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19-2032; Rev 4; 8/08
Remote 1C Accurate Digital Temperature Sensors with SPI-Compatible Serial Interface
General Description
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 (Ps) or microcontrollers (Cs) that contain an on-chip, diodeconnected transistor. Remote accuracy is 1C when the temperature of the remote diode is between 0C and +125C and the temperature of the MAX6627/MAX6628 is +30C. The temperature is converted to a 12-bit + sign word with 0.0625C resolution. The architecture of the device is capable of interpreting data as high as +145C from the remote sensor. The MAX6627/MAX6628 temperature should never exceed +125C. These sensors are 3-wire serial interface SPITM compatible, allowing the MAX6627/MAX6628 to be readily connected to a variety of Cs. 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 (30A, 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 -55C and +125C, and come in space-saving 8-pin SOT23 and lead-free TDFN packages.
Features
o Accuracy 1C (max) from 0C TRJ +125C, TA = +30C 2.4C (max) from -55C TRJ +100C, 0C TA +70C o 12-Bit + Sign, 0.0625C Resolution o Low Power Consumption 30A (typ) (MAX6628) 200A (typ) (MAX6627) o Operating Temperature Range (-55C to +125C) o Measurement Temperature Range, Remote Junction (-55C to +145C) 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)
MAX6627/MAX6628
Ordering Information
PART MAX6627MKA#T MAX6627MTA+T MAX6628MKA#T MAX6628MTA+T PIN-PACKAGE 8 SOT23 8 TDFN-EP* 8 SOT23 8 TDFN-EP* TOP MARK AAEQ +AUT AAER +AUU
Note: All devices are specified over the -55C to +125C 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 0.1F
Applications
Hard Disk Drive Smart Battery Packs Automotive Industrial Control Systems Notebooks, PCs
DXP 2200pF DXN VCC
GND
MAX6627 MAX6628
SDO
CS
C
SPI is a trademark of Motorola, Inc. Pin Configurations appears at end of data sheet.
SCK
________________________________________________________________ Maxim Integrated Products
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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.
Remote 1C Accurate Digital Temperature Sensors with SPI-Compatible Serial Interface MAX6627/MAX6628
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 = +70C) 8-Pin SOT23 (derate 9.7mW/C above +70C)............777mW 8-Pin TDFN (derate 18.5mW/C above +70C) ......1481.5mW Operating Temperature Range .........................-55C to +125C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
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, -55C TA +125C, unless otherwise noted. Typical values are at TA = +25C, VCC = +3.3V, unless otherwise noted.)
PARAMETER TEMPERATURE 0C TRJ +125C, TA = +30C, VCC = +3.3V -55C TRJ +100C, 0C TA +70C, VCC = +3.3V -55C TRJ +145C, 0C TA +70C, VCC = +3.3V -55C TRJ +125C, -55C TA +125C, VCC = +3.3V Power-Supply Sensitivity Resolution Time Between Conversion Starts Conversion Time POWER SUPPLY Supply Voltage Range Supply Current, SCK Idle VCC ISDO IIDLE ICONV Average Operating Current Power-On Reset (POR) Threshold Current Sourcing for Diode ICC Shutdown, VCC = +0.8V ADC idle, CS = low ADC converting MAX6627 MAX6628 VCC, falling edge High level Low level 80 8 360 200 30 1.6 100 10 120 12 3.0 5.5 5 20 600 400 50 A V A A V tSAMPLE tCONV MAX6627 MAX6628 180 -1.0 -2.4 -4.5 -5.5 0.25 0.0625 0.5 8 250 320 0.5 1 +2.4 C +4.5 +5.5 0.7 C/V C s ms SYMBOL CONDITIONS MIN TYP MAX UNITS
Accuracy (Note 1)
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Remote 1C Accurate Digital Temperature Sensors with SPI-Compatible Serial Interface
ELECTRICAL CHARACTERISTICS (continued)
(3.0V VCC 5.5V, -55C TA +125C, unless otherwise noted. Typical values are at TA = +25C, VCC = +3.3V, unless otherwise noted.)
PARAMETER LOGIC INPUTS (CS, SCK) Logic Input Low Voltage Logic Input High Voltage Input Leakage Current LOGIC OUTPUTS (SDO) Output Low Voltage Output High Voltage VOL VOH ISINK = 1.6mA ISOURCE = 1.6mA VCC 0.4 5 100 100 CLOAD = 10pF CLOAD = 10pF CLOAD = 10pF CLOAD = 10pF 80 80 50 80 0.4 V VIL VIH ILEAK VCS = VSCK = GND or VCC 0.7 x VCC 1 0.3 x VCC V V A SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX6627/MAX6628
TIMING CHARACTERISTICS (Note 2, Figure 2) Serial-Clock Frequency SCK Pulse Width High SCK Pulse Width Low CS Fall to SCK Rise CS Fall to Output Enable CS Rise to Output Disable SCK Fall to Output Data Valid fSCL tCH tCL tCSS tDV tTR tDO MHz ns ns ns ns ns ns
Note 1: TRJ is the temperature of the remote junction. Note 2: Serial timing characteristics guaranteed by design.
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Remote 1C Accurate Digital Temperature Sensors with SPI-Compatible Serial Interface MAX6627/MAX6628
Typical Operating Characteristics
(VCC = +3.3V, TA = +25C, unless otherwise noted.)
AVERAGE OPERATING CURRENT vs. SUPPLY VOLTAGE
MAX6627/8 toc01
TEMPERATURE ERROR vs. TEMPERATURE
MAX6627/8 toc02
POWER-ON-RESET THRESHOLD vs. TEMPERATURE
2.4 POWER-ON-RESET THRESHOLD (V) 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 -55 -30 -5 20 45 70 95 120 145
MAX6627/8 toc03
300 AVERAGE OPERATING CURRENT (A) 250 200 150 100 MAX6628 50 0 3.0 3.5 4.0 4.5 5.0
3 2 TEMPERATURE ERROR (C) 1 0 -1 -2 MAX6627 -3 TA = 0C TA = +25C TA = +70C
2.6
MAX6627
5.5
-55 -30
-5
20
45
70
95
120 145
SUPPLY VOLTAGE (V)
TEMPERATURE (C)
TEMPERATURE (C)
TEMPERATURE ERROR vs. POWER-SUPPLY NOISE FREQUENCY
MAX6627/8 toc04
RESPONSE TO THERMAL SHOCK
MAX6627/8 toc05
TEMPERATURE ERROR vs. DXP/DXN CAPACITANCE
MAX6627/8 toc06
12 10 TEMPERATURE ERROR (C) 8 6
VIN = SQUARE WAVE APPLIED TO VCC WITH NO 0.1F CAPACITOR
5
125 100 75 50 25 0
TEMPERATURE ERROR (C)
4
TEMPERATURE (C)
3
VIN = 250mVp-p 4 2 0 10 100 1k 10k 100k 1M 10M 100M FREQUENCY (Hz)
2
1
0 -2 0 2 4 6 TIME (s) 8 10 12 14 0 5000 10,000 15,000 20,000 CAPACITANCE (pF)
Pin Description
PIN 1 2 3 4 5 6 7 8 -- NAME GND DXN DXP VCC SCK CS SDO N.C. EP Ground Combined Current Sink and ADC Negative Input for Remote Diode. DXN is normally biased to a diode voltage above ground. Combined Current Source and ADC Positive Input for Remote Diode. Place a 2200pF capacitor between DXP and DXN for noise filtering. Supply Voltage Input. Bypass with a 0.1F to GND. SPI Clock Input 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. SPI Data Output No Connect. Internally not connected. Can be connected to GND for improved thermal conductivity. Exposed Pad. Internally connected to GND. Connect to a large ground plane to maximize thermal performance. Not intended as an electrical connection point. FUNCTION
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Remote 1C Accurate Digital Temperature Sensors with SPI-Compatible Serial Interface
Detailed Description
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 Ps or Cs, that contain an on-chip, diode-connected transistor. Remote accuracy is 1C when the temperature of the remote diode is between 0C and +125C and the temperature of the MAX6627/MAX6628 is +30C. Data is available as a 12-bit + sign word with 0.0625C resolution. The operating range of the device extends from -55C to +125C, although the architecture of the device is capable of interpreting data up to +145C. The device itself should never exceed +125C. The MAX6627/MAX6628 are designed to work in conjunction with an external C or other intelligent device serving as the master in thermostatic, process-control, or monitoring applications. The C 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 taking 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 -55C and +125C. The MAX6627/MAX6628 come in space-saving 8-pin SOT23 and TDFN packages.
MAX6627/MAX6628
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,
0.25s CONVERSION TIME MAX6627 ADC CONVERTING
0.5s SAMPLE RATE
8s SAMPLE RATE
ADC IDLE MAX6628
Figure 1. Free-Running Conversion Time and Rate Relationships
Table 1. Data Output Format
D15 Sign D14 MSB Data D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 LSB Data D2 Low D1 High-Z D0 High-Z
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Remote 1C Accurate Digital Temperature Sensors with SPI-Compatible Serial Interface MAX6627/MAX6628
tCSS CS
SCK tDV SDO D15 D3 D2 D1 D0 tDO tTR
Figure 2. SPI Timing Diagram
Table 2. Temperature Data Format (Two's Complement)
TEMPERATURE (C) 150 125 25 0.0625 0 -0.0625 -25 -55 DIGITAL OUTPUT (BINARY) D15-D3 0,1001,0110,0000 0,0111,1101,0000 0,0001,1001,0000 0,0000,0000,0001 0,0000,0000,0000 1,1111,1111,1111 1,1110,0111,0000 1,1100,1001,0000 D2 0 0 0 0 0 0 0 0 D1, D0 XX XX XX XX XX XX XX XX
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 10A at the highest expected temperature. The forward voltage must be less than 0.95V at 100A at the lowest expected temperature. The base resistance has to be less than 100. 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.
0C. 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.
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.
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.
Table 3. SOT23-Type Remote-Sensor Transistor Manufacturers
MANUFACTURER Central Semiconductor (USA) Motorola (USA) Rohm Semiconductor (Japan) Siemens (Germany) Zetex (England) MODEL CMPT3904 MMBT3904 SST3904 SMBT3904 FMMT3904CT-ND
Applications Information
Remote-Diode Selection
Temperature accuracy depends upon having a goodquality, diode-connected, small-signal transistor.
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Note: Transistors must be diode connected (short the base to the collector).
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Remote 1C Accurate Digital Temperature Sensors with SPI-Compatible Serial Interface
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. 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.
MAX6627/MAX6628
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 +30C 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 20M leakage path from DXP to ground causes approximately +1C 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. 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 3V/C, and it takes approximately 200V of voltage error at DXP/DXN to cause a +1C 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
10mils
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 1 series resistance introduces about +1/2C error.
GND 10mils DXP MINIMUM 10mils DXN 10mils GND
Figure 3. Recommended DXP/DXN PC Traces
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Remote 1C Accurate Digital Temperature Sensors with SPI-Compatible Serial Interface MAX6627/MAX6628
Functional Diagram
VCC
DXP 12-BIT + SIGN ADC SPI INTERFACE
SDO SCK CS
DXN
Pin Configurations
N.C. SDO 7 CS 6 SCK 5
TOP VIEW
GND DXN DXP 1 2 3 8 7 N.C. SDO CS SCK
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MAX6627 MAX6628
6 5
MAX6627 MAX6628 +
VCC 4
SOT23
1 GND
2 DXN
3 DXP
4 VCC
TDFN
Package Information Chip Information
PROCESS: BiCMOS
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE 8 SOT23 8 TDFN-EP PACKAGE CODE K8F-4 T833-2 DOCUMENT NO. 21-0078 21-0137
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Remote 1C Accurate Digital Temperature Sensors with SPI-Compatible Serial Interface
Revision History
REVISION NUMBER 0 1 2 3 4 REVISION DATE -- -- -- 4/06 8/08 Initial release -- -- -- Added missing exposed pad description, updated ordering part numbers, and updated pin name for pin 7. DESCRIPTION PAGES CHANGED -- -- -- -- 1-4, 6, 8-11
MAX6627/MAX6628
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
(c) 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

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