1°C Temperature Sensor with Beta Compensation
Datasheet
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 EMC1402 automatically corrects up to 100 ohms
of series resistance.
5.6
Programmable External Diode Ideality Factor
The EMC1402 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 EMC1402 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.
5.7
Diode Faults
The EMC1402 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 5.8)
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 0.000degC (-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.
5.8
5.9
Consecutive Alerts
The EMC1402 contains 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 6.11 for more details on the consecutive alert function.
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. The typical filter performance is shown in Figure 5.2 and Figure 5.3.
SMSC EMC1402
Revision 1.16 (03-15-07)
DATA1S9HEET
SMSC [ SMSC CORPORATION ]
