LM90
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SNIS126A – MAY 2004 – REVISED MARCH 2013
LM90 ±3°C Accurate, Remote Diode and Local Digital Temperature Sensor with Two-Wire
Interface
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FEATURES
DESCRIPTION
•
The LM90 is an 11-bit digital temperature sensor with
a 2-wire System Management Bus (SMBus) serial
interface. The LM90 accurately measures its own
temperature as well as the temperature of an external
device, such as processor thermal diode or diode
connected transistor such as the 2N3904. The
temperature of any ASIC can be accurately
determined using the LM90 as long as a dedicated
diode (semiconductor junction) is available on the
target die. The LM90 remote sensor accuracy of ±3°C
is factory trimmed for the 1.008 typical non-ideality
factor of the mobile Pentium III thermal diode. The
LM90 has an Offset register to allow measuring other
diodes without requiring continuous software
management.
1
•
•
•
•
•
•
•
•
Accurately Senses Die Temperature of Remote
ICs or Diode Junctions
Offset Register Allows Sensing a Variety of
Thermal Diodes Accurately
On-board Local Temperature Sensing
10 Bit Plus Sign Remote Diode Temperature
Data Format, 0.125°C Resolution
Diode Fault Detection Circuitry
T_CRIT_A Output Useful for System Shutdown
(Open Diode does not Activate T_CRIT_A)
ALERT Output Supports SMBus 2.0 Protocol
SMBus 2.0 Compatible Interface, Supports
TIMEOUT
8-pin VSSOP Package
APPLICATIONS
•
•
•
System Thermal Management
(e.g. Laptop, Desktop, Workstations, Server)
Electronic Test Equipment
Office Electronics
Activation of the ALERT output occurs when any
temperature goes outside a preprogrammed window
set by the HIGH and LOW temperature limit registers
or exceeds the T_CRIT temperature limit. Activation
of the T_CRIT_A occurs when any temperature
exceeds the T_CRIT programmed limit. The LM90 is
pin and register compatible with the LM86, Analog
Devices ADM1032 and Maxim MAX6657/8.
KEY SPECIFICATIONS
•
•
•
•
Supply Voltage 3.0 to 3.6 V
Supply Current 0.8 mA (Typ)
Local Temp Accuracy (Includes Quantization
Error)
– TA=25°C to 125°C, ±4.0 °C (Max)
Remote Diode Temp Accuracy (Includes
Quantization Error)
– TA=30°C to 50°C, TD=60°C to 100°C, ±3.0 °C
(Max)
– TA=0°C to 85°C, TD=25°C to 125°C, ±4.0 °C
(Max)
1
Please 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.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
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LM90
SNIS126A – MAY 2004 – REVISED MARCH 2013
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LM90 Simplified Block Diagram
Connection Diagram
Figure 1. 8-Lead VSSOP - TOP VIEW
See DGK Package
PIN DESCRIPTIONS
2
Label
Pin #
VDD
1
Function
Typical Connection
Positive Supply Voltage Input
DC Voltage from 3.0 V to 3.6 V
Diode Current Source
To Diode Anode. Connected to remote discrete diode conected
transistor junction or to the diode connected transistor junction
on a remote IC whose die temperature is being sensed.
D+
2
D−
3
Diode Return Current Sink
To Diode Cathode.
T_CRIT_A
4
T_CRIT Alarm Output, OpenDrain, Active-Low
Pull-Up Resistor, Controller Interrupt or Power Supply
Shutdown Control
GND
5
Power Supply Ground
Ground
ALERT
6
Interrupt Output, Open-Drain,
Active-Low
Pull-Up Resistor, Controller Interrupt or Alert Line
SMBData
7
SMBus Bi-Directional Data Line, From and to Controller, Pull-Up Resistor
Open-Drain Output
SMBCLK
8
SMBus Input
From Controller, Pull-Up Resistor
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Typical Application
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These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
Absolute Maximum Ratings
(1)
−0.3 V to 6.0 V
Supply Voltage
−0.5 V to 6.0 V
Voltage at SMBData, SMBCLK, ALERT, T_CRIT_A
−0.3 V to (VDD + 0.3
V)
Voltage at Other Pins
D− Input Current
±1 mA
Input Current at All Other Pins
Package Input Current
(2)
±5 mA
(2)
30 mA
SMBData, ALERT, T_CRIT_A Output Sink Current
10 mA
−65°C to +150°C
Storage Temperature
Soldering Information, Lead Temperature
VSSOP Package
(3)
Vapor Phase (60 seconds)
215°C
Infrared (15 seconds)
ESD Susceptibility
(4)
220°C
Human Body Model
2000 V
Machine Model
(1)
(2)
(3)
(4)
200 V
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. DC and AC electrical specifications do not
apply when operating the device beyond its rated operating conditions.
When the input voltage (VI) at any pin exceeds the power supplies (VI < GND or VI > VDD), the current at that pin should be limited to
5 mA. Parasitic components and or ESD protection circuitry are shown in the figure below for the LM90's pins. The nominal breakdown
voltage of D3 is 6.5 V. Care should be taken not to forward bias the parasitic diode, D1, present on pins: D+, D−. Doing so by more than
50 mV may corrupt a temperature measurements.
See http://www.ti.com/packaging/ for other recommendations and methods of soldering surface mount devices.
Human body model, 100pF discharged through a 1.5kΩ resistor. Machine model, 200pF discharged directly into each pin.
Operating Ratings
Operating Temperature Range
0°C to +125°C
TMIN ≤ TA ≤ TMAX
Electrical Characteristics Temperature Range
0°C ≤ TA ≤ +85°C
LM90
Supply Voltage Range (VDD)
+3.0 V to +3.6 V
Temperature-to-Digital Converter Characteristics
Unless otherwise noted, these specifications apply for VDD= +3.0Vdc to 3.6Vdc. Boldface limits apply for TA = TJ = TMIN ≤
TA ≤ TMAX; all other limits TA= TJ= +25°C, unless otherwise noted.
Parameter
Conditions
(3)
Typical (1)
Limits (2)
Units
(Limit)
±1.5
±4
°C (max)
Temperature Error Using Local Diode
TA = +25°C to +125°C
Temperature Error Using Remote Diode of mobile
Pentium III with typical non-ideality of 1.008. (TD is
the Remote Diode Junction Temperature)
TA = +30°C to
+50°C
TD = +25°C to
+100°C
±3
TA = +0°C to +85°C
TD = +25°C to
+125°C
±4
Remote Diode Measurement Resolution
11
Local Diode Measurement Resolution
(1)
(2)
(3)
4
°C (max)
°C (max)
Bits
0.125
°C
8
Bits
1
°C
Typicals are at TA = 25°C and represent most likely parametric norm.
Limits are ensured to AOQL (Average Outgoing Quality Level).
Local temperature accuracy does not include the effects of self-heating. The rise in temperature due to self-heating is the product of the
internal power dissipation of the LM90 and the thermal resistance. See () for the thermal resistance to be used in the self-heating
calculation.
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Temperature-to-Digital Converter Characteristics (continued)
Unless otherwise noted, these specifications apply for VDD= +3.0Vdc to 3.6Vdc. Boldface limits apply for TA = TJ = TMIN ≤
TA ≤ TMAX; all other limits TA= TJ= +25°C, unless otherwise noted.
Typical (1)
Limits (2)
Units
(Limit)
31.25
34.4
ms (max)
SMBus Inactive, 16Hz conversion
rate
0.8
1.7
mA (max)
Shutdown
315
Parameter
Conversion Time of All Temperatures at the Fastest
Setting
Quiescent Current
(5)
Conditions
See
(4)
D− Source Voltage
µA
0.7
Diode Source Current
(D+ − D−)=+ 0.65V; high level
160
Low level
13
V
315
µA (max)
110
µA (min)
20
µA (max)
7
µA (min)
ALERT and T_CRIT_A Output Saturation Voltage
IOUT = 6.0 mA
0.4
V (max)
Power-On Reset Threshold
Measure on VDD input, falling edge
2.4
1.8
V (max)
V (min)
Local and Remote HIGH Default Temperature
settings
See
(6)
+70
°C
Local and Remote LOW Default Temperature
settings
See
(6)
0
°C
Local and Remote T_CRIT Default Temperature
Setting
See
(6)
+85
°C
(4)
This specification is provided only to indicate how often temperature data is updated. The LM90 can be read at any time without regard
to conversion state (and will yield last conversion result).
Quiescent current will not increase substantially with an SMBus.
Default values set at power up.
(5)
(6)
Logic Electrical Characteristics
DIGITAL DC CHARACTERISTICS
Unless otherwise noted, these specifications apply for VDD= +3.0 to 3.6 Vdc. Boldface limits apply for TA = TJ = TMIN to
TMAX; all other limits TA= TJ= +25°C, unless otherwise noted.
Symbol
Parameter
Conditions
Typical (1)
Limits (2)
Units
(Limit)
SMBData, SMBCLK INPUTS
VIN(1)
Logical “1” Input Voltage
2.1
V (min)
VIN(0)
Logical “0”Input Voltage
0.8
V (max)
VIN(HYST)
SMBData and SMBCLK Digital Input
Hysteresis
400
mV
IIN(1)
Logical “1” Input Current
VIN = VDD
0.005
±10
µA (max)
IIN(0)
Logical “0” Input Current
VIN = 0 V
−0.005
±10
µA (max)
CIN
Input Capacitance
5
pF
ALL DIGITAL OUTPUTS
IOH
High Level Output Current
VOH = VDD
10
µA (max)
VOL
SMBus Low Level Output Voltage
IOL = 4mA
IOL = 6mA
0.4
0.6
V (max)
(1)
(2)
Typicals are at TA = 25°C and represent most likely parametric norm.
Limits are ensured to AOQL (Average Outgoing Quality Level).
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SMBus DIGITAL SWITCHING CHARACTERISTICS
Unless otherwise noted, these specifications apply for VDD= +3.0 Vdc to +3.6 Vdc, CL (load capacitance) on output lines =
80 pF. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = +25°C, unless otherwise noted.
The switching characteristics of the LM90 fully meet or exceed the published specifications of the SMBus version 2.0. The
following parameters are the timing relationships between SMBCLK and SMBData signals related to the LM90. They adhere
to but are not necessarily the SMBus bus specifications.
Symbol
Parameter
Conditions
Typical (1)
Limits (2)
Units
(Limit)
100
10
kHz (max)
kHz (min)
4.7
25
µs (min)
ms (max)
fSMB
SMBus Clock Frequency
tLOW
SMBus Clock Low Time
from VIN(0)max to VIN(0)max
tHIGH
SMBus Clock High Time
from VIN(1)min to VIN(1)min
tR,SMB
SMBus Rise Time
See
(3)
1
µs (max)
tF,SMB
SMBus Fall Time
See
(4)
0.3
µs (max)
tOF
Output Fall Time
tTIMEOUT
µs (min)
250
ns (max)
SMBData and SMBCLK Time Low for Reset of
Serial Interface (5)
25
35
ms (min)
ms (max)
tSU;DAT
Data In Setup Time to SMBCLK High
250
ns (min)
tHD;DAT
Data Out Stable after SMBCLK Low
300
900
ns (min)
ns (max)
tHD;STA
Start Condition SMBData Low to SMBCLK Low
(Start condition hold before the first clock falling
edge)
100
ns (min)
tSU;STO
Stop Condition SMBCLK High to SMBData Low
(Stop Condition Setup)
100
ns (min)
tSU;STA
SMBus Repeated Start-Condition Setup Time,
SMBCLK High to SMBData Low
0.6
µs (min)
tBUF
SMBus Free Time Between Stop and Start
Conditions
1.3
µs (min)
(1)
(2)
(3)
(4)
(5)
CL = 400pF,
IO = 3mA (4)
4.0
Typicals are at TA = 25°C and represent most likely parametric norm.
Limits are ensured to AOQL (Average Outgoing Quality Level).
The output rise time is measured from (VIN(0)max + 0.15V) to (VIN(1)min − 0.15V).
The output fall time is measured from (VIN(1)min - 0.15V) to (VIN(1)min + 0.15V).
Holding the SMBData and/or SMBCLK lines Low for a time interval greater than tTIMEOUT will reset the LM90's SMBus state machine,
therefore setting SMBData and SMBCLK pins to a high impedance state.
SMBus Communication
6
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Pin
Name
VDD
SNIS126A – MAY 2004 – REVISED MARCH 2013
PIN #
D1
D2
D3
D4
D5
D6
D7
R1
SNP
1
x
x
(1)
x
x
x
D+
2
D−
3
T_CRIT_
A
4
x
x
x
ALERT
6
x
x
x
SMBData
7
x
x
x
SMBCLK
8
(1)
ESD
CLAMP
x
x
x
x
x
x
x
x
x
Note: An “x” indicates that the diode exists.
Figure 2. ESD Protection Input Structure
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FUNCTIONAL DESCRIPTION
The LM90 temperature sensor incorporates a delta VBE based temperature sensor using a Local or Remote and
a 10-bit plus sign ADC (Delta-Sigma Analog-to-Digital Converter). The LM90 is compatible with the serial SMBus
version 2.0 two-wire interface. Digital comparators compare the measured Local Temperature (LT) to the Local
High (LHS), Local Low (LLS) and Local T_CRIT (LCS) user-programmable temperature limit registers. The
measured Remote Temperature (RT) is digitally compared to the Remote High (RHS), Remote Low (RLS) and
Remote T_CRIT (RCS) user-programmable temperature limit registers. Activation of the ALERT output indicates
that a comparison is greater than the limit preset in a T_CRIT or HIGH limit register or less than the limit preset
in a LOW limit register. The T_CRIT_A output responds as a true comparator with built in hysteresis. The
hysteresis is set by the value placed in the Hysteresis register (TH). Activation of T_CRIT_A occurs when the
temperature is above the T_CRIT setpoint. T_CRIT_A remains activated until the temperature goes below the
setpoint calculated by T_CRIT − TH. The hysteresis register impacts both the remote temperature and local
temperature readings.
The LM90 may be placed in a low power consumption (Shutdown) mode by setting the RUN/STOP bit found in
the Configuration register. In the Shutdown mode, the LM90's SMBus interface remains while all circuitry not
required is turned off.
The Local temperature reading and setpoint data registers are 8-bits wide. The format of the 11-bit remote
temperature data is a 16-bit left justified word. Two 8-bit registers, high and low bytes, are provided for each
setpoint as well as the temperature reading. Two offset registers (RTOLB and RTOHB) can be used to
compensate for non_ideality error, discussed further in DIODE NON-IDEALITY. The remote temperature reading
reported is adjusted by subtracting from or adding to the actual temperature reading the value placed in the
offset registers.
CONVERSION SEQUENCE
The LM90 takes approximately 31.25 ms to convert the Local Temperature (LT), Remote Temperature (RT), and
to update all of its registers. Only during the conversion process the busy bit (D7) in the Status register (02h) is
high. These conversions are addressed in a round robin sequence. The conversion rate may be modified by the
Conversion Rate Register (04h). When the conversion rate is modified a delay is inserted between conversions,
the actual conversion time remains at 31.25ms. Different conversion rates will cause the LM90 to draw different
amounts of supply current as shown in Figure 3.
Figure 3. Conversion Rate Effect on Power Supply Current
8
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THE ALERT OUTPUT
The LM90's ALERT pin is an active-low open-drain output that is triggered by a temperature conversion that is
outside the limits defined by the temperature setpoint registers. Reset of the ALERT output is dependent upon
the selected method of use. The LM90's ALERT pin is versatile and will accommodate three different methods of
use to best serve the system designer: as a temperature comparator, as a temperature based interrupt flag, and
as part of an SMBus ALERT system. The three methods of use are further described below. The ALERT and
interrupt methods are different only in how the user interacts with the LM90.
Each temperature reading (LT and RT) is associated with a T_CRIT setpoint register (LCS, RCS), a HIGH
setpoint register (LHS and RHS) and a LOW setpoint register (LLS and RLS). At the end of every temperature
reading, a digital comparison determines whether that reading is above its HIGH or T_CRIT setpoint or below its
LOW setpoint. If so, the corresponding bit in the STATUS REGISTER is set. If the ALERT mask bit is not high,
any bit set in the STATUS REGISTER, with the exception of Busy (D7) and OPEN (D2), will cause the ALERT
output to be pulled low. Any temperature conversion that is out of the limits defined by the temperature setpoint
registers will trigger an ALERT. Additionally, the ALERT mask bit in the Configuration register must be cleared to
trigger an ALERT in all modes.
ALERT Output as a Temperature Comparator
When the LM90 is implemented in a system in which it is not serviced by an interrupt routine, the ALERT output
could be used as a temperature comparator. Under this method of use, once the condition that triggered the
ALERT to go low is no longer present, the ALERT is de-asserted (Figure 4). For example, if the ALERT output
was activated by the comparison of LT > LHS, when this condition is no longer true the ALERT will return HIGH.
This mode allows operation without software intervention, once all registers are configured during set-up. In order
for the ALERT to be used as a temperature comparator, bit D0 (the ALERT configure bit) in the FILTER and
ALERT CONFIGURE REGISTER (xBF) must be set high. This is not the power on default default state.
Figure 4. ALERT Comparator Temperature Response Diagram
ALERT Output as an Interrupt
The LM90's ALERT output can be implemented as a simple interrupt signal when it is used to trigger an interrupt
service routine. In such systems it is undesirable for the interrupt flag to repeatedly trigger during or before the
interrupt service routine has been completed. Under this method of operation, during a read of the STATUS
REGISTER the LM90 will set the ALERT mask bit (D7 of the Configuration register) if any bit in the STATUS
REGISTER is set, with the exception of Busy (D7) and OPEN (D2). This prevents further ALERT triggering until
the master has reset the ALERT mask bit, at the end of the interrupt service routine. The STATUS REGISTER
bits are cleared only upon a read command from the master (see Figure 5) and will be re-asserted at the end of
the next conversion if the triggering condition(s) persist(s). In order for the ALERT to be used as a dedicated
interrupt signal, bit D0 (the ALERT configure bit) in the FILTER and ALERT CONFIGURE REGISTER (xBF) must
be set low. This is the power on default state.
The following sequence describes the response of a system that uses the ALERT output pin as a interrupt flag:
1. Master Senses ALERT low
2. Master reads the LM90 STATUS REGISTER to determine what caused the ALERT
3. LM90 clears STATUS REGISTER, resets the ALERT HIGH and sets the ALERT mask bit (D7 in the
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Configuration register).
4. Master attends to conditions that caused the ALERT to be triggered. The fan is started, setpoint limits are
adjusted, etc.
5. Master resets the ALERT mask (D7 in the Configuration register).
Figure 5. ALERT Output as an Interrupt Temperature Response Diagram
ALERT Output as an SMBus ALERT
When the ALERT output is connected to one or more ALERT outputs of other SMBus compatible devices and to
a master, an SMBus alert line is created. Under this implementation, the LM90's ALERT should be operated
using the ARA (Alert Response Address) protocol. The SMBus 2.0 ARA protocol, defined in the SMBus
specification 2.0, is a procedure designed to assist the master in resolving which part generated an interrupt and
service that interrupt while impeding system operation as little as possible.
The SMBus alert line is connected to the open-drain ports of all devices on the bus thereby AND'ing them
together. The ARA is a method by which with one command the SMBus master may identify which part is pulling
the SMBus alert line LOW and prevent it from pulling it LOW again for the same triggering condition. When an
ARA command is received by all devices on the bus, the devices pulling the SMBus alert line LOW, first, send
their address to the master and second, release the SMBus alert line after recognizing a successful transmission
of their address.
The SMBus 1.1 and 2.0 specification state that in response to an ARA (Alert Response Address) “after
acknowledging the slave address the device must disengage its SMBALERT pulldown”. Furthermore, “if the host
still sees SMBALERT low when the message transfer is complete, it knows to read the ARA again”. This SMBus
“disengaging of SMBALERT” requirement prevents locking up the SMBus alert line. Competitive parts may
address this “disengaging of SMBALERT” requirement differently than the LM90 or not at all. SMBus systems
that implement the ARA protocol as suggested for the LM90 will be fully compatible with all competitive parts.
The LM90 fulfills “disengaging of SMBALERT” by setting the ALERT mask bit (bit D7 in the Configuration
register, at address 09h) after successfully sending out its address in response to an ARA and releasing the
ALERT output pin. Once the ALERT mask bit is activated, the ALERT output pin will be disabled until enabled by
software. In order to enable the ALERT the master must read the STATUS REGISTER, at address 02h, during
the interrupt service routine and then reset the ALERT mask bit in the Configuration register to 0 at the end of
the interrupt service routine.
The following sequence describes the ARA response protocol.
1. Master Senses SMBus alert line low
2. Master sends a START followed by the Alert Response Address (ARA) with a Read Command.
3. Alerting Device(s) send ACK.
4. Alerting Device(s) send their Address. While transmitting their address, alerting devices sense whether their
address has been transmitted correctly. (The LM90 will reset its ALERT output and set the ALERT mask bit
once its complete address has been transmitted successfully.)
5. Master/slave NoACK
6. Master sends STOP
7. Master attends to conditions that caused the ALERT to be triggered. The STATUS REGISTER is read and
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fan started, setpoint limits adjusted, etc.
8. Master resets the ALERT mask (D7 in the Configuration register).
The ARA, 000 1100, is a general call address. No device should ever be assigned this address.
Bit D0 (the ALERT configure bit) in the FILTER and ALERT CONFIGURE REGISTER (xBF) must be set low in
order for the LM90 to respond to the ARA command.
The ALERT output can be disabled by setting the ALERT mask bit, D7, of the Configuration register. The power
on default is to have the ALERT mask bit and the ALERT configure bit low.
Figure 6. ALERT Output as an SMBus ALERT Temperature Response Diagram
T_CRIT_A OUTPUT and T_CRIT LIMIT
T_CRIT_A is activated when any temperature reading is greater than the limit preset in the critical temperature
setpoint register (T_CRIT), as shown in Figure 7. The Status Register can be read to determine which event
caused the alarm. A bit in the Status Register is set high to indicate which temperature reading exceeded the
T_CRIT setpoint temperature and caused the alarm, see STATUS REGISTER (SR).
Local and remote temperature diodes are sampled in sequence by the A/D converter. The T_CRIT_A output and
the Status Register flags are updated after every Local and Remote temperature conversion. T_CRT_A follows
the state of the comparison, it is reset when the temperature falls below the setpoint RCS-TH. The Status
Register flags are reset only after the Status Register is read and if a temperature conversion(s) is/are below the
T_CRIT setpoint, as shown in Figure 7
Figure 7. T_CRIT_A Temperature Response Diagram
POWER ON RESET DEFAULT STATES
LM90 always powers up to these known default states. The LM90 remains in these states until after the first
conversion.
1. Command Register set to 00h
2. Local Temperature set to 0°C
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3. Remote Diode Temperature set to 0°C until the end of the first conversion.
4. Status Register set to 00h.
5. Configuration register set to 00h; ALERT enabled, Remote T_CRIT alarm enabled and Local T_CRIT alarm
enabled
6. 85°C Local and Remote T_CRIT temperature setpoints
7. 70°C Local and Remote HIGH temperature setpoints
8. 0°C Local and Remote LOW temperature setpoints
9. Filter and Alert Configure Register set to 00h; filter disabled, ALERT output set as an SMBus ALERT
10. Conversion Rate Register set to 8h; conversion rate set to 16 conv./sec.
SMBus INTERFACE
The LM90 operates as a slave on the SMBus, so the SMBCLK line is an input and the SMBData line is bidirectional. The LM90 never drives the SMBCLK line and it does not support clock stretching. According to
SMBus specifications, the LM90 has a 7-bit slave address. All bits A6 through A0 are internally programmed and
can not be changed by software or hardware.
The complete slave address is:
A6
A5
A4
A3
A2
A1
A0
1
0
0
1
1
0
0
TEMPERATURE DATA FORMAT
Temperature data can only be read from the Local and Remote Temperature registers; the setpoint registers
(T_CRIT, LOW, HIGH) are read/write.
Remote temperature data is represented by an 11-bit, two's complement word with an LSB (Least Significant Bit)
equal to 0.125°C. The data format is a left justified 16-bit word available in two 8-bit registers:
Temperature
Digital Output
Binary
Hex
+125°C
0111 1101 0000 0000
7D00h
+25°C
0001 1001 0000 0000
1900h
+1°C
0000 0001 0000 0000
0100h
+0.125°C
0000 0000 0010 0000
0020h
0°C
0000 0000 0000 0000
0000h
−0.125°C
1111 1111 1110 0000
FFE0h
−1°C
1111 1111 0000 0000
FF00h
−25°C
1110 0111 0000 0000
E700h
−55°C
1100 1001 0000 0000
C900h
Local Temperature data is represented by an 8-bit, two's complement byte with an LSB (Least Significant Bit)
equal to 1°C:
Temperature
12
Digital Output
Binary
Hex
+125°C
0111 1101
7Dh
+25°C
0001 1001
19h
+1°C
0000 0001
01h
0°C
0000 0000
00h
−1°C
1111 1111
FFh
−25°C
1110 0111
E7h
−55°C
1100 1001
C9h
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OPEN-DRAIN OUTPUTS
The SMBData, ALERT and T_CRIT_A outputs are open-drain outputs and do not have internal pull-ups. A “high”
level will not be observed on these pins until pull-up current is provided by some external source, typically a pullup resistor. Choice of resistor value depends on many system factors but, in general, the pull-up resistor should
be as large as possible. This will minimize any internal temperature reading errors due to internal heating of the
LM90. The maximum resistance of the pull-up to provide a 2.1V high level, based on LM90 specification for High
Level Output Current with the supply voltage at 3.0V, is 82kΩ(5%) or 88.7kΩ(1%).
DIODE FAULT DETECTION
The LM90 is equipped with operational circuitry designed to detect fault conditions concerning the remote diode.
In the event that the D+ pin is detected as shorted to VDD or floating, the Remote Temperature High Byte (RTHB)
register is loaded with +127°C, the Remote Temperature Low Byte (RTLB) register is loaded with 0, and the
OPEN bit (D2) in the status register is set. As a result, if the Remote T_CRIT setpoint register (RCS) is set to a
value less than +127°C the ALERT output pin will be pulled low, if the Alert Mask is disabled. If the Remote
HIGH Setpoint High Byte Register (RHSHB) is set to a value less than +127°C then ALERT will be pulled low, if
the Alert Mask is disabled. The OPEN bit itself will not activate the ALERT or T_CRIT_A outputs. If the remote
temperature reading is greater than its T_CRIT level when the OPEN bit is set the T_CRIT_A will remain
inactive.
In the event that the D+ pin is shorted to ground or D−, the Remote Temperature High Byte (RTHB) register is
loaded with −128°C (1000 0000) and the OPEN bit (D2) in the status register will not be set. Since operating the
LM90 at −128°C is beyond it's operational limits, this temperature reading represents this shorted fault condition.
If the value in the Remote Low Setpoint High Byte Register (RLSHB) is more than −128°C and the Alert Mask is
disabled, ALERT will be pulled low.
Remote diode temperature sensors that have been previously released and are competitive with the LM90 output
a code of 0°C if the external diode is short-circuited. This change is an improvement that allows a reading of 0°C
to be truly interpreted as a genuine 0°C reading and not a fault condition.
COMMUNICATING with the LM90
The data registers in the LM90 are selected by the Command Register. At power-up the Command Register is
set to “00”, the location for the Read Local Temperature Register. The Command Register latches the last
location it was set to. Each data register in the LM90 falls into one of four types of user accessibility:
1. Read only
2. Write only
3. Read/Write same address
4. Read/Write different address
A Write to the LM90 will always include the address byte and the command byte. A write to any register requires
one data byte.
Reading the LM90 can take place either of two ways:
1. If the location latched in the Command Register is correct (most of the time it is expected that the Command
Register will point to one of the Read Temperature Registers because that will be the data most frequently
read from the LM90), then the read can simply consist of an address byte, followed by retrieving the data
byte.
2. If the Command Register needs to be set, then an address byte, command byte, repeat start, and another
address byte will accomplish a read.
The data byte has the most significant bit first. At the end of a read, the LM90 can accept either acknowledge or
No Acknowledge from the Master (No Acknowledge is typically used as a signal for the slave that the Master has
read its last byte). It takes the LM90 31.25ms to measure the temperature of the remote diode and internal diode.
When retrieving all 10 bits from a previous remote diode temperature measurement, the master must insure that
all 10 bits are from the same temperature conversion. This may be achieved by using one-shot mode or by
setting the conversion rate and monitoring the busy bit such that no conversion occurs in between reading the
MSB and LSB of the last temperature conversion.
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SMBus Timing Diagrams
Figure 8. (a) Serial Bus Write to the internal Command Register followed by a the Data Byte
Figure 9. (b) Serial Bus Write to the Internal Command Register
Figure 10. (c) Serial Bus Read from a Register with the Internal Command Register preset to desired
value
SERIAL INTERFACE RESET
In the event that the SMBus Master is RESET while the LM90 is transmitting on the SMBData line, the LM90
must be returned to a known state in the communication protocol. This may be done in one of two ways:
1. When SMBData is LOW, the LM90 SMBus state machine resets to the SMBus idle state if either SMBData
or SMBCLK are held low for more than 35ms (tTIMEOUT). Note that according to SMBus specification 2.0 all
devices are to timeout when either the SMBCLK or SMBData lines are held low for 25-35ms. Therefore, to
insure a timeout of all devices on the bus the SMBCLK or SMBData lines must be held low for at least 35ms.
2. When SMBData is HIGH, have the master initiate an SMBus start. The LM90 will respond properly to an
SMBus start condition at any point during the communication. After the start the LM90 will expect an SMBus
Address address byte.
14
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DIGITAL FILTER
In order to suppress erroneous remote temperature readings due to noise, the LM90 incorporates a userconfigured digital filter. The filter is accessed in the FILTER and ALERT CONFIGURE REGISTER at BFh. The
filter can be set according to the following table.
D2
D1
Filter
0
0
No Filter
0
1
Level 1
1
0
Level 1
1
1
Level 2
Level 2 sets maximum filtering.
Figure 12 depict the filter output to in response to a step input and an impulse input. Figure 13 depicts the digital
filter in use in a Pentium 4 processor system. Note that the two curves, with filter and without, have been
purposely offset so that both responses can be clearly seen. Inserting the filter does not induce an offset as
shown.
Filter Output Response to a Step Input
Figure 11. a) Step Response
Figure 12. b) Impulse Response
The filter on and off curves were purposely offset to better show noise performance.
Figure 13. Digital Filter Response in a Pentium 4 processor System
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Fault Queue
In order to suppress erroneous ALERT or T_CRIT triggering the LM90 incorporates a Fault Queue. The Fault
Queue acts to insure a remote temperature measurement is genuinely beyond a HIGH, LOW or T_CRIT setpoint
by not triggering until three consecutive out of limit measurements have been made, see Figure 14. The fault
queue defaults off upon power-up and may be activated by setting bit D0 in the Configuration register (09h) to
“1”.
Figure 14. Fault Queue Temperature Response Diagram
One-Shot Register
The One-Shot register is used to initiate a single conversion and comparison cycle when the device is in standby
mode, after which the device returns to standby. This is not a data register and it is the write operation that
causes the one-shot conversion. The data written to this address is irrelevant and is not stored. A zero will
always be read from this register.
LM90 REGISTERS
COMMAND REGISTER
Selects which registers will be read from or written to. Data for this register should be transmitted during the
Command Byte of the SMBus write communication.
P7
P6
P5
P4
P3
P2
P1
P0
Command Select
P0-P7: Command Select
Command Select Address
16
Power On Default State
Register
Name
Register Function
Read Address
hex
Write Address
hex
binary
decimal
00h
NA
0000 0000
0
LT
01h
NA
0000 0000
0
RTHB
02h
NA
0000 0000
0
SR
03h
09h
0000 0000
0
C
04h
0Ah
0000 1000
8 (16 conv./sec)
CR
Conversion Rate
05h
0Bh
0100 0110
70
LHS
Local HIGH Setpoint
06h
0Ch
0000 0000
0
LLS
Local LOW Setpoint
07h
0Dh
0100 0110
70
RHSHB
Remote HIGH Setpoint High Byte
08h
0Eh
0000 0000
0
RLSHB
Remote LOW Setpoint High Byte
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Local Temperature
Remote Temperature High Byte
Status Register
Configuration
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Command Select Address
Power On Default State
binary
Register
Name
decimal
Register Function
Read Address
hex
Write Address
hex
NA
0Fh
10h
NA
0000 0000
0
RTLB
11h
11h
0000 0000
0
RTOHB
Remote Temperature Offset High
Byte
12h
12h
0000 0000
0
RTOLB
Remote Temperature Offset Low
Byte
13h
13h
0000 0000
0
RHSLB
Remote HIGH Setpoint Low Byte
14h
14h
0000 0000
0
RLSLB
Remote LOW Setpoint Low Byte
19h
19h
0101 0101
85
RCS
Remote T_CRIT Setpoint
20h
20h
0101 0101
85
LCS
Local T_CRIT Setpoint
21h
21h
0000 1010
10
TH
B0h-BEh
B0h-BEh
BFh
BFh
0000 0000
0
RDTF
Remote Diode Temperature Filter
FEh
NA
0000 0001
1
RMID
Read Manufacturer's ID
FFh
NA
0010 0001
33
RDR
Read Stepping or Die Revision
Code
One Shot
Writing to this register will initiate
a one shot conversion
Remote Temperature Low Byte
T_CRIT Hysteresis
Manufacturers Test Registers
LOCAL and REMOTE TEMPERATURE REGISTERS (LT, RTHB, RTLB)
Table 1. LOCAL and REMOTE TEMPERATURE REGISTERS (LT, RTHB) (Read Only Address 00h, 01h):
BIT
D7
D6
D5
D4
D3
D2
D1
D0
Value
SIGN
64
32
16
8
4
2
1
For LT and RTHB D7–D0: Temperature Data. LSB = 1°C. Two's complement format.
Table 2. LOCAL and REMOTE TEMPERATURE REGISTERS (RTLB) (Read Only Address 10h):
BIT
D7
D6
D5
D4
D3
D2
D1
D0
Value
0.5
0.25
0.125
0
0
0
0
0
For RTLB D7–D5: Temperature Data. LSB = 0.125°C. Two's complement format.
The maximum value available from the Local Temperature register is 127; the minimum value available from the
Local Temperature register is -128. The maximum value available from the Remote Temperature register is
127.875; the minimum value available from the Remote Temperature registers is −128.875.
STATUS REGISTER (SR)
Table 3. STATUS REGISTER (SR) (Read Only Address 02h):
D7
D6
D5
D4
D3
D2
D1
D0
Busy
LHIGH
LLOW
RHIGH
RLOW
OPEN
RCRIT
LCRIT
Power up default is with all bits “0” (zero).
D0: LCRIT: When set to “1” indicates a Local Critical Temperature alarm.
D1: RCRIT: When set to “1” indicates a Remote Diode Critical Temperature alarm.
D2: OPEN: When set to “1” indicates a Remote Diode disconnect.
D3: RLOW: When set to “1” indicates a Remote Diode LOW Temperature alarm
D4: RHIGH: When set to “1” indicates a Remote Diode HIGH Temperature alarm.
D5: LLOW: When set to “1” indicates a Local LOW Temperature alarm.
D6: LHIGH: When set to “1” indicates a Local HIGH Temperature alarm.
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D7: Busy: When set to “1” ADC is busy converting.
CONFIGURATION REGISTER
Table 4. CONFIGURATION REGISTER (Read Address 03h /Write Address 09h):
D7
D6
D5
D4
D3
D2
D1
D0
ALERT mask
RUN/STOP
0
Remote
T_CRIT_A
mask
0
Local
T_CRIT_A
mask
0
Fault Queue
Power up default is with all bits “0” (zero)
D7: ALERT mask: When set to “1” ALERT interrupts are masked.
D6: RUN/STOP: When set to “1” SHUTDOWN is enabled.
D5: is not defined and defaults to “0”.
D4: Remote T_CRIT mask: When set to “1” a diode temperature reading that exceeds T_CRIT setpoint will not
activate the T_CRIT_A pin.
D3: is not defined and defaults to “0”.
D2: Local T_CRIT mask: When set to “1” a Local temperature reading that exceeds T_CRIT setpoint will not
activate the T_CRIT_A pin.
D1: is not defined and defaults to “0”.
D0: Fault Queue: when set to “1” three consecutive remote temperature measurements outside the HIGH, LOW,
or T_CRIT setpoints will trigger an “Outside Limit” condition resulting in setting of status bits and associated
output pins..
CONVERSION RATE REGISTER
Table 5. CONVERSION RATE REGISTER (Read Address 04h /Write Address 0Ah)
Value
Conversion Rate
00
62.5 mHz
01
125 mHz
02
250 mHz
03
500 mHz
04
1 Hz
05
2 Hz
06
4 Hz
07
8 Hz
08
16 Hz
09
32 Hz
10-255
Undefined
LOCAL and REMOTE HIGH SETPOINT REGISTERS (LHS, RHSHB, and RHSLB)
Table 6. LOCAL and REMOTE HIGH SETPOINT REGISTERS (LHS, RHSHB) (Read Address 05h, 07h /Write
Address 0Bh, 0Dh):
18
BIT
D7
D6
D5
D4
D3
D2
D1
D0
Value
SIGN
64
32
16
8
4
2
1
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For LHS and RHSHB: HIGH setpoint temperature data. Power up default is LHIGH = RHIGH = 70°C. 1LSB =
1°C. Two's complement format.
Table 7. LOCAL and REMOTE HIGH SETPOINT REGISTERS (RHSLB) (Read/Write Address 13h):
BIT
D7
D6
D5
D4
D3
D2
D1
D0
Value
0.5
0.25
0.125
0
0
0
0
0
For RHSLB: Remote HIGH Setpoint Low Byte temperature data. Power up default is 0°C. 1LSB = 0.125°C.
Two's complement format.
LOCAL and REMOTE LOW SETPOINT REGISTERS (LLS, RLSHB, and RLSLB)
Table 8. LOCAL and REMOTE LOW SETPOINT REGISTERS (LLS, RLSHB) (Read Address 06h, 08h, /Write
Address 0Ch, 0Eh):
BIT
D7
D6
D5
D4
D3
D2
D1
D0
Value
SIGN
64
32
16
8
4
2
1
For LLS and RLSHB: HIGH setpoint temperature data. Power up default is LHIGH = RHIGH = 0°C. 1LSB = 1°C.
Two's complement format.
Table 9. LOCAL and REMOTE LOW SETPOINT REGISTERS (RLSLB) (Read/Write Address 14h):
BIT
D7
D6
D5
D4
D3
D2
D1
D0
Value
0.5
0.25
0.125
0
0
0
0
0
For RLSLB: Remote HIGH Setpoint Low Byte temperature data. Power up default is 0°C. 1LSB = 0.125°C. Two's
complement format.
REMOTE TEMPERATURE OFFSET REGISTERS (RTOHB and RTOLB)
Table 10. REMOTE TEMPERATURE OFFSET REGISTERS (RTOHB) (Read/Write Address 11h):
BIT
D7
D6
D5
D4
D3
D2
D1
D0
Value
SIGN
64
32
16
8
4
2
1
For RTOHB: Remote Temperature Offset High Byte. Power up default is LHIGH = RHIGH = 0°C. 1LSB = 1°C.
Two's complement format.
Table 11. REMOTE TEMPERATURE OFFSET REGISTERS (RTOLB) (Read/Write Address 12h):
BIT
D7
D6
D5
D4
D3
D2
D1
D0
Value
0.5
0.25
0.125
0
0
0
0
0
For RTOLB: Remote Temperature Offset High Byte. Power up default is 0°C. 1LSB = 0.125°C. Two's
complement format.
The offset value written to these registers will automatically be added to or subtracted from the remote
temperature measurement that will be reported in the Remote Temperature registers.
LOCAL and REMOTE T_CRIT REGISTERS (RCS and LCS)
Table 12. LOCAL and REMOTE T_CRIT REGISTERS (RCS and LCS) (Read/Write Address 20h, 19h):
BIT
D7
D6
D5
D4
D3
D2
D1
D0
Value
SIGN
64
32
16
8
4
2
1
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D7–D0: T_CRIT setpoint temperature data. Power up default is T_CRIT = 85°C. 1 LSB = 1°C, two's complement
format.
T_CRIT HYSTERESIS REGISTER (TH)
Table 13. T_CRIT HYSTERESIS REGISTER (TH) (Read and Write Address 21h):
BIT
D7
D6
D5
D4
D3
D2
D1
D0
16
8
4
2
1
Value
D7–D0: T_CRIT Hysteresis temperature. Power up default is TH = 10°C. 1 LSB = 1°C, maximum value = 31.
FILTER and ALERT CONFIGURE REGISTER
Table 14. FILTER and ALERT CONFIGURE REGISTER (Read and Write Address BFh):
BIT
D7
D6
D5
D4
D3
Value
0
0
0
0
0
D2
D1
Filter Level
D0
ALERT Configure
D7-D3: is not defined defaults to "0".
D2-D1: input filter setting as defined the table below:
D2
D1
Filter Level
0
0
No Filter
0
1
Level 1
1
0
Level 1
1
1
Level 2
Level 2 sets maximum filtering.
D0: when set to "1" comparator mode is enabled.
MANUFACTURERS ID REGISTER
(Read Address FEh) Default value 01h.
DIE REVISION CODE REGISTER
(Read Address FFh) Default value 21h. This register will increment by 1 every time there is a revision to the die.
Application Hints
The LM90 can be applied easily in the same way as other integrated-circuit temperature sensors, and its remote
diode sensing capability allows it to be used in new ways as well. It can be soldered to a printed circuit board,
and because the path of best thermal conductivity is between the die and the pins, its temperature will effectively
be that of the printed circuit board lands and traces soldered to the LM90's pins. This presumes that the ambient
air temperature is almost the same as the surface temperature of the printed circuit board; if the air temperature
is much higher or lower than the surface temperature, the actual temperature of the of the LM90 die will be at an
intermediate temperature between the surface and air temperatures. Again, the primary thermal conduction path
is through the leads, so the circuit board temperature will contribute to the die temperature much more strongly
than will the air temperature.
To measure temperature external to the LM90's die, use a remote diode. This diode can be located on the die of
a target IC, allowing measurement of the IC's temperature, independent of the LM90's temperature. The LM90
has been optimized to measure the remote diode of a Pentium III processor as shown in Figure 15. A discrete
diode can also be used to sense the temperature of external objects or ambient air. Remember that a discrete
diode's temperature will be affected, and often dominated, by the temperature of its leads.
20
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Figure 15. Mobile Pentium III or 3904 Temperature vs LM90 Temperature Reading
Most silicon diodes do not lend themselves well to this application. It is recommended that a 2N3904 transistor
base emitter junction be used with the collector tied to the base.
A diode connected 2N3904 approximates the junction available on a Pentium III microprocessor for temperature
measurement. Therefore, the LM90 can sense the temperature of this diode effectively.
DIODE NON-IDEALITY
Diode Non-Ideality Factor Effect on Accuracy
When a transistor is connected as a diode, the following relationship holds for variables VBE, T and If:
where
•
•
•
•
•
•
•
•
(2)
−19
q = 1.6×10 Coulombs (the electron charge),
T = Absolute Temperature in Kelvin
k = 1.38×10−23joules/K (Boltzmann's constant),
η is the non-ideality factor of the process the diode is manufactured on,
IS = Saturation Current and is process dependent,
If= Forward Current through the base emitter junction
VBE = Base Emitter Voltage drop
(2)
In the active region, the -1 term is negligible and may be eliminated, yielding the following equation
(3)
In the above equation, η and IS are dependant upon the process that was used in the fabrication of the particular
diode. By forcing two currents with a very controlled ration (N) and measuring the resulting voltage difference, it
is possible to eliminate the IS term. Solving for the forward voltage difference yields the relationship:
(4)
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The non-ideality factor, η, is the only other parameter not accounted for and depends on the diode that is used
for measurement. Since ΔVBE is proportional to both η and T, the variations in η cannot be distinguished from
variations in temperature. Since the non-ideality factor is not controlled by the temperature sensor, it will directly
add to the inaccuracy of the sensor. For the Pentium III Intel specifies a ±1% variation in η from part to part. As
an example, assume a temperature sensor has an accuracy specification of ±3°C at room temperature of 25 °C
and the process used to manufacture the diode has a non-ideality variation of ±1%. The resulting accuracy of the
temperature sensor at room temperature will be:
TACC = ± 3°C + (±1% of 298 °K) = ±6 °C
(5)
The additional inaccuracy in the temperature measurement caused by η, can be eliminated if each temperature
sensor is calibrated with the remote diode that it will be paired with. The following table shows the variations in
non-ideality for a variety of processors.
η, non-ideality
Processor Family
min
typ
max
Pentium II
1
1.0065
1.0173
Pentium III CPUID 67h
1
1.0065
1.0125
Pentium III CPUID
68h/PGA370Socket/Celeron
1.0057
1.008
1.0125
Pentium 4, 423 pin
0.9933
1.0045
1.0368
Pentium 4, 478 pin
0.9933
1.0045
1.0368
MMBT3904
AMD Athlon MP model 6
1.003
1.002
1.008
1.016
Compensating for Diode Non-Ideality
In order to compensate for the errors introduced by non-ideality, the temperature sensor is calibrated for a
particular processor. These temperature sensors are always calibrated to the typical non-ideality of a given
processor type. The LM90 is calibrated for the non-ideality of a mobile Pentium III processor, 1.008. When a
temperature sensor calibrated for a particular processor type is used with a different processor type or a given
processor type has a non-ideality that strays from the typical, errors are introduced. Figure 16 shows the
minimum and maximum errors introduced to a temperature sensor calibrated specifically to the typical value of
the processor type it is connected to. The errors in this figure are attributed only to the variation in non-ideality
from the typical value. In Figure 17 is a plot of the errors that result from using a temperature sensor calibrated
for a Pentium II, the LM84, with a typical Pentium 4 or AMD Athlon MP Model 6.
Figure 16. Error Caused by Non-Ideality Factor
22
Figure 17. Errors Induced when Temperature
Sensor is Not Calibrated to Typical Non-Ideality
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Figure 18. Compensating for an Untargeted Non-Ideality Factor
Temperature errors associated with non-ideality may be reduced in a specific temperature range of concern
through use of the offset registers (11h and 12h). Figure 18 shows how the offset register may be used to
compensate for the non-ideality errors shown in Figure 17. For the case of non-ideality=1.008, the offset register
was set to −0.5°C resulting in the calculated residual error as shown in Figure 18. This offset has resulted in an
error of less than 0.05°C for the temperatures measured in the critical range between 60 to 100°C. This method
yeilds a first order correction factor.
PCB LAYOUT for MINIMIZING NOISE
Figure 19. Ideal Diode Trace Layout
In a noisy environment, such as a processor mother board, layout considerations are very critical. Noise induced
on traces running between the remote temperature diode sensor and the LM90 can cause temperature
conversion errors. Keep in mind that the signal level the LM90 is trying to measure is in microvolts. The following
guidelines should be followed:
1. Place a 0.1 µF power supply bypass capacitor as close as possible to the VDDpin and the recommended 2.2
nF capacitor as close as possible to the LM90's D+ and D− pins. Make sure the traces to the 2.2nF capacitor
are matched.
2. The recommended 2.2nF diode bypass capacitor actually has a range of TBDpF to 3.3nF. The average
temperature accuracy will not degrade. Increasing the capacitance will lower the corner frequency where
differential noise error affects the temperature reading thus producing a reading that is more stable.
Conversely, lowering the capacitance will increase the corner frequency where differential noise error affects
the temperature reading thus producing a reading that is less stable.
3. Ideally, the LM90 should be placed within 10cm of the Processor diode pins with the traces being as straight,
short and identical as possible. Trace resistance of 1Ω can cause as much as 1°C of error. This error can be
compensated by using the Remote Temperature Offset Registers, since the value placed in these registers
will automatically be subtracted from or added to the remote temperature reading.
4. Diode traces should be surrounded by a GND guard ring to either side, above and below if possible. This
GND guard should not be between the D+ and D− lines. In the event that noise does couple to the diode
lines it would be ideal if it is coupled common mode. That is equally to the D+ and D− lines.
5. Avoid routing diode traces in close proximity to power supply switching or filtering inductors.
6. Avoid running diode traces close to or parallel to high speed digital and bus lines. Diode traces should be
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LM90
SNIS126A – MAY 2004 – REVISED MARCH 2013
www.ti.com
kept at least 2cm apart from the high speed digital traces.
7. If it is necessary to cross high speed digital traces, the diode traces and the high speed digital traces should
cross at a 90 degree angle.
8. The ideal place to connect the LM90's GND pin is as close as possible to the Processors GND associated
with the sense diode.
9. Leakage current between D+ and GND should be kept to a minimum. One nano-ampere of leakage can
cause as much as 1°C of error in the diode temperature reading. Keeping the printed circuit board as clean
as possible will minimize leakage current.
Noise coupling into the digital lines greater than 400mVp-p (typical hysteresis) and undershoot less than 500mV
below GND, may prevent successful SMBus communication with the LM90. SMBus no acknowledge is the most
common symptom, causing unnecessary traffic on the bus. Although the SMBus maximum frequency of
communication is rather low (100kHz max), care still needs to be taken to ensure proper termination within a
system with multiple parts on the bus and long printed circuit board traces. An RC lowpass filter with a 3db
corner frequency of about 40MHz is included on the LM90's SMBCLK input. Additional resistance can be added
in series with the SMBData and SMBCLK lines to further help filter noise and ringing. Minimize noise coupling by
keeping digital traces out of switching power supply areas as well as ensuring that digital lines containing high
speed data communications cross at right angles to the SMBData and SMBCLK lines.
24
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LM90
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SNIS126A – MAY 2004 – REVISED MARCH 2013
REVISION HISTORY
Changes from Original (March 2013) to Revision A
•
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 24
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25
PACKAGE OPTION ADDENDUM
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10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LM90CIMM/NOPB
ACTIVE
VSSOP
DGK
8
1000
RoHS & Green
SN
Level-1-260C-UNLIM
0 to 125
T11C
LM90CIMMX/NOPB
ACTIVE
VSSOP
DGK
8
3500
RoHS & Green
SN
Level-1-260C-UNLIM
0 to 125
T11C
(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)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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