EMC1813 datasheet(28/102 Pages) MICROCHIP

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Rate of Change

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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 5-3)

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

For example, setting the conversion rate to 1 conversion per second and the number of ROC samples to

65 samples would give an approximate ROC period of 65 seconds or approximately 1 minute.

The gain applied to the result is stored in 6.10.27 ROC GAIN (Address 3Dh). The effective gains are

shown in the register definition.

Since this is sampled over time, there is a bit for each channel that indicates a change in slope has

occurred. These bits (one for each channel) assert when the result of two consecutive sample differences

exceeds the threshold limit as defined by the Hysteresis value defined in 6.10.28 ROC CONFIG

(Address 3Eh). The ROC calculations are not affected.

The Limit registers (6.10.32 R LIMH and 6.10.33 R LIML ) and Results registers (6.10.30 R RESH and

6.10.31 R2/3 RESL) are signed, two's-complement numbers stored in two consecutive registers.

If the Rate of Change result stored in registers 40h and 44h exceeds the programmed limit, the

appropriate STATUS register bits will be set in 6.10.29 ROC STATUS (Address 3Fh). The ALERT pin

may be asserted or masked, as set by 6.10.28 ROC CONFIG (Address 3Eh). The MASK bit does not

prevent the Status bits from updating, but if set, it prevents the ALERT pin from asserting.

In addition to the functions described above, two additional temperature values are stored in register for

retrieval. The maximum temperature for a given sample period is stored in a register (4Ah) that updates

every sample period and in a second register (4Dh, 4Fh) that stores a “global value” and cleared only

when read. The purpose of this register is to determine a maximum or minimum temperature,

independent of the sample period.

Below is an example of setting up the Rate of Change feature and interpreting the results.

Enable Standby mode: Write a value of 40h into register 03h.

Set ROC gain: Write a value of 09h in register 3Dh. This sets the gain value of two for both Ext1

and Ext2/3.

Set ROC samples Ext1, Ext2/3: Write a value of 02h/02h in registers 43h/48h. This sets the ROC

samples to five for both EXT1 and Ext2/3.

Set ROC Alert Limit Ext1/Ext2: Write a value of 01h/01h in registers 41h/46h. This sets the ROC

limit to two for both Ext1 and Ext2/3.

Enable ROC and Hysteresis: Write a value of 20h in register 3Eh. This enables the ROC and sets

the hysteresis value to zero.

ROC example:

Stabilize ambient temperature of device to +25°C.

Initiate One-Shot conversion: Write a value of FFh in register 0Fh.

Multi-Channel Low-Voltage Remote Di...

System Block Diagram

Datasheet

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