TC648EUA Microchip Technology, TC648EUA Datasheet - Page 12

• Manufacturer Part Number: TC648EUA
• Description: IC PWM FAN SPEED CTRLR 8-MSOP
• Manufacturer: Microchip Technology
• Type: Controller - PWM Fanr

Specifications of TC648EUA

• 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,
• Motor Type: DC Brushless
• No. Of Outputs: 1
• Output Current: 5mA
• Output Voltage: 4.4V
• Supply Voltage Range: 3V To 5.5V
• Driver Case Style: MSOP
• No. Of Pins: 8
• 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

TC648
Per Section 1.0, “Electrical Characteristics”, the leak-
age current at the V
conservative to design for a divider current, I
100 µA. If V
EQUATION
We can further specify R
the divider voltage is equal to our desired V
yields the following:
EQUATION
Solving for the relationship between R
in the following equation:
EQUATION
For this example, R
tionship back into the original equation yields the
resistor values:
In this case, the standard values of 34.8 k
15.4 k
would be more than adequate.
5.4
The TC648 is designed to drive an external transistor
or MOSFET for modulating power to the fan. This is
shown as Q
V
minimum sink current of 1 mA. Bipolar transistors or
MOSFETs may be used as the power switching ele-
ment, as is shown in Figure 5-6. When high current
gain is needed to drive larger fans, two transistors may
be used in a Darlington configuration. These circuit
topologies are shown in Figure 5-6: (a) shows a single
NPN transistor used as the switching element; (b) illus-
trates the Darlington pair; and (c) shows an N-channel
MOSFET.
One major advantage of the TC648’s PWM control
scheme versus linear speed control is that the power
dissipation in the pass element is kept very low.
Generally, low cost devices in very small packages,
such as TO-92 or SOT, can be used effectively. For
DS21448C-page 12
OUT
pin has a minimum source current of 5 mA and a
R
R
1
I
1
DIV
are very close to the calculated values and
Output Drive Transistor Selection
= R
+ R
R
DD
2
= 1e
2
1
2
x
= 15.3 k , and R
= 5.0V then…
=
in Figures 5-1, 5-6, 5-7,and 5-8. The
–4
V
AS
V
A =
1e
1
5.0V
DD
AS
=
= (2.27) R
–4
V
A
- V
AS
pin is no more than 1 µA. It is
V
R
1
R
DD
= 50,000 = 50 k
AS
1
and R
1
5.0V
+ R
+ R
x R
2
2
2
=
2
1
2
. Substituting this rela-
, therefore
= 34.7 k
by the condition that
R
2
x (5 - 1.53)
1
1.53
and R
AS
. This
2
results
DIV
and
, of
fans with nominal operating currents of no more than
200 mA, a single transistor usually suffices. Above
200 mA, the Darlington or MOSFET solution is
recommended. For the power dissipation to be kept
low, it is imperative that the pass transistor be fully sat-
urated when "on".
Table 5-1 gives examples of some commonly available
transistors and MOSFETs. This table should be used
as a guide only since there are many transistors and
MOSFETs which will work just as well as those listed.
The critical issues when choosing a device to use as
Q1 are: (1) the breakdown voltage (V
(MOSFET)) must be large enough to withstand the
highest voltage applied to the fan (Note: This will occur
when the fan is off); (2) 5 mA of base drive current must
be enough to saturate the transistor when conducting
the full fan current (transistor must have sufficient
gain); (3) the V
ficiently drive the gate of the MOSFET to minimize the
R
be within the transistor's/MOSFET's current handling
capability; and (5) power dissipation must be kept
within the limits of the chosen device.
A base-current limiting resistor is required with bipolar
transistors. The correct value for this resistor can be
determined as follows:
V
“Electrical Characteristics”; V
chosen transistor data sheet. It is now possible to solve
for R
EQUATION
Some applications benefit from the fan being powered
from a negative supply to keep motor noise out of the
positive supply rails. This can be accomplished by the
method shown in Figure 5-7. Zener diode D
the -12V power supply voltage, holding transistor Q
when V
the anode of D
on. Operation is otherwise the same as in the case of
fan operation from +12V.
OH
DS(on)
BASE
is specified as 80% of V
OUT
of the device; (4) rated fan current draw must
.
is low. When V
OUT
R
1
V
V
BASE
I
increases by V
BASE
OH
R BASE
voltage must be high enough to suf-
=
= V
= R
= I
V
2002 Microchip Technology Inc.
OH
FAN
OUT
I
BE (SAT)
BASE
BASE
- V
BE (SAT)
/ h
OH
BE(SAT)
is high, the voltage at
x I
FE
, causing Q
DD
+ V
BASE
is given in the
(BR)CEO
in Section 1.0,
R BASE
1
1
or V
offsets
to turn
1
DS
off