Datasheet

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APPLICATION INFORMATION
ADC CONVERTER
ADC
Mux
Digital
Filter
LPFand
SignalConditioning
Data
Registers
60kHz
TEMPERATURE SENSOR
DV
BE
+
KT
q
In
(
N
)
(1)
ADCand
Signal
Processing
Mux
Local
Temperature
Registers
LPFand
SignalConditioning
SW1 SW2
I
1
I
2
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 (V
BE
) depends on the current through it and the ambient temperature. The change in
V
BE
when the diode is operated at two different currents, I
1
and I
2
, is shown in Equation 1 :
Where:
k is Boltzmann ’ s constant,
q is the charge of the carrier,
T is the absolute temperature in degrees Kelvin, and
N is the ratio of the two currents.
Figure 12. Integrated Local Temperature Sensor
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Product Folder Link(s): AMC6821