Datasheet

LM76

SNIS109E –JANUARY 2000–REVISED MARCH 2013

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SHUTDOWN MODE

Shutdown mode is enabled by setting the shutdown bit in the Configuration register via the Serial Bus. Shutdown

mode reduces power supply current to 5 μA typical. T_CRIT_A is reset if previously set. Since conversions are

stoped during shutdown, T_CRIT_A and INT will not be operational. The Serial Bus interface remains active.

Activity on the clock and data lines of the Serial Bus may slightly increase shutdown mode quiescent current.

Registers can be read from and written to in shutdown mode. The LM76 takes miliseconds to respond to the

shutdown command.

INT AND T_CRIT_A OUTPUT

The INT 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 from some external source, typically a pull-up 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 errors due to internal heating of the LM76. The maximum resistance of the

pull up, based on LM76 specification for High Level Output Current, to provide a 2 volt high level, is 30K ohms.

FAULT QUEUE

A fault queue of up to 4 faults is provided to prevent false tripping when the LM76 is used in noisy environments.

The 4 faults must occur consecutively to set flags as well as INT and T_CRIT_A outputs. The fault queue is

enabled by setting bit 4 of the Configuration Register high (see CONFIGURATION REGISTER ).

INTERNAL REGISTER STRUCTURE

There are four data registers in the LM76, selected by the Pointer register. At power-up the Pointer is set to “00”;

the location for the Temperature Register. The Pointer register latches the last location it was set to. In Interrupt

Mode, a read from the LM76 resets the INT output. Placing the device in Shutdown mode resets the INT and

T_CRIT_A outputs. All registers are read and write, except the Temperature register which is read only.

A write to the LM76 will always include the address byte and the Pointer byte. A write to the Configuration

LOW

, T

HIGH

, and T_CRIT registers require two data bytes.

Reading the LM76 can take place either of two ways: If the location latched in the Pointer is correct (most of the

time it is expected that the Pointer will point to the Temperature register because it will be the data most

frequently read from the LM76), then the read can simply consist of an address byte, followed by retrieving the

corresponding number of data bytes. If the Pointer needs to be set, then an address byte, pointer byte, repeat

start, and another address byte plus required number of data bytes will accomplish a read.

Product Folder Links: LM76