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 gen-

eral, the pull-up resistor should be as large as possible. This

will minimize any errors due to internal heating of the LM92.

The maximum resistance of the pull up, based on LM92

specification for High Level Output Current, to provide a 2

volt high level, is 30K ohms.

1.7 FAULT QUEUE

A fault queue of 4 faults is provided to prevent false tripping

when the LM92 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 Section 1.11).

1.8 INTERNAL REGISTER STRUCTURE

10105107

There are four data registers in the LM92, 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 LM92 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 LM92 will always include the address byte and

the Pointer byte. A write to the Configuration register re-

quires one data byte, while the T

registers require two data bytes.

Reading the LM92 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 reg-

ister because it will be the data most frequently read from the

LM92), 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.

The first data byte is the most significant byte with most

significant bit first, permitting only as much data as neces-

sary to be read to determine the temperature condition. For

instance, if the first four bits of the temperature data indi-

cates a critical condition, the host processor could immedi-

ately take action to remedy the excessive temperature. At

the end of a read, the LM92 can accept either Acknowledge

or No Acknowledge from the Master (No Acknowledge is

typically used as a signal for the slave that the Master has

read its last byte).

An inadvertent 8-bit read from a 16-bit register, with the D7

bit low, can cause the LM92 to stop in a state where the SDA

line is held low as shown in Figure 4. This can prevent any

further bus communication until at least 9 additional clock

cycles have occurred. Alternatively, the master can issue

clock cycles until SDA goes high, at which time issuing a

“Stop” condition will reset the LM92.

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