SMSC EMCT03-ACZL 1â°c triple smbus temperature sensor Datasheet

EMCT03
1°C Triple SMBus
Temperature Sensor
Datasheet
General Description
Features
The EMCT03 is a System Management Bus (SMBus)
temperature sensor that is capable of monitoring three
temperature zones. The three temperature zones
consist of two external and one internal temperature
diode. The internal 11 bit sigma-delta ADC architecture
with digital filtering attributes to superb linearity and
immunity to interference and noise. An extended
temperature format may be selected for compatibility
with a broad range of CPUs. Selectable conversion
rates and standby mode support low-power operation.
■
Low Power; 3.0V to 3.6V Supply
— Programmable conversion rate
— < 1mA at 16 Conversions per Second
— < 3uA in Standby Mode
■
■
SMBus 2.0 Compliant interface
Two External Temperature Monitors:
—
—
—
—
■
Range -64°C to +191°C
0.125°C resolution
±1°C Accuracy 40°C to 80°C
Diode Fault Reporting
Internal Temperature Monitor
— Range 0°C to +85°C
— 0.125°C resolution
— ±3°C Accuracy 0°C to 85°C
■
■
Programmable Conversion Rate
MSOP-8 3x3mm Package; Green, Lead-Free
Package also available.
Simplified Block Diagram
EMCT03
Switching
Current
Configuration
Register
Analog Mux
DN1
DP2
11-bit
Sigma Delta
ADC
Remote Temp
Register 2
Digital Mux
and
Byte Interlock
DN2
Local Temp
Diode
Local Temp
Register
SMCLK
Status Register
SMSC EMCT03
DATASHEET
SMBus Interface
Remote Temp
Register 1
DP1
SMDATA
Revision 2.3 (04-19-05)
1°C Triple SMBus Temperature Sensor
Datasheet
ORDER NUMBER(S):
EMCT03-ACZB for 8-pin MSOP package
EMCT03-ACZB-TR for 8-pin MSOP package (Tape and Reel)
EMCT03-ACZL for 8-pin MSOP package (Green Lead-Free)
EMCT03-ACZL-TR for 8-pin MSOP package (Green Lead-Free, Tape and Reel)
Evaluation Board Available upon request.
80 Arkay Drive
Hauppauge, NY 11788
(631) 435-6000
FAX (631) 273-3123
Copyright © SMSC 2005. All rights reserved.
Circuit diagrams and other information relating to SMSC products are included as a means of illustrating typical applications. Consequently,
complete information sufficient for construction purposes is not necessarily given. Although the information has been checked and is believed to be
accurate, no responsibility is assumed for inaccuracies. SMSC reserves the right to make changes to specifications and product descriptions at any
time without notice. Contact your local SMSC sales office to obtain the latest specifications before placing your product order. The provision of this
information does not convey to the purchaser of the described semiconductor devices any licenses under any patent rights or other intellectual
property rights of SMSC or others. All sales are expressly conditional on your agreement to the terms and conditions of the most recently dated
version of SMSC's standard Terms of Sale Agreement dated before the date of your order (the "Terms of Sale Agreement"). The product may
contain design defects or errors known as anomalies which may cause the product's functions to deviate from published specifications. Anomaly
sheets are available upon request. SMSC products are not designed, intended, authorized or warranted for use in any life support or other
application where product failure could cause or contribute to personal injury or severe property damage. Any and all such uses without prior written
approval of an Officer of SMSC and further testing and/or modification will be fully at the risk of the customer. Copies of this document or other
SMSC literature, as well as the Terms of Sale Agreement, may be obtained by visiting SMSC’s website at http://www.smsc.com. SMSC is a
registered trademark of Standard Microsystems Corporation (“SMSC”). Product names and company names are the trademarks of their respective
holders.
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AND ANY AND ALL WARRANTIES ARISING FROM ANY COURSE OF DEALING OR USAGE OF TRADE.
IN NO EVENT SHALL SMSC BE LIABLE FOR ANY DIRECT, INCIDENTAL, INDIRECT, SPECIAL, PUNITIVE, OR CONSEQUENTIAL
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WHETHER BASED ON CONTRACT; TORT; NEGLIGENCE OF SMSC OR OTHERS; STRICT LIABILITY; BREACH OF WARRANTY; OR
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OR NOT SMSC HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
Revision 2.3 (04-19-05)
2
DATASHEET
SMSC EMCT03
1°C Triple SMBus Temperature Sensor
Datasheet
Chapter 1 Pin Configuration
DP1
1
DN1
2
DP2
3
DN2
4
EMCT03
TOP VIEW
8
SMCLK
7
SMDATA
6
VDD
5
GND
Figure 1.1 EMCT03 Pin Configuration
Table 1.1 Pin Description
PIN
PIN NO.
DESCRIPTION
DP1
1
Positive Analog Input for External Temperature Diode 1
DN1
2
Negative Analog Input for External Temperature Diode 1
DP2
3
Positive Analog Input for External Temperature Diode 2
DN2
4
Negative Analog Input for External Temperature Diode 2
GND
5
Ground
VDD
6
Supply Voltage
SMDATA
7
System Management Bus Data Input/Output, open drain output
SMCLK
8
System Management Bus Clock Input
Table 1.2 Absolute Maximum Ratings
DESCRIPTION
Supply Voltage VDD
Voltage on any other pin
Operating Temperature Range
Storage Temperature Range
ESD Rating, All Pins Human Body Model
SMSC EMCT03
3
DATASHEET
RATING
UNIT
-0.3 to 5.0
V
-0.3 to VDD+0.3
V
0 to 85
°C
-55 to 150
°C
2000
V
Revision 2.3 (04-19-05)
1°C Triple SMBus Temperature Sensor
Datasheet
Chapter 2 Electrical Characteristics
VDD=3.3V±10%, AmbientTemp=0°C to 85°C, except as noted below.
CHARACTERISTIC
MIN
TYP
MAX
UNIT
3.0
3.3
3.6
V
3
1.75
1
700
500
3
mA
mA
mA
µA
µA
µA
DC Power
Supply Voltage VDD
Current Consumption from VDD:
16 sets of conversions per second
8 sets of conversions per second
4 full sets of conversions per second
2 full sets of conversions per second
1 full set of conversions per second
Power Down
POR Threshold
2.5
V
Internal Temperature Monitor
Temperature Accuracy
Ambient Temp 0°C to 85°C
±1
Temperature Resolution
±3
°C
°C
0.125
Two External Temperature Monitors
Temperature Accuracy
Remote Diode 40°C to 80°C, Ambient Temp 15°C to 70°C
Remote Diode 0°C to 125°C
Temperature Resolution
Current Source
Low Level
High Level
±1
±3
°C
°C
0.125
°C
10
170
µA
µA
60
ms
ADC
Conversion Time for all three sensors
Wake-up from STOP mode
(During one shot command or transition to RUN mode)
1
Resolution
11
ms
bit
Differential Non Linearity
±1
LSB
Integral Non Linearity
±1
LSB
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DATASHEET
SMSC EMCT03
1°C Triple SMBus Temperature Sensor
Datasheet
TLOW
THIGH
THD:STA
TR
SMCLK
THD:STA
TSU:STO
TF
THD:DAT TSU:DAT
TSU:STA
SMDATA
TBUF
P
S
S
S - Start Condition
P - Stop Condition
P
Figure 2.1 System Management Bus Timing Diagram
VDD=3.3V±10%, Temp=0°C to 85°C, unless otherwise noted.
CHARACTERISTIC
MIN
TYP
MAX
UNIT
400
kHz
50
ns
System Management Bus Timing
Operating Frequency, FSMB
10
Spike Suppression
Bus free time Start to Stop, TBUF
1.3
µs
Hold time Start THD:STA
0.6
µs
Setup time Start TSU:STA
0.6
µs
Setup time Stop TSU:STO
0.6
µs
Data hold time THD:DAT
0.3
Data setup time TSU:DAT
100
ns
Clock Low period TLOW
1.3
µs
Clock High Period THIGH
0.6
µs
0.9
µs
Clock/Data Fall Time, TF
300
ns
Clock/Data Rise Time, TR
300
ns
Input High Current
10
µA
Input Low Current
-10
µA
Input Capacitance
10
pF
Low Input Level
0.8
V
System Management Bus SMCLK, SMDATA
High Input Level
2.0
Hysteresis
500
Low Output Level @ 4mA
SMSC EMCT03
V
mV
0.4
5
DATASHEET
V
Revision 2.3 (04-19-05)
1°C Triple SMBus Temperature Sensor
Datasheet
Chapter 3 Product Description
The EMCT03 is an SMBus sensor that is capable of monitoring three temperature zones. The part
may be used as a companion to one of SMSC’s broad line of SIO host circuits, or other devices
capable of performing the SMBus host function.
EMCT03
Host
(SMSC SIO)
DP1
DN1
SMBus
Interface
SMBus
DP2
DN2
Internal
Diode
Figure 3.1 System Overview
In cooperation with the host device, thermal management can be performed as outlined in Figure 3.1
above. Thermal management consists of the host reading the temperature data from the remote and
internal temperature diodes of the EMCT03 and controlling the speed of one or multiple fans. Since
the EMCT03 incorporates one internal and two external temperature diodes, three separate thermal
zones can be monitored and controlled with this application. Also, measured temperature levels can
quickly be compared to preset limits within the host device which in turn will take the appropriate action
when values are found to be out of limit.
The EMCT03 has two basic modes of operation:
3.1
■
Run Mode: In this mode, the EMCT03 continuously converts temperature data and updates its
registers. The conversion rate is configured by the lower bits in the configuration register as
described in Table 3.11, "Configuration Register, Conversion Rate," on page 11.
■
Standby Mode: In this mode, the EMCT03 is powered down, drawing a maximum current of only
3uA. The SMBus is still operational and a one-shot command can be given which will force the
circuit to complete one full set of temperature conversions. The EMCT03 will return to Standby
Mode after the one shot conversion has finished.
Temperature Monitors
Thermal diode temperature measurements are based on the change in forward bias voltage of a diode
when operated at two different currents:
Vbe _ high − Vbe _ low = n
KT  I high 

ln
q  I low 
(1)
where:
K is Boltzmann’s constant
T is Absolute Temperature in Kelvin
q is Charge Electron
n is Diode Ideality factor
The change in forward bias voltage is now proportional to absolute temperature T.
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DATASHEET
SMSC EMCT03
1°C Triple SMBus Temperature Sensor
Datasheet
VDD
Ihigh
Internal or
Remote Diode
Ilow
Ibias
Bias
Diode
fs
fs
fs
fs/2048
Delta Vbe
Sample
&
Hold
1-bit
Sigma
Delta
Modulator
Digital
Averaging
Filter
11-bit
Accurate
Conversion
Figure 3.2 Block Diagram of Temperature Measurement Circuit
Figure 3.2 shows a detailed block diagram of the temperature measurement circuit. As shown, the
EMCT03 incorporates switched capacitor technology that samples the external remote temperature
diode voltage at two bias currents and holds the difference voltage. The sample frequency is 100kHz
and the current levels Ihigh and Ilow are 170uA and 10uA respectively. The negative terminal for the
remote temperature diode, DN, is internally biased with a forward diode voltage referenced to ground.
The output of the switched capacitor sample and hold circuit interfaces to a single-bit sigma delta
analog-to-digital converter. This ADC runs at 100kHz sample frequency and its output is digitally filtered
and averaged over 2048 samples effectively generating 11 bit accuracy.
The advantages of this architecture over Nyquist rate FLASH or SAR converters are superb linearity
and inherent noise immunity. The linearity can be directly attributed to the sigma delta ADC single-bit
comparator while the noise immunity is achieved by the digital averaging filter. The overall effective
bandwidth of the system is fs/2048 which translates to a 50Hz bandwidth at 100kHz sample rate.
Conversion time equals about 20ms per temperature monitor which equals 60ms total for three
monitors when configured for maximum conversion rate (default).
The 11 bit conversion can be displayed in either legacy format or in extended range format. In Legacy
format, the temperature range covers –64ºC to 127ºC while in extended format, temperature readings
span -64ºC to 191ºC. It should be noted that the latter range is really meant to cover thermal diodes
with a non ideal curvature caused by factor n in equation (1) not being equal to exactly 1.000. In
general, it is not recommended to run silicon based thermal diodes at temperatures above 150ºC.
3.2
System Management Bus Interface Protocol
The EMCT03 communicates with a host controller, such as an SMSC SIO, through the SMBus. The
SMBus is a two wire serial communication protocol between a computer host and its peripheral
devices. Detailed timing diagrams can be found in the electrical characteristics of the SMBus. The
EMCT03 is SMBus 2.0 compatible and supports Write Byte and Read Byte as valid protocols as shown
below:
SMSC EMCT03
7
DATASHEET
Revision 2.3 (04-19-05)
1°C Triple SMBus Temperature Sensor
Datasheet
3.2.1
Write Byte
The write Byte is used to write one byte of data to the registers as shown in Table 3.1 below:
Table 3.1 SMBus Write Byte Protocol
Start
Slave Address
WR
ACK
Register Address
ACK
Register Data
ACK
STOP
1
7
1
1
8
1
8
1
1
3.2.2
Read Byte
The Read Byte protocol is used to read one byte of data from the registers as shown in Table 3.2
below:
Table 3.2 SMBus Read Byte Protocol
Start
Slave Address
WR
ACK
Register Address
ACK
START
Slave Address
RD
ACK
Register Data
NACK
STOP
1
7
1
1
8
1
1
7
1
1
8
1
1
3.2.3
SMBus Address
Attempting to communicate with the EMCT03 SMBus interface with an invalid slave address or invalid
protocol, results in no response from the part and will not affect its register content. The EMCT03
supports stretching of the SMCLK signal by other devices on the SMBus but will not perform this
operation itself.
Table 3.3 SMBus Address
CONDITION
EMCT03 ADDRESS
EMCT03 Default Address
3.3
1001100xb
Register Allocation
The following registers are accessible through the SMBus:
Table 3.4 Register Table
REGISTER
READ
ADDRESS
REGISTER
WRITE
ADDRESS
00h
N/A
Legacy Format Internal Temperature High Byte
00h
23h
N/A
Legacy Format Internal Temperature Low Byte
00h
01h
N/A
Legacy Format Remote Temperature 1 High Byte
00h
10h
N/A
Legacy Format Remote Temperature 1 Low Byte
00h
F8h
N/A
Legacy Format Remote Temperature 2 High Byte
00h
F9h
N/A
Legacy Format Remote Temperature 2 Low Byte
00h
Revision 2.3 (04-19-05)
REGISTER NAME
8
DATASHEET
DEFAULT
VALUE
SMSC EMCT03
1°C Triple SMBus Temperature Sensor
Datasheet
Table 3.4 Register Table (continued)
REGISTER
READ
ADDRESS
REGISTER
WRITE
ADDRESS
FAh
N/A
Extended Format Remote Temperature 1 High Byte
00h
FBh
N/A
Extended Format Remote Temperature 1 Low Byte
00h
FCh
N/A
Extended Format Remote Temperature 2 High Byte
00h
FDh
N/A
Extended Format Remote Temperature 2 Low Byte
00h
02h
N/A
Status register
00h
03h
09h
Configuration register
47h
N/A
0Fh
One Shot Command
--
FEh
N/A
Manufacturer Identifier
5Dh
FFh
N/A
Silicon Revision Identifier
01h
11h, 16h, 4Ah,
60h, 61h, 62h,
79h, 7Ah
11h, 16h, 4Ah,
60h, 61h, 62h,
79h, 7Ah
DEFAULT
VALUE
REGISTER NAME
Reserved Registers for production test
During Power on Reset (POR), the default values are stored in the registers. A POR is initiated when
power is first applied to the part and the voltage on the VDD supply surpasses the POR level as
specified in the electrical characteristics. Any reads to undefined registers will return 00h. Writes to any
undefined registers will not have an effect.
The EMCT03 uses an interlock mechanism that prevents changes in register content when fresh
readings come in from the ADC during successive reads from a host. When the High Byte is read, the
last conversion value is latched into the High Byte and Low Byte. Please note that the interlock
mechanism is only effective when reading the High Byte first.
3.4
Temperature Monitor Registers
As shown in Table 3.4, each temperature monitor has two byte wide data registers. The external
monitors are equipped with both legacy and extended data format. The 11 bit data temperature is
stored aligned to the left resulting in the High Byte to contain temperature in 1°C steps and the Low
Byte to contain fractions of °C as outlined below:
Table 3.5 High Byte Temperature Register
REGISTER
Temperature High Byte Registers
00h, 01h, F8h, FAh, FCh
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
SIGN
64
32
16
8
4
2
1
Table 3.6 Low Byte Temperature Register
REGISTER
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Temperature Low Byte Registers 23h,
10h, F9h, FBh, FDh
0.500
0.250
0.125
0
0
0
0
0
SMSC EMCT03
9
DATASHEET
Revision 2.3 (04-19-05)
1°C Triple SMBus Temperature Sensor
Datasheet
3.5
Legacy Temperature Data Format Registers 00h, 23h, 01h,
10h, F8h, F9h:
For registers displaying legacy temperature data format, the temperature range spans from –63.875ºC
to +127.875ºC with 0,125ºC resolution. Temperatures outside this range are clipped to –63.875ºC and
+127.875ºC. Data is stored in the registers in 2’s complement as shown in Table 3.7:
Table 3.7 Legacy Temperature Data Format
3.6
TEMPERATURE (°C)
2’S COMPLEMENT
HEX
Diode Fault
1000 0000 0000 0000
8000
= -63.875
1100 0000 0010 0000
C020
-63
1100 0001 0000 0000
C100
-1
1111 1111 0000 0000
FF00
0
0000 0000 0000 0000
0000
+0.125
0000 0000 0010 0000
0020
+1
0000 0001 0000 0000
0100
+127
0111 1111 0000 0000
7F00
≥ +127.875
0111 1111 1110 0000
7FE0
Extended Temperature Data Format Registers FAh, FBh, FCh,
FDh
For registers displaying extended temperature data format, a value of 64d is subtracted from the
Legacy Format output. This effectively extends the range to cover higher external temperature
measurements while still maintaining the 2’s complement format. Obviously, the host will have to
compensate and add 64d to the read temperature data. This format spans from –63.875ºC to
+191.875ºC with 0.125ºC resolution. Temperatures outside this range are limited to –63.875ºC and
+191.875ºC. Table 3.8 shows example temperature readings and register content for this data format.
Table 3.8 Extended Temperature Data Format
ACTUAL TEMP.
(°C)
-64°C OFFSET
(°C)
Diode Fault
2’S COMPLEMENT
OF -64°C OFFSET
HEX
1000 0000 0000 0000
8000
= -63.875
-127.875
1000 0000 0010 0000
8020
-63
-127
1000 0001 0000 0000
8100
-1
-65
1011 1111 0000 0000
BF00
0
-64
1100 0000 0000 0000
C000
+0.125
-63.875
1100 0000 0010 0000
C020
+1
-63
1100 0001 0000 0000
C100
+63
-1
1111 1111 0000 0000
FF00
+64
0
0000 0000 0000 0000
0000
Revision 2.3 (04-19-05)
10
DATASHEET
SMSC EMCT03
1°C Triple SMBus Temperature Sensor
Datasheet
Table 3.8 Extended Temperature Data Format (continued)
ACTUAL TEMP.
(°C)
-64°C OFFSET
(°C)
2’S COMPLEMENT
OF -64°C OFFSET
HEX
+65
1
0000 0001 0000 0000
0100
+191
127
0111 1111 0000 0000
7F00
= +191.875
127.875
0111 1111 1110 0000
7FE0
Table 3.7 and Table 3.8 show that temperature data is stored in 2’s complement in both Legacy and
Extended Temperature Data Format. Both extended and legacy temperature formats are updated
simultaneously after every conversion cycle. Code 8000h is reserved for diode fault signaling which
occurs when open or short conditions are present between the external DP and DN pins.
3.7
Status Register
Table 3.9 Status Register
REGISTER
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
DEF
Status
Busy
-
-
-
-
-
D2
D1
00h
The Status register is a read only register and returns the operational status of the part. It indicates an
external diode fault conditions through bit 0 and 1. When either D1 or D2 is set, a faulty diode
connection is detected for external diode 1 or external diode 2 respectively. Also, when diode faults
are detected, temperature readings for the faulty external diode will return 8000h. The EMCT03 detects
both open and short conditions for the DP1/2 and DN1/2 pins. Bit 7 of the status register will be set
when the internal ADC is busy converting data.
3.8
Configuration Register
Table 3.10 Configuration Register
REGISTER
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
DEF
Configuration
-
nRun/Stop
-
-
-
CR2
CR1
CR0
47h
Bits 0 through bit 2 of the configuration register set the ADC conversion rate of the part:
Table 3.11 Configuration Register, Conversion Rate
CR2, CR1, CR0
SMSC EMCT03
CONVERSION RATE
000
Reserved
001
Reserved
010
Reserved
011
1 Conversions per second
100
2 Conversions per second
101
4 Conversions per second
110
8 Conversions per second
111
16 Conversions per second
11
DATASHEET
Revision 2.3 (04-19-05)
1°C Triple SMBus Temperature Sensor
Datasheet
A conversion for all 3 temperature readings takes about 60ms. Therefore, the maximum conversion
rate, equals 16 conversions per second.
Bits 6 set of the Configuration Register sets the power mode of the part:
Table 3.12 Configuration Registers Data Format
NRUN/STOP
0
1
DESCRIPTION
Run Mode
Standby Mode
In Run Mode, the EMCT03 will operate at the preset conversion rate. In Standby Mode, the part is
powered down to minimize current consumption. The SMBus is fully operational in either mode. In
Standby Mode, a WRITE command to the One Shot register will trigger a one time conversion of the
3 temperature monitors. After the part finishes the conversion, it will go back to Standby Mode. The
host can now read the updated temperature information.
Revision 2.3 (04-19-05)
12
DATASHEET
SMSC EMCT03
1°C Triple SMBus Temperature Sensor
Datasheet
Chapter 4 Application Information
This chapter provides information on maintaining accuracy when using diodes as remote sensors with
SMSC Environmental Monitoring and Control devices. It is assumed that the users have some
familiarity with hardware design and transistor characteristics.
SMSC supplies a family Environmental Monitoring and Control (EMC) devices that are capable of
accurately measuring temperatures. Most devices include an internal temperature sensor along with
the ability to measure one or more external sensors. The characteristics of an appropriate diode for
use as the external sensor are listed in this chapter. Recommendations for the printed circuit board
layout are provided to help reduce error caused by electical noise or trace resistance.
4.1
Maintaining Accuracy
4.1.1
Physical Factors
Temperature measurement is performed by measuring the change in forward bias voltage of a diode
when two different currents are forced through the junction. The circuit board itself can impact the
ability to accurately measure these small changes in voltage. For example, an excessive amount of
series resistance can introduce error in the measurement.
4.1.1.1
Layout
Apply the following guidelines when designing the printed circuit board:
1. Route the remote diode traces on the top layer.
2. Place a ground guard signal on both sides of the differential pair. This guard band should be
connected to the ground plane at least every 0.25 inches.
3. Place a ground plane on the layer immediately below the diode traces.
4. Keep the diode traces as short as possible.
5. Keep the diode traces parallel, and the length of the two traces identical within 0.3 inches.
6. Use a trace width of 0.01 inches with a 0.01 inch guard band on each side.
7. Keep the diode traces away from sources of high frequency noise such as power supply filtering
or high speed digital signals.
8. When the diode traces must cross high speed digital signals, make them cross at a 90 degree
angle.
9. Avoid joints of copper to solder that can introduce thermocouple effects.
These recommendations are illustrated in Figure 4.1 Routing the Diode Traces on page 14.
SMSC EMCT03
13
DATASHEET
Revision 2.3 (04-19-05)
1°C Triple SMBus Temperature Sensor
Datasheet
.01 GAP MIN.
.01 WIDE MIN.
.01 WIDE MIN.
.01 GAP MIN.
DP or DN
GND PLANE
.01 GAP MIN.
DP or DN
COPPER TRACE
COPPER TRACE
GND PLANE
BOARD MATERIAL
COPPER PLANE (TO SHIELD FROM NOISE)
RECOMMEND VIA STICTCHING AT .25 INCH INTERVALS.
Figure 4.1 Routing the Diode Traces
4.1.1.2
Bypass Capacitors
Accurate temperature measurements require a clean, stable power supply. Locate a 0.1µF capacitor
as close as possible to the power pin with a good ground. A low ESR capacitor (such as a 10µF
ceramic) should be placed across the power source. Add additional power supply filtering in systems
that have a noisy power supply.
A capacitor may be placed across the DP/DN pair at the remote sensor in noisy environments. Do not
exceed a value of 100 pF if this capacitor is installed.
4.1.1.3
Manufacturing
Circuit board assembly processes may leave a residue on the board. This residue can result in
unexpected leakage currents that may introduce errors if the circuit board is not clean. For example,
processes that use water-soluble soldering fluxes have been known to cause problems if the board is
not kept clean.
4.1.1.4
Thermal Considerations
Keep the sensor in good thermal contact with the component to be measured. The temperature of the
leads of a discrete diode will greatly impact the temperature of the diode junction. Make use of the
printed circuit board to disperse any self-heating that may occur.
4.1.1.5
Remote Sensors Connected by Cables
When connecting remote diodes with a cable (instead of traces on the PCB) use shielded twisted pair
cable. The shield should be attached to ground near the EMCT03, and should be left unconnected at
the sensor end. Belden 8451 cable is a good choice for this application.
4.1.2
Sensor Characteristics
The characteristics of the diode junction used for temperature sensing will affect the accuracy of the
measurement.
4.1.2.1
Selecting a Sensor
A diode connected small signal transistor is recommended. Silicon diodes are not a good choice for
remote sensors. Small signal transistors such as the 2N3904 or the 2N3906 are recommended.
Desired characteristics for the sensor include the following:
1. Constant value of hFE in the range of 7.5 to 130 microamps. Variation in hFE from one device to
another or one manufacturer to another cancels out of the temperature equations.
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DATASHEET
SMSC EMCT03
1°C Triple SMBus Temperature Sensor
Datasheet
2. The lowest emitter and base resistance values will also be helpful as a matter of series input
resistance
4.1.2.2
Compensating for Ideality of the diode
The remote diode may have an ideality factor based on the manufacturing process. Inaccuracy in the
temperature measurement resulting from this ideality factor may be eliminated by calibrating the
remote diode with the temperature sensor. The EMCT03 is trimmed to an ideality factor of 1.008.
4.1.2.3
Circuit Connections
The more negative terminal for the remote temperature diode, DN, is internally biased with a forward
diode voltage. Terminal DN is not referenced to ground. Remote temperature diodes can be
constructed as shown in Figure 4.2 Remote Temperature Diode Examples on page 15.
To DP
To DP
To DP
To DN
To DN
To DN
Local Ground
Typical Remote Parasitic
Substrate Transistor
e.g. CPU substrate PNP
Typical Remote
Discrete PNP Transistor
e.g 2N3906
Typical Remote
Discrete NPN Transistor
e.g. 2N3904
Figure 4.2 Remote Temperature Diode Examples
Environmental Monitoring and Control (EMC) devices supplied by SMSC are designed to make
accurate temperature measurements. Careful design of the printed circuit board and proper selection
of the remote sensing diode will help to maintain the accuracy.
SMSC EMCT03
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DATASHEET
Revision 2.3 (04-19-05)
1°C Triple SMBus Temperature Sensor
Datasheet
Chapter 5 Package Outline
Figure 5.1 8-Pin MSOP Package Outline - 3x3mm Body 0.65mm Pitch
Table 5.1 8-Pin MSOP Package Parameters
MIN
NOMINAL
MAX
REMARKS
A
0.80
~
1.10
Overall Package Height
A1
0.05
~
0.15
Standoff
A2
0.75
0.85
0.95
Body Thickness
D
2.80
3.00
3.20
X Body Size
E
4.65
4.90
5.15
Y Span
E1
2.80
~
3.20
Y body Size
H
0.08
~
0.23
Lead Foot Thickness
L
0.40
~
0.80
Lead Foot Length
L1
0.95 REF
e
Lead Length
0.65 BSC
Lead Pitch
θ
0o
W
0.22
~
0.38
Lead Width
ccc
~
~
0.10
Coplanarity
~
8o
Lead Foot Angle
Notes:
1. Controlling Unit: millimeters.
2. Tolerance on the true position of the leads is ± 0.065 mm maximum.
3. Package body dimensions D and E1 do not include mold protrusion or flash. Dimensions D and
E1 to be determined at datum plane H. Maximum mold protrusion or flash is 0.15mm (0.006 inches)
per end, and 0.15mm (0.006 inches) per side.
4. Dimension for foot length L measured at the gauge plane 0.25 mm above the seating plane.
5. Details of pin 1 identifier are optional but must be located within the zone indicated.
Revision 2.3 (04-19-05)
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DATASHEET
SMSC EMCT03
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