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EMC1212-AGZQ-TR

BBUS Compliant Dual Temperature Monitor with Beta Compensation

SMSC -> Microchip 

3.2

Temperature Monitor

BBUS Compliant Dual Temperature Monitor with Beta Compensation

Datasheet

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

when operated at two or more different currents.

ΔVBE

= VBE _ HIGH

− VBE _ LOW

= ηkT

q

ln⎜⎜⎝⎛

I HIGH

I LOW

⎟⎟⎠⎞

where:

k = Boltzmann’s constant

T = absolute temperature in Kelvin

q = electron charge

η = diode ideality factor

As can be seen in this equation, the delta VBE voltage is directly proportional to temperature. Figure 3.2

shows a block diagram of the temperature monitoring circuitry. The delta VBE is first sampled at an

effective rate of 3.125kHz and then measured by the internal 11 bit delta sigma ADC.

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 20.75ms integration time. The input bandwidth

of the system is fs/2048, this translates to 50Hz at a 100kHz clock frequency.

IHIGH

ILOW

CPU

substrate

PNP

Beta

Compensation

Circuitry

Resistance

Error

Correction

Input

Filter &

Sampler

11-bit

delta-sigma

ADC

Figure 3.2 Block Diagram of Temperature Monitoring

The temperature data format is an offset 2’s complement with a range of -64°C to +191.875°C as

shown in Table 3.1.

Table 3.1 EMC1212 Temperature Data Format

2’S COMPLEMENT FORMAT

TEMPERATURE (°C)

Diode Fault or -64

-63.875

-63

-1

0

BINARY

100 0000 0000

100 0000 0001

100 0000 1000

110 1111 1000

110 0000 0000

400h

401h

408h

6F8h

600h

HEX

Revision 1.1 (02-07-07)

8

DATASHEET

SMSC EMC1212

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