Datasheet

SMSC EMC1201/EMC1202

7

Revision 1.0 (06-14-06)

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

EMC1201 and EMC1202 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

EMC1202 Temperature Monitoring

The EMC1202, incorporates one internal diode and can monitor an additional temperature zone via

one external diode. An internal analog multiplexer switches between the internal and external diode.

Total conversion time for one internal and one external temperature reading is about 40ms. The

external diode 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 EMC1202 External Diode Examples

3.2

SMSC BudgetBus™ Sensor Interface

The EMC1201 and EMC1202 communicate with a host controller, such as the KBC1100, through the

proprietary single wire SMSC BudgetBus™ Sensor Interface known as BBUS. The BBUS is a single

fs

Delta Vbe

Sample

&

Hold

I

bias

I

low

I

high

fs

1-bit

Sigma

Delta

Modulator

fs

Digital

Averaging

Filter

fs/2048

11-bit

Accurate

Conversion

V

DD

Internal or

Remote Diode

Bias

Diode

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