA Low Level (Note 4) − 14 − mA From Stop Bit to Conversion Complete (Both Channels) One-shot Mode with Averaging Switched On − 73 94 ms One-shot Mode with Averaging Off (Conversion Rate = 16, 32, or 64 Conversions per Second) − 11 14 ms Open-Drain Digital Outputs (THERM, ALERT/THERM2) Output Low Voltage, VOL IOUT = −6.0 mA − − 0.4 V High Level Output Leakage Current, IOH VOUT = VDD − 0.1 1.0 mA Logic Input High Voltage, VIH SCLK, SDATA 2.1 − − V Logic Input Low Voltage, VIL SCLK, SDATA − − 0.8 V Hysteresis − 500 − mV SMBus Interface (Notes 4 and 5) SDA Output Low Voltage, VOL − − 0.4 V Logic Input Current, IIH, IIL IOUT = −6.0 mA −1.0 − +1.0 mA SMBus Input Capacitance, SCLK, SDATA − 5.0 − pF SMBus Clock Frequency − − 400 kHz SMBus Timeout (Note 6) User Programmable − 25 32 ms SCLK Falling Edge to SDATA Valid Time Master Clocking in Data − − 1.0 ms 1. 2. 3. 4. 5. 6. See Table 11 for information on other conversion rates. Averaging enabled. Guaranteed by characterization, not production tested. Guaranteed by design, not production tested. See Timing Specifications section for more information. Disabled by default. See the Serial Bus Interface section for details to enable it. www.onsemi.com 4 ADT7481 TYPICAL PERFORMANCE CHARACTERISTICS 3.5 DEV 1 DEV 2 DEV 3 DEV 4 DEV 5 DEV 6 DEV 7 3.0 2.5 2.0 DEV 8 DEV 9 DEV 10 DEV 11 DEV 12 DEV 13 DEV 14 DEV 15 DEV 16 MEAN HIGH 4S LOW 4S 1.5 1.0 0.5 0 −0.5 −1.0 −50 0 50 100 DEV 1 DEV 2 DEV 3 DEV 4 DEV 5 DEV 6 DEV 7 3.0 TEMPERATURE ERROR (°C) TEMPERATURE ERROR (°C) 3.5 2.5 2.0 1.0 0.5 0 −0.5 −1.0 −50 150 3.0 2.5 2.0 1.0 0.5 0 −0.5 0 5 50 100 0 −5 −10 D+ To VCC −15 −20 −25 150 10 1 100 LEAKAGE RESISTANCE (MW) Figure 5. Remote 2 Temperature Error vs. Temperature Figure 6. Temperature Error vs. D+/D− Leakage Resistance 0 1000 −2 900 −4 800 DEV 2BC 700 −6 IDD (mA) TEMPERATURE ERROR (°C) 150 D+ To GND TEMPERATURE (°C) −8 −10 DEV 3 −12 500 DEV 4BC 400 DEV 3BC 200 DEV 4 −16 600 300 DEV 2 −14 −18 100 10 DEV 15 DEV 16 MEAN HIGH 4S LOW 4S 1.5 −1.0 −50 50 Figure 4. Remote 1 Temperature Error vs. Temperature TEMPERATURE ERROR (°C) TEMPERATURE ERROR (°C) DEV 8 DEV 9 DEV 10 DEV 11 DEV 12 DEV 13 DEV 14 0 TEMPERATURE (°C) Figure 3. Local Temperature Error vs. Temperature DEV 1 DEV 2 DEV 3 DEV 4 DEV 5 DEV 6 DEV 7 DEV 15 DEV 16 HIGH 4S LOW 4S 1.5 TEMPERATURE (°C) 3.5 DEV 8 DEV 9 DEV 10 DEV 11 DEV 12 DEV 13 DEV 14 100 0 5 10 15 20 0 0.01 25 CAPACITANCE (nF) 0.1 1 10 CONVERTION RATE (Hz) Figure 7. Temperature Error vs. D+/D− Capacitance Figure 8. Operating Supply Current vs. Conversion Rate www.onsemi.com 5 100 ADT7481 422 4.4 420 4.2 DEV 2BC 418 4.0 416 3.8 414 IDD (mA) IDD (mA) TYPICAL PERFORMANCE CHARACTERISTICS (Cont’d) DEV 3BC DEV 4BC 412 DEV 2 DEV 3 DEV 4 3.6 3.4 3.2 410 408 3.0 3.1 3.2 3.3 3.4 3.5 3.0 3.0 3.6 3.1 3.2 VDD (V) Figure 9. Operating Supply Current vs. Voltage 35 TEMPERATURE ERROR (°C) 15 10 5 10 100 20 3.6 100 mV 15 10 50 mV 5 0 1000 20 mV 0 100 200 300 400 500 600 NOISE FREQUENCY (MHz) FSCL (kHz) Figure 11. Standby Supply Current vs. SCLK Frequency Figure 12. Temperature Error vs. Common-Mode Noise Frequency 80 TEMPERATURE ERROR (°C) ISTBY (mA) 20 1 3.5 25 25 0 3.4 Figure 10. Standby Supply Current vs. Voltage DEV 2BC DEV 3BC DEV 4BC 30 3.3 VDD (V) 70 60 100 mV 50 40 30 50 mV 20 10 20 mV 0 −10 0 100 200 300 400 500 600 NOISE FREQUENCY (MHz) Figure 13. Temperature Error vs. Differential Mode Noise Frequency www.onsemi.com 6 ADT7481 Theory of Operation This technique requires calibration to null the effect of the absolute value of VBE, which varies from device to device. The technique used in the ADT7481 measures the change in VBE when the device is operated at two different currents. Figure 14 shows the input signal conditioning used to measure the output of a remote temperature sensor. This figure shows the remote sensor as a substrate transistor, but it could equally be a discrete transistor. If a discrete transistor is used, the collector is not grounded and is linked to the base. To prevent ground noise interfering with the measurement, the more negative terminal of the sensor is not referenced to ground, but is biased above ground by an internal diode at the D− input. C1 may optionally be added as a noise filter with a recommended maximum value of 1,000 pF. To measure DVBE, the operating current through the sensor is switched among two related currents. The currents through the temperature diode are switched between I, and N × I, giving DVBE. The temperature can then be calculated using the DVBE measurement. The resulting DVBE waveforms pass through a 65 kHz low-pass filter to remove noise and then to a chopper-stabilized amplifier. This amplifies and rectifies the waveform to produce a dc voltage proportional to DVBE. The ADC digitizes this voltage producing a temperature measurement. To reduce the effects of noise, digital filtering is performed by averaging the results of 16 measurement cycles for low conversion rates. At rates of 16, 32, and 64 conversions/second, no digital averaging takes place. Signal conditioning and measurement of the local temperature sensor is performed in the same manner. The ADT7481 is a local and dual remote temperature sensor and over/under temperature alarm. When the ADT7481 is operating normally, the on-board ADC operates in a free-running mode. The analog input multiplexer alternately selects either the on-chip temperature sensor to measure its local temperature, or either of the remote temperature sensors. The ADC digitizes these signals and the results are stored in the local, Remote 1, and Remote 2 temperature value registers. The local and remote measurement results are compared with the corresponding high, low, and THERM temperature limits, stored in on-chip registers. Out-of-limit comparisons generate flags that are stored in the status register. A result that exceeds the high temperature limit, the low temperature limit, or remote diode open circuit will cause the ALERT output to assert low. Exceeding THERM temperature limits causes the THERM output to assert low. The ALERT output can be reprogrammed as a second THERM output. The limit registers can be programmed, and the device controlled and configured via the serial SMBus. The contents of any register can also be read back via the SMBus. Control and configuration functions consist of switching the device between normal operation and standby mode, selecting the temperature measurement scale, masking or enabling the ALERT output, switching Pin 8 between ALERT and THERM2, and selecting the conversion rate. Temperature Measurement Method A simple method of measuring temperature is to exploit the negative temperature coefficient of a diode, measuring the base-emitter voltage (VBE) of a transistor operated at constant current. I N×I IBIAS VDD VOUT+ D+ REMOTE SENSING TRANSISTOR To ADC C1* D− VOUT− BIAS DIODE LOW-PASS FILTER fC = 65 kHz *CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS. C1 = 1000 pF MAX Figure 14. Input Signal Conditioning Temperature Measurement Results The local temperature measurement is an 8-bit measurement with 1°C resolution. The remote temperature measurements are 10-bit measurements, with the 8 MSBs stored in one register and the 2 LSBs stored in another register. Table 6 is a list of the temperature measurement registers. The results of the local and remote temperature measurements are stored in the local and remote temperature value registers and are compared with limits programmed into the local and remote high and low limit registers. www.onsemi.com 7 ADT7481 Temperature Measurement Range Table 6. REGISTER ADDRESS FOR THE TEMPERATURE VALUES Temperature Channel Register Address, MSBs The temperature measurement range for both local and remote measurements is, by default, 0°C to +127°C. However, the ADT7481 can be operated using an extended temperature range. The temperature range in the extended mode is −64°C to +191°C. The user can switch between these two temperature ranges by setting or clearing Bit 2 in the Configuration 1 register. A valid result is available in the next measurement cycle after changing the temperature range. Bit 2 Configuration Register 2 = 0 = 0°C to +127°C = default Bit 2 Configuration Register 2 = 1 = −64°C to +191°C In extended temperature mode, the upper and lower temperatures that can be measured by the ADT7481 are limited by the remote diode selection. While the temperature registers can have values from −64°C to +191°C, most temperature sensing diodes have a maximum temperature range of −55°C to +150°C. Note that while both local and remote temperature measurements can be made while the part is in extended temperature mode, the ADT7481 should not be exposed to temperatures greater than those specified in the Absolute section. Furthermore, the device is only guaranteed to operate as specified at ambient temperatures from −40°C to +120°C. Register Address, LSBs Local 0x00 N/A Remote 1 0x01 0x10 (2 MSBs) Remote 2 0x30 0x33 (2 MSBs) If Bit 3 of the Configuration 1 register is set to 1, then the Remote 2 temperature values can be read from the following register addresses: Remote 2, MSBs = 0x01 Remote 2, LSBs = 0x10 The above is true only when Bit 3 of the Configuration 1 register is set. To read the Remote 1 temperatures, this bit needs to be switched back to 0. Only the two MSBs in the remote temperature low byte are used. This gives the remote temperature measurement a resolution of 0.25°C. Table 7 shows the data format for the remote temperature low byte. Table 7. EXTENDED TEMPERATURE RESOLUTION (REMOTE TEMPERATURE LOW BYTE) Extended Resolution Remote Temperature Low Byte 0.00°C 0 000 0000 0.25°C 0 100 0000 0.50°C 1 000 0000 0.75°C 1 100 0000 Temperature Data Format The ADT7481 has two temperature data formats. When the temperature measurement range is from 0°C to +127°C (default), the temperature data format is binary for both local and remote temperature results. See the Temperature Measurement Range section for information on how to switch between the two data formats. When the measurement range is in extended mode, an offset binary data format is used for both local and remote results. Temperature values in the offset binary data format are offset by +64. Examples of temperatures in both data formats are shown in Table 8. When reading the full remote temperature value, including both the high and low byte, the two registers should be read LSB first and then the MSB. This is because reading the LSB will cause the MSB to be locked until it is read. This is to guarantee that the two values read are derived from the same temperature measurement. The MSB register updates only after it has been read. The MSB will not lock if a SMBus repeat start is used between reading the two registers. There needs to be a stop between reading the LSB and MSB. If the LSB register is read but not the MSB register, then fail-safe protection is provided by the THERM and ALERT signals which update with the latest temperature measurements rather than the register values. The ADC updates the temperature registers at a rate determined by the Conversion Rate/Channel Selector Register. The temperature registers are not updated if an I2C read is taking place. This is to prevent the register from being corrupted during the read. When reading the full external temperature value, read the LSB first. This causes the MSB to be locked (that is, the ADC does not write to it) until it is read. This feature ensures that the results read back from the two registers come from the same measurement. Table 8. TEMPERATURE DATA FORMAT (LOCAL AND REMOTE TEMPERATURE HIGH BYTE) Temperature −55°C 0°C +1°C +10°C +25°C +50°C +75°C +100°C +125°C +127°C +150°C Binary 0 000 0000 (Note 2) 0 000 0000 0 000 0001 0 000 1010 0 001 1001 0 011 0010 0 100 1011 0 110 0100 0 111 1101 0 111 1111 0 111 1111 (Note 3) Offset Binary (Note 1) 0 000 1001 0 100 0000 0 100 0001 0 100 1010 0 101 1001 0 111 0010 1 000 1011 1 010 0100 1 011 1101 1 011 1111 1 101 0110 1. Offset binary scale temperature values are offset by +64. 2. Binary scale temperature measurement returns 0 for all temperatures 127°C. www.onsemi.com 8 ADT7481 The power-on default value of the address pointer register is 0x00, so if a read operation is performed immediately after power-on, without first writing to the address pointer, the value of the local temperature will be returned since its register address is 0x00. The user may switch between measurement ranges at any time. Switching the range will also switch the data format. The next temperature result following the switching will be reported back to the register in the new format. However, the contents of the limit registers will not change. It is up to the user to ensure that when the data format changes, the limit registers are reprogrammed as necessary. More information on this can be found in the Limit Registers section. Temperature Value Registers The ADT7481 has five registers to store the results of local and remote temperature measurements. These registers can only be written to by the ADC and read by the user over the SMBus. • The local temperature value register is at Address 0x00. • The Remote 1 temperature value high byte register is at Address 0x01, with the Remote 1 low byte register at Address 0x10. • The Remote 2 temperature value high byte register is at Address 0x30, with the Remote 2 low byte register at Address 0x33. • The Remote 2 temperature values can also be read from Address 0x01 for the high byte, and Address 0x10 for the low byte if Bit 3 of Configuration Register 1 is set to 1. • To read the Remote 1 temperature values, set Bit 3 of Configuration Register 1 to 0. • The power-on default value for all five registers is 0x00. Registers The registers in the ADT7481 are eight bits wide. These registers are used to store the results of remote and local temperature measurements, high and low temperature limits, and to configure and control the device. A description of these registers follows. Address Pointer Register The address pointer register does not have, nor does it require, an address because the first byte of every write operation is automatically written to this register. The data in this first byte always contains the address of another register on the ADT7481, which is stored in the address pointer register. It is to this register address that the second byte of a write operation is written to, or to which a subsequent read operation is performed. Table 9. CONFIGURATION 1 REGISTER (READ ADDRESS 0x03, WRITE ADDRESS 0x09) Bit Mnemonic Function 7 Mask Setting this bit to 1 masks all ALERTs on the ALERT pin. Default = 0 = ALERT enabled. This applies only if Pin 8 is configured as ALERT, otherwise it has no effect. 6 Mon/STBY Setting this bit to 1 places the ADT7481 in standby mode, that is, it suspends all temperature measurements (ADC). The SMBus remains active and values can be written to, and read from, the registers. However THERM and ALERT are not active in standby mode, and their states in standby mode are not reliable. Default = 0 = temperature monitoring enabled. 5 AL/TH This bit selects the function of Pin 8. Default = 0 = ALERT. Setting this bit to 1 configures Pin 8 as the THERM2 pin. 4 Reserved 3 Remote 1/2 Setting this bit to 1 enables the user to read the Remote 2 values from the Remote 1 registers. When default = 0, Remote 1 temperature values and limits are read from these registers. 2 Temp Range Setting this bit to 1 enables the extended temperature measurement range of −64°C to +191°C. When using the default = 0, the temperature range is 0°C to +127°C. 1 Mask R1 Setting this bit to 1 masks ALERTs due to the Remote 1 temperature exceeding a programmed limit. Default = 0. 0 Mask R2 Setting this bit to 1 masks ALERTs due to the Remote 2 temperature exceeding a programmed limit. Default = 0. Reserved for future use. Table 10. CONFIGURATION 2 REGISTER (ADDRESS 0x24) Bit Mnemonic Function 7 Lock Bit Setting this bit to 1 locks all lockable registers to their current values. This prevents tampering with settings until the device is powered down. Default = 0. Res Reserved for future use. Conversion Rate/Channel Selector Register 0x0B. For example, a conversion rate of eight conversions/second means that beginning at 125 ms intervals, the device performs a conversion on the local and the remote temperature channels. This register can be written to, and read back from, the SMBus. The default value of this register is 0x08, giving a The conversion rate/channel selector register for reads is at Address 0x04, and at Address 0x0A for writes. The four LSBs of this register are used to program the conversion times from 15.5 ms (Code 0x0A) to 16 seconds (Code 0x00). To program the ADT7481 to perform continuous measurements, set the conversion rate register to www.onsemi.com 9 ADT7481 rate of 16 conversions per second. Using slower conversion times greatly reduces the device power consumption. Bit 7 in this register can be used to disable averaging of the temperature measurements. All temperature channels are measured by default. It is possible to configure the ADT7481 to measure the temperature of one channel only. This can be configured using Bit 4 and Bit 5 (see Table 11). Table 11. CONVERSION RATE/CHANNEL SELECTOR REGISTER (READ ADDRESS 0x04, WRITE ADDRESS 0x0A) Bit Mnemonic Function 7 Averaging Setting this bit to 1 disables averaging of the temperature measurements at the slower conversion rates (averaging cannot take place at the three faster rates, so setting this bit has no effect). When default = 0, averaging is enabled. Reserved for future use. Do not write to this bit. 6 Reserved Channel Selector These bits are used to select the temperature measurement channels: 00 = Round Robin = Default = All Channels Measured 01 = Local Temperature Only Measured 10 = Remote 1 Temperature Only Measured 11 = Remote 2 Temperature Only Measured Conversion Rates These bits set how often the ADT7481 measures each temperature channel. Conversion rates are as follows: Conversions/sec 0000 = 0.0625 0001 = 0.125 0010 = 0.25 0011 = 0.5 0100 = 1 0101 = 2 0110 = 4 0111 = 8 = Default 1000 = 16 1001 = 32 1010 = 64 1011 = Continuous Measurements Limit Registers Time (seconds) 16 8 4 2 1 500 m 250 m 125 m 62.5 m 31.25 m 15.5 m 73 m (Averaging Enabled) It is important to remember that the temperature limits data format is the same as the temperature measurement data format. So if the temperature measurement uses the default binary scale, then the temperature limits also use the binary scale. If the temperature measurement scale is switched, however, the temperature limits do not automatically switch. The user must reprogram the limit registers to the desired value in the correct data format. For example, if the remote low limit is set at 10°C and the default binary scale is being used, the limit register value should be 0000 1010b. If the scale is switched to offset binary, the value in the low temperature limit register should be reprogrammed to be 0100 1010b. The ADT7481 has three limits for each temperature channel: high, low, and THERM temperature limits for local, Remote 1, and Remote 2 temperature measurements. The remote temperature high and low limits span two registers each to contain an upper and lower byte for each limit. There is also a THERM hysteresis register. All limit registers can be written to, and read back from, the SMBus. See Table 16 for details of the limit register addresses and power-on default values. C will result in an out-of-limit condition, setting a flag in the status register. If the low limit register is programmed with 0°C, measuring 0°C or lower will result in an out-of-limit condition. Exceeding either the local or remote THERM limit asserts THERM low. When Pin 8 is configured as THERM2, exceeding either the local or remote high limit asserts THERM2 low. A default hysteresis value of 10°C is provided that applies to both THERM channels. This hysteresis value may be reprogrammed. Status Registers The status registers are read-only registers, at Address 0x02 (Status Register 1) and Address 0x23 (Status Register 2). They contain status information for the ADT7481. www.onsemi.com 10 ADT7481 been serviced by the master reading the device address, provided the error condition has gone away and the status register flag bits have been reset. When Flag 1 and/or Flag 0 of Status Register 1, or Flag 1 of Status Register 2 are set, the THERM output goes low to indicate that the temperature measurements are outside the programmed limits. The THERM output does not need to be reset, unlike the ALERT output. Once the measurements are within the limits, the corresponding status register bits are reset automatically, and the THERM output goes high. The user may add hysteresis by programming Register 0x21. The THERM output will be reset only when the temperature falls below the THERM limit minus hysteresis. When Pin 8 is configured as THERM2, only the high temperature limits are relevant. If Flag 6 and Flag 4 of Status Register 1, or Flag 4 of Status Register 2 are set, the THERM2 output goes low to indicate that the temperature measurements are outside the programmed limits. Flag 5 and Flag 3 of Status Register 1, and Flag 3 of Status Register 2 have no effect on THERM2. The behavior of THERM2 is otherwise the same as THERM. Bit 0 of Status Register 2 gets set whenever the ALERT output is asserted low. Thus, the user need only read Status Register 2 to determine if the ADT7481 is responsible for the ALERT. This bit gets reset when the ALERT output gets reset. If the ALERT output is masked, then this bit is not set. Table 12. STATUS REGISTER 1 BIT ASSIGNMENTS Bit Mnemonic 7 BUSY 6 Function ALERT 1 when ADC Converting No LHIGH (Note 1) 1 when Local High Temperature Limit Tripped Yes 5 LLOW (Note 1) 1 when Local Low Temperature Limit Tripped Yes 4 R1HIGH 1 when Remote 1 High Temperature Limit Tripped Yes 3 R1LOW (Note 1) 1 when Remote 1 Low Temperature Limit Tripped Yes 2 D1 OPEN (Note 1) 1 when Remote 1 Sensor Open Circuit Yes 1 R1THRM1 1 when Remote1 THERM Limit Tripped No 0 LTHRM1 1 when local THERM Limit Tripped No 1. These flags stay high until the status register is read, or they are reset by POR. Table 13. STATUS REGISTER 2 BIT ASSIGNMENTS Bit Mnemonic Function ALERT 7 Res Reserved for Future Use No 6 Res Reserved for Future Use No 5 Res Reserved for Future Use No 4 R2HIGH (Note 1) 1 when Remote 2 High Temperature Limit Tripped Yes 3 R2LOW (Note 1) 1 when Remote 2 Low Temperature Limit Tripped Yes 2 D2 OPEN (Note 1) 1 when Remote 2 Sensor Open Circuit Yes 1 R2THRM1 1 when Remote 2 THERM Limit Tripped No 0 ALERT 1 when ALERT Condition Exists No Offset Register Offset errors may be introduced into the remote temperature measurement by clock noise or by the thermal diode being located away from the hot spot. To achieve the specified accuracy on this channel, these offsets must be removed. The offset values are stored as 10-bit, twos complement values. • The Remote 1 offset MSBs are stored in Register 0x11 and the LSBs are stored in Register 0x12 (low byte, left justified). • The Remote 2 offset MSBs are stored in Register 0x34 and the LSBs are stored in Register 0x35 (low byte, left justified). The Remote 2 offset can be written to, or read from, the Remote 1 offset registers if Bit 3 of the Configuration 1 register is set to 1. This bit should be set to 0 (default) to read the Remote 1 offset values. 1. These flags stay high until the status register is read, or they are reset by POR. The eight flags that can generate an ALERT are NOR’d together. When any flag is high, the ALERT interrupt latch is set and the ALERT output goes low (provided that the flag(s) is/are not masked out). Reading the Status 1 register will clear the five flags (Bit 6 through Bit 2) in Status Register 1, provided the error conditions that caused the flags to be set have gone away. Reading the Status 2 register will clear the three flags (Bit 4 through Bit 2) in Status Register 2, provided the error conditions that caused the flags to be set have gone away. A flag bit can only be reset if the corresponding value register contains an in-limit measurement, or if the sensor is good. The ALERT interrupt latch is not reset by reading the status register. It will be reset when the ALERT output has Only the upper two bits of the LSB registers are used. The MSB of the MSB offset register is the sign bit. The minimum offset that can be programmed is −128°C, and the maximum is +127.75°C. The value in the offset register is added to, or subtracted from, the measured value of the remote temperature. The offset register powers up with a default value of 0°C and will have no effect unless the user writes a different value to it. www.onsemi.com 11 ADT7481 generated. The default value is that one out-of-limit measurement generates an ALERT. The maximum value that can be chosen is 4. The purpose of this register is to allow the user to perform some filtering of the output. This is particularly useful at the fastest three conversion rates, where no averaging takes place. This register is at Address 0x22. This register has other functions that are listed in Table 15. Table 14. SAMPLE OFFSET REGISTER CODES Offset Value 0x11/0x34 0x12/0x35 −128°C 1000 0000 00 00 0000 −4°C 1111 1100 00 00 0000 −1°C 1111 1111 00 000000 −0.25°C 1111 1111 10 00 0000 0°C 0000 0000 00 00 0000 +0.25°C 0000 0000 01 00 0000 +1°C 0000 0001 00 00 0000 Bit Name Description +4°C 0000 0100 00 00 0000 7 +127.75°C 0111 1111 11 00 0000 SCL Timeout Set to 1, enables the SMBus SCL timeout bit. Default = 0 = Timeout disabled. See the Serial Bus Interface section for more information. 6 SDA Timeout Set to 1 to enable the SMBus SDA Timeout Bit. Default = 0 = Timeout disabled. See the Serial Bus Interface section for more information. 5 Mask Local Setting this bit to 1 masks ALERTs due to the local temperature exceeding a programmed limit. Default = 0. 4 Res Consecutive Table 15. CONSECUTIVE ALERT REGISTER BIT One-shot Register The one-shot register is used to initiate a conversion and comparison cycle when the ADT7481 is in standby mode, after which the device returns to standby. Writing to the one-shot register address (0x0F) causes the ADT7481 to perform a conversion and comparison on both the local and the remote temperature channels. This is not a data register as such, and it is the write operation to Address 0x0F that causes the one-shot conversion. The data written to this address is irrelevant and is not stored. However the ALERT and THERM outputs are not operational in one-shot mode and should not be used. ALERT Consecutive ALERT Register The value written to this register determines how many out-of-limit measurements must occur before an ALERT is Reserved for future use. These bits set the number of consecutive out-of-limit measurements that have to occur before an ALERT is generated. 000x = 1 001x = 2 011x = 3 111x = 4 Table 16. LIST OF REGISTERS Read Address (Hex) Write Address (Hex) N/A N/A Address Pointer Undefined 00 N/A Local Temperature Value 0000 0000 (0x00) 01 N/A Remote 1 Temperature Value High Byte 0000 0000 (0x00) Bit 3 Conf Reg = 0 No 01 N/A Remote 2 Temperature Value High Byte 0000 0000 (0x00) Bit 3 Conf Reg = 1 No 02 N/A Status Register 1 Undefined No 03 09 Configuration Register 1 0000 0000 (0x00) Yes 04 0A Conversion Rate/Channel Selector 0000 0111 (0x07) Yes 05 0B Local Temperature High Limit 0101 0101 (0x55) (85°C) Yes 06 0C Local Temperature Low Limit 0000 0000 (0x00) (0°C) Yes 07 0D Remote 1 Temp High Limit High Byte 0101 0101 (0x55) (85°C) Bit 3 Conf Reg = 0 Yes 07 0D Remote 2 Temp High Limit High Byte 0101 0101 (0x55) (85°C) Bit 3 Conf Reg = 1 Yes 08 0E Remote 1 Temp Low Limit High Byte 0000 0000 (0x00) (0°C) Bit 3 Conf Reg = 0 Yes Remote 2 Temp Low Limit High Byte 0000 0000 (0x00) (0°C) Bit 3 Conf Reg = 1 Mnemonic Power-On Default Comment Lock No No 08 0E N/A 0F (Note 1) 10 N/A Remote 1 Temperature Value Low Byte 0000 0000 Bit 3 Conf Reg = 0 10 N/A Remote 2 Temperature Value Low Byte 0000 0000 Bit 3 Conf Reg = 1 No 11 11 Remote 1 Temperature Offset High Byte 0000 0000 Bit 3 Conf Reg = 0 Yes One-Shot Yes N/A www.onsemi.com 12 No ADT7481 Table 16. LIST OF REGISTERS (continued) Read Address (Hex) Write Address (Hex) Comment Lock 11 11 Remote 2 Temperature Offset High Byte 0000 0000 Bit 3 Conf Reg = 1 Yes 12 12 Remote 1 Temperature Offset Low Byte 0000 0000 Bit 3 Conf Reg = 0 Yes 12 12 Remote 2 Temperature Offset Low Byte 0000 0000 Bit 3 Conf Reg = 1 Yes 13 13 Remote 1 Temp High Limit Low Byte 0000 0000 Bit 3 Conf Reg = 0 Yes 13 13 Remote 2 Temp High Limit Low Byte 0000 0000 Bit 3 Conf Reg = 1 Yes 14 14 Remote 1 Temp Low Limit Low Byte 0000 0000 Bit 3 Conf Reg = 0 Yes 14 14 Remote 2 Temp Low Limit Low Byte 0000 0000 Bit 3 Conf Reg = 1 Yes 19 19 Remote 1 THERM Limit 0101 0101 (0x55) (85°C) Bit 3 Conf Reg = 0 Yes 19 19 Remote 2 THERM Limit 0101 0101 (0x55) (85°C) Bit 3 Conf Reg = 1 Yes 20 20 Local THERM Limit 0101 0101 (0x55) (85°C) Yes 21 21 THERM Hysteresis 0000 1010 (0x0A) (10°C) Yes 22 22 Consecutive ALERT 0000 0001 (0x01) Yes 23 N/A Status Register 2 0000 0000 (0x00) No 24 24 Configuration 2 Register 0000 0000 (0x00) Yes 30 N/A Remote 2 Temperature Value High Byte 0000 0000 (0x00) No 31 31 Remote 2 Temp High Limit High Byte 0101 0101 (0x55) (85°C) Yes 32 32 Remote 2 Temp Low Limit High Byte 0000 0000 (0x00) (0°C) Yes 33 N/A Remote 2 Temperature Value Low Byte 0000 0000 (0x00) No 34 34 Remote 2 Temperature Offset High Byte 0000 0000 (0x00) Yes 35 35 Remote 2 Temperature Offset Low Byte 0000 0000 (0x00) Yes 36 36 Remote 2 Temp High Limit Low Byte 0000 0000 (0x00) (0°C) Yes 37 37 Remote 2 Temp Low Limit Low Byte 0000 0000 (0x00) (0°C) Yes 39 39 Remote 2 THERM Limit 0101 0101 (0x55) (85°C) Yes 3D N/A Device ID 1000 0001 (0x81) 3E N/A Manufacturer ID 0100 0001 (0x41) Mnemonic Power-On Default N/A 1. Writing to Address 0F causes the ADT7481 to perform a single measurement. It is not a data register as such, and it does not matter what data is written to it. Serial Bus Interface Addressing the Device Control of the ADT7481 is achieved via the serial bus. The ADT7481 is connected to this bus as a slave device under the control of a master device. The ADT7481 has an SMBus timeout feature. When this is enabled, the SMBus will typically timeout after 25 ms of no activity. However, this feature is not enabled by default. Set Bit 7 (SCL timeout bit) of the consecutive alert register (Address 0x22) to enable the SCL timeout. Set Bit 6 (SDA timeout bit) of the consecutive alert register (Address 0x22) to enable the SDA timeout. The ADT7481 supports packet error checking (PEC) and its use is optional. It is triggered by supplying the extra clock for the PEC byte. The PEC byte is calculated using CRC−8. The frame check sequence (FCS) conforms to CRC−8 by the polynomial: In general, every SMBus device has a 7-bit device address, except for some devices that have extended, 10-bit addresses. When the master device sends a device address over the bus, the slave device with that address responds. The ADT7481 is available with one device address, 0x4C (1001 100b). An ADT7481−1 is also available. The only difference between the ADT7481 and the ADT7481−1 is the SMBus address. The ADT7481−1 has a fixed SMBus address of 0x4B (1001 011b). The addresses mentioned in this datasheet are 7-bit addresses. The R/W bit needs to be added to arrive at an 8-bit address. Other than the different SMBus addresses, the ADT7481 and the ADT7481−1 are functionally identical. The serial bus protocol operates as follows: The master initiates data transfer by establishing a start condition, defined as a high-to-low transition on the serial data line (SDATA) while the serial clock line (SCLK) remains high. This indicates that an address/data stream C(x) + x 8 ) x 2 ) x 1 ) 1 Consult the SMBus 1.1 specification information (www.smbus.org). (eq. 1) for more www.onsemi.com 13 ADT7481 override the acknowledge bit by pulling the data line high during the low period before the ninth 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. 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. In the case of the ADT7481, write operations contain either one or two bytes, while read operations contain one byte. To write data to one of the device data registers or to read data from it, the address pointer register must be set so that the correct data register is addressed. The first byte of a write operation always contains a valid address that is stored in the address pointer register. If data is to be written to the device, the write operation contains a second data byte that is written to the register selected by the address pointer register. This procedure is illustrated in Figure 15. The device address is sent over the bus followed by R/W set to 0 and followed by two data bytes. The first data byte is the address of the internal data register to be written to, which is stored in the address pointer register. The second data byte is the data to be written to the internal data register. follows. 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, that is, whether data will be written to, or read from, the slave device. The peripheral with the address corresponding 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 remain idle while the selected device waits for data to be read from or written to it. If the R/W bit is 0, the master writes to the slave device. If the R/W bit is 1, the master reads from the slave device. Data is sent over the serial bus in a sequence of nine clock pulses, eight bits of data followed by an acknowledge bit from the slave device. Transitions on the data line must occur during the low period of the clock signal and remain stable during the high period, since a low-to-high transition when the clock is high may be interpreted as a stop signal. The number of data bytes that can be transmitted over the serial bus in a single read or write operation is limited only by what the master and slave devices can handle. 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 tenth clock pulse to assert a stop condition. In read mode, the master device will 1 9 9 1 SCLK 1 SDATA 0 START BY MASTER 0 1 1 1 0 R/W D7 FRAME 1 SERIAL BUS ADDRESS BYTE D6 D5 D4 D3 D2 D1 D0 ACK. BY ADT7481 FRAME 2 ADDRESS POINTER REGISTER BYTE ACK. BY ADT7481 1 9 SCLK (CONTINUED) SDATA (CONTINUED) D7 D6 D5 D4 D3 D2 D1 FRAME 3 DATA BYTE D0 ACK. BY STOP BY ADT7481 MASTER Figure 15. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register 1 9 9 1 SCLK SDATA START BY MASTER 1 0 0 1 1 0 1 FRAME 1 SERIAL BUS ADDRESS BYTE D7 R/W ACK. BY ADT7481 D6 D5 D4 D3 D2 D0 ACK. BY ADT7481 FRAME 2 ADDRESS POINTER REGISTER BYTE Figure 16. Writing to the Address Pointer Register Only www.onsemi.com 14 D1 STOP BY MASTER ADT7481 9 1 1 9 SCLK SDATA START BY MASTER 1 0 0 1 1 0 1 FRAME 1 SERIAL BUS ADDRESS BYTE R/W D7 D6 ACK. BY ADT7481 D5 D4 D3 D2 FRAME 2 DATA BYTE FROM ADT7481 Figure 17. Reading Data from a Previously Selected Register www.onsemi.com 15 D1 D0 ACK. BY ADT7481 STOP BY MASTER ADT7481 When reading data from a register there are two possible scenarios: 1. If the address pointer register value of the ADT7481 is unknown or not the desired value, it is necessary to set it to the correct value before data can be read from the desired data register. This is done by performing a write to the ADT7481 as before, but only the data byte containing the register read address is sent, as data is not to be written to the register. This is shown in Figure 16. A read operation is then performed consisting of the serial bus address, R/W bit set to 1, followed by the data byte read from the data register (shown in Figure 17). 2. If the address pointer register is already at the desired address, data can be read from the corresponding data register without first writing to the address pointer register, and the bus transaction shown in Figure 16 can be omitted. a general call address that must not be used as a specific device address. 3. The device with a low ALERT output responds to the alert response address, and the master reads the address from the responding device. An LSB of 1 is added because the device address is comprised of seven bits. The address of the device is now known and it can be interrogated in the usual way. 4. If more than one device has a low ALERT output, the one with the lowest device address will have priority, in accordance with normal SMBus arbitration. 5. Once the ADT7481 has responded to the alert response address, it will reset its ALERT output, provided that the error condition that caused the ALERT no longer exists. If the SMBALERT line remains low, the master sends the ARA again, and so on until all devices with low ALERT outputs respond. Masking the ALERT Output The ALERT output can be masked for local, Remote 1, Remote 2 or all three channels. This is done by setting the appropriate mask bits in either the Configuration 1 register (read address = 0x03, write address = 0x09) or in the consecutive ALERT register (address = 0x22) To mask ALERTs due to local temperature, set Bit 5 of the consecutive ALERT register to 1. Default = 0. To mask ALERTs due to Remote 1 temperature, set Bit 1 of the Configuration 1 register to 1. Default = 0. To mask ALERTs due to Remote 2 temperature, set Bit 0 of the Configuration 1 register to 1. Default = 0. To mask ALERTs due to any channel, set Bit 7 of the Configuration 1 register to 1. Default = 0. NOTES:Remember that some of the ADT7481 registers have different addresses for read and write operations. The write address of a register must be written to the address pointer if data is to be written to that register, but it may not be possible to read data from that address. The read address of a register must be written to the address pointer before data can be read from that register. ALERT Output Pin 8 can be configured as an ALERT output. The ALERT output goes low whenever an out-of-limit measurement is detected, or if the remote temperature sensor is open circuit. It is an open-drain output and requires a pullup. Several ALERT outputs can be wire-OR’ed together, so that the common line will go low if one or more of the ALERT outputs goes low. The ALERT output can be used as an interrupt signal to a processor, or it may be used as an SMBALERT. Slave devices on the SMBus cannot normally signal to the bus master that they want to talk, but the SMBALERT function allows them to do so. One or more ALERT outputs can be connected to a common SMBALERT line connected to the master. When the SMBALERT line is pulled low by one of the devices, the following procedure occurs as illustrated in Figure 18. Low Power Standby Mode The ADT7481 can be put into low power standby mode by setting Bit 6 (Mon/STBY bit) of the Configuration 1 register (Read Address 0x03, Write Address 0x09) to 1. The ADT7481 operates normally when Bit 6 is 0. When Bit 6 is 1, the ADC is inhibited, and any conversion in progress is terminated without writing the result to the corresponding value register. The SMBus is still enabled in low power standby mode. Power consumption in this standby mode is reduced to a typical of 5 mA if there is no SMBus activity, or up to 30 mA if there are clock and data signals on the bus. When the device is in standby mode, it is still possible to initiate a one-shot conversion of both channels by writing to the one-shot register (Address 0x0F), after which the device will return to standby. It does not matter what is written to the one-shot register, all data written to it is ignored. It is also possible to write new values to the limit register while in standby mode. ALERT and THERM are not available in MASTER RECEIVES SMBALERT START ALERT RESPONSE ADDRESS MASTER SENDS ARA AND READ COMMAND RD ACK DEVICE ADDRESS NO STOP ACK DEVICE SENDS ITS ADDRESS Figure 18. Use of SMBALERT 1. SMBALERT is pulled low. 2. Master initiates a read operation and sends the alert response address (ARA = 0001 100). This is www.onsemi.com 16 ADT7481 measurement channels. The power-on hysteresis default value is 10°C, but this may be reprogrammed to any value after powerup. The hysteresis loop on the THERM outputs is useful when THERM is used for on/off control of a fan. The user’s system can be set up so that when THERM asserts, a fan can be switched on to cool the system. When THERM goes high again, the fan can be switched off. Programming a hysteresis value protects from fan jitter, a condition wherein the temperature hovers around the THERM limit, and the fan is constantly being switched on and off. standby mode and, therefore, should not be used because the state of these pins is unreliable. Sensor Fault Detection The ADT7481 has internal sensor fault detection circuitry at its D+ input. This circuit can detect situations where a remote diode is not connected, or is incorrectly connected, to the ADT7481. If the voltage at D+ exceeds VDD − 1.0 V (typical), it signifies an open circuit between D+ and D−, and consequently, trips the simple voltage comparator. The output of this comparator is checked when a conversion is initiated. Bit 2 (D1 open flag) of the Status Register 1 (Address 0x02) is set if a fault is detected on the Remote 1 channel. Bit 2 (D2 open flag) of the Status Register 2 (Address 0x23) is set if a fault is detected on the Remote 2 channel. If the ALERT pin is enabled, setting this flag will cause ALERT to assert low. If a remote sensor is not used with the ADT7481, then the D+ and D− inputs of the ADT7481 need to be tied together to prevent the open flag from being continuously set. Most temperature sensing diodes have an operating temperature range of −55°C to +150°C. Above 150°C, they lose their semiconductor characteristics and approximate conductors instead. This results in a diode short, setting the open flag. The remote diode in this case no longer gives an accurate temperature measurement. A read of the temperature result register will give the last good temperature measurement. The user should be aware that while the diode fault is triggered, the temperature measurement on the remote channels is likely to be inaccurate. Table 17. THERM HYSTERESIS THERM Hysteresis Binary Representation 0°C 0 000 0000 1°C 0 000 0001 10°C 0 000 1010 Figure 19 shows how the THERM and ALERT outputs operate. A user may wish to use the ALERT output as a SMBALERT to signal to the host via the SMBus that the temperature has risen. The user could use the THERM output to turn on a fan to cool the system, if the temperature continues to increase. This method would ensure that there is a fail-safe mechanism to cool the system, without the need for host intervention. TEMPERATURE 1005C 905C THERM LIMIT 805C THERM LIMIT − HYSTERESIS 705C Interrupt System HIGH TEMP LIMIT 605C The ADT7481 has two interrupt outputs, ALERT and THERM. Both outputs have different functions and behavior. ALERT is maskable and responds to violations of software-programmed temperature limits or an open-circuit fault on the remote diode. THERM is intended as a fail-safe interrupt output that cannot be masked. If the Remote 1, Remote 2, or local temperature exceeds the programmed high temperature limits, or equals or exceeds the low temperature limits, the ALERT output is asserted low. An open-circuit fault on the remote diode also causes ALERT to assert. ALERT is reset when serviced by a master reading its device address, provided the error condition has gone away, and the status register has been reset. The THERM output asserts low if the Remote 1, Remote 2, or local temperature exceeds the programmed THERM limits. The THERM temperature limits should normally be equal to or greater than the high temperature limits. THERM is automatically reset when the temperature falls back within the (THERM − hysteresis) limit. The local and remote THERM limits are set by default to 85°C. A hysteresis value can be programmed, in which case THERM will reset when the temperature falls to the limit value minus the hysteresis value. This applies to both local and remote 505C 405C RESET BY MASTER ALERT 1 4 THERM 2 3 Figure 19. Operation of the ALERT and THERM Interrupts • If the measured temperature exceeds the high • • • temperature limit, the ALERT output will assert low. If the temperature continues to increase and exceeds the THERM limit, the THERM output asserts low. This can be used to throttle the CPU clock or switch on a fan. The THERM output de-asserts (goes high) when the temperature falls to THERM limit minus hysteresis. In Figure 19, the default hysteresis value of 10°C is shown. The ALERT output de-asserts only when the temperature has fallen below the high temperature limit, and the master has read the device address and cleared the status register. www.onsemi.com 17 ADT7481 collector connected to the substrate. Discrete types can be either a PNP or an NPN transistor connected as a diode (base shorted to collector). If an NPN transistor is used, the collector and base are connected to D+ and the emitter to D−. If a PNP transistor is used, the collector and base are connected to D− and the emitter to D+. To reduce the error due to variations in both substrate and discrete transistors, a number of factors should be taken into consideration: • The ideality factor, nf, of the transistor is a measure of the deviation of the thermal diode from ideal behavior. The ADT7481 is trimmed for an nf value of 1.008. Use the following equation to calculate the error introduced at a temperature, T (°C), when using a transistor where nf does not equal 1.008. Consult the processor data sheet for the nf values. Pin 8 on the ADT7481 can be configured as either an ALERT output or as an additional THERM output. THERM2 will assert low when the temperature exceeds the programmed local and/or remote high temperature limits. It is reset in the same manner as THERM, and it is not maskable. The programmed hysteresis value also applies to THERM2. Figure 20 shows how THERM and THERM2 might operate together to implement two methods of cooling the system. In this example, the THERM2 limits are set lower than the THERM limits. The THERM2 output could be used to turn on a fan. If the temperature continues to rise and exceeds the THERM limits, the THERM output could provide additional cooling by throttling the CPU. TEMPERATURE 905C THERM LIMIT DT + ǒn f * 1.008Ǔń1.008 805C 705C 605C THERM2 LIMIT 505C 405C • 305C THERM2 1 THERM 4 2 3 Figure 20. Operation of the THERM and THERM2 Interrupts When the THERM2 limit is exceeded, the THERM2 signal asserts low. • If the temperature continues to increase and exceeds the THERM limit, the THERM output asserts low. • , there is no hysteresis value shown. • As the system cools further, and the temperature falls below the THERM2 limit, the THERM2 signal resets. Again, no hysteresis value is shown for THERM2. ǒ273.15 Kelvin ) TǓ (eq. 2) To factor this in, the user can write the DT value to the offset register. It will then automatically be added to, or subtracted from, the temperature measurement by the ADT7481. Some CPU manufacturers specify the high and low current levels of the substrate transistors. The high current level of the ADT7481, IHIGH, is 233ĂmA. The low level current, ILOW, is 14ĂmA. If the ADT7481 current levels do not match the current levels specified by the CPU manufacturer, it may become necessary to remove an offset. The CPU data sheet will advise whether this offset needs to be removed and how to calculate it. This offset may be programmed to the offset register. It is important to note that if more than one offset must be considered, the algebraic sum of these offsets must be programmed to the offset register. If a discrete transistor is being used with the ADT7481, the best accuracy is obtained by choosing devices according to the following criteria: • Base-emitter voltage greater than 0.25 V at 6 mA, at the highest operating temperature. • Base-emitter voltage less than 0.95 V at 100 mA, at the lowest operating temperature. • Base resistance less than 100 W. • Small variation in hFE (say 50 to 150) that indicates tight control of VBE characteristics. The temperature measurement could be either the local or the remote temperature measurement. Applications Information Noise Filtering For temperature sensors operating in noisy environments, previous practice was to place a capacitor across the D+ and D− pins to help combat the effects of noise. However, large capacitances affect the accuracy of the temperature measurement, leading to a recommended maximum capacitor value of 1,000 pF. Transistors, such as 2N3904, 2N3906, or equivalents in SOT−23 packages, are suitable devices to use. Thermal Inertia and Self-heating Accuracy depends on the temperature of the remote sensing diode and/or the local temperature sensor being at the same temperature as that being measured. A number of factors can affect this. Ideally, the sensor should be in good thermal contact with the part of the system being measured; otherwise, the thermal inertia caused by the sensor’s mass Factors Affecting Diode Accuracy Remote Sensing Diode The ADT7481 is designed to work with substrate transistors built into processors or with discrete transistors. Substrate transistors will generally be PNP types with the www.onsemi.com 18 ADT7481 causes a lag in the response of the sensor to a temperature change. In the case of the remote sensor, this should not be a problem, since it will either be a substrate transistor in the processor or a small package device, such as an SOT−23, placed in close proximity to it. The on-chip sensor, however, will often be remote from the processor and only monitors the general ambient temperature around the package. In practice, the ADT7481 package will be in electrical, and hence, thermal contact with a PCB and may also be in a forced airflow. How accurately the temperature of the board and/or the forced airflow reflects the temperature to be measured will also affect the accuracy of the measurement. Self-heating, due to the power dissipated in the ADT7481 or the remote sensor, causes the chip temperature of the device (or remote sensor) to rise above ambient. However, the current forced through the remote sensor is so small that self-heating is negligible. The worst-case condition occurs when the ADT7481 is converting at 64 conversions per second while sinking the maximum current of 1 mA at the ALERT and THERM output. In this case, the total power dissipation in the device is about 4.5 mW. The thermal resistance, qJA, of the MSOP−10 package is about 142°C/W. 3. Try to minimize the number of copper/solder joints that can cause thermocouple effects. Where copper/solder joints are used, make sure that they are in both the D+ and D− path and at the same temperature. Thermocouple effects should not be a major problem as 1°C corresponds to about 200 mV, and thermocouple voltages are about 3 mV/°C of temperature difference. Unless there are two thermocouples with a large temperature differential between them, thermocouple voltages should be much less than 200 mV. 4. Place a 0.1 mF bypass capacitor close to the VDD pin. In extremely noisy environments, an input filter capacitor may be placed across D+ and D− close to the ADT7481. This capacitance can affect the temperature measurement, so care must be taken to ensure that any capacitance seen at D+ and D− is a maximum of 1,000 pF. This maximum value includes the filter capacitance, plus any cable or stray capacitance between the pins and the sensor diode. 5. If the distance to the remote sensor is more than 8 inches, the use of twisted pair cable is recommended. A total of 6 feet to 12 feet of cable is needed. For really long distances (up to 100 feet), use shielded twisted pair, such as Belden No. 8451 microphone cable. Connect the twisted pair to D+ and D− and the shield to GND close to the ADT7481. Leave the remote end of the shield unconnected to avoid ground loops. Layout Considerations Digital boards can be electrically noisy environments, and the ADT7481 measures very small voltages from the remote sensor, so care must be taken to minimize noise induced at the sensor inputs. Take the following precautions: 1. Place the ADT7481 as close as possible to the remote sensing diode. Provided that the worst noise sources such as clock generators, data/address buses, and CRTs are avoided, this distance can range from 4 to 8 inches. 2. Route the D+ and D− tracks close together, in parallel, with grounded guard tracks on each side. To minimize inductance and reduce noise pick up, a 5 mil track width and spacing is recommended. Provide a ground plane under the tracks if possible. GND Because the measurement technique uses switched current sources, excessive cable or filter capacitance can affect the measurement. When using long cables, the filter capacitance can be reduced or removed. Application Circuit Figure 22 shows a typical application circuit for the ADT7481, using discrete sensor transistors. The pullups on SCLK, SDATA, and ALERT are required only if they are not already provided elsewhere in the system. The SCLK and SDATA pins of the ADT7481 can be interfaced directly to the SMBus of an I/O controller, such as the Intel® 820 chipset. 5 MIL 5 MIL D+ 5 MIL 5 MIL D− 5 MIL 5 MIL GND 5 MIL Figure 21. Typical Arrangement of Signal Tracks www.onsemi.com 19 ADT7481 VDD ADT7481 D1+ 2N3904/06 or CPU THERMAL DIODE D1− D2+ 3.0 V to 3.6 V 0.1 mF TYP 10 kW SCLK SMBUS CONTROLLER SDATA ALERT D2− VDD 5.0 V or 12 V THERM TYP 10 kW GND FAN ENABLE FAN CONTROL CIRCUIT Figure 22. Typical Application Circuit Table 18. ORDERING INFORMATION Device Order Number* Package Type Shipping† Branding SMBus Address ADT7481ARMZ−REEL 10-lead MSOP 3,000 Tape & Reel T08 4C ADT7481ARMZ−1RL 10-lead MSOP 3,000 Tape & Reel T0M 4B †For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging Specifications Brochure, BRD8011/D. *The “Z’’ suffix indicates Pb-Free package available. www.onsemi.com 20 ADT7481 PACKAGE DIMENSIONS MSOP10 CASE 846AC ISSUE O NOTES: 1. DIMENSIONING AND TOLERANCING PER ANSI Y14.5M, 1982. 2. CONTROLLING DIMENSION: MILLIMETER. 3. DIMENSION “A” DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.15 (0.006) PER SIDE. 4. DIMENSION “B” DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSION. INTERLEAD FLASH OR PROTRUSION SHALL NOT EXCEED 0.25 (0.010) PER SIDE. 5. 846B−01 OBSOLETE. NEW STANDARD 846B−02 −A− −B− K D 8 PL 0.08 (0.003) PIN 1 ID G SEATING PLANE T B S A S H L J MILLIMETERS MIN MAX 2.90 3.10 2.90 3.10 0.95 1.10 0.20 0.30 0.50 BSC 0.05 0.15 0.10 0.21 4.75 5.05 0.40 0.70 DIM A B C D G H J K L C 0.038 (0.0015) −T− M INCHES MIN MAX 0.114 0.122 0.114 0.122 0.037 0.043 0.008 0.012 0.020 BSC 0.002 0.006 0.004 0.008 0.187 0.199 0.016 0.028 SOLDERING FOOTPRINT* 10X 1.04 0.041 0.32 0.0126 3.20 0.126 8X 10X 4.24 0.167 0.50 0.0196 SCALE 8:1 5.28 0.208 mm Ǔ ǒinches *For additional information on our Pb-Free strategy and soldering details, please download the ON Semiconductor Soldering and Mounting Techniques Reference Manual, SOLDERRM/D. ON Semiconductor and are trademarks of Semiconductor Components Industries, LLC dba ON Semiconductor or its subsidiaries in the United States and/or other countries. ON Semiconductor owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. 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