TC670 View Datasheet(PDF) - Microchip Technology
Part Name
Description
MFG CO.
'TC670' PDF : 14 Pages View PDF
3.0 PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 3-1.
TABLE 3-1: PIN FUNCTION TABLE
Pin
No.
Symbol
Description
1 THRESHOLD Analog Input
2
GND
Ground Terminal
3
CLEAR Digital Input
4
VDD
Bias Supply Input
5
ALERT Digital (Open-Drain) Output
6
SENSE Analog Input
3.1 Analog Input (THRESHOLD)
The voltage set at the THRESHOLD input represents
the fan speed at which the TC670 will signal a fan
speed warning by pulling the ALERT output low. The
threshold voltage to fan speed correlation can be seen
in Figures 2-2 and 2-3.
3.2 Ground (GND)
The GND pin (Pin 2) of the TC670 should be connected
directly to the analog ground plane of the circuit board.
Care should be taken to keep this pin away from
switching signals, such as the fan excitation signals in
order to avoid false signals on the SENSE pin.
TC670
3.3 Digital Input (CLEAR)
The CLEAR input is used to reset or blank the ALERT
output. When the CLEAR input is driven high, the
ALERT output will be high-impedance (the ALERT
output requires a pull-up resistor).
3.4 Bias Supply Input (VDD)
Bias Supply Input, 3.0V to 5.5V. The bias supply input
should be bypassed to ground with a 0.1 µF ceramic
capacitor.
3.5 Digital (Open-Drain) Output
(ALERT)
The ALERT output is an open-drain output that
requires an external pull-up resistor. The ALERT output
is pulled low when the sensed fan speed (detected by
the pulses occurring at the SENSE input) falls below
the speed that is represented by the voltage at the
THRESHOLD pin. The ALERT output is latched in this
state until power is cycled or the CLEAR input is
toggled.
3.6 Analog Input (SENSE)
Voltage pulses, which are generated by the fan current
flowing through a sense resistor, are detected at the
SENSE pin and used to calculate the fan speed.
2003 Microchip Technology Inc.
DS21688C-page 5
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