Single/Dual Single-Wire Temp Sensor in SOT23-5 Using SMSC BudgetBus
TM
Sensor Interface
Datasheet
Chapter 3 Product Description
The EMC1201 and EMC1202 are SOT23 temperature sensors with a proprietary single wire SMSC
BudgetBus™ Sensor Interface. Temperature information is communicated to a host device via the
serial bus. All intelligence regarding the interpretation of temperature resides in the host.
shows a typical system overview:
EMC1202
DP
DN
BBUS
Host
(KBC1100)
BBUS
Interface
Figure 3.1 System Overview
Thermal management consists of the host acquiring the temperature data from the EMC1201 or
EMC1202 and controlling the speed of one or more fans. Because the EMC1202 incorporates one
internal and one external temperature diode, up to two separate thermal zones can be monitored and
controlled. The host has the ability to compare measured temperature levels to preset limits and take
the appropriate action when values are found to be out of limit. The EMC1202 is compatible with CPU
substrate diodes.
3.1
Temperature Monitors
Thermal diode temperature measurements are based on the change in forward bias voltage (ΔV
BE
) of
a diode when operated at two different currents:
where:
Δ
V
BE
=
V
BE
_
HIGH
−
V
BE
_
LOW
⎛
I
ln
⎜
HIGH
=
⎜
I
q
⎝
LOW
η
kT
⎞
⎟
⎟
⎠
k
= Boltzmann’s constant
T
= absolute temperature in Kelvin
q
= electron charge
η
= diode ideality factor
The change in
Δ
V
BE
voltage is proportional to absolute temperature T.
Revision 1.0 (06-14-06)
DATASHEET
6
SMSC EMC1201/EMC1202
SMSC [ SMSC CORPORATION ]
