Datasheet

SMSC EMC1203/EMC1204

5

Revision 1.1 (06-12-06)

DATASHEET

Figure 3.2 Detailed Block Diagram of Temperature Monitor Architecture

Figure 3.2 shows a detailed block diagram of the temperature measurement circuit. As shown, the

EMC1203 and EMC1204 incorporates switched capacitor technology that samples the temperature

diode voltage at two bias currents and holds the difference voltage. The sample frequency is 100kHz

and the current levels Ihigh and Ilow are 170uA and 10uA respectively.

The output of the switched capacitor sample and hold circuit interfaces to a single bit delta sigma

analog to digital converter. This ADC runs at 100kHz sample frequency and its output is digitally filtered

and averaged over 2048 samples effectively generating 11 bit accuracy.

The advantages of this architecture over Nyquist rate FLASH or SAR converters are superb linearity

and inherent noise immunity. The linearity can be directly attributed to the delta sigma ADC single bit

comparator while the noise immunity is achieved by the digital averaging filter. The overall effective

bandwidth of the system is fs/2048 which translates to a 50Hz bandwidth at 100kHz sample rate.

Conversion time equals about 20ms per temperature monitor.

3.1.1

EMC1203 Temperature Monitoring

The EMC1203, incorporates one internal diode and can monitor two additional temperature zones with

two external diodes.An internal analog multiplexer switches between the internal and external diodes.

Total conversion time for one internal and two external temperature readings is about 60ms. The

external diodes can be either a CPU substrate diode or a discrete diode connected transistor like the

2N3904 or 2N3906. External diode connected transistors examples are shown in Figure 3.3:

Figure 3.3 EMC1203 External Diode Examples

3.1.2

EMC1204 Temperature Monitoring

The EMC1204, incorporates one internal diode and can monitor three external diodes. Total conversion

time for one internal and three external temperature reading is 80ms. An internal multiplexer switches

between internal and external diodes. The external thermal diode connected to DP1 and DN1 can

Delta Vbe

Sample

&

Hold

I

bias

I

low

I

high

1-bit

Sigma

Delta

Modulator

Digital

Averaging

Filter

V

DD

Internal

or External

Diode

Bias

Diode

11-bit Output

Local Ground

to

DP

Typical remote

substrate transistor

i.e. CPU substrate PNP

Typical remote

discrete PNP transistor

i.e. 2N3906

Typical remote

discrete NPN transistor

i.e. 2N3904

to

DN

to

DP

to

DN

to

DP

to

DN