EMC1812 datasheet(22/102 Pages) MICROCHIP

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Figure 5-3. Temperature Filter Step Response

Samples

Disable

Level 2

Level 1

Figure 5-4. Temperature Filter Impulse Response

Samples

Disabled

Level 1

Level 2

The filter consists of a running average on the external diode channel. The Level 1 filter is a running

average of 4x while the Level 2 filter is a running average of 8x. For the first measurement immediately

after power-up, the filter will be filled with the results of the first measurement. After this, the filter is

operated normally. Any temperature comparisons are done with the filtered results that are stored in the

user register.

5.13

Beta Compensation

The EMC1812/13/14/15/33 devices are configured to monitor the temperature of basic diodes (for

example 2N3904) or CPU thermal diodes. It automatically detects the type of external diode (CPU diode

or diode connected transistor) and determines the optimal setting to reduce temperature errors

introduced by beta variation. Compensating for this error is also known as implementing the transistor or

BJT model for temperature measurement.

For discrete transistors configured with the collector and base shorted together, the beta is generally

sufficiently high, such that the percent change in beta variation is very small. For example, a 10%

variation in beta for two forced emitter currents with a transistor whose ideal beta is 50 would contribute

approximately 0.25°C error at +100°C. However, for substrate transistors where the base-emitter junction

is used for temperature measurement and the collector is tied to the substrate, the proportional beta

variation will cause large errors. For example, a 10% variation in beta for two forced emitter currents, with

a transistor whose ideal beta is 0.5, would contribute approximately +8.25°C error at +100°C.

For the EMC1814 and EMC1815 devices, the External Diode 2/3 (EMC1814) and External Diode

channels 3/4 do not support beta compensation.

At the beginning of every conversion, the optimal beta compensation factor setting is determined and

applied. The BETA(N)<2:0> bits are automatically updated to indicate the current setting. This is the

Multi-Channel Low-Voltage Remote Di...

System Block Diagram

Datasheet

DS20005751A-page 22

EMC1812 Datasheet(PDF) 22 Page - Microchip Technology