TC642BEPA Microchip Technology, TC642BEPA Datasheet - Page 12

• Manufacturer Part Number: TC642BEPA
• Description: IC PWM FAN SPEED CTRLR 8-DIP
• Manufacturer: Microchip Technology
• Type: PWM Fan Speed Controllerr

Specifications of TC642BEPA

• Applications: Fan Controller, Brushless (BLDC)
• Number Of Outputs: 1
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: 8-DIP (0.300", 7.62mm)
• Motor Type: PWM
• No. Of Outputs: 1
• Output Current: 5mA
• Output Voltage: 4.4V
• Supply Voltage Range: 3V To 5.5V
• Driver Case Style: DIP
• No. Of Pins: 8
• Operating Temperature Range: -40°C To +85°C
• Product: Fan / Motor Controllers / Drivers
• Operating Supply Voltage: 6 V
• Supply Current: 400 uA
• Mounting Style: Through Hole
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Voltage - Load: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

TC642B/TC647B
By modulating the voltage applied to the gate of the
MOSFET (Q
fan is also modulated. When the V
gate of the MOSFET is turned on, pulling the voltage at
the drain of Q
12V across the fan for the t
the duty cycle of the drive pulse is 100% (full on,
t
is decreased (pulse on time “t
will slow down proportionally. With the TC642B and
TC647B devices, the duty cycle is controlled by either
the V
duty cycle. This is described in more detail in Section
5.5, “Output Drive Device Selection”.
4.3
Often overlooked in fan speed control is the actual start-
up control period. When starting a fan from a non-oper-
ating condition (fan speed is zero revolutions per minute
(RPM)), the desired PWM duty cycle or average fan
voltage can not be applied immediately. Since the fan is
at a rest position, the fan’s inertia must be overcome to
get it started. The best way to accomplish this is to apply
the full rated voltage to the fan for a minimum of one
second. This will ensure that in all operating environ-
ments, the fan will start and operate properly. An exam-
ple of the start-up timing is shown in Figure 1-1.
A key feature of the TC642B/TC647B device is the
start-up timer. When power is first applied to the device,
(when the device is brought out of the shutdown mode
of operation) the V
32 PWM cycles (one second for C
drive the fan to full speed for this time-frame.
During the start-up period, the SENSE pin is being
monitored for fan pulses. If pulses are detected during
this period, the fan speed controller will then move to
PWM operation (see Section 4.5, “Minimum Fan
Speed”, for more details on operation when coming out
of start-up). If pulses are not detected during the start-
up period, the start-up timer is activated again. If pulses
are not detected at the SENSE pin during this addi-
tional start-up period, the FAULT output will go low to
indicate that a fan fault condition has occurred. See
Section 4.7, “FAULT Output”, for more details.
DS21756B-page 12
on
= t), the fan will run at full speed. As the duty cycle
IN
or V
Fan Start-up
MIN
DRIVE
DRIVE
input, with the higher voltage setting the
), the voltage that is applied to the
OUT
to zero volts. This places the full
output will go to a high state for
on
period of the pulse. When
on
” is lowered), the fan
OUT
F
= 1 F). This will
pulse is high, the
4.4
The frequency of the PWM pulse train is controlled by
the C
frequency of the PWM pulse train can be set to the
desired value. The typical PWM frequency for a 1.0 F
capacitor is 30 Hz. The frequency can be adjusted by
raising or lowering the value of the capacitor. The C
pin functions as a ramp generator. The voltage at this
pin will ramp from 1.20V to 2.60V (typically) as a saw-
tooth waveform. An example of this is shown in
Figure 4-3.
FIGURE 4-3:
The duty cycle of the PWM output is controlled by the
voltage at the V
ever is greater). The duty cycle of the PWM output is
produced by comparing the voltage at the V
voltage ramp at the C
pin is 1.20V, the duty cycle will be 0%. When the volt-
age at the V
100% (these are both typical values). The V
duty cycle relationship is shown in Figure 4-4.
The lower value of 1.20V is referred to as V
the 2.60V threshold is referred to as V
tion for duty cycle is shown in the equation below. The
voltage range between V
ized as V
minimum and maximum values of 1.3V and 1.5V,
respectively.
EQUATION
F
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
pin. By attaching a capacitor to the C
0
Duty Cycle (%) =
PWM Frequency & Duty Cycle Control
(C
CSPAN
C
F
F
= 1 µF
IN
& V
pin is 2.60V, the PWM duty cycle will be
IN
20
and has a typical value of 1.4V with
IN
input pin (or the V
Pins)
F
C
PWM DUTY CYCLE
pin. When the voltage at the V
Time (msec)
F
40
CMIN
2003 Microchip Technology Inc.
V
Pin Voltage.
(V
CMIN
IN
V
and V
CMAX
- V
60
CMIN
MIN
- V
CMAX
CMAX
) * 100
CMIN
V
voltage, which-
CMAX
80
is character-
IN
. A calcula-
IN
F
CMIN
pin to the
to PWM
pin, the
100
and
IN
F