TC648BEOA Microchip Technology, TC648BEOA Datasheet - Page 19

• 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

data sheet. With the values for the thermistor and the
values for V
the values for R
Example: The following design goals are desired:
• Duty Cycle = 50% (V
• Duty Cycle = 100% (V
Using a 100 k thermistor (25°C value), we look up the
thermistor values at the desired temperatures:
• R
• R
Substituting these numbers into the given equations
produces the following numbers for R
• R
• R
FIGURE 5-2:
V
Figure 5-2 graphs R
and V
above.
5.3
As with any component, there are a number of sources
for thermistors. A listing of companies that manufacture
thermistors can be found at www.temperatures.com/
thermivendors.html. This website lists over forty
suppliers of thermistor products. A brief list is shown
here:
-
-
-
-
IN
2003 Microchip Technology Inc.
(T1) = 30°C
Temperature (T2) = 60°C
T
T
, and R
1
2
Products
Thermometrics
Ametherm
U.S. Sensor
Advanced Thermal
(T1) = 79428
(T2) = 22593
= 34.8 k
= 14.7 k
140
120
100
IN
80
60
40
20
0
, versus temperature for the example shown
20
Thermistor Selection
R
IN
TEMP
TEMP
30
, you now have two equations from which
™
1
®
40
and R
™
Vary With Temperature.
V
®
Temperature (ºC)
T
@ 30°C
@ 60°C
IN
50
, R
Voltage
How Thermistor Resistance,
IN
2
IN
TEMP
can be found.
= 1.90V) with Temperature
60
= 2.60V) with
NTC Thermistor
100 k
-
-
-
-
70
(R
Quality Thermistor
Sensor Scientific
Vishay
muRata
@ 25ºC
1
80
in parallel with R
1
90
and R
®
®
100
4.000
3.500
3.000
2.500
2.000
1.500
1.000
0.500
0.000
2
.
™
™
T
TC646B/TC648B/TC649B
)
5.4
The SENSE network (comprised of R
C
detect commutation of the fan motor. R
the fan current into a voltage. C
voltage signal to the SENSE pin. The goal of the
SENSE network is to provide a voltage pulse to the
SENSE pin that has a minimum amplitude of 90 mV.
This will ensure that the current pulse caused by the
fan commutation is recognized by the TC646B/
TC649B device.
A 0.1 µF ceramic capacitor is recommended for
C
resistors be used. Using a 0.1 µF capacitor results in
reasonable values for R
typical SENSE network.
FIGURE 5-3:
The required value of R
rent rating of the fan and the fan current waveshape. A
key point is that the current rating of the fan specified
by the manufacturer may be a worst-case rating, with
the actual current drawn by the fan being lower than
this rating. For the purposes of setting the value for
R
to get the nominal value. This can be done by using an
oscilloscope current probe or using a voltage probe
with a low-value resistor (0.5 ). Another good tool for
this exercise is the TC642 Evaluation Board. This
board allows the R
ily changed while allowing the voltage waveforms to be
monitored to ensure the proper levels are being
reached.
Table 5-1 shows values of R
nominal operating current of the fan. The fan currents
are average values. If the fan current falls between two
of the values listed, use the higher resistor value.
SENSE
SENSE
SENSE
SENSE
) allows the TC646B and TC649B devices to
. Smaller values will require that larger sense
, the operating fan current should be measured
Note:
FanSense Network
(R
V
OUT
SENSE
See Table 5-1 for R
SENSE
and C
(0.1 µF typical)
Typical Sense Network.
SENSE
C
SENSE
and C
SENSE
715
SENSE
R
ISO
SENSE
will change with the cur-
. Figure 5-3 illustrates a
SENSE
SENSE
FAN
)
SENSE
DS21755B-page 19
R
according to the
values to be eas-
SENSE
AC couples this
SENSE
values.
SENSE
converts
and