TC648EUA713 Microchip Technology, TC648EUA713 Datasheet - Page 10

• Manufacturer Part Number: TC648EUA713
• Description: IC PWM FAN SPEED CONTRLR 8-MSOP
• Manufacturer: Microchip Technology
• Type: Controller - PWM Fanr

Specifications of TC648EUA713

• 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-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Product: Fan / Motor Controllers / Drivers
• Operating Supply Voltage: 3 V to 5.5 V
• Supply Current: 400 uA
• 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

TC648
5.1
The temperature signal connected to V
voltage in the range of 1.25V to 2.65V (typical) for 0%
to 100% of the temperature range of interest. The
circuit in Figure 5-2 illustrates a convenient way to pro-
vide this signal using a temperature dependent voltage
divider circuit.
FIGURE 5-2:
Circuit.
RT
are standard resistors. The supply voltage (V
divided between R
RT
of RT
tance of the thermistor at various temperatures is
obtained from the manufacturer’s specifications. Ther-
mistors are often referred to in terms of their resistance
at 25°C.
Generally, the thermistor shown in Figure 5-2 is a non-
linear device with a negative temperature coefficient
(also called an NTC thermistor). In Figure 5-2, R
used to linearize the thermistor temperature response
and R
coefficient at the V
configuration produces an output voltage delta of 1.4V,
which is well within the range of the V
specification of the TC648. A 100 k NTC thermistor is
selected for this application in order to keep I
minimum.
For the voltage range at V
2.65V, the temperature range of this configuration is
0°C to 50°C. If a different temperature range is required
from this circuit, R
resistance value of the thermistor at the center of this
new temperature range. It is suggested that a maxi-
mum temperature range of 50°C be used with this cir-
cuit due to thermistor linearity limitations. With this
change, R
equations:
DS21448C-page 10
NTC Thermistor
1
1
100 k @25˚C
and R
is a conventional NTC thermistor and R
1
2
and R
is used to produce a positive temperature
Temperature Sensor Design
RT
1
2
. For convenience, the parallel combination
1
1
is adjusted according to the following
will be referred to as R
IN
2
1
and the parallel combination of
should be chosen to equal the
node. As an added benefit, this
Temperature Sensing
IN
V DD
to be equal to 1.25V to
R
R
I DIV
1
2
= 100 k
= 23.2 k
TEMP
IN
must output a
. The resis-
1
DIV
C(SPAN)
V IN
and R
DD
to a
) is
1
is
2
EQUATION
These two equations facilitate solving for the two
unknown variables, R
thermistors may be obtained from AN679, “Tempera-
ture Sensing Technologies”, and AN685, “Thermistors
in Single Supply Temperature Sensing Circuits”, which
can be downloaded from Microchip's web site at
www.microchip.com.
5.2
The TC648 is configured for minimum speed mode by
grounding V
network such that V
stant, minimum speed when the thermistor is at
minimum temperature. Figure 5-3 shows operation in
minimum speed mode. The 0% and 100% fan speeds
correspond to V
Minimum system temperature (T
lowest measured temperature at which proportional fan
speed control is required by the system. The fan
operates at minimum speed for all temperatures below
T
temperature between T
FIGURE 5-3:
Operation.
Temperature sensor design consists of a two-point
calculation: one at T
ohmic value of the thermistor must be much higher
than that of R
primarily by the values of R
ohmic value of the thermistor must result in a V
2.65V nominal. The design procedure consists of ini-
tially choosing R
MIN
Fan Speed
Where T
R
and R
Minimum
TEMP
Speed
and at speeds proportional to the measured
100%
1
.
0%
is the parallel combination of the thermistor
Minimum Speed Mode
1
and T
AS
R
1
TEMP
and designing the temperature sensor
R
so that minimum speed is determined
IN
1
TEMP
V
2
to be 10 times smaller than the ther-
V
DD
values of 1.25V and 2.65V, typical.
IN
are the chosen temperatures and
DD
MIN
(T
1
operates the fan at relatively con-
T
x R
(T
2
Minimum Fan Speed Mode
and R
x R
MIN
MIN
) + R
and one at T
1
2
) + R
2002 Microchip Technology Inc.
2
and T
2
2
1
. More information about
2
= V(T
and R
MIN
MAX
= V(T
) is defined as the
2
.
MAX
)
2
1
. At T
)
T
. At T
MAX
MAX
MIN
, the
IN
, the
of