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

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

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

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

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