EMC1412 datasheet(21/47 Pages) SMSC

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Multiple Channel 1°C Temperature Sensor with Beta Compensation

Datasheet

SMSC EMC1412

Revision 1.41 (02-23-12)

DATASHEET

6.4.2

Resistance Error Correction (REC)

Parasitic resistance in series with the external diodes will limit the accuracy obtainable from

temperature measurement devices. The voltage developed across this resistance by the switching

diode currents cause the temperature measurement to read higher than the true temperature.

Contributors to series resistance are PCB trace resistance, on die (i.e. on the processor) metal

resistance, bulk resistance in the base and emitter of the temperature transistor. Typically, the error

caused by series resistance is +0.7°C per ohm. The EMC1412 automatically corrects up to 100 ohms

of series resistance.

6.4.3

Programmable External Diode Ideality Factor

The EMC1412 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 EMC1412 provides a 6-bit register for each external diode where

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

APPLICATION NOTE: When monitoring a substrate transistor or CPU diode and beta compensation is enabled, the

Ideality Factor should not be adjusted. Beta Compensation automatically corrects for most

ideality errors.

6.5

Diode Faults

The EMC1412 detects an open on the DP and DN pins, and a short across the DP and DN pins. For

each temperature measurement made, the device checks for a diode fault on the external diode

channel(s). When a diode fault is detected, the ALERT pin asserts (unless masked, see Section 6.6)

and the temperature data reads 00h in the MSB and LSB registers (note: the low limit will not be

checked). A diode fault is defined as one of the following: an open between DP and DN, a short from

VDD to DP, or a short from VDD to DN.

If a short occurs across DP and DN or a short occurs from DP to GND, the low limit status bit is set

and the ALERT pin asserts (unless masked). This condition is indistinguishable from a temperature

measurement of 0.000°C (-64°C in extended range) resulting in temperature data of 00h in the MSB

and LSB registers.

If a short from DN to GND occurs (with a diode connected), temperature measurements will continue

as normal with no alerts.

6.6

Consecutive Alerts

The EMC1412 contain multiple consecutive alert counters. One set of counters applies to the ALERT

pin and the second set of counters applies to the THERM pin. Each temperature measurement channel

has a separate consecutive alert counter for each of the ALERT and THERM pins. All counters are

user programmable and determine the number of consecutive measurements that a temperature

channel(s) must be out-of-limit or reporting a diode fault before the corresponding pin is asserted.

See Section 7.11, "Consecutive ALERT Register" for more details on the consecutive alert function.

6.7

Digital Filter

To reduce the effect of noise and temperature spikes on the reported temperature, the External Diode

channel uses a programmable digital filter. This filter can be configured as Level 1, Level 2, or Disabled

(default) (see Section 7.14). The typical filter performance is shown in Figure 6.2 and Figure 6.3.

EMC1412 Datasheet(PDF) 21 Page - SMSC Corporation

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