AMC6821 datasheet(12/57 Pages) TI2

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APPLICATION INFORMATION

ADC CONVERTER

ADC

Digital

Filter

LPFand

SignalConditioning

Data

Registers

60kHz

TEMPERATURE SENSOR

DVBE +

In(N)

(1)

ADCand

Signal

Processing

Local

Temperature

Registers

LPFand

SignalConditioning

SW1

SW2

Diode

Temperature

Sensor

AMC6821

SBAS386C – MAY 2006 – REVISED JULY 2007

The AMC6821 has an 11-bit, on-chip analog-to-digital converter (ADC), as shown in Figure 11. This ADC

converts the analog input into digital format. The analog input is passed through front-end signal conditioning

circuitry to remove the noise. The resulting signal is then converted by the ADC. To further reduce the effects of

noise, digital filtering is performed by averaging the results of 32 measurement cycles. After digital filtering, the

newest result is stored in the temperature data register (low byte and high byte) in two’s complement format. The

ADC stops when the START bit of Configuration Register 1 is cleared ('0') and runs when START = 1.

Figure 11. On-Chip Analog-to-Digital Converter

The AMC6821 has an integrated temperature sensor (shown in Figure 12) to measure the ambient temperature,

and one remote diode sensor (such as a Pentium thermal diode) input to measure external (CPU) temperature.

The measurement relies on the characteristics of a semiconductor junction operation at a fixed current level. The

forward voltage of the diode (VBE) depends on the current through it and the ambient temperature. The change in

VBE when the diode is operated at two different currents, I1 and I2, is shown in Equation 1:

Where:

is Boltzmann’s constant,

is the charge of the carrier,

is the absolute temperature in degrees Kelvin, and

is the ratio of the two currents.

Figure 12. Integrated Local Temperature Sensor

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