MAX6654MEE+TG11

MAX6654 1°C Accurate Remote/Local Temperature Sensor with SMBus Serial Interface General Description The MAX6654 is a precise digital thermometer that reports the temperature of both a remote P-N junction and its own die. The remote junction can be a diode-connected transistor—typically a low-cost, easily mounted 2N3904 NPN type or 2N3906 PNP type—that replaces conventional thermistors or thermocouples. Remote accuracy is ±1°C for multiple transistor manufacturers, with no calibration needed. The remote junction can also be a common-collector PNP, such as a substrate PNP of a microprocessor (µP). The 2-wire serial interface accepts standard System Management Bus (SMBus), Write Byte, Read Byte, Send Byte, and Receive Byte commands to program the alarm thresholds and to read temperature data. Measurements can be done automatically and autonomously, with the conversion rate programmed by the user, or programmed to operate in a single-shot mode. The adjustable conversion rate allows the user to optimize supply current and temperature update rate to match system needs. When the conversion rate is faster than 1Hz, the conversion results are available as a 7-bit-plus-sign byte with a 1°C LSB. When the conversion rate is 1Hz or slower, the MAX6654 enters the extended mode. In this mode, 3 additional bits of temperature data are available in the extended resolution register, providing 10-bit-plus-sign resolution with a 0.125°C LSB. Single-shot conversions also have 0.125°C per LSB resolution when the conversion rate is 1Hz or slower. A parasitic resistance cancellation (PRC) mode can also be invoked for conversion rates of 1Hz or slower by setting bit 4 of the configuration register to 1. In PRC mode, the effect of series resistance on the leads of the external diode is canceled. The 11-bit conversion in PRC mode is performed in 3.15V. Note 3: The conversion time doubles for the extended resolution mode. This causes the average operating current to approximately double. Note 4: The serial interface resets when SMBCLK is low for more than tTIMEOUT. Note 5: Note that a transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SMBCLK’s falling edge. Maxim Integrated 3 MAX6654 1°C Accurate Remote/Local Temperature Sensor with SMBus Serial Interface Typical Operating Characteristics (VCC = +3.3V to +5.5V, TA = +25°C, unless otherwise noted.) 0 -1 -2 -50 -30 -10 10 30 50 70 90 110 130 150 12 VIN = 500mVp-p REMOTE 8 4 0 100 10k 1M 100M 1k 10M 100k FREQUENCY (Hz) STANDBY SUPPLY CURRENT vs. SUPPLY VOLTAGE 6 5 4 3 2 1 MAX6654 toc05 100 STANDBY SUPPLY CURRENT (μA) MAX6654 toc04 VCC = +5V 7 TEMPERATURE ERROR (°C) 1 FREQUENCY (Hz) TEMPERATURE ERROR vs. DXP-DXN CAPACITANCE 90 80 70 60 50 40 0 0 10 20 30 40 50 60 70 80 90 100 DXP-DXN CAPACITANCE (nF) 4 2 0 1 TEMPERATURE (°C) 8 MAX6654 toc03 VIN = 500mVp-p LOCAL TEMPERATURE ERROR (°C) 1 3 MAX6654 toc02 16 MAX6654 toc01 FAIRCHILD 2N3904 TEMPERATURE ERROR (°C) TEMPERATURE ERROR (°C) 2 TEMPERATURE ERROR vs. COMMON-MODE NOISE FREQUENCY TEMPERATURE ERROR vs. POWER-SUPPLY NOISE FREQUENCY TEMPERATURE ERROR vs. REMOTE-DIODE TEMPERATURE 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 SUPPLY VOLTAGE (V) Maxim Integrated MAX6654 1°C Accurate Remote/Local Temperature Sensor with SMBus Serial Interface Pin Description PIN NAME 1, 5, 9, 13, 16 N.C. No Connection. Not internally connected. May be used for PCB trace routing. 2 VCC Supply Voltage Input. +3.0V to +5.5V. Bypass to GND with a 0.1µF capacitor. A 200Ω series resistor is recommended but not required for additional noise filtering. 3 DXP Combined Current Source and ADC Positive Input for Remote-Junction Channel. If a remotesensing junction is not used, connect DXP to DXN. 4 DXN Combined Current Sink and ADC Negative Input. DXN is internally biased to a diode voltage above ground. 6 ADD1 SMBus Slave Address Select Input. ADD0 and ADD1 are sampled upon power-up. 7, 8 GND Ground 10 ADD0 SMBus Slave Address Select Input. ADD0 and ADD1 are sampled upon power-up. 11 ALERT SMBus Alert (Interrupt) Output. Open drain. 12 SMBDATA 14 SMBCLK 15 STBY Maxim Integrated FUNCTION SMBus Serial-Data Input/Output. Open drain. SMBus Serial-Clock Input Hardware standby input. Temperature and comparison threshold data are retained in standby mode. Low = standby mode, high = operating mode. 5 MAX6654 1°C Accurate Remote/Local Temperature Sensor with SMBus Serial Interface Detailed Description The MAX6654 is a temperature sensor that communicates through an SMBus/I2C-compatible interface with a µP in thermal-management applications. Essentially an 11-bit serial analog-to-digital converter (ADC) with a sophisticated front end, the MAX6654 measures the change in diode voltage at different current levels to calculate temperature. It contains a current source, a multiplexer, an ADC, an SMBus interface, and associated control logic (Figure 1). Temperature data from the ADC is loaded into data registers, where it is automatically compared with data previously stored in four over/undertemperature alarm registers. ADC and Multiplexer The ADC is an averaging type that integrates over a 60ms period (each channel, typically, in the 8-bit “legacy” mode), with excellent noise rejection. The multiplexer automatically steers bias currents through the remote and local diodes. The ADC and associated circuitry measure their forward voltages and compute their temperatures. Both channels are automatically converted once the conversion process has started, either in free-running or single-shot mode. If one of the two channels is not used, the device still performs both measurements, and the user can ignore the results of the unused channel. If the remote-diode channel is unused, connect DXP to DXN rather than leave the pins open. The DXN input is biased at 1VBE above ground by an internal diode to set up the ADC inputs for a differential measurement. The worst-case DXP-DXN differential input voltage range is 0.28V to 0.9V. Excess resistance in series with the remote diode causes about +1/2°C error per ohm when the parasitic resistance cancellation mode is not being used. When the parasitic resistance cancellation mode is being used, excess resistance of up to 100Ω will not cause any discernable error. A 200µV offset voltage forced on DXPDXN causes about 1°C error. A/D Conversion Sequence A conversion sequence consists of a local temperature measurement and a remote temperature measurement. Each time a conversion begins, whether initiated automatically in the free-running autoconvert mode (RUN/STOP = 0) or by writing a “One-Shot” command, both channels are converted, and the results of both measurements are available after the end of conversion. A BUSY status bit in the status byte shows that the device is actually performing a new conversion; however, even if the ADC is busy, the results of the previous conversion are always available. 6 Table 1. Remote-Sensor Transistor Manufacturers MANUFACTURER MODEL NUMBER Central Semiconductor (USA) CMPT3904 Fairchild Semiconductor (USA) 2N3904, 2N3906 ON Semiconductor (USA) 2N3904, 2N3906 Rohm Semiconductor (USA) SST3904 Samsung (Korea) KST3904-TF Siemens (Germany) SMBT3904 Zetex (England) FMMT3904CT-ND Note: Transistors must be diode connected (base shorted to collector). Remote-Diode Selection The MAX6654 can directly measure the die temperature of CPUs and other ICs having on-board temperature-sensing diodes as shown in the Typical Operating Circuit, or it can measure the temperature of a discrete diode-connected transistor. For best accuracy, the discrete transistor should be a small-signal device with its collector and base connected together. Accuracy has been experimentally verified for all of the devices listed in Table 1. The transistor must be a small-signal type with a relatively high forward voltage; otherwise, the A/D input voltage range can be violated. The forward voltage must be >0.28V at 10µA; check to ensure this is true at the highest expected temperature. The forward voltage must be