Remote High Limit

RDTS Measurement

LM63 ALERT Pin

Status Register: RTDS High

Time

LM63

SNAS190E – SEPTEMBER 2002 – REVISED MAY 2013

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THE ALERT/TACH PIN AS ALERT OUTPUT

The ALERT/Tach pin is a multi-use pin. In this section, we will address the ALERT active-low open-drain output

function. When the ALERT/Tach Select bit is written as a zero in the Configuration Register the ALERT output is

selected. Also, when the ALERT Mask bit in the Configuration register is written as zero the ALERT interrupts

are enabled.

The LM63'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 in the following sections: ALERT

OUTPUT AS A TEMPERATURE COMPARATOR, ALERT OUTPUT AS AN INTERRUPT, and ALERT OUTPUT

AS AN SMBus ALERT. The ALERT and interrupt methods are different only in how the user interacts with the

LM63.

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: ALERT OUTPUT AS A

TEMPERATURE COMPARATOR, ALERT OUTPUT AS AN INTERRUPT, and ALERT OUTPUT AS AN SMBus

ALERT.

ALERT OUTPUT AS A TEMPERATURE COMPARATOR

When the LM63 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 7). 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.

Figure 7. ALERT Output as Temperature Comparator Response Diagram

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