ADT7461A

ADT7461A +15C Temperature Monitor with Series Resistance Cancellation The ADT7461A is a dual−channel digital thermometer and undertemperature/overtemperature alarm, intended for use in PCs and thermal management systems. It is pin− and register−compatible with the ADM1032 and ADT7461. A feature of the ADT7461A is series resistance cancellation, where up to 1.5 kW (typical) of resistance in series with the temperature monitoring diode can be automatically cancelled from the temperature result, allowing noise filtering. The ADT7461A has a configurable ALERT output and an extended, switchable temperature measurement range. The ADT7461A can measure the temperature of a remote thermal diode accurate to ±1°C and the ambient temperature accurate to ±3°C. The temperature measurement range defaults to 0°C to +127°C, compatible with the ADM1032, but it can be switched to a wider measurement range of −64°C to +191°C. The ADT7461A communicates over a 2−wire serial interface, compatible with system management bus (SMBus) standards. The default SMBus address of the ADT7461A is 0x4C. An ADT7461A−2 is available with an SMBus address of 0x4D. This is useful if more than one ADT7461A is used on the same SMBus. An ALERT output signals when the on−chip or remote temperature is out of range. The THERM output is a comparator output that allows on/off control of a cooling fan. The ALERT output can be reconfigured as a second THERM output, if required. Features http://onsemi.com 1 MSOP−8 CASE 846AB MARKING DIAGRAM 8 T1x AYWG G 1 • • • • • • • • • • • • • • • • • • • • On−Chip and Remote Temperature Sensor 0.25°C Resolution/1°C Accuracy on Remote Channel 1°C Resolution/1°C Accuracy on Local Channel Automatically Cancels Up to 1.5 kW (Typ) of Resistance in Series with Remote Diode to Allow Noise Filtering Extended, Switchable Temperature Measurement Range 0°C to +127°C (Default) or –64°C to +191°C Pin− and Register−Compatible with ADM1032 and ADT7461 2−Wire SMBus Serial Interface with SMBus Alert Support Programmable Over/Undertemperature Limits Offset Registers for System Calibration Up to Two Overtemperature Fail−Safe THERM Outputs Small 8−Lead MSOP 240 mA Operating Current, 5 mA Standby Current These are Pb−Free Devices Desktop and Notebook Computers Industrial Controllers Smart Batteries Automotive Embedded Systems Burn−In Applications Instrumentation 1 T1x A Y W G = Refer to Order Info Table = Assembly Location = Year = Work Week = Pb−Free Package (Note: Microdot may be in either location) PIN ASSIGNMENT VDD D+ D– THERM 1 2 3 4 8 7 6 5 SCLK SDATA ALERT/THERM2 GND (Top View) Applications ORDERING INFORMATION See detailed ordering and shipping information in the package dimensions section on page 18 of this data sheet. © Semiconductor Components Industries, LLC, 2009 December, 2009 − Rev. 6 Publication Order Number: ADT7461A/D ADT7461A ADDRESS POINTER REGISTER ON−CHIP TEMPERATURE SENSOR CONVERSION RATE REGISTER LOCAL TEMPERATURE VALUE REGISTER A−TO−D CONVERTER BUSY RUN/STANDBY REMOTE TEMPERATURE VALUE REGISTER REMOTE OFFSET REGISTER LOCAL TEMPERATURE LOW−LIMIT REGISTER LOCAL TEMPERATURE HIGH−LIMIT REGISTER REMOTE TEMPERATURE LOW−LIMIT REGISTER REMOTE TEMPERATURE HIGH−LIMIT REGISTER LOCAL THERM LIMIT REGISTERS EXTERNAL THERM LIMIT REGISTERS CONFIGURATION REGISTERS INTERRUPT MASKING 6 4 DIGITAL MUX LIMIT COMPARATOR D+ 2 D– 3 ANALOG MUX EXTERNAL DIODE OPEN−CIRCUIT STATUS REGISTER DIGITAL MUX ALERT/THERM2 THERM ADT7461A 1 5 7 SMBus INTERFACE 8 VDD GND SDATA SCLK Figure 1. Functional Block Diagram ABSOLUTE MAXIMUM RATINGS Parameter Positive Supply Voltage (VDD) to GND D+ D− to GND SCLK, SDATA, ALERT, THERM Input Current, SDATA, THERM Input Current, D− ESD Rating, All Pins (Human Body Model) Maximum Junction Temperature (TJ Max) Storage Temperature Range Rating −0.3, +3.6 −0.3 to VDD + 0.3 −0.3 to +0.6 −0.3 to +3.6 −1, +50 ±1 1500 150 −65 to +150 Unit V V V V mA mA V °C °C Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect device reliability. NOTE: This device is ESD sensitive. Use standard ESD precautions when handling. THERMAL CHARACTERISTICS Package Type 8−Lead MSOP qJA 142 qJC 43.74 Unit °C/W http://onsemi.com 2 ADT7461A PIN ASSIGNMENT Pin No. 1 2 3 4 5 6 7 Mnemonic VDD D+ D− THERM GND ALERT/THERM2 SDATA SCLK Positive Supply, 3.0 V to 3.6 V. Positive Connection to Remote Temperature Sensor. Negative Connection to Remote Temperature Sensor. Open−Drain Output. Can be used to turn a fan on/off or throttle a CPU clock in the event of an overtemperature condition. Requires pullup resistor. Supply Ground Connection. Open−Drain Logic Output Used as Interrupt or SMBus ALERT. This can also be configured as a second THERM output. Requires pullup resistor. Logic Input/Output, SMBus Serial Data. Open−Drain Output. Requires pullup resistor. Logic Input, SMBus Serial Clock. Requires pullup resistor. Description 8 SMBus TIMING SPECIFICATIONS (Note 1) Parameter fSCLK tLOW tHIGH tR tF tSU; STA tHD; STA (Note 2) tSU; DAT (Note 3) tSU; STO (Note 4) tBUF 1. 2. 3. 4. Limit at TMIN and TMAX 400 1.3 0.6 300 300 600 600 100 600 1.3 Unit kHz max ms min ms min ns max ns max ns min ns min ns min ns min ms min − Clock low period, between 10% points. Clock high period, between 90% points. Clock/data rise time. Clock/data fall time. Start condition setup time. Start condition hold time. Data setup time. Stop condition setup time. Bus free time between stop and start conditions. Description Guaranteed by design, but 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. tLOW SCLK tR tF tHD;STA tHD;STA tHD;DAT SDATA tHIGH tSU;DAT tSU;STA tSU;STO tBUF STOP START START STOP Figure 2. Serial Bus Timing http://onsemi.com 3 ADT7461A ELECTRICAL CHARACTERISTICS TA = −40°C to +125°C, VDD = 3.0 V to 3.6 V, unless otherwise noted. Parameter Power Supply Supply Voltage, VDD Average Operating Supply Current, IDD Undervoltage Lockout Threshold Power−On−Reset Threshold Temperature−To−Digital Converter Local Sensor Accuracy 0°C ≤ TA ≤ +70°C 0°C ≤ TA ≤ +85°C −40°C ≤ TA ≤ +100°C − − ±1.0 ±1.5 ±2.5 − ±1.0 ±1.5 ±2.5 − − °C 0.0625 Conversions/Sec Rate (Note 1) Standby mode VDD input, disables ADC, rising edge 3.0 − − 1.0 3.30 240 5.0 2.55 − 3.6 350 30 − 2.5 V mA V V Conditions Min Typ Max Unit Resolution Remote Diode Sensor Accuracy 0°C ≤ TA ≤ +70°C, −55°C ≤ TD (Note 2) ≤ +150°C 0°C ≤ TA ≤ +85°C, −55°C ≤ TD (Note 2) ≤ +150°C −40°C ≤ TA ≤ +100°C, −55°C ≤ TD (Note 2) ≤ +150°C − − 1.0 − °C °C Resolution Remote Sensor Source Current High level (Note 3) Middle level (Note 3) Low level (Note 3) From stop bit to conversion complete, one−shot mode with averaging switched on One−shot mode with averaging off (that is, conversion rate = 16−, 32−, or 64−conversions per second) Maximum Series Resistance Cancelled Resistance split evenly on both the D+ and D– inputs − − 0.25 220 82 13.5 40 6.0 1.5 °C mA Conversion Time − − − 52 8.0 − ms ms kW Open−Drain Digital Outputs (THERM, ALERT/THERM2) Output Low Voltage, VOL High Level Output Leakage Current, IOH SMBus Interface (Note 3 and 4) Logic Input High Voltage, VIH SCLK, SDATA Logic Input Low Voltage, VIL SCLK, SDATA Hysteresis SDA Output Low Voltage, VOL Logic Input Current, IIH, IIL SMBus Input Capacitance, SCLK, SDATA SMBus Clock Frequency SMBus Timeout (Note 5) SCLK Falling Edge to SDATA Valid Time 1. 2. 3. 4. 5. User programmable Master clocking in data 3.0 V ≤ VDD ≤ 3.6 V 3.0 V ≤ VDD ≤ 3.6 V 2.1 − − − −1.0 − − − − − − 500 − − 5.0 − 25 − − 0.8 − 0.4 +1.0 − 400 64 1.0 V V mV mA mA pF kHz ms ms IOUT = −6.0 mA VOUT = VDD − − − 0.1 0.4 1.0 V mA See Table 5 for information on other conversion rates. Guaranteed by characterization, but not production tested. Guaranteed by design, but not production tested. See SMBus Timing Specifications section for more information. Disabled by default. Detailed procedures to enable it are in the Serial Bus Interface section of the datasheet. http://onsemi.com 4 ADT7461A TYPICAL CHARACTERISTICS 3.5 3.0 TEMPERATURE ERROR (5C) 2.5 2.0 1.5 1.0 0.5 0 –0.5 –1.0 –50 0 50 TEMPERATURE (5C) 100 150 DEV 1 DEV 2 DEV 3 DEV 4 DEV 5 DEV 6 DEV 7 DEV 8 DEV 9 DEV 10 DEV 11 DEV 12 DEV 13 DEV 14 DEV 15 DEV 16 MEAN HIGH 4R LOW 4R 3.5 3.0 TEMPERATURE ERROR (5C) 2.5 2.0 1.5 1.0 0.5 0 –0.5 –1.0 –50 0 50 TEMPERATURE (5C) 100 150 DEV 1 DEV 2 DEV 3 DEV 4 DEV 5 DEV 6 DEV 7 DEV 8 DEV 9 DEV 10 DEV 11 DEV 12 DEV 13 DEV 14 DEV 15 DEV 16 HIGH 4R LOW 4R Figure 3. Local Temperature Error vs. Temperature Figure 4. Remote Temperature Error vs. Actual Temperature 10 5 TEMPERATURE ERROR (5C) 0 TEMPERATURE ERROR (5C) D+ TO GND 0 –2 –4 –6 –8 –10 –12 –14 –16 1 10 LEAKAGE RESISTANCE (MΩ) 100 –18 0 5 10 DEV 4 DEV 3 DEV 2 –5 D+ TO VCC –10 –15 –20 –25 15 20 25 CAPACITANCE (nF) Figure 5. Temperature Error vs. D+/D− Leakage Resistance 1000 900 800 700 IDD (mA) DEV 2BC Figure 6. Temperature Error vs. D+/D− Capacitance 422 420 DEV 2BC 418 416 414 412 410 408 3.0 DEV 3BC DEV 4BC 500 400 300 200 100 0 0.01 0.1 1 CONVERSION RATE (Hz) 10 100 DEV 4BC DEV 3BC IDD (mA) 600 3.1 3.2 3.3 VDD (V) 3.4 3.5 3.6 Figure 7. Operating Supply Current vs. Conversion Rate Figure 8. Operating Supply Current vs. Voltage http://onsemi.com 5 ADT7461A TYPICAL CHARACTERISTICS 4.4 DEV 2 4.2 4.0 DEV 3 IDD (mA) 3.8 DEV 4 3.6 3.4 3.2 3.0 3.0 ISTBY (mA) 35 30 25 20 15 10 5 0 DEV 2BC DEV 3BC DEV 4BC 3.1 3.2 3.3 VDD (V) 3.4 3.5 3.6 1 10 FSCL (kHz) 100 1000 Figure 9. Standby Supply Current vs. Voltage Figure 10. Standby Supply Current vs. Clock Frequency 80 70 25 TEMPERATURE ERROR (5C) TEMPERATURE ERROR (5C) 20 100mV 15 60 50 40 30 20 10 0 100mV 10 50mV 5 20mV 0 50mV 20mV 0 100 200 300 400 NOISE FREQUENCY (MHz) 500 600 –10 0 100 200 300 400 NOISE FREQUENCY (MHz) 500 600 Figure 11. Temperature Error vs. Common−Mode Noise Frequency Figure 12. Temperature Error vs. Differential−Mode Noise Frequency 60 50 TEMPERATURE ERROR (5C) 40 30 20 10 0 0 500 1000 SERIES RESISTANCE W ) ( 1500 2000 Figure 13. Temperature Error vs. Series Resistance http://onsemi.com 6 ADT7461A Differences between the ADT7461A and the ADT7461 Series Resistance Cancellation Although the ADT7461A is pin− and register−compatible with the ADT7461, there are some specification differences between the two devices. A summary of these differences is shown below in Table 1. Table 1. Differences Between the ADT7461A and the ADT7461 Specification Supply Voltage Maximum Local Sensor Accuracy Maximum Series Resistance Cancellation Average Operating Supply Current 16 Conversions/Sec Standby Mode Max Conversion Time One Shot, Averaging On One Shot, Averaging Off Remote Sensor Current Levels High Mid Low ADT7461A 3.0 to 3.6 1.0 1.5 ADT7461 3.0 to 5.5 3.0 3.0 Unit V °C kW mA 240 5.0 52 8.0 170 5.5 114.6 12.56 ms Parasitic resistance to the D+ and D− inputs to the ADT7461A, seen in series with the remote diode, is caused by a variety of factors, including PCB track resistance and track length. This series resistance appears as a temperature offset in the remote sensor’s temperature measurement. This error typically causes a 0.5°C offset per ohm of parasitic resistance in series with the remote diode. The ADT7461A automatically cancels the effect of this series resistance on the temperature reading, giving a more accurate result, without the need for user characterization of this resistance. The ADT7461A is designed to automatically cancel typically up to 1.5 kW of resistance. By using an advanced temperature measurement method, this process is transparent to the user. This feature permits resistances to be added to the sensor path to produce a filter, allowing the part to be used in noisy environments. See the section on Noise Filtering for more details. Temperature Measurement Method mA 220 82 13.5 96 36 6.0 Theory of Operation The ADT7461A is a local and remote temperature sensor and over/under temperature alarm, with the added ability to automatically cancel the effect of 1.5 kW (typical) of resistance in series with the temperature monitoring diode. When the ADT7461A 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 the remote temperature sensor. The ADC digitizes these signals and the results are stored in the local and remote temperature value registers. The local and remote measurement results are compared with the corresponding high, low, and THERM temperature limits, stored in eight on−chip registers. Out−of−limit comparisons generate flags that are stored in the status register. A result that exceeds the high temperature limit or the low temperature limit causes the ALERT output to assert. The ALERT output also asserts if an external diode fault is detected. Exceeding the THERM temperature limits causes the THERM output to assert low. The ALERT output can be reprogrammed as a second THERM output. The limit registers are programmed and the device controlled and configured via the serial SMBus. The contents of any register are also read back via the SMBus. Control and configuration functions consist of switching the device between normal operation and standby mode, selecting the temperature measurement range, masking or enabling the ALERT output, switching Pin 6 between ALERT and THERM2, and selecting the conversion rate. 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. However, 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 ADT7461A measures the change in VBE when the device operates at three different currents. Previous devices used only two operating currents, but it is the use of a third current that allows automatic cancellation of resistances in series with the external temperature sensor. Figure 14 shows the input signal conditioning used to measure the output of an external temperature sensor. This figure shows the external sensor as a substrate transistor, but it can equally be a discrete transistor. If a discrete transistor is used, the collector is not grounded but 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 be added as a noise filter (a recommended maximum value of 1000 pF). However, a better option in noisy environments is to add a filter, as described in the Noise Filtering section. See the Layout Considerations section for more information on C1. To measure DVBE, the operating current through the sensor is switched among three related currents. As shown in Figure 14, N1 x I and N2 x I are different multiples of the current, I. The currents through the temperature diode are switched between I and N1 x I, giving DVBE1; and then between I and N2 x I, giving DVBE2. The temperature is then calculated using the two DVBE measurements. This method also cancels the effect of any series resistance on the temperature measurement. The resulting DVBE waveforms are passed through a 65 kHz low−pass filter to remove noise and then to a http://onsemi.com 7 ADT7461A 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 VDD I N1 y I N2 y I IBIAS cycles for low conversion rates. At rates of 16−, 32−, and 64−conversions/second, no digital averaging occurs. Signal conditioning and measurement of the internal temperature sensor are performed in the same manner. D+ REMOTE SENSING TRANSISTOR C11 D– BIAS DIODE VOUT+ TO ADC fC = 65kHz VOUT– 1CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS. C1 = 1000pF MAX. Figure 14. Input Signal Conditioning Temperature Measurement Results The results of the local and remote temperature measurements are stored in the local and remote temperature value registers and compared with limits programmed into the local and remote high and low limit registers. The local temperature value is in Register 0x00 and has a resolution of 1°C. The external temperature value is stored in two registers, with the upper byte in Register 0x01 and the lower byte in Register 0x10. Only the two MSBs in the external temperature low byte are used giving the external temperature measurement a resolution of 0.25°C. Table 2 lists the data format for the external temperature low byte. Table 2. Extended Temperature Resolution (Remote Temperature Low Byte Extended Resolution 0.00°C 0.25°C 0.50°C 0.75°C Remote Temperature Low Byte 0 000 0000 0 100 0000 1 000 0000 1 100 0000 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. Temperature Measurement Range The extended temperature range is selected by setting Bit 2 of the configuration register to 1. The temperature range is 0°C to 127°C when Bit 2 equals 0. A valid result is available in the next measurement cycle after changing the temperature range. In extended temperature mode, the upper and lower temperature that can be measured by the ADT7461A is limited by the remote diode selection. The temperature registers can have values from −64°C to +191°C. However, most temperature sensing diodes have a maximum temperature range of −55°C to +150°C. Above +150°C, they may lose their semiconductor characteristics and approximate conductors instead. This results in a diode short. In this case, a read of the temperature result register gives the last good temperature measurement. Therefore, the temperature measurement on the external channel may not be accurate for temperatures that are outside the operating range of the remote sensor. It should be noted that although both local and remote temperature measurements can be made while the part is in extended temperature mode, the ADT7461A itself should not be exposed to temperatures greater than those specified in the absolute maximum ratings section. Further, the device is only guaranteed to operate as specified at ambient temperatures from −40°C to +120°C. Temperature Data Format The temperature measurement range for both internal and external measurements is, by default, 0°C to +127°C. However, the ADT7461A can be operated using an extended temperature range. The extended measurement range is −64°C to +191°C. Therefore, the ADT7461A can be used to measure the full temperature range of an external diode, from −55°C to +150°C. The ADT7461A has two temperature data formats. When the temperature measurement range is from 0°C to 127°C (default), the temperature data format for both internal and external temperature results is binary. When the measurement range is in extended mode, an offset binary data format is used for both internal and external results. Temperature values are offset by 64°C in the offset binary data format. Examples of temperatures in both data formats are shown in Table 3. http://onsemi.com 8 ADT7461A Table 3. Temperature Data Format (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 Temperature Value Registers The ADT7461A has three registers to store the results of local and remote temperature measurements. These registers can only be written to by the ADC and can be read by the user over the SMBus. The local temperature value register is at Address 0x00. The external temperature value high byte register is at Address 0x01, with the low byte register at Address 0x10. The power−on default for all three registers is 0x00. Configuration Register 1. Offset binary scale temperature values are offset by 64°C. 2. Binary scale temperature measurement returns 0°C for all temperatures < 0°C. 3. Binary scale temperature measurement returns 127°C for all temperatures > 127°C. The user can switch between measurement ranges at any time. Switching the range likewise switches the data format. The next temperature result following the switching is reported back to the register in the new format. However, the contents of the limit registers do 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 is found in the Limit Registers section. ADT7461A Registers The ADT7461A contains 22, 8−bit registers in total. These registers store the results of remote and local temperature measurements, high and low temperature limits, and configure and control the device. See the Address Pointer Register section through the Consecutive ALERT Register section of this data sheet for more information on the ADT7461A registers. Additional details are shown in Table 4 through Table 8. The entire register map is available in Table 9. Address Pointer Register The configuration register is Address 0x03 at read and Address 0x09 at write. Its power−on default is 0x00. Only four bits of the configuration register are used. Bit 0, Bit 1, Bit 3, and Bit 4 are reserved; the user does not write to them. Bit 7 of the configuration register masks the ALERT output. If Bit 7 is 0, the ALERT output is enabled. This is the power−on default. If Bit 7 is set to 1, the ALERT output is disabled. This applies only if Pin 6 is configured as ALERT. If Pin 6 is configured as THERM2, then the value of Bit 7 has no effect. If Bit 6 is set to 0, which is power−on default, the device is in operating mode with ADC converting. If Bit 6 is set to 1, the device is in standby mode and the ADC does not convert. The SMBus does, however, remain active in standby mode; therefore, values can be read from or written to the ADT7461A via the SMBus. The ALERT and THERM outputs are also active in standby mode. Changes made to the registers in standby mode that affect the THERM or ALERT outputs cause these signals to be updated. Bit 5 determines the configuration of Pin 6 on the ADT7461A. If Bit 5 is 0 (default), then Pin 6 is configured as an ALERT output. If Bit 5 is 1, then Pin 6 is configured as a THERM2 output. Bit 7, the ALERT mask bit, is only active when Pin 6 is configured as an ALERT output. If Pin 6 is set up as a THERM2 output, then Bit 7 has no effect. Bit 2 sets the temperature measurement range. If Bit 2 is 0 (default value), the temperature measurement range is set between 0°C to +127°C. Setting Bit 2 to 1 sets the measurement range to the extended temperature range (−64°C to +191°C). Table 4. Configuration Register Bit Assignments Bit 7 6 5 4, 3 2 1, 0 Name MASK1 RUN/STOP ALERT/ THERM2 Reserved Temperature Range Select Reserved 0 = 0°C to 127°C 1 = Extended range Function 0 = ALERT Enabled 1 = ALERT Masked 0 = Run 1 = Standby 0 = ALERT 1 = THERM2 Power−On Default 0 0 0 0 0 0 The address pointer register itself 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 ADT7461A that is stored in the address pointer register. It is to this register address that the second byte of a write operation is written, or to which a subsequent read operation is performed. The power−on default value of the address pointer register is 0x00. Therefore, if a read operation is performed immediately after power−on, without first writing to the address pointer, the value of the local temperature is returned because its register address is 0x00. http://onsemi.com 9 ADT7461A Conversion Rate Register The conversion rate register is Address 0x04 at read and Address 0x0A at write. The lowest four bits of this register are used to program the conversion rate by dividing the internal oscillator clock by 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, or 1024 to give conversion times from 15.5 ms (Code 0x0A) to 16 seconds (Code 0x00). For example, a conversion rate of eight conversions per second means that beginning at 125 ms intervals, the device performs a conversion on the internal and the external temperature channels. The conversion rate register can be written to and read back over the SMBus. The higher four bits of this register are unused and must be set to 0. The default value of this register is 0x08, giving a rate of 16 conversions per second. Use of slower conversion times greatly reduces the device power consumption. Table 5. Conversion Rate Register Codes Code 0x00 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0x09 0x0A 0x0B to 0xFF Conversion/Second 0.0625 0.125 0.25 0.5 1 2 4 8 16 32 64 Reserved Time (Seconds) 16 8 4 2 1 500 m 250 m 125 m 62.5 m 31.25 m 15.5 m hysteresis value can be reprogrammed to any value after powerup (Register Address 0x21). It is important to remember that the temperature limits data format is the same as the temperature measurement data format. Therefore, if the temperature measurement uses default binary, 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 with the default binary scale, the limit register value is 0000 1010b. If the scale is switched to offset binary, the value in the low temperature limit register needs to be reprogrammed to 0100 1010b. Status Register Limit Registers The ADT7461A has eight limit registers: high, low, and THERM temperature limits for both local and remote 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 over, the SMBus. See Table 9 for details of the limit register addresses and their power−on default values. When Pin 6 is configured as an ALERT output, the high limit registers perform a > comparison, while the low limit registers perform a ≤ comparison. For example, if the high limit register is programmed with 80°C, then measuring 81°C results 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 results in an out−of−limit condition. Exceeding either the local or remote THERM limit asserts THERM low. When Pin 6 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 The status register is a read−only register at Address 0x02. It contains status information for the ADT7461A. When Bit 7 of the status register is high, it indicates that the ADC is busy converting. The other bits in this register flag the out−of−limit temperature measurements (Bit 6 to Bit 3, and Bit 1 to Bit 0) and the remote sensor open circuit (Bit 2). If Pin 6 is configured as an ALERT output, the following applies: If the local temperature measurement exceeds its limits, Bit 6 (high limit) or Bit 5 (low limit) of the status register asserts to flag this condition. If the remote temperature measurement exceeds its limits, then Bit 4 (high limit) or Bit 3 (low limit) asserts. Bit 2 asserts to flag an open circuit condition on the remote sensor. These five flags are NOR’ed together, so if any of them is high, the ALERT interrupt latch is set and the ALERT output goes low. Reading the status register clears the five flags, Bit 6 to Bit 2, provided the error conditions causing the flags to be set have gone away. A flag bit can be reset only 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 resets when the ALERT output has been serviced by the master reading the device address, provided the error condition has gone away and the status register flag bits are reset. When Flag 1 and/or Flag 0 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 automatically reset and the THERM output goes high. The user may add hysteresis by programming Register 0x21. The THERM output is reset only when the temperature falls to limit value minus the hysteresis value. When Pin 6 is configured as THERM2, only the high temperature limits are relevant. If Flag 6 and/or Flag 4 are set, the THERM2 output goes low to indicate that the temperature measurements are outside the programmed limits. Flag 5 and Flag 3 have no effect on THERM2. The behavior of THERM2 is otherwise the same as THERM. http://onsemi.com 10 ADT7461A Table 6. Status Register Bit Assignments Bit 7 6 5 4 3 2 1 0 Name BUSY LHIGH (Note 1) LLOW (Note 1) RHIGH (Note 1) RLOW (Note 1) OPEN (Note 1) RTHRM LTHRM Function 1 when ADC is converting 1 when local high temperature limit is tripped 1 when local low temperature limit is tripped 1 when remote high temperature limit is tripped 1 when remote low temperature limit is tripped 1 when remote sensor is an open circuit 1 when remote THERM limit is tripped 1 when local THERM limit is tripped One−Shot Register The one−shot register is used to initiate a conversion and comparison cycle when the ADT7461A is in standby mode, after which the device returns to standby. Writing to the one−shot register address (0x0F) causes the ADT7461A to perform a conversion and comparison on both the internal and the external 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. Consecutive ALERT Register 1. These flags stay high until the status register is read or they are reset by POR unless Pin 6 is configured as THERM2. Then, only Bit 2 remains high until the status register is read or is reset by POR. Offset Register The value written to this register determines how many out−of−limit measurements must occur before an ALERT is 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. Table 8. Consecutive ALERT Register Codes Register Value yxxx 000x yxxx 001x yxxx 011x yxxx 111x NOTE: Number of Out−of−Limit Measurements Required 1 2 3 4 Offset errors can be introduced into the remote temperature measurement by clock noise or when the thermal diode is located away from the hot spot. To achieve the specified accuracy on this channel, these offsets must be removed. The offset value is stored as a 10−bit, twos complement value in Register 0x11 (high byte) and Register 0x12 (low byte, left justified). Only the upper two bits of Register 0x12 are used. The MSB of Register 0x11 is the sign bit. The minimum, programmable offset 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 has no effect unless the user writes a different value to it. Table 7. Sample Offset Register Codes Offset Value −128°C −4°C −1°C −0.25°C 0°C +0.25°C +1°C +4°C +127.75°C 0x11 1000 0000 1111 1100 1111 1111 1111 1111 0000 0000 0000 0000 0000 0001 0000 0100 0111 1111 0x12 00 00 0000 00 00 0000 00 000000 10 00 0000 00 00 0000 01 00 0000 00 00 0000 00 00 0000 11 00 0000 x = don’t care bits, and y = SMBus timeout bit. Default = 0. See SMBus section for more information. http://onsemi.com 11 ADT7461A Table 9. List of Registers Read Address (Hex) Not Applicable 00 01 02 03 04 05 06 07 08 Not Applicable 10 11 12 13 14 19 20 21 22 FE FF Write Address (Hex) Not Applicable Not Applicable Not Applicable Not Applicable 09 0A 0B 0C 0D 0E 0F (Note 1) Not Applicable 11 12 13 14 19 20 21 22 Not Applicable Not Applicable Address Pointer Local Temperature Value External Temperature Value High Byte Status Configuration Conversion Rate Local Temperature High Limit Local Temperature Low Limit External Temperature High Limit High Byte External Temperature Low Limit High Byte One−Shot External Temperature Value Low Byte External Temperature Offset High Byte External Temperature Offset Low Byte External Temperature High Limit Low Byte External Temperature Low Limit Low Byte External THERM Limit Local THERM Limit THERM Hysteresis Consecutive ALERT Manufacturer ID Die Revision Code 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0101 0101 (0x55) (85°C) 0101 0101 (0x55) (85°C) 0000 1010 (0x0A) (10°C) 0000 0001 (0x01) 0100 0001 (0x41) 0101 0111 (0x57) Name Power−On Default Undefined 0000 0000 (0x00) 0000 0000 (0x00) Undefined 0000 0000 (0x00) 0000 1000 (0x08) 0101 0101 (0x55) (85°C) 0000 0000 (0x00) (0°C) 0101 0101 (0x55) (85°C) 0000 0000 (0x00) (0°C) 1. Writing to Address 0x0F causes the ADT7461A to perform a single measurement. It is not a data register, and it does not matter what data is written to it. Serial Bus Interface Control of the ADT7461A is carried out via the serial bus. The ADT7461A is connected to this bus as a slave device, under the control of a master device. The ADT7461A has an SMBus timeout feature. When this is enabled, the SMBus times out after typically 25 ms of no activity. However, this feature is not enabled by default. Bit 7 of the consecutive alert register (Address = 0x22) should be set to enable it. Addressing the Device 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 ADT7461Ais available with one device address, 0x4C (1001 100b). An ADT7461A−2 is also available. The ADT7461A−2 has an SMBus address of 0x4D (1001 101b). This is to allow two ADT7461A devices on the same bus, or if the default address conflicts with an existing device on the SMBus. The serial bus protocol operates as follows: 1. The master initiates a data transfer by establishing a start condition, defined as a high−to−low transition on SDATA, the serial data line, while SCLK, the serial clock line, remains high. This indicates that an address/data stream 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 an R/W bit, which determines the direction of the data transfer, that is, whether data is 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 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, the master writes to the slave device. If the R/W bit is a 1, the master reads from the slave device. 2. 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 can be interpreted as a stop signal. The number of data bytes that can be http://onsemi.com 12 ADT7461A transmitted over the serial bus in a single read or write operation is limited only by what the master and slave devices can handle. 3. When all data bytes have been read or written, stop conditions are established. In write mode, the master pulls the data line high during the tenth clock pulse to assert a stop condition. In read mode, the master device overrides 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 takes 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 are transferable 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 1 SCLK beginning and cannot subsequently be changed without starting a new operation. For the ADT7461A, 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. This is 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. 9 1 9 SDATA START BY MASTER A6 A5 A4 A3 A2 A1 A0 R/W ACK. BY ADT7461A D7 D6 D5 D4 D3 D2 D1 D0 ACK. BY ADT7461A FRAME 1 SERIAL BUS ADDRESS BYTE 1 SCLK (CONTINUED) FRAME 2 ADDRESS POINTER REGISTER BYTE 9 SDATA (CONTINUED) D7 D6 D5 D4 D3 D2 D1 D0 ACK. BY STOP BY ADT7461A MASTER FRAME 3 DATA BYTE Figure 15. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register 1 SCLK 9 1 9 SDATA START BY MASTER A6 A5 A4 A3 A2 A1 A0 R/W ACK. BY ADT7461A D7 D6 D5 D4 D3 D2 D1 D0 ACK. BY STOP BY ADT7461A MASTER FRAME 1 SERIAL BUS ADDRESS BYTE FRAME 2 ADDRESS POINTER REGISTER BYTE Figure 16. Writing to the Address Pointer Register Only 1 SCLK 9 1 9 SDATA START BY MASTER A6 A5 A4 A3 A2 A1 A0 R/W ACK. BY ADT7461A D7 D6 D5 D4 D3 D2 D1 D0 ACK. BY STOP BY ADT7461A MASTER FRAME 1 SERIAL BUS ADDRESS BYTE FRAME 2 ADDRESS POINTER REGISTER BYTE Figure 17. Reading from a Previously Selected Register http://onsemi.com 13 ADT7461A When reading data from a register there are two possibilities. • If the address pointer register value of the ADT7461A is unknown or not the desired value, it is first necessary to set it to the correct value before data can be read from the desired data register. This is done by writing to the ADT7461A as before, but only the data byte containing the register read address is sent, because data is not to be written to the register see 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 see Figure 17. • If the address pointer register is known to be 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. Notes: MASTER RECEIVES SMBALERT START ALERT RESPONSE ADDRESS MASTER SENDS ARA AND READ COMMAND RD ACK DEVICE ADDRESS DEVICE SENDS ITS ADDRESS NO STOP ACK Figure 18. Use of SMBALERT • It is possible to read a data byte from a data register • without first writing to the address pointer register. However, if the address pointer register is already at the correct value, it is not possible to write data to a register without writing to the address pointer register because the first data byte of a write is always written to the address pointer register. Some of the 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. 1. SMBALERT is pulled low. 2. Master initiates a read operation and sends the alert response address (ARA = 0001 100). This is a general call address that must not be used as a specific device address. 3. The device whose ALERT output is low responds to the alert response address and the master reads its device address. As the device address is seven bits, an LSB of 1 is added. The address of the device is now known and it can be interrogated in the usual way. 4. If more than one device’s ALERT output is low, the one with the lowest device address takes priority, in accordance with normal SMBus arbitration. Once the ADT7461A has responded to the alert response address, it resets 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 whose ALERT outputs were low have responded. Low Power Standby Mode ALERT Output This is applicable when Pin 6 is 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 resistor. Several ALERT outputs can be wire−OR’ed together, so that the common line goes 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 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 that is connected to the master. When the SMBALERT line is pulled low by one of the devices, the following procedure occurs (see Figure 18): The ADT7461A can be put into low power standby mode by setting Bit 6 of the configuration register. When Bit 6 is low, the ADT7461A operates normally. When Bit 6 is high, the ADC is inhibited, and any conversion in progress is terminated without writing the result to the corresponding value register. However, the SMBus is still enabled. Power consumption in the standby mode is reduced to 5 mA if there is no SMBus activity, or 30 mA if there are clock and data signals on the bus. When the device is in standby mode, it is possible to initiate a one−shot conversion of both channels by writing to the one−shot register (Address 0x0F), after which the device returns 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. If the values stored in the temperature value registers are outside the new limits, an ALERT is generated, even though the ADT7461A is still in standby. http://onsemi.com 14 ADT7461A Sensor Fault Detection At its D+ input, the ADT7461A contains internal sensor fault detection circuitry. This circuit can detect situations where an external remote diode is either not connected or incorrectly connected to the ADT7461A. A simple voltage comparator trips if the voltage at D+ exceeds VDD − 1 V (typical), signifying an open circuit between D+ and D−. The output of this comparator is checked when a conversion is initiated. Bit 2 of the status register (open flag) is set if a fault is detected. If the ALERT pin is enabled, setting this flag causes ALERT to assert low. If the user does not wish to use an external sensor with the ADT7461A, tie the D+ and D− inputs together to prevent continuous setting of the open flag. The ADT7461A Interrupt System Figure 19 shows how the THERM and ALERT outputs operate. The ALERT output can be used as a SMBALERT to signal to the host via the SMBus that the temperature has risen. The user can use the THERM output to turn on a fan to cool the system, if the temperature continues to increase. This method ensures that there is a fail−safe mechanism to cool the system, without the need for host intervention. TEMPERATURE 1005C 905C 805C 705C 605C 505C 405C RESET BY MASTER ALERT 1 THERM 2 3 4 THERM LIMIT THERM LIMIT−HYSTERESIS HIGH TEMP LIMIT The ADT7461A has two interrupt outputs, ALERT and THERM. Both have different functions and behavior. ALERT is maskable and responds to violations of software programmed temperature limits or an open−circuit fault on the external diode. THERM is intended as a fail−safe interrupt output that cannot be masked. If the external 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 external 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 external or local temperature exceeds the programmed THERM limits. THERM temperature limits should normally be equal to or greater than the high temperature limits. THERM is reset automatically when the temperature falls back within the THERM limit. The external and local limits are set by default to 85°C. A hysteresis value can be programmed; in which case, THERM resets when the temperature falls to the limit value minus the hysteresis value. This applies to both local and remote measurement channels. The power−on hysteresis default value is 10°C, but this can be reprogrammed to any value after powerup. The hysteresis loop on the THERM outputs is useful when THERM is used, for example, as an on/off controller for a fan. The user’s system can be set up so that when THERM asserts, a fan is 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, where the temperature hovers around the THERM limit, and the fan is constantly switched. Table 10. THERM Hysteresis THERM Hysteresis 0°C 1°C 10°C Binary Representation 0 000 0000 0 000 0001 0 000 1010 Figure 19. Operation of the ALERT and THERM Interrupts • If the measured temperature exceeds the high THERM limit, the THERM output asserts low. This can be used to throttle the CPU clock or switch on a fan. • The THERM output deasserts (goes high) when the temperature falls to THERM limit minus hysteresis. In , the default hysteresis value of 10°C is shown. • The ALERT output deasserts only when the temperature has fallen below the high temperature limit, and the master has read the device address and cleared the status register. • Pin 6 on the ADT7461A can be configured as either an ALERT output or as an additional THERM output. • THERM2 asserts low when the temperature exceeds the programmed local and/or remote high temperature limits. It is reset in the same manner as THERM and is not maskable. • The programmed hysteresis value also applies to THERM2. Figure 20 shows how THERM and THERM2 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 is used to turn on a fan. If the temperature continues to rise and exceeds the THERM limits, the THERM output provides additional cooling by throttling the CPU. • If the temperature continues to increase and exceeds the temperature limit, the ALERT output asserts low. http://onsemi.com 15 ADT7461A TEMPERATURE 905C 805C 705C 605C 505C 405C 305C 1 THERM2 THERM 2 3 4 THERM2 LIMIT THERM LIMIT Remote Sensing Diode Figure 20. Operation of the THERM and THERM2 Interrupts signal asserts low. • If the temperature continues to increase and exceeds the THERM limit, the THERM output asserts low. • The THERM output deasserts (goes high) when the temperature falls to THERM limit minus hysteresis. In Figure 20, 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. Both the external and internal temperature measurements cause THERM and THERM2 to operate as described. Application Information Noise Filtering • When the THERM2 limit is exceeded, the THERM2 The ADT7461A is designed to work with substrate transistors built into processors or with discrete transistors. Substrate transistors are generally PNP types with the collector connected to the substrate. Discrete types are either PNP or NPN transistors connected as diodes (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, consider several factors: • The ideality factor, nF, of the transistor is a measure of the deviation of the thermal diode from ideal behavior. The ADT7461A is trimmed for an nF value of 1.008. The following equation may be used to calculate the error introduced at a temperature, T (°C), when using a transistor whose nF does not equal 1.008. Consult the processor data sheet for the nF values. DT = (nF − 1.008)/1.008 x (273.15 Kelvin + T) To factor this in, the user writes the DT value to the offset register. It is then automatically added to, or subtracted from, the temperature measurement. • Some CPU manufacturers specify the high and low current levels of the substrate transistors. The high current level of the ADT7461A, IHIGH, is 220 mA and the low level current, ILOW, is 13.5 mA. If the ADT7461A 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 should advise whether this offset needs to be removed and how to calculate it. This offset is 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 used with the ADT7461A, 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 (50 to 150) that indicates tight control of VBE characteristics Transistors, such as the 2N3904, 2N3906, or equivalents in SOT−23 packages are suitable devices to use. Thermal Inertia and Self−Heating For temperature sensors operating in noisy environments, the industry standard 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. Although this capacitor reduces the noise, it does not eliminate it, making it difficult to use the sensor in a very noisy environment. The ADT7461A has a major advantage over other devices when it comes to eliminating the effects of noise on the external sensor. The series resistance cancellation feature allows a filter to be constructed between the external temperature sensor and the part. The effect of any filter resistance seen in series with the remote sensor is automatically cancelled from the temperature result. The construction of a filter allows the ADT7461A and the remote temperature sensor to operate in noisy environments. Figure 21 shows a low−pass R−C−R filter, where R = 100 W and C = 1 nF. This filtering reduces both common−mode and differential noise. 100W REMOTE TEMPERATURE SENSOR 1nF 100W D– D+ Figure 21. Filter Between Remote Sensor and ADT7461A Factors Affecting Diode Accuracy Accuracy depends on the temperature of the remote sensing diode and/or the internal temperature sensor being at the same temperature as that being measured. Many factors can affect this. Ideally, place the sensor in good thermal contact with the part of the system being measured. http://onsemi.com 16 ADT7461A If it is not, the thermal inertia caused by the sensor’s mass 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 is either a substrate transistor in the processor or a small package device, such as the SOT−23, placed in close proximity to it. The on−chip sensor, however, is often remote from the processor and only monitors the general ambient temperature around the package. How accurately the temperature of the board and/or the forced airflow reflects the temperature to be measured dictates the accuracy of the measurement. Self−heating due to the power dissipated in the ADT7461A 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. In the case of the ADT7461A, the worst−case condition occurs when the device 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 8−lead MSOP is approximately 142°C/W. Layout Considerations • Try to minimize the number of copper/solder joints that Digital boards can be electrically noisy environments, and the ADT7461A is measuring very small voltages from the remote sensor, so care must be taken to minimize noise induced at the sensor inputs. Take the following precautions: • Place the ADT7461A as close as possible to the remote sensing diode. Provided that the worst noise sources, that is, clock generators, data/address buses, and CRTs are avoided, this distance can be 4 inches to 8 inches. • Route the D+ and D– tracks close together, in parallel, with grounded guard tracks on each side. To minimize inductance and reduce noise pickup, a 5 mil track width and spacing is recommended. Provide a ground plane under the tracks, if possible. GND 5 MIL 5 MIL D+ 5 MIL 5 MIL D– 5 MIL 5 MIL GND 5 MIL 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 big temperature differential between them, thermocouple voltages should be much less than 200 mV. • Place a 0.1 mF bypass capacitor close to the VDD pin. In extremely noisy environments, place an input filter capacitor across D+ and D− close to the ADT7461A. This capacitance can effect the temperature measurement, so ensure that any capacitance seen at D+ and D− is, at maximum, 1,000 pF. This maximum value includes the filter capacitance, plus any cable or stray capacitance between the pins and the sensor diode. • 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 is needed. For really long distances (up to 100 feet), use a shielded twisted pair, such as the Belden No. 8451 microphone cable. Connect the twisted pair to D+ and D− and the shield to GND close to the ADT7461A. Leave the remote end of the shield unconnected to avoid ground loops. 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 23 shows a typical application circuit for the ADT7461A, using a discrete sensor transistor connected via a shielded, twisted pair cable. The pullups on SCLK, SDATA, and ALERT are required only if they are not provided elsewhere in the system. The SCLK pin and the SDATA pin of the ADT7461A can be interfaced directly to the SMBus of an I/O controller, such as the IntelR 820 chipset.. Figure 22. Typical Arrangement of Signal Tracks http://onsemi.com 17 ADT7461A VDD 3V TO 3.6V 0.1mF TYP 10kW SMBUS CONTROLLER 5V OR 12V ADT7461A D+ Dć SHIELD 2N3906 OR CPU THERMAL DIODE SCLK SDATA ALERT/ THERM2 THERM GND VDD TYP 10kW FAN ENABLE FAN CONTROL CIRCUIT Figure 23. Typical Application Circuit ORDERING INFORMATION Device Order Number* ADT7461AARMZ ADT7461AARMZ−R ADT7461AARMZ−RL7 ADT7461AARMZ−002 ADT7461AARMZ−2RL ADT7461AARMZ2RL7 8−Lead MSOP T1L 4D T1K 4C Package Description Branding SMBus Address Shipping† 50 Tube 3000 Tape & Reel 1000 Tape & Reel 50 Tube 3000 Tape & Reel 1000 Tape & Reel †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. http://onsemi.com 18 ADT7461A PACKAGE DIMENSIONS MSOP8 CASE 846AB−01 ISSUE O D 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. 846A-01 OBSOLETE, NEW STANDARD 846A-02. MILLIMETERS NOM MAX −− 1.10 0.08 0.15 0.33 0.40 0.18 0.23 3.00 3.10 3.00 3.10 0.65 BSC 0.40 0.55 0.70 4.75 4.90 5.05 MIN −− 0.05 0.25 0.13 2.90 2.90 INCHES NOM −− 0.003 0.013 0.007 0.118 0.118 0.026 BSC 0.016 0.021 0.187 0.193 MIN −− 0.002 0.010 0.005 0.114 0.114 HE E PIN 1 ID e b 8 PL 0.08 (0.003) M TB S A S −T− PLANE 0.038 (0.0015) A1 SEATING A c L DIM A A1 b c D E e L HE MAX 0.043 0.006 0.016 0.009 0.122 0.122 0.028 0.199 SOLDERING FOOTPRINT* 8X 1.04 0.041 0.38 0.015 8X 3.20 0.126 4.24 0.167 5.28 0.208 6X 0.65 0.0256 SCALE 8:1 mm inches *For additional information on our Pb−Free strategy and soldering details, please download the ON Semiconductor Soldering and Mounting Techniques Reference Manual, SOLDERRM/D. Protected by U.S. Patents 5,195,827; 5,867,012; 5,982,221; 6,097,239; 6,133,753; 6,169,442; 7,010,440 ; other patents pending. ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner. PUBLICATION ORDERING INFORMATION LITERATURE FULFILLMENT: Literature Distribution Center for ON Semiconductor P.O. Box 5163, Denver, Colorado 80217 USA Phone: 303−675−2175 or 800−344−3860 Toll Free USA/Canada Fax: 303−675−2176 or 800−344−3867 Toll Free USA/Canada Email: orderlit@onsemi.com N. American Technical Support: 800−282−9855 Toll Free USA/Canada Europe, Middle East and Africa Technical Support: Phone: 421 33 790 2910 Japan Customer Focus Center Phone: 81−3−5773−3850 ON Semiconductor Website: www.onsemi.com Order Literature: http://www.onsemi.com/orderlit For additional information, please contact your local Sales Representative http://onsemi.com 19 ADT7461A/D