f75387 Feature Integration Technology Inc., f75387 Datasheet - Page 13

• Manufacturer Part Number: f75387
• Description: ?1o C Accuracy H/w Monitor Ic With Automatic Fan Speed Control
• Manufacturer: Feature Integration Technology Inc.

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
CPU/GPU D+ and D-(connect to pin 9 GND) with an external 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.
6.8.
Also, if the CPU, GPU or external circuits provide thermal diode for temperature measurement, the F75387 is
capable to these situations. The build-in reference table is for PNP 2N3906 transistor, and each different kind of
thermal diode should be matched with specific and BJT gain. In the Figure 6-1, the transistor is directly connected
into temperature pins. For detail, please refer to application circuit.
6.9.
6.10. Over Temperature Signal (OVT#)
The F75387 can provide two external thermal sensors to detect temperature. Two types of OVT# are supported.
1. When monitored temperature exceeds the over-temperature threshold value, OVT# will be asserted until the
temperature goes below the hysteresis temperature.
2. When monitored temperature is not in the target range for the queue time, OVT# will be asserted until the
temperature goes into the target range for the queue time.
Monitor Temperature from thermal diode
ADC Noise Filtering
T
OVT#
HYST
Target High
Target Low
To
OVT#
Queue Time
11
July, 2007
F75387
0.27P