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TIME

(Active Low)

Measured Temperature

THIGH Limit

TLOW Limit

ALERT 5HVHW %LW VHW WR ³1´

One

Conversion Time

ALERT

TIME

Measured Temperature

THIGH Limit

TLOW Limit

ALERT pin

LM73

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SNIS141D – OCTOBER 2005 – REVISED MAY 2009

ALERT FUNCTION

The ALERT output is an over-temperature indicator. At the end of every temperature conversion, the measured

temperature is compared to the value in the THIGH Register. If the measured temperature exceeds the value

stored in THIGH, the ALERT output goes active (see Figure 7). This over-temperature condition will also cause the

ALRT_STAT bit in the Control/Status Register to change value (this bit mirrors the logic level of the ALERT pin).

The ALERT pin and the ALRT_STAT bit are cleared when any of the following occur:

1. The measured temperature falls below the value stored in the TLOW Register

2. A "1" is written to the ALERT Reset bit in the Configuration Register

3. The master resets it through an SMBus Alert Response Address (ARA) procedure

If ALERT has been cleared by the master writing a "1" to the ALERT Reset bit, while the measured temperature

still exceeds the THIGH setpoint, ALERT will go active again after the completion of the next temperature

conversion.

Each temperature reading is associated with a Temperature High (THI) and a Temperature Low (TLOW) flag in

the Control/Status Register. A digital comparison determines whether that reading is above the THIGH setpoint or

below the TLOW setpoint. If so, the corresponding flag is set. All digital comparisons to the THIGH, and TLOW values

are based on an 11-bit temperature comparison. Regardless of the resolution setting of the LM73, the lower

three temperature LSBs will not affect the state of the ALERT output, THI flag, and TLOW flag.

Figure 7. ALERT Temperature Response Cleared when Temperature Crosses TLOW

Figure 8. ALERT Temperature Response Cleared by Writing a "1" to the ALERT Reset Bit.

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