CAT6095

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8

Temperature Sensor Operation

The CAT6095 temperature sensor (TS) combines a

Proportional to Absolute Temperature (PTAT) sensor with

a

S−D modulator, yielding a 12 bit plus sign digital

temperature representation.

The TS runs on an internal clock, and starts a new

conversion cycle at least every 100 ms. The result of the

most recent conversion is stored in the Temperature Data

Register (TDR), and remains there following a TS

Shut−Down. Reading from the TDR does not interfere with

the conversion cycle.

The value stored in the TDR is compared against limits

stored in the High Limit Register (HLR), the Low Limit

Register (LLR) and/or Critical Temperature Register

(CTR). If the measured value is outside the alarm limits or

above the critical limit, then the EVENT pin may be

asserted. The EVENT output function is programmable, via

the Configuration Register for interrupt mode, comparator

mode and polarity.

The temperature limit registers can be Read or Written by

the host, via the serial interface. At power−on, all the

(writable) internal registers default to 0x0000, and should

therefore be initialized by the host to the desired values. The

EVENT output starts out disabled (corresponding to

polarity active low); thus preventing irrelevant event bus

activity before the limit registers are initialized. While the

TS is enabled (not shut−down), event conditions are

normally generated by a change in measured temperature as

recorded in the TDR, but limit changes can also trigger

events as soon as the new limit creates an event condition,

i.e. asynchronously with the temperature sampling activity.

In order to minimize the thermal resistance between

sensor and PCB, it is recommended that the exposed

backside die attach pad (DAP) be soldered to the PCB

ground plane.

Registers

The CAT6095 contains eight 16−bit wide registers

allocated to TS functions, as shown in Table 6. Upon

power−up, the internal address counter points to the

capability register.

Capability Register (User Read Only)

This register lists the capabilities of the TS, as detailed in

the corresponding bit map.

Configuration Register (Read/Write)

This register controls the various operating modes of the

TS, as detailed in the corresponding bit map.

Temperature Trip Point Registers (Read/Write)

The CAT6095 features 3 temperature limit registers, the

HLR, LLR and CLR mentioned earlier. The temperature

value recorded in the TDR is compared to the various limit

values, and the result is used to activate the EVENT pin. To

avoid undesirable EVENT pin activity, this pin is

automatically disabled at power−up to allow the host to

initialize the limit registers and the converter to complete the

first conversion cycle under nominal supply conditions.

Data format is two’s complement with the LSB representing

0.25

°C, as detailed in the corresponding bit maps.

Temperature Data Register (User Read Only)

This register stores the measured temperature, as well as

trip status information. B15, B14 and B13 are the trip status

bits, representing the relationship between measured

temperature and the 3 limit values; these bits are not affected

by EVENT status or by Configuration register settings.

Measured temperature is represented by bits B12 to B0. Data

format is two’s complement, where B12 represents the sign,

B11 represents 128

°C, etc. and B0 represents 0.0625°C.

Manufacturer ID Register (Read Only)

The manufacturer ID assigned by the PCI−SIG trade

organization to the CAT6095 device is 0x1B09.

Device ID and Revision Register (Read Only)

This register contains manufacturer specific device ID

and device revision information.