F81867
(1) Monitor Temperature from “thermistor”
The F81867 can connect two thermistors to measure environment temperature or remote
temperature. The specification of thermistor should be considered to (1) β value is 3435K (2)
resistor value is 10KΩ at 25°C. In the Figure 7-1, the thermistor is connected by a serial resistor
with 10KΩ, then connected to VREF.
(2) Monitor Temperature from “thermal diode”
Also, if the CPU, GPU or external circuits provide thermal diode for temperature
measurement, the F81867 is capable to these situations. The build-in reference table is for PNP
2N3906 transistor. In the Figure 7-1, the transistor is directly connected into temperature pins.
ADC Noise Filtering
The ADC is integrating type with inherently good noise rejection. Micro-power operation
places constraints on high-frequency noise rejection; therefore, careful PCB board layout and
suitable external filtering are required for high-accuracy remote measurement in electronically
noisy environment. High frequency EMI is best filtered at D+ and D- with an external 2200pF or
3300pF capacitor. Too high capacitance may introduce errors due to the rise time of the switched
current source. Nearly all noise sources tested cause the ADC measurement to be higher than
the actual temperature, depending on the frequency and amplitude.
Over Temperature Signal (OVT#)
OVT# alert for temperature is shown as figure 7-3. When monitored temperature exceeds
the over-temperature threshold value, OVT# will be asserted until the temperature goes below the
hysteresis temperature.
TOVT
T
HYST
OVT#
(Level mode)
OVT#
(SMI mode)
Fig 7-3
Temperature PME#
PME# interrupt for temperature is shown as figure 7-4. Temperature exceeding high limit or
going below hysteresis will cause an interrupt if the previous interrupt has been reset by writing
35
Dec, 2011
V0.12P
FINTEK [ FEATURE INTEGRATION TECHNOLOGY INC. ]
