TC642COA Microchip Technology, TC642COA Datasheet - Page 11

• Manufacturer Part Number: TC642COA
• Description: IC PWM FAN SPEED CONTRLR 8-SOIC
• Manufacturer: Microchip Technology
• Type: Controller - PWM Fanr

Specifications of TC642COA

• Package / Case: 8-SOIC (3.9mm Width)
• Operating Temperature: 0°C ~ 70°C
• Applications: Fan Controller, Brushless (BLDC)
• Number Of Outputs: 1
• Voltage - Supply: 3 V ~ 5.5 V
• Mounting Type: Surface Mount
• Product: Fan / Motor Controllers / Drivers
• Operating Supply Voltage: 6 V
• Supply Current: 1 mA
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Voltage - Load: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

We can further specify R
the divider voltage is equal to our desired V
yields the following equation:
EQUATION
Solving for the relationship between R
in the following equation:
EQUATION
In this example, R
tionship back into the previous equation yields the
resistor values:
In this case, the standard values of 31.6 k
18.2 k
would be more than adequate.
5.3
One boundary condition which may impact the selec-
tion of the minimum fan speed is the irregular activation
of the Diagnostic Timer due to the TC642 “missing” fan
commutation pulses at low speeds. This is a natural
consequence of low PWM duty cycles (typically 25% or
less). Recall that the SENSE function detects commu-
tation of the fan as disturbances in the current through
R
gized (i.e., V
V
rotating normally, but the commutation events are
occurring during the PWM’s off-time.
The phase relationship between the fan’s commutation
and the PWM edges tends to “walk around” as the
system operates. At certain points, the TC642 may fail
to capture a pulse within the 32-cycle missing pulse
detector window. When this happens, the 3-cycle
Diagnostic Timer will be activated, the V
be active continuously for three cycles and, if the fan is
operating normally, a pulse will be detected. If all is
well, the system will return to normal operation. There
is no harm in this behavior, but it may be audible to the
user as the fan accelerates briefly when the Diagnostic
Timer fires. For this reason, it is recommended that
V
OUT
MIN
SENSE
2002 Microchip Technology Inc.
be set no lower than 1.8V.
output is “off” most of the time. The fan may be
. These can only occur when the fan is ener-
are very close to the calculated values and
Operations at Low Duty Cycle
R
2
OUT
= 18.1 k , and R
V
R
MIN
1
is “on”). At very low duty cycles, the
= R
1
=
= (1.762) R
2
x
1
V
and R
V
R
DD
DD
1
V
+ R
- V
MIN
x R
2
1
. Substituting this rela-
2
2
MIN
= 31.9 k
2
by the condition that
1
and R
OUT
output will
MIN
2
results
. This
and
5.4
The FanSense network, comprised of R
C
the fan motor (FanSense technology). This network
can be thought of as a differentiator and threshold
detector. The function of R
current into a voltage. C
voltage signal and provide a ground-referenced input to
the SENSE pin. Designing a proper SENSE network is
simply a matter of scaling R
essary amount of gain (i.e., the current-to-voltage con-
version
recommended for C
larger sense resistors, and higher value capacitors are
bulkier and more expensive. Using a 0.1 µF capacitor
results in reasonable values for R
illustrates a typical SENSE network. Figure 5-5 shows
the waveforms observed using a typical SENSE net-
work.
FIGURE 5-4:
FIGURE 5-5:
SENSE
2
1
Ch1 100mV
, allows the TC642 to detect commutation of
SENSE
FanSense Network
(R
ratio).
V
OUT
SENSE
[
Ch2
A
(0.1 F Typ.)
and C
Waveform @ Sense Resistor
Tek Run: 10.0kS/s Sample
Waveform @ Sense Pin
C
R
SENSE
SENSE
100mV
0.1 µF
SENSE Network.
SENSE Waveforms.
BASE
SENSE
SENSE
T
T
SENSE
. Smaller values require
SENSE
M5.00ms Ch1
serves to AC-couple this
ceramic
GND
)
]
V
Fan
is to convert the fan
DD
to provide the nec-
SENSE
DS21444C-page 11
Q
TC642
1
R
SENSE
capacitor
. Figure 5-4
SENSE
142mV
GND
90mV
50mV
GND
and
is