LM64 datasheet(12/42 Pages) TI2

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6.3 Feature Description

6.3.1 Conversion Sequence

The LM64 takes approximately 31.25 ms to convert the Local Temperature (LT), Remote Temperature (RT), and

to update all of its registers. The Conversion Rate may be modified using the Conversion Rate Register. When

the conversion rate is modified a delay is inserted between conversions, the actual conversion time remains at

31.25 ms. Different Conversion Rates will cause the LM64 to draw different amounts of supply current as shown

in Figure 6-1.

0.01

0.1

1.0

100

CONVERSION RATE (Hz)

200

500

800

1100

1400

1700

2000

2300

2600

Figure 6-1. Supply Current vs Conversion Rate

6.3.2 The ALERT Output

When the ALERT Mask bit in the Configuration register is written as zero the ALERT interrupts are enabled.

The LM64's ALERT pin is versatile and can produce three different methods of use to best serve the system

designer: (1) as a temperature comparator (2) as a temperature-based interrupt flag, and (3) as part of an

SMBus ALERT System. The three methods of use are further described below. The ALERT and interrupt

methods are different only in how the user interacts with the LM64.

The remote temperature (RT) reading is associated with a T_CRIT Setpoint Register, and both local and

remote temperature (LT and RT) readings are associated with a HIGH setpoint register (LHS and RHS). The

RT is also associated with a LOW setpoint register (RLS). At the end of every temperature reading a digital

comparison determines whether that reading is above its HIGH or T_CRIT setpoint or below its LOW setpoint.

If so, the corresponding bit in the ALERT Status Register is set. If the ALERT mask bit is low, any bit set in

the ALERT Status Register, with the exception of Busy or Open, will cause the ALERT output to be pulled low.

Any temperature conversion that is out of the limits defined in the temperature setpoint registers will trigger an

ALERT. Additionally, the ALERT Mask Bit must be cleared to trigger an ALERT in all modes.

The three different ALERT modes will be discussed in the following sections.

6.3.2.1 ALERT Output as a Temperature Comparator

When the LM64 is used in a system in which does not require temperature-based interrupts, the ALERT output

could be used as a temperature comparator. In this mode, once the condition that triggered the ALERT to go low

is no longer present, the ALERT is negated (Figure 6-2). For example, if the ALERT output was activated by the

comparison of LT > LHS, when this condition is no longer true, the ALERT will return HIGH. This mode allows

operation without software intervention, once all registers are configured during set-up. In order for the ALERT

to be used as a temperature comparator, the Comparator Mode bit in the Remote Diode Temperature Filter and

Comparator Mode Register must be asserted. This is not the power-on default state.

LM64

SNAS207B – MAY 2004 – REVISED JANUARY 2024

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