F71862
Monitor Temperature from “thermistor”
The F71862 can connect three thermistor to measure environment temperature or
remote temperature. The specification of thermistor should be considered to (1) β value is
3435K (2) resistor value is 10K ohm at 25°C. In the Figure 7-1, the thermistor is connected
by a serial resistor with 10K ohm, then connected to VREF.
Monitor Temperature from “thermal diode”
Also, if the CPU, GPU or external circuits provide thermal diode for temperature
measurement, the F71862 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 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 7-2. When monitored temperature
exceeds the over-temperature threshold value, OVT# will be asserted until the temperature
goes below the hysteresis temperature.
43
July, 2008
V.28P
FINTEK [ FEATURE INTEGRATION TECHNOLOGY INC. ]
