EMC1702 datasheet(28/60 Pages) MICROCHIP

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EMC1702

DS20006455A



2020 Microchip Technology Inc.

As well, the THERM pin will be asserted if the measured current or source voltage meet or exceed

the user programmed Vcrit Limit values. In this case, the THERM pin will remain asserted until all

measured voltages drop below the Vcrit Limit minus the Vcrit Hysteresis (see Section 5.27).

4.6

Temperature Measurement

The EMC1702 can monitor the temperature of one externally connected diode. The external diode

channel is configured with Resistance Error Correction and Beta Compensation based on user settings

and system requirements.

The EMC1702 also measures the internal or ambient temperature.

The device contains programmable High, Low, and Tcrit limits for all measured temperature channels.

If the measured temperature drops below the Low limit or above the High limit, the ALERT pin can be

asserted (based on user settings). If the measured temperature meets or exceeds the Tcrit limit, the

THERM pin is asserted unconditionally, providing two tiers of temperature detection.

4.6.1

Resistance Error Correction

The EMC1702 includes active Resistance Error Correction to remove the effect of up to 100 ohms of

series resistance. Without this automatic feature, voltage developed across the parasitic resistance in

the remote diode path causes the temperature to read higher than what the true temperature is. The

error induced by parasitic resistance is approximately +0.7°C per ohm. Sources of series resistance

include bulk resistance in the remote temperature transistor junctions, series resistance in the CPU

resistance due to off-board connections, and resistance in the printed circuit board traces and package

leads. Resistance Error Correction in the EMC1702 eliminates the need to characterize and

compensate for parasitic resistance in the remote diode path.

The Resistance Error Correction can be disabled for each channel.

APPLICATION NOTE: When measuring AMD diodes, disable REC.

4.6.2

Beta Compensation

The forward current gain, or beta, of a transistor is not constant as emitter currents change. The

variation in beta causes an error in temperature reading. Compensating for this error is also known as

implementing the BJT or transistor 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 error. 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.

The Beta Compensation circuitry in the EMC1702 corrects for this beta variation to eliminate any error

which would normally be induced. It automatically detects the appropriate beta setting to use and will

properly recognize and measure a discrete diode.

4.6.3

Ideality Factor

The EMC1702 is designed for external diodes with an ideality factor of 1.008. Not all external diodes,

processor or discrete, will have this exact value. This variation of the ideality factor introduces error in

the temperature measurement which must be corrected for. This correction is typically done using

programmable offset registers. Since an ideality factor mismatch introduces an error that is a function

of temperature, this correction is only accurate within a small range of temperatures. To provide

maximum flexibility to the user, the EMC1702 provides a register for each external diode where the

ideality factor of the diode used may be programmed to eliminate errors across all temperatures.

EMC1702 Datasheet(PDF) 28 Page - Microchip Technology

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