EMC1822 datasheet(30/103 Pages) MICROCHIP

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Table 7-10. Consecutive ALERT/ THERM Settings

Number of consecutive Out-of-Limit measurements

(default for CALRT<2:0>)

(default for CTHRM<2:0>)

7.17

“Hottest Of” Comparison

At the end of every measurement cycle, the EMC1822/23/24/25/43 devices compare all of the user-

selectable internal and external diode channels to determine which of these channels is reporting the

hottest temperature. The hottest temperature is stored in the Hottest Temperature registers and the

appropriate Status bit is set in the Hottest Status register. If multiple temperature channels measure the

same temperature and are equal to the hottest temperature, the hottest status will be displayed for all

selected temperature channels with the hottest temperature measurement.

As an optional feature, the EMC1822/23/24/25/43 devices can also flag an event if the hottest

temperature channel changes by enabling the REMHOT (Remember Hottest) bit (see 8.11.45 HOTTEST

CONFIG). For example, suppose that external diode channels 1, 3 and 4 are programmed to be

compared in the “Hottest Of” Comparison. If the External Diode 1 channel reports the hottest temperature

of the three, its temperature is copied into the Hottest Temperature registers (in addition to the External

Diode 1 Temperature registers) and it is flagged in the Hottest Status bit. If, on the next measurement, the

External Diode 3 channel temperature has increased such that it is now the hottest temperature, the

EMC1822/23/24/25/43 devices can flag this event as an interrupt condition and assert the ALERT pin.

7.18

Rate of Change

The Rate of Change (ROC) function approximates the derivative of the temperature using a difference

equation. The equation below is the basis for calculation.

The ROC can be enabled for the first two standard diode connections. If Diode 2 is an anti-parallel

connected diode, the ROC feature is applied to diode 3. For the EMC1843 the ROC only applies to

External Diode 1.

Rate of Change

▵

��

▵

��= ��max −��0 ×��

��−1

Where:

T(tmax)

temperature at the end of the interval

T(t0)

temperature at the beginning of the interval

The ROC period (T0 to Tmax) can be approximated by the combination of conversion rate (see Table 7-4)

and ROC samples (address 43h, 48h). The table below shows the samples defined by the bit settings.

Multi-Channel Low Voltage Temp Sens...

System Block Diagram

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