TC648BEOA Microchip Technology, TC648BEOA Datasheet - Page 12

• Manufacturer Part Number: TC648BEOA
• Description: IC PWM FAN SPEED CTRLR SD 8-SOIC
• Manufacturer: Microchip Technology
• Type: Controller - PWM Fanr

Specifications of TC648BEOA

• Applications: Fan Controller, Brushless (BLDC)
• Number Of Outputs: 1
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Motor Type: PWM
• No. Of Outputs: 1
• Output Current: 5mA
• Output Voltage: 4.4V
• Supply Voltage Range: 3V To 5.5V
• Driver Case Style: SOIC
• No. Of Pins: 8
• Operating Temperature Range: -40°C To +85°C
• Product: Fan / Motor Controllers / Drivers
• Operating Supply Voltage: 3 V to 5.5 V
• Supply Current: 400 uA
• Mounting Style: SMD/SMT
• 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

TC646B/TC648B/TC649B
FIGURE 4-2:
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 TC646B,
TC648B and TC649B devices, the duty cycle is con-
trolled by the V
the V
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-
operating condition (fan speed is zero revolutions per
minute (RPM)), the desired PWM duty cycle or average
fan voltage cannot be applied immediately. Since the
fan is at a rest position, the fan’s inertia must be over-
come 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
environments, the fan will start and operate properly.
An example of the start-up timing is shown in
Figure 1-1.
A key feature of the TC646B/TC648B/TC649B devices
is the start-up timer. When power is first applied to the
device, or when the device is brought out of the shut-
down/auto-shutdown modes of operation, the V
output will go to a high state for 32 PWM cycles (one
second for C
speed for this time frame.
During the start-up period for the TC646B and TC649B
devices, 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. If
pulses are not detected during the start-up period, the
DS21755B-page 12
on
= t), the fan will run at full speed. As the duty cycle
AS
TC646B
TC648B
TC649B
V
Fan Start-up
input (auto-shutdown). This is described in
DD
DRIVE
GND
F
DRIVE
IN
= 1 µF). This will drive the fan to full
V
OUT
input and can also be terminated by
), the voltage that is applied to the
to zero volts. This places the full
PWM Fan Drive.
on
period of the pulse. When
on
” is lowered), the fan
OUT
G
FAN
pulse is high, the
12V
D
S
Q
DRIVE
OUT
start-up timer is activated again. If pulses are not
detected at the SENSE pin during this additional
period, the FAULT output will go low to indicate that a
fan fault condition has occurred. See Section 4.7,
“FAULT/OTF Output”, for more details.
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 µF
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
output is produced by comparing the voltage at the V
pin to the voltage ramp at the C
at the V
the voltage at the V
will be 100% (these are both typical values). The
V
Figure 4-4.
The lower value of 1.20V is referred to as “V
the 2.60V threshold is referred to as “V
lation 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
IN
-to-PWM duty cycle relationship is shown in
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
IN
0
Duty Cycle (%) =
PWM Frequency & Duty Cycle
Control (C
C
pin is 1.20V, the duty cycle will be 0%. When
CSPAN
F
= 1 µF
IN
“ and has a typical value of 1.4V, with
20
input pin. The duty cycle of the PWM
IN
pin is 2.60V, the PWM duty cycle
F
C
PWM DUTY CYCLE
Time (msec)
F
40
& V
CMIN
2003 Microchip Technology Inc.
V
Pin Voltage.
(V
CMIN
IN
V
IN
and V
CMAX
F
- V
Pins)
pin. When the voltage
60
CMIN
- V
CMAX
) * 100
CMIN
V
CMAX
CMAX
80
is character-
”. A calcu-
CMIN
F
pin, the
100
” and
IN
F