TC665TEUN View Datasheet(PDF) - Microchip Technology
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TC665TEUN Datasheet PDF : 36 Pages
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See Section 7.4 for more details on selecting the
appropriate current sense resistor and coupling
capacitor values.
VOUT RISO
FAN
TC664
TC665
SENSE
CSENSE
GND
RSENSE
FIGURE 4-7:
Fan Current Sensing.
By selecting FPPR (bits 2-1<01>) in the Configuration
Register, the TC664/TC665 devices can be pro-
grammed to calculate RPM data for fans with 1, 2, 4 or
8 current pulses per rotation. The default state
assumes a fan with 2 pulses per rotation.
The measured RPM data is then stored in the RPM-
OUTPUT (RPM) Register. This register is a 9-Bit read
only register which stores RPM data with 25 RPM res-
olution. By setting RES (bit 6<0>) of the Configuration
Register to a ‘1’, the RPM data can be read with
25 RPM resolution. If this bit is left in the default state
of '0', the RPM data will only be readable with resolu-
tion of 50 RPMs, which represents 8-bit data.
The maximum fan RPM reading is 12775 RPM. If this
value is exceeded, a counter overflow bit in the Status
Register is set. RCO (bit 3<0>) in the Status Register
represents the RPM counter overflow bit for the RPM-
OUTPUT Register. This bit will automatically be reset
to zero if the fan RPM reading has been below the max-
imum value of 12775 RPM for 2.4 seconds.
See Table 6-1 for RPM and Status Register command
byte assignments.
TC664/TC665
4.8 Fan Fault Threshold and
Indication (FAULT)
For the TC664/TC665 devices, a fault condition exists
whenever a fan’s sensed RPM level falls below the
user programmable threshold. The RPM threshold
value for fan fault detection is set in the FAN_FAULT
Register (8-bit, read/write).
The RPM threshold represents the fan speed at which
the TC664/TC665 devices will indicate a fan fault. This
threshold can be set at lower levels to indicate fan
locked rotor conditions, or set to higher levels to give
indications for predictive fan failure. It is recommended
that the RPM threshold be at least 10% lower than the
minimum fan speed which occurs at the lowest duty
cycle set point. The default value for the fan RPM
threshold is 500 RPM. If the fan's sensed RPM is less
than the fan fault threshold for 2.4 seconds (typical), a
fan fault condition is indicated.
When a fault condition, due to low fan RPM, occurs, a
logic low is asserted at the FAULT output and the FF
(bit 0<0>) in the Status Register is set to '1'. The FAULT
output and the fault bit in the Status Register can be
reset by setting FFCLR (bit 7<0>) in the Configuration
Register to a '1'.
For the TC665 device, a fault condition is also indicated
when an Over Temperature Fault condition occurs.
This condition occurs when the VOUT duty cycle
exceeds the 100% value, indicating that no additional
cooling capability is available. For this condition, a logic
low is asserted at the FAULT output and OTF (bit 5<X>)
of the Status Register, the over temperature fault indi-
cator, is set to a ‘1’ (The TC664 also indicates an over
temperature condition via the OTF bit in the status reg-
ister). If the duty cycle then decreases below 100%, the
FAULT output will be released and OTF (bit 5<X>) of
the Status Register will be reset to ‘0’.
4.9 Low Power Shutdown Mode
Some applications may have operating conditions
where fan cooling is not required as a result of low
ambient temperature or light system load. During these
times it may be desirable to shut the fans down to save
power and reduce system noise.
The TC664/TC665 devices can be put into a low power
shutdown mode by setting SDM (bit 0<0>) in the Con-
figuration Register to a ‘1’ (this bit is the shutdown bit).
When the TC664/TC665 devices are in shutdown
mode, all functions except for the SMBus interface are
suspended. During this mode of operation, the TC664
and TC665 devices will draw a typical supply current of
only 5 µA. Normal operation will resume as soon as Bit
0 in the Configuration Register is reset to ‘0’.
When the TC664/TC665 devices are brought out of a
shutdown mode by resetting SDM (bit 0<0>) in the
Configuration Register, all of the registers, except for
the Configuration and FAN_FAULT Registers assume
2002-2013 Microchip Technology Inc.
DS21737B-page 13
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