ADT7461A

ADT7461A AD | Alldatasheet

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±1°C Temperature Monitor with Series Resistance Cancellation ADT7461A Rev. A Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2006 Analog Devices, Inc. All rights reserved.

FEATURES

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 kΩ (typical) 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/under temperature limits Offset registers for system calibration Up to two overtemperature fail-safe THERM outputs Small 8-lead MSOP 240 μA operating current, 5 μA standby current

APPLICATIONS

Desktop and notebook computers Industrial controllers Smart batteries Automotive Embedded systems Burn-in applications Instrumentation FUNCTIONAL BLOCK DIAGRAM A-TO-D CONVERTER RUN/STANDBYBUSY REMOTE OFFSET REGISTER LIMIT COMPARATOR STATUS REGISTER INTERRUPT MASKING REMOTE TEMPERATURE VALUE REGISTER LOCAL TEMPERATURE VALUE REGISTER ON-CHIP TEMPERATURE SENSOR ANALOG MUX EXTERNAL DIODE OPEN-CIRCUIT SMBus INTERFACEADT7461A 1 5 7 VDD GND SDATA SCLK THERM ALERT/THERM2 DIGITAL MUX CONFIGURATION REGISTERS EXTERNAL THERM LIMIT REGISTERS LOCAL THERM LIMIT REGISTERS REMOTE TEMPERATURE HIGH-LIMIT REGISTER REMOTE TEMPERATURE LOW-LIMIT REGISTER LOCAL TEMPERATURE HIGH-LIMIT REGISTER LOCAL TEMPERATURE LOW-LIMIT REGISTER CONVERSION RATE REGISTER ADDRESS POINTER REGISTER DIGITAL MUX 05571-001 Figure 1.

Rev. A | Page 2 of 24 TABLE OF CONTENTS

REVISION HISTORY

5/06—Rev. 0 to Rev. A Added Differences Between the ADT7461A and 4/06—Revision 0: Initial Version

switched to a wider measurement range of −64°C to +191°C. compatible with system management bus (SMBus) standards. is useful if more than one ADT7461A is used on the same SMBus. can be reconfigured as a second THERM output, if required. Table 1. Differences Between the ADT7461A and the ADT7461

16 Conversions/sec 240 170 μA

Rev. A | Page 4 of 24 SPECIFICATIONS TA = −40°C to +125°C, VDD = 3 V to 3.6 V , unless otherwise noted. Table 2. Parameter Min Typ Max Unit Test Conditions POWER SUPPLY Supply Voltage, VDD 3.0 3.30 3.6 V Average Operating Supply Current, IDD 240 350 μA 0.0625 conversions/sec rate1 5 30 μA Standby mode Undervoltage Lockout Threshold 2.55 V VDD input, disables ADC, rising edge Power-On-Reset Threshold 1 2.5 V TEMPERATURE-TO-DIGITAL CONVERTER Local Sensor Accuracy ±1 °C 0°C ≤ TA ≤ +70°C Resolution 1 °C Remote Diode Sensor Accuracy ±1 °C 0°C ≤ TA ≤ +70°C, −55°C ≤ TD2 ≤ +150°C Resolution 0.25 °C Remote Sensor Source Current 220 μA High level3 82 μA Middle level3 13.5 μA Low level3 Conversion Time 40 52 ms From stop bit to conversion complete, one-shot mode with averaging switched on 6 8 ms One-shot mode with averaging off (that is, conversion rate = 16-, 32-, or 64-conversions per second) Maximum Series Resistance Cancelled 1. 5 kΩ Resistance split evenly on both the D+ and D– inputs OPEN-DRAIN DIGITAL OUTPUTS (THERM, ALERT/THERM2) Output Low Voltage, VOL 0.4 V IOUT = −6.0 mA High Level Output Leakage Current, IOH 0.1 1 μA VOUT = VDD SMBus INTERFACE3, 4 Logic Input High Voltage, VIH 2.1 V 3 V ≤ VDD ≤ 3.6 V SCLK, SDATA Logic Input Low Voltage, VIL 0.8 V 3 V ≤ VDD ≤ 3.6 V SCLK, SDATA Hysteresis 500 mV SDA Output Low Voltage, VOL 0.4 V IOUT = −6.0 mA Logic Input Current, IIH, IIL −1 +1 μA SMBus Input Capacitance, SCLK, SDATA 5 pF SMBus Clock Frequency 400 kHz SMBus Timeout5 25 64 ms User programmable SCLK Falling Edge to SDATA Valid Time 1 μs Master clocking in data 1 See Table 10 for information on other conversion rates. 2 Guaranteed by characterization, but not production tested. 3 Guaranteed by design, but not production tested. 4 See SMBus Timing Specifications section for more information. 5 Disabled by default. Detailed procedures to enable it are in the Serial Bus Interface section of this data sheet.

1 Guaranteed by design, but not production tested. 2 Time from 10% of SDATA to 90% of SCLK. 3 Time for 10% or 90% of SDATA to 10% of SCLK. 4 Time for 90% of SCLK to 10% of SDATA. Figure 2. Serial Bus Timing

Table 5. Thermal Resistance degradation or loss of functionality.

Figure 3. Pin Configuration Table 6. Pin Function Descriptions 1 VDD Positive Supply, 3 V to 3.6 V. 2 D+ Positive Connection to Remote Temperature Sensor. 3 D− Negative Connection to Remote Temperature Sensor. overtemperature condition. Requires pull-up resistor. 5 GND Supply Ground Connection. THERM output. Requires pull-up resistor. 7 SDATA Logic Input/Output, SMBus Serial Data. Open-Drain Output. Requires pull-up resistor. 8 SCLK Logic Input, SMBus Serial Clock. Requires pull-up resistor.

Rev. A | Page 10 of 24 THEORY OF OPERATION The ADT7461A is a local and remote temperature sensor and over/under temperature alarm, with the added ability to auto- matically cancel the effect of 1.5 kΩ (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. SERIES RESISTANCE CANCELLATION 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 kΩ 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 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 15 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. T o 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 ΔVBE, the operating current through the sensor is switched among three related currents. As shown in Figure 15, N1 × I and N2 × I are different multiples of the current, I. The currents through the temperature diode are switched between I and N1 × I, giving ΔVBE1; and then between I and N2 × I, giving ΔVBE2. The temperature is then calculated using the two ΔVBE measurements. This method also cancels the effect of any series resistance on the temperature measurement. The resulting ΔVBE waveforms are passed 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 ΔVBE. 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 occurs. Signal conditioning and measurement of the internal temperature sensor are performed in the same manner.

1CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS. C1 = 1000pF MAX. Figure 15. Input Signal Conditioning remote high and low limit registers. format for the external temperature low byte. Table 7. Extended Temperature Resolution range. The extended measurement range is −64°C to +191°C. temperature range of an external diode, from −55°C to +150°C. next measurement cycle after changing the temperature range. specified at ambient temperatures from −40°C to +120°C.

Table 8. Temperature Data Format (Temperature High Byte) 1 Offset binary scale temperature values are offset by 64°C.

2 Binary scale temperature measurement returns 0°C for all

3 Binary scale temperature measurement returns 127°C for all

The user can switch between measurement ranges at any time. to which a subsequent read operation is performed. Address 0x01, with the low byte register at Address 0x10. The power-on default for all three registers is 0x00. Bit 3, and Bit 4 are reserved; the user does not write to them. Bit 7 of the configuration register masks the ALERT output. ured as THERM2, then the value of Bit 7 has no effect. Bit 5 determines the configuration of Pin 6 on the ADT7461A. output, then Bit 7 has no effect. range to the extended temperature range (−64°C to +191°C). Table 9. Configuration Register Bit Assignments

7 MASK1 0 = ALERT Enabled 0

6 RUN/STOP 0 = Run 0

5 ALERT/THERM2 0 = ALERT 0

2 Temperature Range

version times greatly reduces the device power consumption. Table 10. Conversion Rate Register Codes lower results in an out-of-limit condition. to any value after power-up (Register Address 0x21). with the default binary scale, the limit register value is 0000 1010b. perature limit register needs to be reprogrammed to 0100 1010b. contains status information for the ADT7461A. to Bit 0) and the remote sensor open circuit (Bit 2). asserts to flag an open circuit condition on the remote sensor. ALERT interrupt latch is set and the ALERT output goes low. tion has gone away and the status register flag bits are reset.

otherwise the same as THERM. Table 11. Status Register Bit Assignments

7 BUSY 1 when ADC converting

6 LHIGH 1 1 when local high temperature limit tripped

5 LLOW 1 1 when local low temperature limit tripped

4 RHIGH 1 1 when remote high temperature limit tripped

3 RLOW 1 1 when remote low temperature limit tripped

2 OPEN 1 1 when remote sensor open circuit

1 RTHRM 1 when remote THERM limit tripped

0 LTHRM 1 when local THERM limit tripped

1 These flags stay high until the status register is read or they are reset by POR

status register is read or is reset by POR. accuracy on this channel, these offsets must be removed. justified). Only the upper two bits of Register 0x12 are used. subtracted from, the measured value of the remote temperature. no effect unless the user writes a different value to it. Table 12. Sample Offset Register Codes irrelevant and is not stored. limit measurements must occur before an ALERT is generated. register is at Address 0x22. Table 13. Consecutive ALERT Register Bit Default = 0. See the Serial Bus Interface section.

Table 14. List of Registers

00 Not Applicable Local Temperature Value 0000 0000 (0x00)

01 Not Applicable External Temperature Value High Byte 0000 0000 (0x00)

02 Not Applicable Status Undefined

10 Not Applicable External Temperature Value Low Byte 0000 0000

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. enabled, the SMBus times out after typically 25 ms of no activity. except for some devices that have extended 10-bit addresses. is 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).

1. The master initiates a data transfer by establishing a start
2. Data is sent over the serial bus in a sequence of nine clock

when the clock is high can be interpreted as a stop signal. by what the master and slave devices can handle.

SOT-23, placed in close proximity to it. 8-lead MSOP is approximately 142°C/W .

• 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 GND 5MIL 5MIL 5MIL 5MIL 5MIL 5MIL 5MIL 05571-011

Figure 23. Typical Arrangement of Signal Tracks

• 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 big temperature differential between them, thermocouple voltages should be much less than 200 mV .
• Place a 0.1 μF 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.

0.65 BSC

1.10 MAX

Figure 25. 8-Lead Mini Small Outline Package [MSOP]

Rev. A | Page 23 of 24 NOTES

Rev. A | Page 24 of 24 NOTES ©2006 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D05571-0-5/06(A)