+5V
SCL
GND
SDA
V+
SMBus
Controller
8
5
7
6
DX1
DX2
DX3
DX4
1
2
3
4
1 Channel Local
2 Channels Remote
TMP422-EP
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SBOS577 –SEPTEMBER 2011
±1°C REMOTE TEMPERATURE AND ±2.5°C LOCAL
TEMPERATURE SENSOR IN SOT23-8
Check for Samples: TMP422-EP
1FEATURES SUPPORTS DEFENSE, AEROSPACE AND
MEDICAL APPLICATIONS
234•SOT23-8 Package
•Controlled Baseline
• ±1°C Remote Diode Sensor (Max)
•One Assembly/Test Site
• ±2.5°C Local Temperature Sensor (Max)
•One Fabrication Site
•Series Resistance Cancellation
•Available in Military (–55°C to 125°C)
•n-Factor Correction Temperature Range(1)
•Two-Wire/ SMBus™Serial Interface •Extended Product Life Cycle
•Multiple Interface Addresses •Extended Product-Change Notification
•Diode Fault Detection •Product Traceability
•RoHS Compliant and NO Sb/Br
APPLICATIONS
•Processor/FPGA Temperature Monitoring
•LCD/ DLP®/LCOS Projectors
•Servers
•Central Office Telecom Equipment
•Storage Area Networks (SAN)
(1) Additional temperature ranges available - contact factory
DESCRIPTION
The TMP422 is a remote temperature sensor monitor with a built-in local temperature sensor. The remote
temperature sensor diode-connected transistors are typically low-cost, NPN- or PNP-type transistors or diodes
that are an integral part of microcontrollers, microprocessors, or FPGAs.
Remote accuracy is ±1°C for multiple IC manufacturers, with no calibration needed. The two-wire serial interface
accepts SMBus write byte, read byte, send byte, and receive byte commands to configure the device.
The TMP422 includes series resistance cancellation, programmable non-ideality factor, wide remote temperature
measurement range (up to 150°C), and diode fault detection.
The TMP422 is available in a SOT23-8 package.
1Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
2DLP is a registered trademark of Texas Instruments.
3SMBus is a trademark of Intel Corporation.
4All other trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date. Copyright ©2011, Texas Instruments Incorporated
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
TMP422-EP
SBOS577 –SEPTEMBER 2011
www.ti.com
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
Table 1. ORDERING INFORMATION(1)
ORDERABLE PART PACKAGE PACKAGE
PRODUCT PACKAGE-LEAD VID NUMBER
NUMBER DESIGNATOR(2) MARKING
TMP422 TMP422AMDCNTEP SOT23-8 DCN TMP4 V62/11618-01XE
(1) For the most current package and ordering information see the Package Option Addendum at the end of this document, or see the TI
web site at www.ti.com.
(2) Package drawings, standard packing quantities, thermal data, symbolization, and PCB design guidelines are available at
www.ti.com/sc/package.
ABSOLUTE MAXIMUM RATINGS(1)
Over operating free-air temperature range, unless otherwise noted. TMP422 UNIT
Power Supply, VS+7 V
Pins 1, 2, 3, and 4 only –0.5 to VS+ 0.5 V
Input Voltage Pins 6 and 7 only –0.5 to 7 V
Input Current 10 mA
Power dissipation, PD230 mW
Storage Temperature Range –65 to +150 °C
Junction Temperature (TJmax) +150 °C
Human Body Model (HBM) 3000 V
ESD Rating Charged Device Model (CDM) 1000 V
Machine Model (MM) 200 V
(1) Stresses above these ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods may
degrade device reliability. These are stress ratings only, and functional operation of the device at these or any other conditions beyond
those specified is not implied.
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SBOS577 –SEPTEMBER 2011
ELECTRICAL CHARACTERISTICS
At TA=–55°C to +125°C and VS= 2.7V to 5.5V, unless otherwise noted.
PARAMETER CONDITIONS MIN TYP MAX UNIT
TEMPERATURE ERROR
Local Temperature Sensor TELOCAL TA=–55°C to +125°C±1.25 ±2.5 °C
Remote Temperature Sensor(1) TEREMOTE TA= +15°C to +85°C, TD=–55°C to +125°C, VS= 3.3V 0.25 ±1°C
TA=–55°C to +125°C, TD=–55°C to +125°C, VS= 3.3V ±1±3°C
TA=–55°C to +125°C, TD=–55°C to +125°C±3±5°C
vs Supply (Local/Remote) VS= 2.7V to 5.5V ±0.2 ±0.72 °C/V
TEMPERATURE MEASUREMENT
Conversion Time (per channel) 100 115 130 ms
Resolution
Local Temperature Sensor (programmable) 12 Bits
Remote Temperature Sensor 12 Bits
Remote Sensor Source Currents
High Series Resistance 3kΩMax 120 μA
Medium High 60 μA
Medium Low 12 μA
Low 6 μA
Remote Transistor Ideality Factor ηOptimized Ideality Factor 1.008
SMBus INTERFACE
Logic Input High Voltage (SCL, SDA) VIH 2.1 V
Logic Input Low Voltage (SCL, SDA) VIL 0.8 V
Hysteresis 500 mV
SMBus Output Low Sink Current 6 mA
SDA Output Low Voltage VOL IOUT = 6mA 0.15 0.4 V
Logic Input Current 0 ≤VIN ≤6V –1 +1 μA
SMBus Input Capacitance (SCL, SDA) 3 pF
SMBus Clock Frequency 3.4 MHz
SMBus Timeout 25 30 35 ms
SCL Falling Edge to SDA Valid Time 1 μs
DIGITAL INPUTS
Input Capacitance 3 pF
Input Logic Levels
Input High Voltage VIH 0.7(V+) (V+)+0.5 V
Input Low Voltage VIL –0.5 0.3(V+) V
Leakage Input Current IIN 0V ≤VIN ≤VS1μA
POWER SUPPLY
Specified Voltage Range VS2.7 5.5 V
Quiescent Current IQ0.0625 Conversions per Second 32 38 μA
Eight Conversions per Second 400 525 μA
Serial Bus Inactive, Shutdown Mode 3 10 μA
Serial Bus Active, fS= 400kHz, Shutdown Mode 90 μA
Serial Bus Active, fS= 3.4MHz, Shutdown Mode 350 μA
Undervoltage Lockout UVLO 2.3 2.4 2.6 V
Power-On Reset Threshold POR 1.6 2.3 V
TEMPERATURE RANGE
Specified Range –55 +125 °C
Thermal Resistance, θJA 164 °C/W
junction-to-ambient SOT23
Thermal Resistance, junction-to-case θJC 108 °C/W
SOT23
(1) Tested with less than 5Ωeffective series resistance and 100pF differential input capacitance.
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1
2
3
4
8
7
6
5
V+
SCL
GND
DX1
DX2
DX3
DX4
SDA
TMP422
TMP422-EP
SBOS577 –SEPTEMBER 2011
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PIN CONFIGURATION
DCN PACKAGE
SOT23-8
(TOP VIEW)
PIN ASSIGNMENTS
TMP422
NO. NAME DESCRIPTION
1 DX1 Channel 1 remote temperature sensor connection pin. Also sets the TMP422 address; see Table 10.
2 DX2 Channel 1 remote temperature sensor connection pin. Also sets the TMP422 address; see Table 10.
3 DX3 Channel 2 remote temperature sensor connection pin. Also sets the TMP422 address; see Table 10.
4 DX4 Channel 2 remote temperature sensor connection pin. Also sets the TMP422 address; see Table 10.
5 GND Ground
6 SDA Serial data line for SMBus, open-drain; requires pull-up resistor to V+.
7 SCL Serial clock line for SMBus, open-drain; requires pull-up resistor to V+.
8 V+ Positive supply voltage (2.7V to 5.5V)
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3
2
1
0
-1
-2
-3
AmbientTemperature,T ( C)°
A
-50 -25 1251007550250
RemoteTemperatureError( C)°
V+=3.3V
T =+25 C
REMOTE °
30TypicalUnitsShown
h=1.008
LocalTemperatureError( )°C
AmbientTemperature,T (
A°C)
3
2
1
0
-1
-2
-3
-50 125-25 0 25 50 75 100
50UnitsShown
V+=3.3V
60
40
20
0
-20
-40
-60
LeakageResistance(M )W
0 5 10 15 20 25 30
RemoteTemperatureError( C)°
R GND-
R V+-
RemoteTemperatureError( )°C
RW( )
S
2.0
1.5
1.0
0.5
0
-0.5
-1.0
-1.5
-2.0
0 3500500 1000 1500 2000 2500 3000
V+=2.7V
V+=5.5V
TMP422-EP
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SBOS577 –SEPTEMBER 2011
TYPICAL CHARACTERISTICS
At TA= +25°C and VS= +5.0V, unless otherwise noted.
REMOTE TEMPERATURE ERROR LOCAL TEMPERATURE ERROR
vs vs
TEMPERATURE TEMPERATURE
Figure 1. Figure 2.
REMOTE TEMPERATURE ERROR
REMOTE TEMPERATURE ERROR vs
SERIES RESISTANCE
vs
LEAKAGE RESISTANCE (Diode-Connected Transistor, 2N3906 PNP)
Figure 3. Figure 4.
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3
2
1
0
-1
-2
-3
Capacitance(nF)
0 0.5 1.0 1.5 2.0 2.5 3.0
RemoteTemperatureError( C)°
RemoteTemperatureError( )°C
R (W)
S
2.0
1.5
1.0
0.5
0
-0.5
-1.0
-1.5
-2.0
0 3500500 1000 1500 2000 2500 3000
V+=2.7V
V+=5.5V
25
20
15
10
5
0
-5
-10
-15
-20
-25
Frequency(MHz)
0 5 10 15
TemperatureError( C)°
Local100mV Noise
PP
Remote100mV Noise
PP
Local250mV Noise
PP
Remote250mV Noise
PP
500
450
400
350
300
250
200
150
100
50
0
ConversionRate(conversions/sec)
0.0625 0.125 0.25 0.5 1 2 4 8
I (mA)
Q
V+=2.7V
V+=5.5V
TMP422-EP
SBOS577 –SEPTEMBER 2011
www.ti.com
TYPICAL CHARACTERISTICS (continued)
At TA= +25°C and VS= +5.0V, unless otherwise noted.
REMOTE TEMPERATURE ERROR
vs REMOTE TEMPERATURE ERROR
SERIES RESISTANCE vs
(GND Collector-Connected Transistor, 2N3906 PNP) DIFFERENTIAL CAPACITANCE
Figure 5. Figure 6.
TEMPERATURE ERROR QUIESCENT CURRENT
vs vs
POWER-SUPPLY NOISE FREQUENCY CONVERSION RATE
Figure 7. Figure 8.
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I ( )
QmA
V+(V)
8
7
6
5
4
3
2
1
0
4.53.0 3.5 4.0 5.55.02.5
TMP422-EP
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SBOS577 –SEPTEMBER 2011
TYPICAL CHARACTERISTICS (continued)
At TA= +25°C and VS= +5.0V, unless otherwise noted.
SHUTDOWN QUIESCENT CURRENT SHUTDOWN QUIESCENT CURRENT
vs vs
SCL CLOCK FREQUENCY SUPPLY VOLTAGE
Figure 9. Figure 10.
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TMP422
DX1(4)
DX2(4)
5
2
1
RS
(2)
RS
(2) CDIFF
(3)
CDIFF
(3)
RS
(2)
RS
(2)
GND
Diode-connectedconfiguration :
(1)
SeriesResistance
Transistor-connectedconfiguration :
(1)
DX3(4)
DX4(4)
4
3
RS
(2)
RS
(2) CDIFF
(3)
0.1 Fm10kW
(typ)
10kW
(typ)
V+
8
7
6
SCL
SDA
+5V
SMBus
Controller
DXP1
DXN1
DXP2
DXN2
TMP422-EP
SBOS577 –SEPTEMBER 2011
www.ti.com
APPLICATION INFORMATION
The TMP422 (three-channel) is a digital temperature sensor that combines a local die temperature measurement
channel and two remote junction temperature measurement channels in a single SOT23-8 package. This device
is two-wire- and SMBus interface-compatible and are specified over a temperature range of –55°C to +125°C.
The TMP422 contains multiple registers for holding configuration information and temperature measurement
results.
The TMP422 requires transistors connected between DX1 and DX2 and between DX3 and DX4. Unused
channels on the TMP422 must be connected to GND.
The TMP422 SCL and SDA interface pins each require pull-up resistors as part of the communication bus. A
0.1μF power-supply bypass capacitor is recommended for local bypassing. Figure 11 illustrates a typical
application for the TMP422.
(1) Diode-connected configuration provides better settling time. Transistor-connected configuration provides better series resistance
cancellation.
(2) RS(optional) should be <1.5kΩin most applications. Selection of RSdepends on application; see the Filtering section.
(3) CDIFF (optional) should be <1000pF in most applications. Selection of CDIFF depends on application; see the Filtering section and
Figure 6,Remote Temperature Error vs Differential Capacitance.
(4) TMP422 SMBus slave address is 1001 100 when connected as shown.
Figure 11. TMP422 Basic Connections
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SBOS577 –SEPTEMBER 2011
SERIES RESISTANCE CANCELLATION
Series resistance in an application circuit that typically results from printed circuit board (PCB) trace resistance
and remote line length is automatically cancelled by the TMP422, preventing what would otherwise result in a
temperature offset. A total of up to 3kΩof series line resistance is cancelled by the TMP422, eliminating the
need for additional characterization and temperature offset correction. See the two Remote Temperature Error vs
Series Resistance typical characteristic curves (Figure 4 and Figure 5) for details on the effects of series
resistance and power-supply voltage on sensed remote temperature error.
DIFFERENTIAL INPUT CAPACITANCE
The TMP422 tolerates differential input capacitance of up to 1000pF with minimal change in temperature error.
The effect of capacitance on sensed remote temperature error is illustrated in Figure 6,Remote Temperature
Error vs Differential Capacitance.
TEMPERATURE MEASUREMENT DATA
Temperature measurement data may be taken over an operating range of –40°C to +127°C for both local and
remote locations.
However, measurements from –55°C to +150°C can be made both locally and remotely by reconfiguring the
TMP422 for the extended temperature range, as described below.
Temperature data that result from conversions within the default measurement range are represented in binary
form, as shown in Table 2, Standard Binary column. Note that although the device is rated to only measure
temperatures down to –55°C, it may read temperatures below this level. However, any temperature below –64°C
results in a data value of –64 (C0h). Likewise, temperatures above +127°C result in a value of 127 (7Fh). The
device can be set to measure over an extended temperature range by changing bit 2 (RANGE) of Configuration
Register 1 from low to high. The change in measurement range and data format from standard binary to
extended binary occurs at the next temperature conversion. For data captured in the extended temperature
range configuration, an offset of 64 (40h) is added to the standard binary value, as shown in the Extended Binary
column of Table 2. This configuration allows measurement of temperatures as low as –64°C, and as high as
+191°C; however, most temperature-sensing diodes only measure with the range of –55°C to +150°C.
Additionally, the TMP422 is rated only for ambient temperatures ranging from –55°C to +125°C. Parameters in
the Absolute Maximum Ratings table must be observed.
Table 2. Temperature Data Format (Local and Remote Temperature High Bytes)
LOCAL/REMOTE TEMPERATURE REGISTER
HIGH BYTE VALUE (1°C RESOLUTION)
STANDARD BINARY(1) EXTENDED BINARY(2)
TEMP
(°C) BINARY HEX BINARY HEX
–64 1100 0000 C0 0000 0000 00
–50 1100 1110 CE 0000 1110 0E
–25 1110 0111 E7 0010 0111 27
0 0000 0000 00 0100 0000 40
1 0000 0001 01 0100 0001 41
5 0000 0101 05 0100 0101 45
10 0000 1010 0A 0100 1010 4A
25 0001 1001 19 0101 1001 59
50 0011 0010 32 0111 0010 72
75 0100 1011 4B 1000 1011 8B
100 0110 0100 64 1010 0100 A4
125 0111 1101 7D 1011 1101 BD
127 0111 1111 7F 1011 1111 BF
150 0111 1111 7F 1101 0110 D6
175 0111 1111 7F 1110 1111 EF
191 0111 1111 7F 1111 1111 FF
(1) Resolution is 1°C/count. Negative numbers are represented in two's complement format.
(2) Resolution is 1°C/count. All values are unsigned with a –64°C offset.
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Both local and remote temperature data use two bytes for data storage. The high byte stores the temperature
with 1°C resolution. The second or low byte stores the decimal fraction value of the temperature and allows a
higher measurement resolution, as shown in Table 3. The measurement resolution for the both the local and
remote channels is 0.0625°C, and is not adjustable.
Table 3. Decimal Fraction Temperature Data Format (Local and Remote Temperature Low Bytes)
TEMPERATURE REGISTER LOW BYTE VALUE
(0.0625°C RESOLUTION)(1)
TEMP
(°C) STANDARD AND EXTENDED BINARY HEX
0 0000 0000 00
0.0625 0001 0000 10
0.1250 0010 0000 20
0.1875 0011 0000 30
0.2500 0100 0000 40
0.3125 0101 0000 50
0.3750 0110 0000 60
0.4375 0111 0000 70
0.5000 1000 0000 80
0.5625 1001 0000 90
0.6250 1010 0000 A0
0.6875 1011 0000 B0
0.7500 1100 0000 C0
0.8125 1101 0000 D0
0.8750 1110 0000 E0
0.9385 1111 0000 F0
(1) Resolution is 0.0625°C/count. All possible values are shown.
Standard Binary to Decimal Temperature Data Calculation Example
High byte conversion (for example, 0111 0011):
Convert the right-justified binary high byte to hexadecimal.
From hexadecimal, multiply the first number by 160= 1 and the second number by 161= 16.
The sum equals the decimal equivalent.
0111 0011b →73h →(3 ×160) + (7 ×161) = 115
Low byte conversion (for example, 0111 0000):
To convert the left-justified binary low-byte to decimal, use bits 7 through 4 and ignore bits 3 through 0
because they do not affect the value of the number.
0111b →(0 ×1/2)1+ (1 ×1/2)2+ (1 ×1/2)3+ (1 ×1/2)4= 0.4375
Note that the final numerical result is the sum of the high byte and low byte. In negative temperatures, the
unsigned low byte adds to the negative high byte to result in a value less than the high byte (for instance, –15 +
0.75 = –14.25, not –15.75).
Standard Decimal to Binary Temperature Data Calculation Example
For positive temperatures (for example, +20°C):
(+20°C)/(+1°C/count) = 20 →14h →0001 0100
Convert the number to binary code with 8-bit, right-justified format, and MSB = '0' to denote a positive sign.
+20°C is stored as 0001 0100 →14h.
For negative temperatures (for example, –20°C):
(|–20|)/(+1°C/count) = 20 →14h →0001 0100
Generate the two's complement of a negative number by complementing the absolute value binary number
and adding 1.
–20°C is stored as 1110 1100 →ECh.
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Product Folder Link(s): TMP422-EP
One-ShotStartRegister
ConfigurationRegisters
StatusRegister
IdentificationRegisters
N-FactorCorrectionRegisters
ConversionRateRegister
LocalandRemoteTemperatureRegisters
SDA
SCL
PointerRegister
I/O
Control
Interface
SoftwareReset
TMP422-EP
www.ti.com
SBOS577 –SEPTEMBER 2011
REGISTER INFORMATION
The TMP422 contains multiple registers for holding configuration information, temperature measurement results,
and status information. These registers are described in Figure 12 and Table 4.
POINTER REGISTER
Figure 12 shows the internal register structure of the TMP422. The 8-bit Pointer Register is used to address a
given data register. The Pointer Register identifies which of the data registers should respond to a read or write
command on the two-wire bus. This register is set with every write command. A write command must be issued
to set the proper value in the Pointer Register before executing a read command. Table 4 describes the pointer
address of the TMP422 registers. The power-on reset (POR) value of the Pointer Register is 00h (0000 0000b).
Figure 12. Internal Register Structure
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Table 4. Register Map
BIT DESCRIPTION
POINTER
(HEX) POR (HEX) 7 6 5 4 3 2 1 0 REGISTER DESCRIPTION
00 00 LT11 LT10 LT9 LT8 LT7 LT6 LT5 LT4 Local Temperature (High Byte) (1)
Remote Temperature 1
01 00 RT11 RT10 RT9 RT8 RT7 RT6 RT5 RT4 (High Byte)(1)
Remote Temperature 2
02 00 RT11 RT10 RT9 RT8 RT7 RT6 RT5 RT4 (High Byte)(1)
Remote Temperature 3
03 00 RT11 RT10 RT9 RT8 RT7 RT6 RT5 RT4 (High Byte)(1)
08 BUSY 0 0 0 0 0 0 0 Status Register
09 00 0 SD 0 0 0 RANGE 0 0 Configuration Register 1
0A 1C/3C 0 REN3 REN2 REN LEN RC 0 0 Configuration Register 2
0B 07 0 0 0 0 0 R2 R1 R0 Conversion Rate Register
0F X X X X X X X X One-Shot Start(2)
10 00 LT3 LT2 LT1 LT0 0 0 PVLD 0 Local Temperature (Low Byte)
11 00 RT3 RT2 RT1 RT0 0 0 PVLD OPEN Remote Temperature 1 (Low Byte)
Remote Temperature 2
12 00 RT3 RT2 RT1 RT0 0 0 PVLD OPEN (Low Byte)
13 00 RT3 RT2 RT1 RT0 0 0 PLVD OPEN Remote Temperature 3 (Low Byte
21 00 NC7 NC6 NC5 NC4 NC3 NC2 NC1 NC0 N Correction 1
22 00 NC7 NC6 NC5 NC4 NC3 NC2 NC1 NC0 N Correction 2
23 00 NC7 NC6 NC5 NC4 NC3 NC2 NC1 NC0 N Correction 3
FC X X X X X X X X Software Reset(3)
FE 55 0 1 0 1 0 1 0 1 Manufacturer ID
FF 21 0 0 1 0 0 0 1 0 TMP422 Device ID
(1) Compatible with Two-Byte Read; see Figure 17.
(2) X = undefined. Writing any value to this register initiates a one-shot start; see the One-Shot Conversion section.
(3) X = undefined. Writing any value to this register initiates a software reset; see the Software Reset section.
TEMPERATURE REGISTERS
The TMP422 has multiple 8-bit registers that hold temperature measurement results. The local channel and each
of the remote channels have a high byte register that contains the most significant bits (MSBs) of the
temperature analog-to-digital converter (ADC) result and a low byte register that contains the least significant bits
(LSBs) of the temperature ADC result. The local channel high byte address is 00h; the local channel low byte
address is 10h. The remote channel high byte is at address 01h; the remote channel low byte address is 11h.
For the TMP422, the second remote channel high byte address is 02h; the second remote channel low byte is
12h. These registers are read-only and are updated by the ADC each time a temperature measurement is
completed.
The TMP422 contains circuitry to assure that a low byte register read command returns data from the same ADC
conversion as the immediately preceding high byte read command. This assurance remains valid only until
another register is read. For proper operation, the high byte of a temperature register should be read first. The
low byte register should be read in the next read command. The low byte register may be left unread if the LSBs
are not needed. Alternatively, the temperature registers may be read as a 16-bit register by using a single
two-byte read command from address 00h for the local channel result, or from address 01h for the remote
channel result (02h for the second remote channel result, and 03h for the third remote channel). The high byte is
output first, followed by the low byte. Both bytes of this read operation are from the same ADC conversion. The
power-on reset value of all temperature registers is 00h.
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STATUS REGISTER
The Status Register reports the state of the temperature ADCs. Table 5 summarizes the Status Register bits.
The Status Register is read-only, and is read by accessing pointer address 08h.
The BUSY bit = '1' if the ADC is making a conversion; it is set to '0' if the ADC is not converting.
CONFIGURATION REGISTER 1
Configuration Register 1 (pointer address 09h) sets the temperature range and controls the shutdown mode. The
Configuration Register is set by writing to pointer address 09h and read by reading from pointer address 09h.
Table 6 summarizes the bits of Configuration Register 1.
The shutdown (SD) bit (bit 6) enables or disables the temperature measurement circuitry. If SD = '0', the TMP422
convert continuously at the rate set in the conversion rate register. When SD is set to '1', the TMP422 stops
converting when the current conversion sequence is complete and enter a shutdown mode. When SD is set to '0'
again, the TMP422 resumes continuous conversions. When SD = '1', a single conversion can be started by
writing to the One-Shot Register. See the One-Shot Conversion section for more information.
The temperature range is set by configuring the RANGE bit (bit 2) of the Configuration Register. Setting this bit
low configures the TMP422 for the standard measurement range (–40°C to +127°C); temperature conversions
will be stored in the standard binary format. Setting bit 2 high configures the TMP422 for the extended
measurement range (–55°C to +150°C); temperature conversions will be stored in the extended binary format
(see Table 2).
The remaining bits of the Configuration Register are reserved and must always be set to '0'. The power-on reset
value for this register is 00h.
CONFIGURATION REGISTER 2
Configuration Register 2 (pointer address 0Ah) controls which temperature measurement channels are enabled
and whether the external channels have the resistance correction feature enabled or not. Table 7 summarizes
the bits of Configuration Register 2.
Table 5. Status Register Format
STATUS REGISTER (Read = 08h, Write = NA)
BIT # D7 D6 D5 D4 D3 D2 D1 D0
BIT NAME BUSY0000000
POR VALUE 0(1) 0000000
(1) The BUSY bit changes to '1'approximately 1ms following power-up. It is high whenever the TMP422 converts a temperature reading.
Table 6. Configuration Register 1 Bit Descriptions
CONFIGURATION REGISTER 1 (Read/Write = 09h, POR = 00h)
POWER-ON RESET
BIT NAME FUNCTION VALUE
7 Reserved —0
0 = Run
6 SD 0
1 = Shut Down
5, 4, 3 Reserved —0
0 = –55°C to +127°C
2 Temperature Range 0
1 = –55°C to +150°C
1, 0 Reserved —0
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The RC bit (bit 2) enables the resistance correction feature for the external temperature channels. If RC = '1',
series resistance correction is enabled; if RC = '0', resistance correction is disabled. Resistance correction should
be enabled for most applications. However, disabling the resistance correction may yield slightly improved
temperature measurement noise performance, and reduce conversion time by about 50%, which could lower
power consumption when conversion rates of two per second or less are selected.
The LEN bit (bit 3) enables the local temperature measurement channel. If LEN = '1', the local channel is
enabled; if LEN = '0', the local channel is disabled.
The REN bit (bit 4) enables external temperature measurement for channel 1. If REN = '1', the first external
channel is enabled; if REN = '0', the external channel is disabled.
The REN2 bit (bit 5) enables the second external measurement channel. If REN2 = '1', the second external
channel is enabled; if REN2 = '0', the second external channel is disabled.
The temperature measurement sequence is: local channel, external channel 1, external channel 2, external
channel 3, shutdown, and delay (to set conversion rate, if necessary). The sequence starts over with the local
channel. If any of the channels are disabled, they are bypassed in the sequence.
CONVERSION RATE REGISTER
The Conversion Rate Register (pointer address 0Bh) controls the rate at which temperature conversions are
performed. This register adjusts the idle time between conversions but not the conversion timing itself, thereby
allowing the TMP422 power dissipation to be balanced with the temperature register update rate. Table 8
describes the conversion rate options and corresponding current consumption. A one-shot command can be
used during the idle time between conversions to immediately start temperature conversions on all enabled
channels.
Table 7. Configuration Register 2 Bit Descriptions
CONFIGURATION REGISTER 2 (Read/Write = 0Ah, POR = 3Ch)
POWER-ON RESET
BIT NAME FUNCTION VALUE
7 Reserved —0
0 = External Channel 3 Disabled
6 REN3 0
1 = External Channel 3 Enabled
0 = External Channel 2 Disabled
5 REN2 1
1 = External Channel 2 Enabled
0 = External Channel 1 Disabled
4 REN 1
1 = External Channel 1 Enabled
0 = Local Channel Disabled
3 LEN 1
1 = Local Channel Enabled
0 = Resistance Correction Disabled
2 RC 1
1 = Resistance Correction Enabled
1, 0 Reserved —0
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=V V
BE2 BE1
-hkT
qln I2
I1
=heff
1.008 300´
300 NADJUST
-
N =300
ADJUST -300 1.008´
heff
TMP422-EP
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SBOS577 –SEPTEMBER 2011
Table 8. Conversion Rate Register
CONVERSION RATE REGISTER (Read/Write = 0Bh, POR = 07h)
AVERAGE IQ(TYP) (μA)
R7 R6 R5 R4 R3 R2 R1 R0 CONVERSIONS/SEC VS= 2.7V VS= 5.5V
0 0 0 0 0 0 0 0 0.0625 11 32
0 0 0 0 0 0 0 1 0.125 17 38
0 0 0 0 0 0 1 0 0.25 28 49
0 0 0 0 0 0 1 1 0.5 47 69
0 0 0 0 0 1 0 0 1 80 103
0 0 0 0 0 1 0 1 2 128 155
00000110 4(1) 190 220
00000111 8(2) 373 413
(1) Conversion rate shown is for only one or two enabled measurement channels. When three channels are enabled, the conversion rate is
2 and 2/3 conversions-per-second. When four channels are enabled, the conversion rate is 2 per second.
(2) Conversion rate shown is for only one enabled measurement channel. When two channels are enabled, the conversion rate is 4
conversions-per-second. When three channels are enabled, the conversion rate is 2 and 2/3 conversions-per-second. When four
channels are enabled, the conversion rate is 2 conversions-per-second.
ONE-SHOT CONVERSION
When the TMP422 is in shutdown mode (SD = 1 in the Configuration Register 1), a single conversion is started
on all enabled channels by writing any value to the One-Shot Start Register, pointer address 0Fh. This write
operation starts one conversion; the TMP422 returns to shutdown mode when that conversion completes. The
value of the data sent in the write command is irrelevant and is not stored by the TMP422. When the TMP422
are in shutdown mode, the conversion sequence currently in process must be completed before a one-shot
command can be issued. One-shot commands issued during a conversion are ignored.
n-FACTOR CORRECTION REGISTER
The TMP422 allows for a different n-factor value to be used for converting remote channel measurements to
temperature. The remote channel uses sequential current excitation to extract a differential VBE voltage
measurement to determine the temperature of the remote transistor. Equation 1 describes this voltage and
temperature.
(1)
The value nin Equation 1 is a characteristic of the particular transistor used for the remote channel. The
power-on reset value for the TMP422 is n= 1.008. The value in the n-Factor Correction Register may be used to
adjust the effective n-factor according to Equation 2 and Equation 3.
(2)
(3)
The n-correction value must be stored in two's-complement format, yielding an effective data range from –128 to
+127. The n-correction value may be written to and read from pointer address 21h. The n-correction value for the
second remote channel may be written and read from pointer address 22h. The register power-on reset value is
00h, thus having no effect unless the register is written to.
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SOFTWARE RESET
The TMP422 may be reset by writing any value to the Software Reset Register (pointer address FCh). This
action restores the power-on reset state to all of the TMP422 registers as well as aborts any conversion in
process. The TMP422 also supports reset via the two-wire general call address (0000 0000). The General Call
Reset section contains more information.
Table 9. n-Factor Range
NADJUST
BINARY HEX DECIMAL n
0111 1111 7F 127 1.747977
0000 1010 0A 10 1.042759
0000 1000 08 8 1.035616
0000 0110 06 6 1.028571
0000 0100 04 4 1.021622
0000 0010 02 2 1.014765
0000 0001 01 1 1.011371
0000 0000 00 0 1.008
1111 1111 FF –1 1.004651
1111 1110 FE –2 1.001325
1111 1100 FC –4 0.994737
1111 1010 FA –6 0.988235
1111 1000 F8 –8 0.981818
1111 0110 F6 –10 0.975484
1000 0000 80 –128 0.706542
GENERAL CALL RESET
The TMP422 supports reset via the two-wire General Call address 00h (0000 0000b). The TMP422
acknowledges the General Call address and respond to the second byte. If the second byte is 06h (0000 0110b),
the TMP422 executes a software reset. This software reset restores the power-on reset state to all TMP422
registers, and aborts any conversion in progress. The TMP422 takes no action in response to other values in the
second byte.
IDENTIFICATION REGISTERS
The TMP422 allows for the two-wire bus controller to query the device for manufacturer and device IDs to enable
software identification of the device at the particular two-wire bus address. The manufacturer ID is obtained by
reading from pointer address FEh. The device ID is obtained by reading from pointer address FFh. The TMP422
returns 55h for the manufacturer code. The TMP422 returns 22h for the device ID. These registers are read-only.
BUS OVERVIEW
The TMP422 is SMBus interface-compatible. In SMBus protocol, the device that initiates the transfer is called a
master, and the devices controlled by the master are slaves. The bus must be controlled by a master device that
generates the serial clock (SCL), controls the bus access, and generates the START and STOP conditions.
To address a specific device, a START condition is initiated. START is indicated by pulling the data line (SDA)
from a high-to-low logic level while SCL is high. All slaves on the bus shift in the slave address byte, with the last
bit indicating whether a read or write operation is intended. During the ninth clock pulse, the slave being
addressed responds to the master by generating an Acknowledge and pulling SDA low.
Data transfer is then initiated and sent over eight clock pulses followed by an Acknowledge bit. During data
transfer SDA must remain stable while SCL is high, because any change in SDA while SCL is high is interpreted
as a control signal.
Once all data have been transferred, the master generates a STOP condition. STOP is indicated by pulling SDA
from low to high, while SCL is high.
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DX1
DX2
DX3
DX4
SCL
SDA
V+
Q0
Address=1001100 Address=1001101 Address=1001110 Address=1001111
Q1
Q2
Q3
Q4
Q5
V+
SCL
SDA
GND Q7
DX1
DX2
DX3
DX4
V+
SCL
SDA
GND
DX1
DX2
DX3
DX4
V+
SCL
SDA
GND
DX1
DX2
DX3
DX4
V+
SCL
SDA
GND
Q6
TMP422-EP
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SBOS577 –SEPTEMBER 2011
SERIAL INTERFACE
The TMP422 operates only as a slave device on either the two-wire bus or the SMBus. Connections to either bus
are made via the open-drain I/O lines, SDA and SCL. The SDA and SCL pins feature integrated spike
suppression filters and Schmitt triggers to minimize the effects of input spikes and bus noise. The TMP422
supports the transmission protocol for fast (1kHz to 400kHz) and high-speed (1kHz to 3.4MHz) modes. All data
bytes are transmitted MSB first.
SERIAL BUS ADDRESS
To communicate with the TMP422, the master must first address slave devices via a slave address byte. The
slave address byte consists of seven address bits, and a direction bit indicating the intent of executing a read or
write operation.
Two-Wire Interface Slave Device Addresses
The TMP422 supports four slave device addresses.
The slave device address is set by the connections between the external transistors and the TMP422 according
to Figure 13 and Table 10. If one of the channels is unused, the respective DXP connection should be connected
to GND, and the DXN connection should be left unconnected. The polarity of the transistor for external channel 2
(pins 3 and 4) sets the least significant bit of the slave address. The polarity of the transistor for external channel
1 (pins 1 and 2) sets the next least significant bit of the slave address.
Table 10. Slave Address Options
TWO-WIRE SLAVE ADDRESS DX1 DX2 DX3 DX4
1001 100 DXP1 DXN1 DXP2 DXN2
1001 101 DXP1 DXN1 DXN2 DXP2
1001 110 DXN1 DXP1 DXP2 DXN2
1001 111 DXN1 DXP1 DXN2 DXP2
Figure 13. TMP422 Connections for Device Address Setup
The TMP422 checks the polarity of the external transistor at power-on, or after software reset, by forcing current
to pin 1 while connecting pin 2 to approximately 0.6V. If the voltage on pin 1 does not pull up to near the V+ of
the TMP422, pin 1 functions as DXP for channel 1, and the second LSB of the slave address is '0'. If the voltage
on pin 1 does pull up to near V+, the TMP422 forces current to pin 2 while connecting pin 1 to 0.6V. If the
voltage on pin 2 does not pull up to near V+, the TMP422 uses pin 2 for DXP of channel 1, and sets the second
LSB of the slave address to '1'. If both pins are shorted to GND or if both pins are open, the TMP422 uses pin 1
as DXP and sets the address bit to '0'. This process is then repeated for channel 2 (pins 3 and 4).
If the TMP422 is to be used with transistors that are located on another IC (such as a CPU, DSP, or graphics
processor), it is recommended to use pin 1 or pin 3 as DXP to ensure correct address detection. If the other IC
has a lower supply voltage or is not powered when the TMP422 tries to detect the slave address, a protection
diode may turn on during the detection process and the TMP422 may incorrectly choose the DXP pin and
corresponding slave address. Using pin 1 and/or pin 3 for transistors that are on other ICs ensures correct
operation independent of supply sequencing or levels.
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SCL
SDA
t(LOW) tRtFt(HDSTA)
t(HDSTA)
t(HDDAT)
t(BUF)
t(SUDAT)
t(HIGH) t(SUSTA) t(SUSTO)
P S S P
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SBOS577 –SEPTEMBER 2011
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READ/WRITE OPERATIONS
Accessing a particular register on the TMP422 is accomplished by writing the appropriate value to the Pointer
Register. The value for the Pointer Register is the first byte transferred after the slave address byte with the R/W
bit low. Every write operation to the TMP422 requires a value for the Pointer Register (see Figure 15).
When reading from the TMP422, the last value stored in the Pointer Register by a write operation is used to
determine which register is read by a read operation. To change which register is read for a read operation, a
new value must be written to the Pointer Register. This transaction is accomplished by issuing a slave address
byte with the R/W bit low, followed by the Pointer Register byte; no additional data are required. The master can
then generate a START condition and send the slave address byte with the R/W bit high to initiate the read
command. See Figure 17 for details of this sequence. If repeated reads from the same register are desired, it is
not necessary to continually send the Pointer Register bytes, because the TMP422 retain the Pointer Register
value until it is changed by the next write operation. Note that register bytes are sent MSB first, followed by the
LSB.
Read operations should be terminated by issuing a Not-Acknowledge command at the end of the last byte to be
read. For a single-byte operation, the master should leave the SDA line high during the Acknowledge time of the
first byte that is read from the slave. For a two-byte read operation, the master must pull SDA low during the
Acknowledge time of the first byte read, and should leave SDA high during the Acknowledge time of the second
byte read from the slave.
TIMING DIAGRAMS
The TMP422 is two-wire and SMBus-compatible. Figure 14 to Figure 17 describe the timing for various
operations on the TMP422. Parameters for Figure 14 are defined in Table 11. Bus definitions are:
Bus Idle: Both SDA and SCL lines remain high.
Start Data Transfer: A change in the state of the SDA line, from high to low, while the SCL line is high, defines
a START condition. Each data transfer initiates with a START condition. Denoted as Sin Figure 14.
Stop Data Transfer: A change in the state of the SDA line from low to high while the SCL line is high defines a
STOP condition. Each data transfer terminates with a repeated START or STOP condition. Denoted as Pin
Figure 14.
Data Transfer: The number of data bytes transferred between a START and a STOP condition is not limited and
is determined by the master device. The receiver acknowledges data transfer.
Acknowledge: Each receiving device, when addressed, is obliged to generate an Acknowledge bit. A device
that acknowledges must pull down the SDA line during the Acknowledge clock pulse in such a way that the SDA
line is stable low during the high period of the Acknowledge clock pulse. Setup and hold times must be taken into
account. On a master receive, data transfer termination can be signaled by the master generating a
Not-Acknowledge on the last byte that has been transmitted by the slave.
Figure 14. Two-Wire Timing Diagram
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Frame 1 Two-Wire Slave Address Byte Frame 2 Pointer Register Byte
1
Start By
Master
ACK By
TMP422
ACK By
TMP422
1 9 1
Frame 3 Data Byte 1
ACK By
TMP422
1
D7
SDA
(Continued)
SCL
(Continued)
D6 D5 D4 D3 D2 D1 D0
9
9
SDA
SCL
0 0 1 1 0 0(1) R/W P7 P6 P5 P4 P3 P2 P1 P0
¼
¼
Stop By
Master
TMP422-EP
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Table 11. Timing Characteristics for Figure 14
FAST MODE HIGH-SPEED MODE
PARAMETER MIN MAX MIN MAX UNIT
SCL Operating Frequency f(SCL) 0.001 0.4 0.001 3.4 MHz
Bus Free Time Between STOP and START Condition t(BUF) 600 160 ns
Hold time after repeated START condition. After this period, the first clock t(HDSTA) 100 100 ns
is generated.
Repeated START Condition Setup Time t(SUSTA) 100 100 ns
STOP Condition Setup Time t(SUSTO) 100 100 ns
Data Hold Time t(HDDAT) 0(1) 0(2) ns
Data Setup Time t(SUDAT) 100 10 ns
SCL Clock LOW Period t(LOW) 1300 160 ns
SCL Clock HIGH Period t(HIGH) 600 60 ns
Clock/Data Fall Time tF300 160 ns
Clock/Data Rise Time tR300 160 ns
for SCL ≤100kHz tR1000
(1) For cases with fall time of SCL less than 20ns and/or the rise or fall time of SDA less than 20ns, the hold time should be greater than
20ns.
(2) For cases with a fall time of SCL less than 10ns and/or the rise or fall time of SDA less than 10ns, the hold time should be greater than
10ns.
(1) Slave address 1001100 shown.
Figure 15. Two-Wire Timing Diagram for Write Word Format
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Frame 1 Two-Wire Slave Address Byte Frame 2 Pointer Register Byte
1
Start By
Master
ACK By
TMP422
ACK By
TMP422
Frame 3 Two-Wire Slave Address Byte Frame 4 Data Byte 1 Read Register
Start By
Master
ACK By
TMP422
NACK By
Master(2)
From
TMP422
1 9 1 9
1 9 1 9
SDA
SCL
0 0 1 R/W P7 P6 P5 P4 P3 P2 P1 P0 ¼
¼
¼
¼
SDA
(Continued)
SCL
(Continued)
1 0 0 1
1 0 0(1)
1 0 0(1) R/W D7 D6 D5 D4 D3 D2 D1 D0
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(1) Slave address 1001100 shown.
(2) Master should leave SDA high to terminate a single-byte read operation.
Figure 16. Two-Wire Timing Diagram for Single-Byte Read Format
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Frame 1 Two-Wire Slave Address Byte Frame 2 Pointer Register Byte
1
Start By
Master
ACK By
TMP422
ACK By
TMP422
Frame 3 Two-Wire Slave Address Byte Frame 4 Data Byte 1 Read Register
Start By
Master
ACK By
TMP422
ACK By
Master
From
TMP422
1 9 1 9
1 9 1 9
SDA
SCL
0 0 1 R/W P7 P6 P5 P4 P3 P2 P1 P0 ¼
¼
¼
¼
SDA
(Continued)
SCL
(Continued)
SDA
(Continued)
SCL
(Continued)
1 0 0 1
1 0 0(1)
1 0 0(1) R/W D7 D6 D5 D4 D3 D2 D1 D0
Frame 5 Data Byte 2 Read Register
Stop By
Master
NACK By
Master(2)
From
TMP422
19
D7 D6 D5 D4 D3 D2 D1 D0
TMP422-EP
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SBOS577 –SEPTEMBER 2011
(1) Slave address 1001100 shown.
(2) Master should leave SDA high to terminate a two-byte read operation.
Figure 17. Two-Wire Timing Diagram for Two-Byte Read Format
HIGH-SPEED MODE
In order for the two-wire bus to operate at frequencies above 400kHz, the master device must issue a
High-Speed mode (Hs-mode) master code (0000 1xxx) as the first byte after a START condition to switch the
bus to high-speed operation. The TMP422 does not acknowledge this byte, but switches the input filters on SDA
and SCL and the output filter on SDA to operate in Hs-mode, allowing transfers at up to 3.4MHz. After the
Hs-mode master code has been issued, the master transmits a two-wire slave address to initiate a data transfer
operation. The bus continues to operate in Hs-mode until a STOP condition occurs on the bus. Upon receiving
the STOP condition, the TMP422 switch the input and output filters back to fast mode operation.
TIMEOUT FUNCTION
The TMP422 reset the serial interface if either SCL or SDA are held low for 30ms (typical) between a START
and STOP condition. If the TMP422 is holding the bus low, the device releases the bus and waits for a START
condition. To avoid activating the timeout function, it is necessary to maintain a communication speed of at least
1kHz for the SCL operating frequency.
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SHUTDOWN MODE (SD)
The TMP422 Shutdown Mode allows the user to save maximum power by shutting down all device circuitry other
than the serial interface, reducing current consumption to typically less than 3μA; see Figure 10,Shutdown
Quiescent Current vs Supply Voltage. Shutdown Mode is enabled when the SD bit (bit 6) of Configuration
Register 1 is high; the device shuts down once the current conversion is completed. When SD is low, the device
maintains a continuous conversion state.
SENSOR FAULT
The TMP422 can sense an open circuit. Short-circuit conditions return a value of –64°C. The detection circuitry
consists of a voltage comparator that trips when the voltage at DXP exceeds (V+) –0.6V (typical). The
comparator output is continuously checked during a conversion. If a fault is detected, the OPEN bit (bit 0) in the
temperature result register is set to '1' and the rest of the register bits should be ignored.
When not using a remote sensor with the TMP422, the DX pins should be connected (refer to Table 10) such
that DXP connections are grounded and DXN connections are left open (unconnected).
UNDERVOLTAGE LOCKOUT
The TMP422 senses when the power-supply voltage has reached a minimum voltage level for the ADC to
function. The detection circuitry consists of a voltage comparator that enables the ADC after the power supply
(V+) exceeds 2.45V (typical). The comparator output is continuously checked during a conversion. The TMP422
does not perform a temperature conversion if the power supply is not valid. The PVLD bit (bit 1, see Table 4) of
the individual Local/Remote Temperature Register is set to '1' and the temperature result may be incorrect.
FILTERING
Remote junction temperature sensors are usually implemented in a noisy environment. Noise is most often
created by fast digital signals, and it can corrupt measurements. The TMP422 has a built-in 65kHz filter on the
inputs of DX1 through DX4 to minimize the effects of noise. However, a bypass capacitor placed differentially
across the inputs of the remote temperature sensor is recommended to make the application more robust against
unwanted coupled signals. The value of this capacitor should be between 100pF and 1nF. Some applications
attain better overall accuracy with additional series resistance; however, this increased accuracy is
application-specific. When series resistance is added, the total value should not be greater than 3kΩ. If filtering is
needed, suggested component values are 100pF and 50Ωon each input; exact values are application-specific.
REMOTE SENSING
The TMP422 is designed to be used with either discrete transistors or substrate transistors built into processor
chips and ASICs. Either NPN or PNP transistors can be used, as long as the base-emitter junction is used as the
remote temperature sense. NPN transistors must be diode-connected. PNP transistors can either be transistor-
or diode-connected (see Figure 11).
Errors in remote temperature sensor readings are typically the consequence of the ideality factor and current
excitation used by the TMP422 versus the manufacturer-specified operating current for a given transistor. Some
manufacturers specify a high-level and low-level current for the temperature-sensing substrate transistors. The
TMP422 uses 6μA for ILOW and 120μA for IHIGH.
The ideality factor (n) is a measured characteristic of a remote temperature sensor diode as compared to an
ideal diode. The TMP422 allow for different n-factor values; see the N-Factor Correction Register section.
The ideality factor for the TMP422 is trimmed to be 1.008. For transistors that have an ideality factor that does
not match the TMP422, Equation 4 can be used to calculate the temperature error. Note that for the equation to
be used correctly, actual temperature (°C) must be converted to kelvins (K).
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T =
ERR
h1.008-
1.008 (273.15+T( C))°´
TERR +ǒ1.004 *1.008
1.008 Ǔ ǒ273.15 )100°CǓ
TERR +1.48°C
TMP422-EP
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SBOS577 –SEPTEMBER 2011
(4)
Where:
n = ideality factor of remote temperature sensor
T(°C) = actual temperature
TERR = error in TMP422 because n ≠1.008
Degree delta is the same for °C and K
For n= 1.004 and T(°C) = 100°C:
(5)
If a discrete transistor is used as the remote temperature sensor with the TMP422, the best accuracy can be
achieved by selecting the transistor according to the following criteria:
1. Base-emitter voltage >0.25V at 6μA, at the highest sensed temperature.
2. Base-emitter voltage <0.95V at 120μA, at the lowest sensed temperature.
3. Base resistance <100Ω.
4. Tight control of VBE characteristics indicated by small variations in hFE (that is, 50 to 150).
Based on these criteria, two recommended small-signal transistors are the 2N3904 (NPN) or 2N3906 (PNP).
MEASUREMENT ACCURACY AND THERMAL CONSIDERATIONS
The temperature measurement accuracy of the TMP422 depends on the remote and/or local temperature sensor
being at the same temperature as the system point being monitored. Clearly, if the temperature sensor is not in
good thermal contact with the part of the system being monitored, then there will be a delay in the response of
the sensor to a temperature change in the system. For remote temperature-sensing applications using a
substrate transistor (or a small, SOT23 transistor) placed close to the device being monitored, this delay is
usually not a concern.
The local temperature sensor inside the TMP422 monitors the ambient air around the device. The thermal time
constant for the TMP422 is approximately two seconds. This constant implies that if the ambient air changes
quickly by 100°C, it would take the TMP422 about 10 seconds (that is, five thermal time constants) to settle to
within 1°C of the final value. In most applications, the TMP422 package is in electrical, and therefore thermal,
contact with the printed circuit board (PCB), as well as subjected to forced airflow. The accuracy of the measured
temperature directly depends on how accurately the PCB and forced airflow temperatures represent the
temperature that the TMP422 is measuring. Additionally, the internal power dissipation of the TMP422 can cause
the temperature to rise above the ambient or PCB temperature. The internal power dissipated as a result of
exciting the remote temperature sensor is negligible because of the small currents used. For a 5.5V supply and
maximum conversion rate of eight conversions per second, the TMP422 dissipate 2.3mW (PDIQ = 5.5V ×
415μA). A θJA of 168°C/W causes the junction temperature to rise approximately +0.39°C above the ambient.
LAYOUT CONSIDERATIONS
Remote temperature sensing on the TMP422 measures very small voltages using very low currents; therefore,
noise at the IC inputs must be minimized. Most applications using the TMP422 will have high digital content, with
several clocks and logic level transitions creating a noisy environment. Layout should adhere to the following
guidelines:
1. Place the TMP422 as close to the remote junction sensor as possible.
2. Route the DXP and DXN traces next to each other and shield them from adjacent signals through the use of
ground guard traces; see Figure 18. If a multilayer PCB is used, bury these traces between ground or VDD
planes to shield them from extrinsic noise sources. 5 mil (0.127mm) PCB traces are recommended.
3. Minimize additional thermocouple junctions caused by copper-to-solder connections. If these junctions are
used, make the same number and approximate locations of copper-to-solder connections in both the DXP
and DXN connections to cancel any thermocouple effects.
Copyright ©2011, Texas Instruments Incorporated Submit Documentation Feedback 23
Product Folder Link(s): TMP422-EP
V+
DXP
DXN
GND
GroundorV+layer
onbottomand/or
top,ifpossible.
1
2
3
4
8
7
6
5
TMP422
0.1mF Capacitor
V+
GND
PCB Via
DX1
DX2
DX3
DX4
TMP422-EP
SBOS577 –SEPTEMBER 2011
www.ti.com
4. Use a 0.1μF local bypass capacitor directly between the V+ and GND of the TMP422; see Figure 19.
Minimize filter capacitance between DXP and DXN to 1000pF or less for optimum measurement
performance. This capacitance includes any cable capacitance between the remote temperature sensor and
the TMP422.
5. If the connection between the remote temperature sensor and the TMP422 is less than 8 in (20.32 cm) long,
use a twisted-wire pair connection. Beyond 8 in, use a twisted, shielded pair with the shield grounded as
close to the TMP422 as possible. Leave the remote sensor connection end of the shield wire open to avoid
ground loops and 60Hz pickup.
6. Thoroughly clean and remove all flux residue in and around the pins of the TMP422 to avoid temperature
offset readings as a result of leakage paths between DXP or DXN and GND, or between DXP or DXN and
V+.
NOTE: Use minimum 5 mil (0.127mm) traces with 5 mil spacing.
Figure 18. Suggested PCB Layer Cross-Section
Figure 19. Suggested Bypass Capacitor Placement and Trace Shielding
24 Submit Documentation Feedback Copyright ©2011, Texas Instruments Incorporated
Product Folder Link(s): TMP422-EP
PACKAGE OPTION ADDENDUM
www.ti.com 6-Oct-2011
Addendum-Page 1
PACKAGING INFORMATION
Orderable Device Status (1) Package Type Package
Drawing Pins Package Qty Eco Plan (2) Lead/
Ball Finish MSL Peak Temp (3) Samples
(Requires Login)
TMP422AMDCNTEP ACTIVE SOT-23 DCN 8 250 Green (RoHS
& no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR
V62/11618-01XE ACTIVE SOT-23 DCN 8 250 Green (RoHS
& no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
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In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
OTHER QUALIFIED VERSIONS OF TMP422-EP :
•Catalog: TMP422
NOTE: Qualified Version Definitions:
PACKAGE OPTION ADDENDUM
www.ti.com 6-Oct-2011
Addendum-Page 2
•Catalog - TI's standard catalog product
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