Rainbow Electronics LM95010 - Manual (Page 8)

Typical Performance Characteristics
Conversion Rate Effect on Power Supply Current
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1.0 Functional Description
The LM95010 is based on a ∆V
be
temperature sensing
method. A differential voltage, representing temperature, is
digitized using a Sigma-Delta analog to digital converter. The
digital temperature data can be retrieved over a simple
single-wire interface called SensorPath. SensorPath has
been defined by National Semiconductor and is optimized
for hardware monitoring. National offers a royalty-free li-
cense in connection with its intellectual property rights in the
SensorPath bus.
The LM95010 has 2 address pins that allow up to 4
LM95010s to be connected to one SensorPath bus. The
physical interface of SensorPath’s SWD signal is identical to
the familiar industry 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
implemented with a microcontroller. For microcontroller’s
with greater functionality an asynchronous attention signal
can be transmitted by the LM95010 to interrupt the micro-
controller and notify it that temperature data has been up-
dated in the readout register.
To optimize the LM95010’s power consumption to the sys-
tem requirements, the LM95010 has a shutdown mode as
well as it 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 5). For
timing purposes SensorPath is designed for capacitive loads
(C
L
) of up to 400pF. Note that in many cases a 3.3V standby
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.
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 LM95010 meets
the
± 15% timing requirments of SensorPath, the LM95010
does not require the Clock Training sequence and does
support this feature. This section defines the "bit signal"
behavior in all the modes. Please refer to the timing dia-
grams in the Electrical Characteristics section (Figure 2 and
Figure 3) while going through this section. Note that the
timing diagrams 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
LM95010 slave as well as the signal as seen when probing
SWD. Signals labels that begin with the label Mout_ depict a
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FIGURE 5. SensorPath SWD simplified schematic
LM95010
www.national.com 8