Datasheet

Revision 1.1 (06-11-08)

6

SMSC EMC1203/EMC1204

DATASHEET

Chapter 3 Product Description

The EMC1203 and EMC1204 are 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. Figure 3.1,

"System Overview" shows a typical system overview:

Figure 3.1 System Overview

In cooperation with the host device, thermal management can be performed as shown in Figure 3.1.

Thermal management consists of the host acquiring the temperature data from the EMC1203 and

EMC1204 controlling the speed of one or more fans. 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 EMC1203 and the DP1/DN1 port of the EMC1204 are compatible with CPU substrate diodes.

Two separate temperature zones are monitored using only two pins on the EMC1204. This is

accomplished using two anti-parallel diodes as shown on the pins DP2/DN3 and DN2/DP3 in

Figure 3.1. This technique maintains high accuracy while minimizing pin count and reducing board

routing complexity. The anti-parallel diode architecture performs very well with diode connected

transistors. It is not compatible with substrate transistors (sometimes called thermal diodes or on-chip

sense junctions).

3.1

Temperature Monitors

Thermal diode temperature measurements are based on the change in forward bias voltage (

ΔV

a diode when operated at two different currents:

The change in

where:

k = Boltzmann’s constant

T = absolute temperature in Kelvin

q = electron charge

EMC1203/

EMC1204

Host

(KBC1100)

BBUS

Interface

DP1

DN1

DP2/DN3

DN2/DP3

BBUS

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

=

−

=

Δ

LOW

HIGH

LOW

BE

HIGH

BE

BE

I

I

q

kT

V

V

V

ln

_

_

η