TC654 查看數據表（PDF） - Microchip Technology
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TC654 Datasheet PDF : 38 Pages
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peak of the voltage pulse at the SENSE pins must
exceed the 100 mV (typical) threshold in order for the
pulse to be counted in the fan RPM measurement.
See Section 7.4 “FanSense Network (RSENSE &
CSENSE)” for more details on selecting the appropriate
current sense resistor and coupling capacitor values.
FAN
1
RISO1
FAN
2
VOUT
TC654/
TC655
SENSE1
CSENSE1
SENSE2
GND
CSENSE2
RISO2
RSENSE1
RSENSE2
FIGURE 4-7:
Fan Current Sensing.
By selecting F1PPR (bits 2-1<01>) and F2PPR (bits 4-
3<01>) in the Configuration Register, the TC654 and
TC655 can be programmed 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-
OUTPUT1 (RPM1, for SENSE1 input) and RPM-OUT-
PUT2 (RPM2, for SENSE2 input) Registers. These
registers are 9-Bit Read-Only registers which store
RPM data with 25 RPM resolution. 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 resolution of 50 RPMs, which represents
8-Bit data.
The maximum fan RPM reading is 12775 RPM. If this
value is exceeded, counter overflow bits in the Status
Register are set. R1CO (bit 3<0>) and R2CO (bit 4<0>)
in the Status Register represent the RPM1 and RPM2
counter overflow bits for the RPM1 and RPM2 regis-
ters, respectively. These bits 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 RPM1, RPM2 and Status Register
command byte assignments.
2002-2014 Microchip Technology Inc.
TC654/TC655
4.8 Fan Fault Threshold and
Indication (FAULT)
For the TC654 and TC655 devices, a fault condition
exists whenever a fan’s sensed RPM level falls below
the user programmable threshold. The RPM threshold
values for fan fault detection are set in the FAN_-
FAULT1 and FAN_FAULT2 Registers (8-bit, read/
write).
The RPM threshold represents the fan speed at which
the TC654/TC655 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
thresholds 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. F1F (bit
0<0>) and F2F (bit 1<0>) in the Status Register are set
to ‘1’ for respective low RPM levels on the SENSE1
and SENSE2 inputs. The FAULT output and the fault
bits in the Status Register can be reset by setting
FFCLR (bit 7<0>) in the Configuration Register to a ‘1’.
For the TC655 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 TC654 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 TC654/TC655 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 TC654/TC655 devices are in Shutdown
mode, all functions except for the SMBus interface are
suspended. During this mode of operation, the TC654
and TC655 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’.
DS20001734C-page 13
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