LM41CIMTX/NOPB National Semiconductor, LM41CIMTX/NOPB Datasheet - Page 10

• Manufacturer Part Number: LM41CIMTX/NOPB
• Description: IC HARDWARE MONITOR 14-TSSOP
• Manufacturer: National Semiconductor

Specifications of LM41CIMTX/NOPB

• Applications: Monitors
• Interface: 1-Wire
• Voltage - Supply: 3 V ~ 3.6 V
• Package / Case: 14-TSSOP
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM41CIMTX

www.national.com
Typical Performance Characteristics
1.0 Functional Description
The LM41 hardware monitor measures up to 2 temperature
zones and 5 power supply voltages. The LM41 uses a ∆V
temperature sensing method. A differential voltage, repre-
senting temperature, is digitized using a Sigma-Delta analog
to digital converter. Internal scaling resistors allow direct
measurement of the +1.6V, +2.5V, +5V, +3.3V and +12V
power supply inputs. The digitized data can be retrieved over
a simple single-wire interface called SensorPath. Sensor-
Path has been defined by National Semiconductor and is
optimized for hardware monitoring. National offers a royalty-
free license in connection with its intellectual property rights
in the SensorPath bus.
The LM41 has one address pin to allow up to two LM41s to
be connected to one SensorPath bus. The physical interface
of SensorPath’s SWD signal is identical to the familiar indus-
try standard SMBus SMBDAT signal. The digital information
is encoded in the pulse width of the signal being transmitted.
Every bit can be synchronized by the master simplifying the
implementation of the master when using a micro-controller.
For micro-controller’s with greater functionality an asynchro-
nous attention signal can be transmitted by the LM41 to
interrupt the micro-controller and notify it that temperature/
voltage data has been updated in the readout registers.
To optimize the LM41’s power consumption to the system
requirements, the LM41 has a shutdown mode and supports
multiple conversion rates.
1.1 SensorPath BUS SWD
SWD is the Single Wire Data line used for communication.
SensorPath uses 3.3V single-ended signaling, with a pull-up
resistor and open-drain low-side drive (see Figure 3). For
timing purposes SensorPath is designed for capacitive loads
(C
rail of the PC will be used as a power supply for both the
sensor and the master. Logic high and low voltage levels for
SWD are TTL compatible. The master may provide an inter-
nal pull-up resistor. In this case the external resistor is not
needed. The minimum value of the pull-up resistor must take
into account the maximum allowable output load current of
4mA.
Remote Diode Temperature Reading Sensitivity to Diode
L
) of up to 400pF. Note that in many cases a 3.3V standby
Filter Capacitance
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be
10
Thermal Diode Capacitor or PCB Leakage Current Effect
1.2 SensorPath BIT SIGNALING
Signals are transmitted over SensorPath using pulse-width
encoding. There are five types of "bit signals":
• Data Bit 0
• Data Bit 1
• Start Bit
• Attention Request
• Reset
All the "bit signals" involve driving the bus to a low level. The
duration of the low level differentiates between the different
"bit-signals". Each "bit signal" has a fixed pulse width. Sen-
sorPath supports a Bus Reset Operation and Clock Training
sequence that allows the slave device to synchronize its
internal clock rate to the master. Since the LM41 meets the
±
not require the Clock Training sequence and does not sup-
port this feature. This section defines the "bit signal" behav-
ior in all the modes. Please refer to the timing diagrams in
the Electrical Characteristics section (Figure 1 and Figure 2)
while going through this section. Note that the timing dia-
grams for the different types of "bit signals" are shown
together to better highlight the timing relationships between
them. However, the different types of "bit signals" appear on
SWD at different points in time. These timing diagrams show
the signals as driven by the master and the LM41 slave as
well as the signal as seen when probing SWD. Signal labels
that begin with the label Mout_ depict a drive by the master.
15% timing requirements of SensorPath, the LM41 does
FIGURE 3. SensorPath SWD simplified schematic
on Remote Diode Temperature Reading
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