19-2032; Rev 4; 8/08 Remote ±1°C Accurate Digital Temperature Sensors with SPI-Compatible Serial Interface Features The MAX6627/MAX6628 precise digital temperature sensors report the temperature of a remote sensor. The remote sensor is a diode-connected transistor, typically a low-cost, easily mounted 2N3904 NPN type that replaces conventional thermistors or thermocouples. The MAX6627/MAX6628 can also measure the die temperature of other ICs, such as microprocessors (µPs) or microcontrollers (µCs) that contain an on-chip, diodeconnected transistor. Remote accuracy is ±1°C when the temperature of the remote diode is between 0°C and +125°C and the temperature of the MAX6627/MAX6628 is +30°C. The temperature is converted to a 12-bit + sign word with 0.0625°C resolution. The architecture of the device is capable of interpreting data as high as +145°C from the remote sensor. The MAX6627/MAX6628 temperature should never exceed +125°C. These sensors are 3-wire serial interface SPI™ compatible, allowing the MAX6627/MAX6628 to be readily connected to a variety of µCs. The MAX6627/MAX6628 are read-only devices, simplifying their use in systems where only temperature data is required. Two conversion rates are available, one that continuously converts data every 0.5s (MAX6627), and one that converts data every 8s (MAX6628). The slower version provides minimal power consumption under all operating conditions (30µA, typ). Either device can be read at any time and provide the data from the last conversion. Both devices operate with supply voltages between +3.0V and +5.5V, are specified between -55°C and +125°C, and come in space-saving 8-pin SOT23 and lead-free TDFN packages. o Accuracy ±1°C (max) from 0°C ≤ TRJ ≤ +125°C, TA = +30°C ±2.4°C (max) from -55°C ≤ TRJ ≤ +100°C, 0°C ≤ TA ≤ +70°C o 12-Bit + Sign, 0.0625°C Resolution o Low Power Consumption 30µA (typ) (MAX6628) 200µA (typ) (MAX6627) o Operating Temperature Range (-55°C to +125°C) o Measurement Temperature Range, Remote Junction (-55°C to +145°C) o 0.5s (MAX6627) or 8s (MAX6628) Conversion Rate o SPI-Compatible Interface o +3.0V to +5.5V Supply Range o 8-Pin SOT23 and TDFN Packages o Lead-Free Version Available (TDFN Package) Ordering Information PART PIN-PACKAGE TOP MARK MAX6627MKA#T 8 SOT23 AAEQ MAX6627MTA+T 8 TDFN-EP* +AUT MAX6628MKA#T 8 SOT23 AAER MAX6628MTA+T 8 TDFN-EP* +AUU Note: All devices are specified over the -55°C to +125°C operating temperature range. #Denotes an RoHS-compliant package. T = Tape and reel. +Denotes a lead-free/RoHS-compliant package. *EP = Exposed pad. Typical Operating Circuit + 3V TO + 5.5V Applications 0.1μF Hard Disk Drive VCC Smart Battery Packs Automotive GND MAX6627 MAX6628 Industrial Control Systems SDO Notebooks, PCs DXP 2200pF CS μC DXN SPI is a trademark of Motorola, Inc. SCK Pin Configurations appears at end of data sheet. ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com. 1 MAX6627/MAX6628 General Description MAX6627/MAX6628 Remote ±1°C Accurate Digital Temperature Sensors with SPI-Compatible Serial Interface ABSOLUTE MAXIMUM RATINGS (All voltages referenced to GND.) VCC ...........................................................................-0.3V to +6V SDO, SCK, DXP, CS .....................................-0.3V to VCC + 0.3V DXN .......................................................................-0.3V to +0.8V SDO Pin Current Range ......................................-1mA to +50mA Current Into All Other Pins ..................................................10mA ESD Protection (Human Body Model)................................2000V Continuous Power Dissipation (TA = +70°C) 8-Pin SOT23 (derate 9.7mW/°C above +70°C)............777mW 8-Pin TDFN (derate 18.5mW/°C above +70°C) ......1481.5mW Operating Temperature Range .........................-55°C to +125°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (3.0V ≤ VCC ≤ 5.5V, -55°C ≤ TA ≤ +125°C, unless otherwise noted. Typical values are at TA = +25°C, VCC = +3.3V, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX 0°C ≤ TRJ ≤ +125°C, TA = +30°C, VCC = +3.3V -1.0 ±0.5 ±1 -55°C ≤ TRJ ≤ +100°C, 0°C ≤ TA ≤ +70°C, VCC = +3.3V -2.4 +2.4 -55°C ≤ TRJ ≤ +145°C, 0°C ≤ TA ≤ +70°C, VCC = +3.3V -4.5 +4.5 -55°C ≤ TRJ ≤ +125°C, -55°C ≤ TA ≤ +125°C, VCC = +3.3V -5.5 +5.5 UNITS TEMPERATURE Accuracy (Note 1) °C Power-Supply Sensitivity 0.25 Resolution Time Between Conversion Starts Conversion Time 0.7 0.0625 tSAMPLE MAX6627 0.5 MAX6628 8 tCONV 180 250 °C/V °C s 320 ms 5.5 V POWER SUPPLY Supply Voltage Range Supply Current, SCK Idle Average Operating Current Power-On Reset (POR) Threshold Current Sourcing for Diode 2 VCC 3.0 ISDO Shutdown, VCC = +0.8V IIDLE ADC idle, CS = low ICONV ADC converting 360 600 MAX6627 200 400 MAX6628 30 50 VCC, falling edge 1.6 ICC 5 20 µA V High level 80 100 120 Low level 8 10 12 _______________________________________________________________________________________ µA µA Remote ±1°C Accurate Digital Temperature Sensors with SPI-Compatible Serial Interface (3.0V ≤ VCC ≤ 5.5V, -55°C ≤ TA ≤ +125°C, unless otherwise noted. Typical values are at TA = +25°C, VCC = +3.3V, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 0.3 x VCC V LOGIC INPUTS (CS, SCK) Logic Input Low Voltage VIL Logic Input High Voltage VIH Input Leakage Current ILEAK 0.7 x VCC VCS = VSCK = GND or VCC V 1 µA LOGIC OUTPUTS (SDO) Output Low Voltage VOL ISINK = 1.6mA Output High Voltage VOH ISOURCE = 1.6mA 0.4 VCC 0.4 V TIMING CHARACTERISTICS (Note 2, Figure 2) Serial-Clock Frequency fSCL 5 MHz SCK Pulse Width High tCH 100 SCK Pulse Width Low tCL 100 ns CS Fall to SCK Rise tCSS CLOAD = 10pF 80 ns CS Fall to Output Enable tDV CLOAD = 10pF 80 ns CS Rise to Output Disable tTR CLOAD = 10pF 50 ns SCK Fall to Output Data Valid tDO CLOAD = 10pF 80 ns ns Note 1: TRJ is the temperature of the remote junction. Note 2: Serial timing characteristics guaranteed by design. _______________________________________________________________________________________ 3 MAX6627/MAX6628 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VCC = +3.3V, TA = +25°C, unless otherwise noted.) AVERAGE OPERATING CURRENT vs. SUPPLY VOLTAGE MAX6627 150 100 MAX6628 TA = +70°C TA = +25°C 1 0 TA = 0°C -1 -2 50 2.4 -3 4.0 4.5 5.0 1.6 1.4 1.2 1.0 -5 20 45 70 95 120 145 -55 -30 -5 20 45 70 95 120 145 TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE ERROR vs. POWER-SUPPLY NOISE FREQUENCY RESPONSE TO THERMAL SHOCK TEMPERATURE ERROR vs. DXP/DXN CAPACITANCE 6 VIN = 250mVp-p 4 100 75 50 0 0 100 1k 10k 100k 1M 10M 100M FREQUENCY (Hz) MAX6627/8 toc06 4 3 2 1 25 2 5 TEMPERATURE ERROR (°C) 125 TEMPERATURE (°C) 8 10 1.8 SUPPLY VOLTAGE (V) VIN = SQUARE WAVE APPLIED TO VCC WITH NO 0.1μF CAPACITOR 10 2.0 0.6 -55 -30 5.5 MAX6627/8 toc05 12 3.5 MAX6627/8 toc04 3.0 2.2 0.8 MAX6627 0 MAX6627/8 toc03 MAX6627/8 toc02 2 2.6 POWER-ON-RESET THRESHOLD (V) 200 3 TEMPERATURE ERROR (°C) 250 POWER-ON-RESET THRESHOLD vs. TEMPERATURE TEMPERATURE ERROR vs. TEMPERATURE MAX6627/8 toc01 AVERAGE OPERATING CURRENT (μA) 300 TEMPERATURE ERROR (°C) MAX6627/MAX6628 Remote ±1°C Accurate Digital Temperature Sensors with SPI-Compatible Serial Interface 0 -2 0 2 4 6 8 10 12 14 TIME (s) 0 5000 10,000 15,000 20,000 CAPACITANCE (pF) Pin Description 4 PIN NAME 1 GND Ground FUNCTION 2 DXN Combined Current Sink and ADC Negative Input for Remote Diode. DXN is normally biased to a diode voltage above ground. 3 DXP Combined Current Source and ADC Positive Input for Remote Diode. Place a 2200pF capacitor between DXP and DXN for noise filtering. 4 VCC Supply Voltage Input. Bypass with a 0.1µF to GND. 5 SCK SPI Clock Input 6 CS 7 SDO SPI Data Output 8 N.C. No Connect. Internally not connected. Can be connected to GND for improved thermal conductivity. — EP Chip Select Input. Pulling CS low initiates an idle state, but the SPI interface is still enabled. A rising edge of CS initiates the next conversion. Exposed Pad. Internally connected to GND. Connect to a large ground plane to maximize thermal performance. Not intended as an electrical connection point. _______________________________________________________________________________________ Remote ±1°C Accurate Digital Temperature Sensors with SPI-Compatible Serial Interface The MAX6627/MAX6628 remote digital thermometers report the temperature of a remote sensor. The remote sensor is a diode-connected transistor—typically, a low-cost, easily mounted 2N3904 NPN type—that replaces conventional thermistors or thermocouples. The MAX6627/MAX6628 can also measure the die temperature of other ICs, such as µPs or µCs, that contain an on-chip, diode-connected transistor. Remote accuracy is ±1°C when the temperature of the remote diode is between 0°C and +125°C and the temperature of the MAX6627/MAX6628 is +30°C. Data is available as a 12-bit + sign word with 0.0625°C resolution. The operating range of the device extends from -55°C to +125°C, although the architecture of the device is capable of interpreting data up to +145°C. The device itself should never exceed +125°C. The MAX6627/MAX6628 are designed to work in conjunction with an external µC or other intelligent device serving as the master in thermostatic, process-control, or monitoring applications. The µC is typically a power management or keyboard controller, generating SPI serial commands by “bit-banging” GPIO pins. Two conversion rates are available; the MAX6627 continuously converts data every 0.5s, and the MAX6628 continuously converts data every 8s. Either device can be read at any time and provide the data from the last conversion. The slower version provides minimal power consumption under all operating conditions. Or, by tak- ADC Conversion Sequence The device powers up as a free-running data converter (Figure 1). The CS pin can be used for conversion control. The rising edge of CS resets the interface and starts a conversion. The falling edge of CS stops any conversion in progress, overriding the latency of the part. Temperature data from the previous completed conversion is available for read (Tables 1 and 2). It is required to maintain CS high for a minimum of 320ms to complete a conversion. Idle Mode Pull CS low to enter idle mode. In idle mode, the ADC is not converting. The serial interface is still active and temperature data from the last completed conversion can still be read. Power-On Reset The POR supply voltage of the MAX6627/MAX6628 is typically 1.6V. Below this supply voltage, the interface is inactive and the data register is set to the POR state, 8s SAMPLE RATE 0.5s SAMPLE RATE 0.25s CONVERSION TIME MAX6627 ing CS low, any conversion in progress is stopped, and the rising edge of CS always starts a fresh conversion and resets the interface. This permits triggering a conversion at any time so that the power consumption of the MAX6627 can be overcome, if needed. Both devices operate with input voltages between +3.0V and +5.5V and are specified between -55°C and +125°C. The MAX6627/MAX6628 come in space-saving 8-pin SOT23 and TDFN packages. ADC CONVERTING ADC IDLE MAX6628 Figure 1. Free-Running Conversion Time and Rate Relationships Table 1. Data Output Format D15 D14 Sign MSB Data D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 LSB Data Low High-Z High-Z _______________________________________________________________________________________ 5 MAX6627/MAX6628 Detailed Description MAX6627/MAX6628 Remote ±1°C Accurate Digital Temperature Sensors with SPI-Compatible Serial Interface tCSS CS SCK tDV tDO tTR SDO D15 D3 D2 D1 D0 Figure 2. SPI Timing Diagram Table 2. Temperature Data Format (Two’s Complement) TEMPERATURE (°C) DIGITAL OUTPUT (BINARY) D15–D3 D2 D1, D0 150 0,1001,0110,0000 0 XX 125 0,0111,1101,0000 0 XX 25 0,0001,1001,0000 0 XX 0.0625 0,0000,0000,0001 0 XX 0 0,0000,0000,0000 0 XX -0.0625 1,1111,1111,1111 0 XX -25 1,1110,0111,0000 0 XX -55 1,1100,1001,0000 0 XX 0°C. When power is first applied and VCC rises above 1.6V (typ), the device starts to convert, although temperature reading is not recommended at VCC levels below 3.0V. Serial Interface Figure 2 is the serial interface timing diagram. The data is latched into the shift register on the falling edge of the CS signal and then clocked out at the SDO pin on the falling edge of SCK with the most-significant bit (MSB) first. There are 16 edges of data per frame. The last 2 bits, D0 and D1, are always in high-impedance mode. The falling edge of CS stops any conversion in progress, and the rising edge of CS always starts a new conversion and resets the interface. It is required to maintain a 320ms minimum pulse width of high CS signal before a conversion starts. Applications Information Remote-Diode Selection Temperature accuracy depends upon having a goodquality, diode-connected, small-signal transistor. 6 Accuracy has been experimentally verified for all of the devices listed in Table 3. The MAX6627/MAX6628 can also directly measure the die temperature of CPUs and other ICs with on-board temperature-sensing diodes. The transistor must be a small-signal type with a relatively high forward voltage. This ensures that the input voltage is within the A/D input voltage range. The forward voltage must be greater than 0.25V at 10µA at the highest expected temperature. The forward voltage must be less than 0.95V at 100µA at the lowest expected temperature. The base resistance has to be less than 100Ω. Tight specification of forward-current gain (+50 to +150, for example) indicates that the manufacturer has good process control and that the devices have consistent characteristics. ADC Noise Filtering The integrating ADC has inherently good noise rejection, especially of low-frequency signals such as 60Hz/120Hz power-supply hum. Micropower operation places constraints on high-frequency noise rejection. Lay out the PCB carefully with proper external noise filtering for high-accuracy remote measurements in electrically noisy environments. Table 3. SOT23-Type Remote-Sensor Transistor Manufacturers MANUFACTURER MODEL Central Semiconductor (USA) CMPT3904 Motorola (USA) MMBT3904 Rohm Semiconductor (Japan) SST3904 Siemens (Germany) Zetex (England) SMBT3904 FMMT3904CT-ND Note: Transistors must be diode connected (short the base to the collector). _______________________________________________________________________________________ Remote ±1°C Accurate Digital Temperature Sensors with SPI-Compatible Serial Interface widths and spacings recommended in Figure 3 are not absolutely necessary (as they offer only a minor improvement in leakage and noise), but use them where practical. 8) Placing an electrically clean copper ground plane between the DXP/DXN traces and traces carrying high-frequency noise signals helps reduce EMI. PCB Layout 1) Place the MAX6627/MAX6628 as close as practical to the remote diode. In a noisy environment, such as a computer motherboard, this distance can be 4in to 8in, or more, as long as the worst noise sources (such as CRTs, clock generators, memory buses, and ISA/PCI buses) are avoided. 2) Do not route the DXP/DXN lines next to the deflection coils of a CRT. Also, do not route the traces across a fast memory bus, which can easily introduce +30°C error, even with good filtering. Otherwise, most noise sources are fairly benign. 3) Route the DXP and DXN traces parallel and close to each other, away from any high-voltage traces such as +12VDC. Avoid leakage currents from PCB contamination. A 20MΩ leakage path from DXP to ground causes approximately +1°C error. 4) Connect guard traces to GND on either side of the DXP/DXN traces (Figure 3). With guard traces in place, routing near high-voltage traces is no longer an issue. Twisted Pair and Shielded Cables For remote-sensor distances longer than 8in, or in particularly noisy environments, a twisted pair is recommended. Its practical length is 6ft to 12ft (typ) before noise becomes a problem, as tested in a noisy electronics laboratory. For longer distances, the best solution is a shielded twisted pair like that used for audio microphones. For example, Belden #8451 works well for distances up to 100ft in a noisy environment. Connect the twisted pair to DXP and DXN and the shield to ground, and leave the shield’s remote end unterminated. Excess capacitance at DXN or DXP limits practical remote-sensor distances (see Typical Operating Characteristics). For very long cable runs, the cable’s parasitic capacitance often provides noise filtering, so the recommended 2200pF capacitor can often be removed or reduced in value. Cable resistance also affects remote-sensor accuracy. A 1Ω series resistance introduces about +1/2°C error. 5) Route as few vias and crossunders as possible to minimize copper/solder thermocouple effects. 6) When introducing a thermocouple, make sure that both the DXP and the DXN paths have matching thermocouples. In general, PCB-induced thermocouples are not a serious problem. A copper solder thermocouple exhibits 3µV/°C, and it takes approximately 200µV of voltage error at DXP/DXN to cause a +1°C measurement error, so most parasitic thermocouple errors are swamped out. 7) Use wide traces. Narrow traces are more inductive and tend to pick up radiated noise. The 10mil GND 10mils 10mils DXP MINIMUM 10mils DXN 10mils GND Figure 3. Recommended DXP/DXN PC Traces _______________________________________________________________________________________ 7 MAX6627/MAX6628 Filter high-frequency electromagnetic interference (EMI) at DXP and DXN with an external 2200pF capacitor connected between the two inputs. This capacitor can be increased to about 3300pF (max), including cable capacitance. A capacitance higher than 3300pF introduces errors due to the rise time of the switchedcurrent source. MAX6627/MAX6628 Remote ±1°C Accurate Digital Temperature Sensors with SPI-Compatible Serial Interface Functional Diagram VCC SDO DXP 12-BIT + SIGN ADC DXN SPI INTERFACE SCK CS Pin Configurations TOP VIEW GND 1 DXN 2 DXP 3 MAX6627 MAX6628 VCC 4 8 N.C. 7 SDO 6 CS 5 SCK N.C. SDO CS SCK 8 7 6 5 MAX6627 MAX6628 + SOT23 1 2 3 4 GND DXN DXP VCC TDFN Package Information Chip Information PROCESS: BiCMOS 8 For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE PACKAGE CODE DOCUMENT NO. 8 SOT23 K8F-4 21-0078 8 TDFN-EP T833-2 21-0137 _______________________________________________________________________________________ Remote ±1°C Accurate Digital Temperature Sensors with SPI-Compatible Serial Interface PAGES CHANGED REVISION NUMBER REVISION DATE 0 — Initial release — 1 — — — 2 — — — 3 4/06 — — 4 8/08 Added missing exposed pad description, updated ordering part numbers, and updated pin name for pin 7. DESCRIPTION 1–4, 6, 8–11 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________ 9 © 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc. MAX6627/MAX6628 Revision History