MICROCHIP TC648VUA

M
TC648
Fan Speed Controller with Auto-Shutdown
and Over-Temperature Alert
Features
• Temperature Proportional Fan Speed for Acoustic
Control and Longer Fan Life
• Efficient PWM Fan Drive
• 3.0V to 5.5V Supply Range:
- Fan Voltage Independent of TC648
Supply Voltage
- Supports any Fan Voltage
• Over-temperature Fault Detection
• Automatic Shutdown Mode for “Green” Systems
• Supports Low Cost NTC/PTC Thermistors
• Space Saving 8-Pin MSOP Package
Applications
•
•
•
•
•
•
Power Supplies
Computers
Portable Computers
Telecom Equipment
UPSs, Power Amps
General Purpose Fan Speed Control
Available Tools
• Fan Controller Demonstration Board (TC642DEMO)
• Fan Controller Evaluation Kit (TC642EV)
Package Types
SOIC/PDIP/MSOP
VIN
1
CF
2
VAS
3
GND
4
TC648
8
VDD
7
VOUT
6
OTF
5
NC
General Description
The TC648 is a switch mode, fan speed controller for
use with brushless DC fans. Temperature proportional
speed control is accomplished using pulse width modulation (PWM). A thermistor (or other voltage output
temperature sensor) connected to the VIN input
furnishes the required control voltage of 1.25V to 2.65V
(typical) for 0% to 100% PWM duty cycle. The TC648
can be configured to operate in either auto-shutdown or
minimum speed mode. In auto-shutdown mode, fan
operation is automatically suspended when measured
temperature (VIN) is lower than a user programmed
minimum setting (VAS). The fan is automatically
restarted, and proportional speed control restored,
when VIN exceeds VAS (plus hysteresis). Operation in
minimum speed mode is similar to auto-shutdown
mode, with the exception that the fan is operated at a
user programmed minimum setting when the measured temperature is low. An integrated Start-up Timer
ensures reliable motor start-up at turn-on, and when
coming out of shutdown or auto-shutdown mode.
The over-temperature fault output (OTF) is asserted
when the PWM reaches 100% duty cycle, indicating a
possible thermal runaway situation.
The TC648 is available in the 8-pin plastic DIP, SOIC
and MSOP packages and is available in the industrial
and extended commercial temperature ranges.
 2002 Microchip Technology Inc.
DS21448C-page 1
TC648
Functional Block Diagram
VIN
+
VOTF
–
–
VDD
OTF
PWM
+
CF
Control
Logic
VOUT
Start-up
Timer
OTF
Clock
Generator
–
VAS
+
SHDN
–
+
VSHDN
GND
DS21448C-page 2
TC648
NC
 2002 Microchip Technology Inc.
TC648
1.0
ELECTRICAL
CHARACTERISTICS
Absolute Maximum Ratings*
Supply Voltage ......................................................... 6V
Input Voltage, Any Pin... (GND – 0.3V) to (VDD + 0.3V)
*Stresses above those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are
stress ratings only and functional operation of the device at
these or any other conditions above those indicated in the
operation sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
Package Thermal Resistance:
PDIP (RθJA)............................................. 125°C/W
SOIC (RθJA) ............................................ 155°C/W
MSOP (R θJA) .......................................... 200°C/W
Specified Temperature Range ........... -40°C to +125°C
Storage Temperature Range.............. -65°C to +150°C
DC ELECTRICAL SPECIFICATIONS
Electrical Characteristics: Unless otherwise specified, TMIN ≤ TA ≤ TMAX, VDD = 3.0V to 5.5V
Symbol
Parameter
Min
Typ
Max
Units
Test Conditions
VDD
Supply Voltage
3.0
—
5.5
V
IDD
Supply Current, Operating
—
0.5
1.0
mA
Pins 6, 7 Open,
CF = 1 µF, VIN = VC(MAX)
IDD(SHDN)
Supply Current, Shutdown/
Auto-shutdown Mode
—
25
—
µA
Pins 6, 7 Open;
Note 1
CF =1 µF, VIN = 0.35V
IIN
VIN, VAS Input Leakage
-1.0
—
+1.0
µA
Note 1
VOUT Output
tR
VOUT Rise Time
—
—
50
µsec
IOH = 5 mA, Note 1
tF
VOUT Fall Time
—
—
50
µsec
IOL = 1 mA, Note 1
IOL
Sink Current at VOUT Output
1.0
—
—
mA
VOL = 10% of VDD
IOH
Source Current at V OUT
Output
5.0
—
—
mA
VOH = 80% of VDD
SENSE Input Threshold
Voltage with Respect to GND
50
70
90
mV
Note 1
Output Low Voltage
—
—
0.3
V
2.5
2.65
2.8
V
SENSE Input
VTH(SENSE)
OTF Output
VOL
IOL = 2.5 mA
VIN , VAS Inputs
VC(MAX),VOTF Voltage at VIN for 100% Duty
Cycle and Overtemp. Fault
VC(SPAN)
VC(MAX) - VC(MIN)
1.3
1.4
1.5
V
VAS
Auto-shutdown Threshold
V C(MAX) ~
VC(SPAN)
—
VC(MAX)
V
VSHDN
Voltage Applied to VIN to
Ensure Reset/Shutdown
—
—
VDD x 0.13
V
VREL
Voltage Applied to VIN to
Release Reset Mode
VDD x 0.19
—
—
V
VHYST
Hysteresis on V SHDN, VREL
—
0.01 x V DD
—
V
VHAS
Hysteresis on Auto-shutdown
Comparator
—
70
—
mV
V DD = 5V
Note 1: Ensured by design, not tested.
 2002 Microchip Technology Inc.
DS21448C-page 3
TC648
DC ELECTRICAL SPECIFICATIONS (CONTINUED)
Electrical Characteristics: Unless otherwise specified, TMIN ≤ TA ≤ TMAX, VDD = 3.0V to 5.5V
Symbol
Parameter
Min
Typ
Max
Units
Test Conditions
Pulse Width Modulator
FOSC
PWM Frequency
26
30
34
Hz
CF = 1.0 µF
tSTARTUP
Start-up Timer
—
32/F
—
Sec
CF = 1.0 µF
Note 1: Ensured by design, not tested.
DS21448C-page 4
 2002 Microchip Technology Inc.
TC648
2.0
PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 2-1.
TABLE 2-1:
Pin No.
PIN FUNCTION TABLE
Symbol
Description
2.3
Analog Input (VAS)
An external resistor divider connected to the VAS input
sets the auto-shutdown threshold. Auto-shutdown
occurs when VIN ≤ VAS. During shutdown, supply
current falls to 25 µA (typical). The fan is automatically
restarted when VIN ≥ (VAS +VHAS) (see Section 5.0,
“Typical Applications” for more details).
1
VIN
Analog Input
2
CF
Analog Output
3
VAS
Analog Input
4
GND
Ground Terminal
GND denotes the ground Terminal.
2.5
5
NC
No Internal Connection
6
OTF
Digital (Open Collector) Output
7
VOUT
Digital Output
8
VDD
Power Supply Input
2.1
Analog Input (VIN)
The thermistor network (or other temperature sensor)
connects to the VIN input. A voltage range of 1.25V to
2.65V (typical) on this pin drives an active duty cycle of
0% to 100% on the VOUT pin (see Section 5.0, “Typical
Applications”, for more details).
2.2
Analog Output (CF)
CF is the positive terminal for the PWM ramp generator
timing capacitor. The recommended CF is 1 µF for
30 Hz PWM operation.
2.4
Ground (GND)
No Connect
No internal connection.
2.6
Digital Output (OTF)
OTF goes low to indicate an over-temperature
condition. This occurs when the voltage at VIN > V OTF
(see Section 1.0, "Electrical Characteristics"). An overtemperature indication is a non-latching condition.
2.7
Digital Output (VOUT)
VOUT is an active high complimentary output that drives
the base of an external NPN transistor (via an appropriate base resistor) or the gate of an N-channel MOSFET. This output has asymmetrical drive (see
Section 1.0, “Electrical Characteristics”).
2.8
Power Supply Input (VDD)
VDD may be independent of the fan’s power supply
(see Section 1.0, “Electrical Characteristics”).
 2002 Microchip Technology Inc.
DS21448C-page 5
TC648
3.0
DETAILED DESCRIPTION
3.5
3.1
PWM
If the voltage on VIN becomes less than the voltage on
VAS, the fan is automatically shut off (auto-shutdown
mode). The TC648 exits auto-shutdown mode when
the voltage on VIN becomes higher than the voltage on
VAS by VHAS (the auto-shutdown hysteresis voltage
(see Figure 3-1)). The Start-up Timer is triggered and
normal operation is resumed upon exiting auto-shutdown mode. The VAS input should be grounded if autoshutdown mode is not used.
The PWM circuit consists of a ramp generator and
threshold detector. The frequency of the PWM is
determined by the value of the capacitor connected to
the CF pin. A frequency of 30 Hz is recommended for
most applications (CF = 1 µF). The PWM is also the
time base for the Start-up Timer (see Section 3.3,
“Start-up Timer”). The PWM voltage control range is
1.25V to 2.65V (typical) for 0% to 100% output duty
cycle.
3.2
VOUT Output
The V OUT pin is designed to drive a low cost transistor
or MOSFET as the low side power switching element in
the system. Various examples of driver circuits will be
shown throughout this data sheet. This output has
asymmetric complementary drive and is optimized for
driving NPN transistors or N-channel MOSFETs. Since
the system relies on PWM rather than linear control,
the power dissipation in the power switch is kept to a
minimum. Generally, very small devices (TO-92 or SOT
packages) will suffice.
3.3
Start-Up Timer
To ensure reliable fan start-up, the Start-up Timer turns
the VOUT output on for 32 cycles of the PWM whenever
the fan is started from the off state. This occurs at
power-up and when coming out of shutdown or autoshutdown mode. If the PWM frequency is 30 Hz
(CF = 1 µF), the resulting start-up time will be
approximately one second.
3.4
Over-Temperature Fault (OTF)
Output
OTF is asserted when the PWM control voltage applied
to VIN becomes greater than that needed to drive 100%
duty cycle (see Section 1.0, “Electrical Characteristics”). This indicates that the fan is at maximum drive,
and the potential exists for system overheating. Either
heat dissipation in the system has gone beyond the
cooling system’s design limits, or some subtle fault
exists (such as fan bearing failure or an airflow obstruction). This output may be treated as a “System Overheat” warning and used to trigger system shutdown or
some other corrective action. OTF will become inactive
when VIN < VOTF.
DS21448C-page 6
3.6
Auto-Shutdown Mode
Shutdown Mode (Reset)
If an unconditional shutdown and/or device reset is
desired, the TC648 may be placed in shutdown mode
by forcing VIN to a logic low (i.e., VIN < V SHDN) (see
Figure 3-1). In this mode, all functions cease and the
OTF output is unconditionally inactive. The TC648
should not be shut down unless all heat producing
activity in the system is at a negligible level. The TC648
exits shutdown mode when VIN becomes greater than
VREL, the release voltage.
Entering shutdown mode also performs a complete
device reset. Shutdown mode resets the TC648 into its
power-up state. OTF is unconditionally inactive in shutdown mode. Upon exiting shutdown mode (VIN >
VREL), the Start-up Timer will be triggered and normal
operation will resume, assuming VIN > VAS + VHAS
Note: If VIN < VAS when the device exits shutdown
mode, the fan will not restart as it will be in auto-shutdown mode.
If VIN is not greater than (VAS + VHAS) upon exiting
shutdown mode, the fan will not be restarted. To ensure
that a complete reset takes place, the user’s circuitry
must ensure that VIN > (VAS + VHAS) when the device
is released from shutdown mode. A recommended
algorithm for management of the TC648 by a host
microcontroller or other external circuitry is given in
Section 5.0, “Typical Applications”. A small amount of
hysteresis, typically one percent of VDD (50 mV at
VDD = 5.0V), is designed into the V SHDN/VREL threshold. The levels specified for V SHDN and VREL in
Section 1.0, “Electrical Characteristics”, include this
hysteresis plus adequate margin to account for normal
variations in the absolute value of the threshold and
hysteresis.
CAUTION: Shutdown mode is unconditional. That is,
the fan will remain off as long as the VIN pin is being
held low or VIN < VAS + VHAS.
 2002 Microchip Technology Inc.
TC648
TC646
Status
Normal
Operation
Auto-Shutdown
Mode
Normal
Operation
ShutDown
Normal
Operation
HI
2.6V
VAS + VHAS
VAS
TEMP.
1.2V
tRESET
VIN
VREL
VSHDN
LO
GND
Time
FIGURE 3-1:
4.0
TC648 Nominal Operation.
SYSTEM BEHAVIOR
The flowcharts describing the TC648’s behavioral
algorithms are shown in Figure 4-1. They can be
summarized as follows:
4.1
Power-Up
(1) Assuming the device is not being held in shutdown or auto-shutdown mode (VIN > VAS)..........
(2) Turn VOUT output on for 32 cycles of the PWM
clock. This ensures that the fan will start from a
dead stop.
(3) Branch to Normal Operation.
(4) End.
4.2
Normal Operation
Normal Operation is an endless loop which may only
be exited by entering shutdown or auto-shutdown
mode. The loop can be thought of as executing at the
frequency of the oscillator and PWM.
(1) Drive VOUT to a duty cycle proportional to VIN on a
cycle by cycle basis.
(2) If an over-temperature fault occurs, (VIN > VOTF),
activate OTF; release OTF when VIN < V OTF.
(3) Is the TC648 in shutdown or auto-shutdown
mode?
If so.....
a. VOUT duty cycle goes to zero.
b. OTF is disabled.
c. Exit the loop and wait for VIN > (VAS + VHAS),
then execute Power-up sequence.
(4) End.
 2002 Microchip Technology Inc.
DS21448C-page 7
TC648
Normal
Operation
Power-Up
Power-on
Reset
OTF = 1
VOUT Duty
Cycle Prop.
to VIN
Yes
Minimum
Speed Mode
VAS ≈ 0V
Yes
No
VIN > VOTF?
No
Yes
VIN < VAS?
OTF = 0
AutoShutdown
VOUT = 0
OTF = 1
No
No
VIN >
(VAS + VHAS)
Yes
VIN < VAS ?
YES
AutoShutdown
VOUT = 0
Fire Start-up
Timer
No
Normal
Operation
Minimum
Speed Mode
VOUT = 0
Yes
VIN ≈ 0V ?
No
VIN > 1.25V
No
VIN > 1.25V ?
No
VOUT = 0
Yes
Yes
Power-Up
VOUT Duty Cycle Proportional to VIN
Yes
VIN > VOTF?
No
OTF = 0
FIGURE 4-1:
DS21448C-page 8
OTF = 1
TC648 Behavioral Algorithm Flowcharts.
 2002 Microchip Technology Inc.
TC648
5.0
TYPICAL APPLICATIONS
analysis. At the very least, anyone contemplating a
design using the TC648 should consult the documentation for both the TC642EV (DS21403) and
TC642DEMO (DS21401). Figure 5-1 shows the base
schematic for the TC642DEMO.
Designing with the TC648 involves the following:
(1) The temperature sensor network must be
configured to deliver 1.25V to 2.65V on VIN for 0%
to 100% of the temperature range to be regulated.
An Excel-based spreadsheet is also available for
designing the thermistor network for the TC64X fan
controllers. This file (TC64X Therm) is available for
downloading from the Microchip website at
www.microchip.com.
(2) The auto-shutdown temperature must be set with
a voltage divider on VAS (if used).
(3) The output drive transistor and base resistor must
be selected.
(4) If reset/shutdown capability is desired, the drive
requirements of the external signal or circuit must
be considered.
The TC642 demonstration and prototyping board
(TC642DEMO) and the TC642 Evaluation Kit
(TC642EV) provide working examples of TC648 circuits and prototyping aids. The TC642DEMO is a
printed circuit board optimized for small size and ease
of inclusion into system prototypes. The TC642EV is a
larger board intended for benchtop development and
+5V*
CB
1 µF
+12V
NTC
R1
Fan
Shutdown**
VIN
VDD
CB
0.01 µF
R2
OTF
+5V
OverTemperature
Interrupt
Q1
RBASE
TC648
VOUT
R3
VAS
CB
0.01 µF
NC
CF
R4
CF
1 µF
NOTES:
FIGURE 5-1:
GND
*See cautions regarding latch-up considerations in Section 5.0, "Typical Applications".
**Optional. See Section 5.0, "Typical Applications", for details.
Typical Application Circuit.
 2002 Microchip Technology Inc.
DS21448C-page 9
TC648
5.1
Temperature Sensor Design
EQUATION
VDD x R2
The temperature signal connected to VIN must output a
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 provide this signal using a temperature dependent voltage
divider circuit.
RTEMP (T1) + R2
VDD x R2
RTEMP (T2) + R2
= V(T1)
= V(T2)
Where T1 and T2 are the chosen temperatures and
RTEMP is the parallel combination of the thermistor
and R1.
VDD
IDIV
RT1
R1 = 100 kΩ
NTC Thermistor
100 kΩ @25˚C
VIN
These two equations facilitate solving for the two
unknown variables, R1 and R2. More information about
thermistors may be obtained from AN679, “Temperature 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
R2 = 23.2 kΩ
FIGURE 5-2:
Circuit.
Temperature Sensing
RT1 is a conventional NTC thermistor and R1 and R2
are standard resistors. The supply voltage (V DD) is
divided between R2 and the parallel combination of
RT1 and R1. For convenience, the parallel combination
of RT1 and R 1 will be referred to as RTEMP. The resistance of the thermistor at various temperatures is
obtained from the manufacturer’s specifications. Thermistors are often referred to in terms of their resistance
at 25°C.
Generally, the thermistor shown in Figure 5-2 is a nonlinear device with a negative temperature coefficient
(also called an NTC thermistor). In Figure 5-2, R 1 is
used to linearize the thermistor temperature response
and R2 is used to produce a positive temperature
coefficient at the VIN node. As an added benefit, this
configuration produces an output voltage delta of 1.4V,
which is well within the range of the V C(SPAN)
specification of the TC648. A 100 kΩ NTC thermistor is
selected for this application in order to keep IDIV to a
minimum.
For the voltage range at VIN to be equal to 1.25V to
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 1 should be chosen to equal the
resistance value of the thermistor at the center of this
new temperature range. It is suggested that a maximum temperature range of 50°C be used with this circuit due to thermistor linearity limitations. With this
change, R2 is adjusted according to the following
equations:
DS21448C-page 10
Minimum Speed Mode
The TC648 is configured for minimum speed mode by
grounding VAS and designing the temperature sensor
network such that VIN operates the fan at relatively constant, 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 VIN values of 1.25V and 2.65V, typical.
Minimum system temperature (TMIN) is defined as the
lowest measured temperature at which proportional fan
speed control is required by the system. The fan
operates at minimum speed for all temperatures below
TMIN and at speeds proportional to the measured
temperature between TMIN and TMAX.
Fan Speed
100%
Minimum
Speed
0%
TMIN
FIGURE 5-3:
Operation.
TMAX
Minimum Fan Speed Mode
Temperature sensor design consists of a two-point
calculation: one at TMIN and one at TMAX. At TMIN, the
ohmic value of the thermistor must be much higher
than that of R1 so that minimum speed is determined
primarily by the values of R1 and R2. At TMAX, the
ohmic value of the thermistor must result in a VIN of
2.65V nominal. The design procedure consists of initially choosing R1 to be 10 times smaller than the ther-
 2002 Microchip Technology Inc.
TC648
mistor resistance at TMIN. R2 is then calculated to
deliver the desired speed at TMIN. The values for R1, R2
and RT1 are then checked at TMAX for 2.65V nominal.
It may be necessary to adjust the values of R1 and R2
after the initial calculation to obtain the desired results.
The design equations are:
EQUATION
R 1 = (0.1)(RT1MIN)
Where: RT1 = Thermistor resistance at TMIN
EQUATION
(RT1MIN)(R1)(VMIN)
R2 =
5.3
Auto-Shutdown Temperature
Design
A voltage divider on VAS sets the temperature at which
the part is automatically shut down if the sensed
temperature at VIN drops below the set temperature at
VAS (i.e. VIN < VAS).
As with the VIN input, 1.25V to 2.65V corresponds to
the temperature range of interest from T1 to T2,
respectively. Assuming that the temperature sensor
network designed previously is linearly related to
temperature, the shutdown temperature TAS is related
to T2 and T1 by:
EQUATION
(RT1MIN + R 1)(VDD - VMIN)
Where V MIN = the value of VIN required for
minimum fan speed. VDD = Power Supply Voltage
2.65 - 1.25V
T2 - T1
VAS =
EQUATION
VMAX =
(RT1MIN)(R1)(V MIN)
R2 (R1 + RT1MAX )(VDD)
Where RT 1MAX = thermistor resistance at TMAX,
VMAX = the value of VIN required for maximum
fan speed.
Because the thermistor characteristics are fixed, it may
not be possible, in certain applications, to obtain the
desired values of VMIN and VMAX using the above
equations. In this case, the circuit in Figure 5-4 can be
used. Diode D1 clamps VIN to the voltage required to
sustain minimum speed. The calculations of R1 and
R2 for the temperature sensor are identical to the
equation on the previous page.
VAS - 1.25
=
TAS - T1
( T1.4V- T )(T
2
1
AS
- T1) + 1.25
For example, if 1.25V and 2.65V at VIN corresponds to
a temperature range of T1 = 0°C to T2 = 125°C, and the
auto-shutdown temperature desired is 25°C, then the
VAS voltage is:
EQUATION
VAS =
1.4V
(25 - 0) + 1.25 = 1.53V
(125 - 0)
The VAS voltage may be set using a simple resistor
divider, as shown in Figure 5-5.
VDD
VDD
R1
R3
RT1
R1
IDIV
VIN
D1
R4
IIN
VAS
R2
R2
GND
FIGURE 5-4:
Minimum Fan Speed Circuit.
 2002 Microchip Technology Inc.
FIGURE 5-5:
VAS Circuit.
DS21448C-page 11
TC648
Per Section 1.0, “Electrical Characteristics”, the leakage current at the VAS pin is no more than 1 µA. It is
conservative to design for a divider current, IDIV, of
100 µA. If VDD = 5.0V then…
EQUATION
5.0V
–4
IDIV = 1e A =
R1 + R2
5.0V
R1 + R2 =
, therefore
= 50,000Ω = 50 kΩ
1e–4A
We can further specify R 1 and R2 by the condition that
the divider voltage is equal to our desired V AS. This
yields the following:
EQUATION
VAS =
VDD x R2
R1 + R2
Solving for the relationship between R1 and R 2 results
in the following equation:
EQUATION
R1 = R2 x
VDD - VAS
VAS
=
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(BR)CEO or VDS
(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 VOUT voltage must be high enough to sufficiently drive the gate of the MOSFET to minimize the
R DS(on) of the device; (4) rated fan current draw must
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:
VOH
R2 x (5 - 1.53)
1.53
For this example, R1 = (2.27) R2. Substituting this relationship back into the original equation yields the
resistor values:
R2 = 15.3 kΩ, and R1 = 34.7 kΩ
In this case, the standard values of 34.8 kΩ and
15.4 kΩ are very close to the calculated values and
would be more than adequate.
5.4
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 saturated when "on".
Output Drive Transistor Selection
The TC648 is designed to drive an external transistor
or MOSFET for modulating power to the fan. This is
shown as Q1 in Figures 5-1, 5-6, 5-7,and 5-8. The
VOUT pin has a minimum source current of 5 mA and a
minimum sink current of 1 mA. Bipolar transistors or
MOSFETs may be used as the power switching element, 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) illustrates the Darlington pair; and (c) shows an N-channel
MOSFET.
= VBE(SAT) + VRBASE
VRBASE = RBASE x IBASE
IBASE
= IFAN / hFE
VOH is specified as 80% of VDD in Section 1.0,
“Electrical Characteristics”; V BE(SAT) is given in the
chosen transistor data sheet. It is now possible to solve
for R BASE.
EQUATION
RBASE =
VOH - VBE(SAT)
IBASE
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 D1 offsets
the -12V power supply voltage, holding transistor Q 1 off
when VOUT is low. When VOUT is high, the voltage at
the anode of D1 increases by VOH, causing Q1 to turn
on. Operation is otherwise the same as in the case of
fan operation from +12V.
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
 2002 Microchip Technology Inc.
TC648
VDD
VDD
VDD
Fan
Fan
Fan
RBASE
RBASE
VOUT
VOUT
Q1
Q1
Q1
VOUT
Q2
GND
GND
GND
a) Single Bipolar Transistor
FIGURE 5-6:
TABLE 5-1:
Device
MMBT2222A
MPS2222A
MPS6602
b) Darlington Transistor Pair
C) N-Channel MOSFET
Output Drive Transistor Circuit Topologies.
TRANSISTORS AND MOSFETS FOR Q1 (VDD = 5V)
Package
Max. V BE(sat)/VGS
(V)
Min. HFE
VCEO/VDS
(V)
Fan Current
(mA)
Suggested
RBASE (Ω)
SOT-23
1.2
50
40
150
800
TO-92
1.2
50
40
150
800
TO-92
1.2
50
40
500
301
SI2302
SOT-23
2.5
NA
20
500
Note 1
MGSF1N02E
SOT-23
2.5
NA
20
500
Note 1
SI4410
SO-8
4.5
NA
30
1000
Note 1
SI2308
SOT-23
4.5
NA
60
500
Note 1
Note 1: A series gate resistor may be used in order to control the MOSFET turn-on and turn-off times.
 2002 Microchip Technology Inc.
DS21448C-page 13
TC648
+5V
VDD
R2*
2.2 kΩ
VOUT
TC648
D1
12.0V
Zener
Fan
Q1*
R4*
10 kΩ
GND
-12V
NOTE: *Value depends on the specific application and is shown for example only.
FIGURE 5-7:
5.5
Powering the Fan from a -12V Supply.
Latch-up Considerations
As with any CMOS IC, the potential exists for latch-up
if signals are applied to the device which are outside
the power supply range. This is of particular concern
during power-up if the external circuitry (such as the
sensor network, V AS divider or shutdown circuit) are
powered by a supply different from that of the TC648.
Care should be taken to ensure that the TC648’s VDD
supply powers up first. If possible, the networks
attached to VIN and VAS should connect to the VDD supply at the same physical location as the IC itself. Even
if the IC and any external networks are powered by the
same supply, physical separation of the connecting
points can result in enough parasitic capacitance and/
or inductance in the power supply connections to delay
one power supply “routing” versus another.
5.6
Power Supply Routing and
Bypassing
Noise present on the VIN and VAS inputs may cause
erroneous operation of the OTF output. As a result,
these inputs should be bypassed with a 0.01 µF capacitor mounted as close to the package as possible. This
is especially true of VIN, which is usually driven from a
high impedance source (such as a thermistor). Additionally, the VDD input should be bypassed with a 1 µF
capacitor and grounds should be kept as short as possible. To keep fan noise off the TC648 ground pin, individual ground returns for the TC648 and the low side of
the fan drive device should be used.
Auto-Shutdown Mode Design Example
Step 1. Calculate R1 and R2 based on using an NTC
having a resistance of 10 kΩ at TMIN (25°C)
and 4.65 kΩ at TMAX (45°C) (see Figure 5-8).
R1 = 20.5 kΩ
R2 = 3.83 kΩ
Step 2. Set auto-shutdown level.
VAS = 1.8V
Limit the divider current to 100 µA
R5 = 33 kΩ
R6 = 18 kΩ
Step 3. Design the output circuit
Maximum fan motor current = 250 mA.
Q1 beta is chosen at 50 from which
R7 = 800 Ω.
5.7
Minimum Speed Mode Design
Example
Given:
Minimum speed = 40%(1.8V)
TMIN = 30°C, TMAX = 95°C
Thermistor = 100 kΩ at 25°C
RTMIN = 79.4 kΩ, RTMAX = 6.5 kΩ
Step 1: Calculate R1:
R1 = 7.9 kΩ (Use closest standard value:
7.87 kΩ)
Calculate R2:
R2 = 4.05 kΩ (Use closest standard value:
4.02 kΩ)
Step 2: Verify VMAX:
VMAX = 2.64V
DS21448C-page 14
 2002 Microchip Technology Inc.
TC648
+5V
RESET
Shutdown
Open-Drain
Device
(Optional)
NTC
10 kΩ
@ 25˚C
1
R1
20.5 kΩ
R2
3.83 kΩ
CB
0.01 µF
CB
1 µF
VIN
+12V
+5V
8
VDD
4
Fan
GND
OTF
6
TC648
3 VAS
CB
0.01 µF
2
R6
CF
18 kΩ
CB
1 µF
FIGURE 5-8:
5.8
Q1
R7
800Ω
+5V
R5
33 kΩ
Thermal
Fault
VOUT
NC
7
5
Design Example.
TC648 as a Microcontroller
Peripheral
In a system containing a microcontroller or other host
intelligence, the TC648 can be effectively managed as
a CPU peripheral. Routine fan control functions can be
performed by the TC648 without processor intervention. The microcontroller receives temperature data
from one or more points throughout the system. It
calculates a fan operating speed based on an algorithm
specifically designed for the application at hand. The
processor controls fan speed using complementary
port bits I/O1 through I/O3.
Resistors R 1 through R6 (5% tolerance) form a crude
3-bit DAC that translates the 3-bit code from the
processor's outputs into a 1.6V DC control signal. A
monolithic DAC or digital pot may be used instead of
the circuit shown in Figure 5-9.
With VAS set at 1.8V, the TC648 enters auto-shutdown
when the processor's output code is 000[B]. Output
codes 001[B] to 111[B] operate the fan from roughly
40% to 100% of full speed. An open-drain output from
the processor (I/O0) can be used to reset the TC648
following detection of a fault condition. The OTF output
can be connected to the processor's interrupt input, or
to another I/O pin, for polled operation.
 2002 Microchip Technology Inc.
DS21448C-page 15
TC648
+12V
+5V
(RESET) (Optional)
Open-Drain
I/O0
Outputs
R1
110 kΩ
(MSB)
I/O1
Analog or Digital
Temperature
Data from one or
more Sensors
CMOS
Outputs
R2
240 kΩ
I/O2
I/O3
+5V
(LSB)
R5
1.5 kΩ
+5V
FIGURE 5-9:
DS21448C-page 16
2 C
F
VOUT 7
.01 µF
R7
R4
33 kΩ
18 kΩ
+5V
R
8
18 kΩ
Fan
+ CB
1 µFR
9
+
R6
1 kΩ
GND
VDD 8
CB
R3
360 kΩ
CMOS
Microcontroller
1 V
IN
TC648
1 µF
3
CB
VAS
OTF
6
800Ω
2N2222A
+5V
R10
10 kΩ
.01 µF
4
NC 5
GND
INT
TC648 as a Microcontroller Peripheral.
 2002 Microchip Technology Inc.
TC648
6.0
PACKAGING INFORMATION
6.1
Package Marking Information
8-Lead PDIP (300 mil)
XXXXXXXX
NNN
YYWW
TC648VPA
025
0215
8-Lead SOIC (150 mil)
XXXXXXXX
YYWW
NNN
YWWNNN
Note:
*
TC648VOA
0215
025
TC648E
215025
XXXXXX
XX...X
YY
WW
NNN
Example:
Example:
8-Lead MSOP
Legend:
Example:
Customer specific information*
Year code (last 2 digits of calendar year)
Week code (week of January 1 is week ‘01’)
Alphanumeric traceability code
In the event the full Microchip part number cannot be marked on one line, it will
be carried over to the next line thus limiting the number of available characters
for customer specific information.
Standard marking consists of Microchip part number, year code, week code, traceability code (facility
code, mask rev#, and assembly code). For marking beyond this, certain price adders apply. Please check
with your Microchip Sales Office.
 2002 Microchip Technology Inc.
DS21448C-page 17
TC648
8-Lead Plastic Dual In-line (P) – 300 mil (PDIP)
E1
D
2
n
1
α
E
A2
A
L
c
A1
β
B1
p
eB
B
Units
Dimension Limits
n
p
Number of Pins
Pitch
Top to Seating Plane
Molded Package Thickness
Base to Seating Plane
Shoulder to Shoulder Width
Molded Package Width
Overall Length
Tip to Seating Plane
Lead Thickness
Upper Lead Width
Lower Lead Width
Overall Row Spacing
Mold Draft Angle Top
Mold Draft Angle Bottom
* Controlling Parameter
§ Significant Characteristic
A
A2
A1
E
E1
D
L
c
§
B1
B
eB
α
β
MIN
.140
.115
.015
.300
.240
.360
.125
.008
.045
.014
.310
5
5
INCHES*
NOM
MAX
8
.100
.155
.130
.170
.145
.313
.250
.373
.130
.012
.058
.018
.370
10
10
.325
.260
.385
.135
.015
.070
.022
.430
15
15
MILLIMETERS
NOM
8
2.54
3.56
3.94
2.92
3.30
0.38
7.62
7.94
6.10
6.35
9.14
9.46
3.18
3.30
0.20
0.29
1.14
1.46
0.36
0.46
7.87
9.40
5
10
5
10
MIN
MAX
4.32
3.68
8.26
6.60
9.78
3.43
0.38
1.78
0.56
10.92
15
15
Notes:
Dimensions D and E1 do not include mold flash or protrusions. Mold flash or protrusions shall not exceed
.010” (0.254mm) per side.
JEDEC Equivalent: MS-001
Drawing No. C04-018
DS21448C-page 18
 2002 Microchip Technology Inc.
TC648
8-Lead Plastic Small Outline (SN) – Narrow, 150 mil (SOIC)
E
E1
p
D
2
B
n
1
h
α
45×
c
A2
A
f
β
L
Units
Dimension Limits
n
p
Number of Pins
Pitch
Overall Height
Molded Package Thickness
Standoff §
Overall Width
Molded Package Width
Overall Length
Chamfer Distance
Foot Length
Foot Angle
Lead Thickness
Lead Width
Mold Draft Angle Top
Mold Draft Angle Bottom
* Controlling Parameter
§ Significant Characteristic
A
A2
A1
E
E1
D
h
L
f
c
B
α
β
MIN
.053
.052
.004
.228
.146
.189
.010
.019
0
.008
.013
0
0
A1
INCHES*
NOM
8
.050
.061
.056
.007
.237
.154
.193
.015
.025
4
.009
.017
12
12
MAX
.069
.061
.010
.244
.157
.197
.020
.030
8
.010
.020
15
15
MILLIMETERS
NOM
8
1.27
1.35
1.55
1.32
1.42
0.10
0.18
5.79
6.02
3.71
3.91
4.80
4.90
0.25
0.38
0.48
0.62
0
4
0.20
0.23
0.33
0.42
0
12
0
12
MIN
MAX
1.75
1.55
0.25
6.20
3.99
5.00
0.51
0.76
8
0.25
0.51
15
15
Notes:
Dimensions D and E1 do not include mold flash or protrusions. Mold flash or protrusions shall not exceed
.010” (0.254mm) per side.
JEDEC Equivalent: MS-012
Drawing No. C04-057
 2002 Microchip Technology Inc.
DS21448C-page 19
TC648
8-Lead Plastic Micro Small Outline Package (MS) (MSOP)
E
p
E1
D
2
B
n
1
α
A2
A
c
φ
A1
(F)
L
β
Units
Number of Pins
Pitch
Dimension Limits
n
p
Overall Height
NOM
MAX
8
0.65
.026
A
.044
.030
Standoff
A1
.002
E
.184
Molded Package Width
MIN
8
A2
Overall Width
MAX
NOM
Molded Package Thickness
§
MILLIMETERS*
INCHES
MIN
1.18
.038
0.76
.006
0.05
.193
.200
.034
0.86
0.97
4.67
4.90
.5.08
0.15
E1
.114
.118
.122
2.90
3.00
3.10
Overall Length
D
.114
.118
.122
2.90
3.00
3.10
Foot Length
L
.016
.022
.028
0.40
0.55
0.70
Footprint (Reference)
.035
.037
.039
0.90
0.95
1.00
Foot Angle
F
φ
6
0
Lead Thickness
c
.004
.006
.008
0.10
0.15
0.20
Lead Width
B
α
.010
.012
.016
0.25
0.30
0.40
Mold Draft Angle Top
Mold Draft Angle Bottom
β
0
6
7
7
7
7
*Controlling Parameter
§ Significant Characteristic
Notes:
Dimensions D and E1 do not include mold flash or protrusions. Mold flash or protrusions shall not
exceed. 010" (0.254mm) per side.
Drawing No. C04-111
DS21448C-page 20
 2002 Microchip Technology Inc.
TC648
6.2
Taping Form
Component Taping Orientation for 8-Pin SOIC (Narrow) Devices
User Direction of Feed
PIN 1
W
P
Standard Reel Component Orientation
for 713 Suffix Device
Carrier Tape, Number of Components Per Reel and Reel Size
Package
8-Pin SOIC (N)
Carrier Width (W)
Pitch (P)
Part Per Full Reel
Reel Size
12 mm
8 mm
2500
13 in
Component Taping Orientation for 8-Pin MSOP Devices
User Direction of Feed
PIN 1
W
P
Standard Reel Component Orientation
for 713 Suffix Device
Carrier Tape, Number of Components Per Reel and Reel Size
Package
8-Pin MSOP
 2002 Microchip Technology Inc.
Carrier Width (W)
Pitch (P)
Part Per Full Reel
Reel Size
12 mm
8 mm
2500
13 in
DS21448C-page 21
TC648
NOTES:
DS21448C-page 22
 2002 Microchip Technology Inc.
TC648
ON-LINE SUPPORT
Microchip provides on-line support on the Microchip
World Wide Web site.
The web site is used by Microchip as a means to make
files and information easily available to customers. To
view the site, the user must have access to the Internet
and a web browser, such as Netscape® or Microsoft®
Internet Explorer. Files are also available for FTP
download from our FTP site.
Connecting to the Microchip Internet Web Site
The Microchip web site is available at the following
URL:
www.microchip.com
SYSTEMS INFORMATION AND
UPGRADE HOT LINE
The Systems Information and Upgrade Line provides
system users a listing of the latest versions of all of
Microchip's development systems software products.
Plus, this line provides information on how customers
can receive the most current upgrade kits.The Hot Line
Numbers are:
1-800-755-2345 for U.S. and most of Canada, and
1-480-792-7302 for the rest of the world.
092002
The file transfer site is available by using an FTP service to connect to:
ftp://ftp.microchip.com
The web site and file transfer site provide a variety of
services. Users may download files for the latest
Development Tools, Data Sheets, Application Notes,
User's Guides, Articles and Sample Programs. A variety of Microchip specific business information is also
available, including listings of Microchip sales offices,
distributors and factory representatives. Other data
available for consideration is:
• Latest Microchip Press Releases
• Technical Support Section with Frequently Asked
Questions
• Design Tips
• Device Errata
• Job Postings
• Microchip Consultant Program Member Listing
• Links to other useful web sites related to
Microchip Products
• Conferences for products, Development Systems,
technical information and more
• Listing of seminars and events
 2002 Microchip Technology Inc.
DS21448C-page23
TC648
READER RESPONSE
It is our intention to provide you with the best documentation possible to ensure successful use of your Microchip product. If you wish to provide your comments on organization, clarity, subject matter, and ways in which our documentation
can better serve you, please FAX your comments to the Technical Publications Manager at (480) 792-4150.
Please list the following information, and use this outline to provide us with your comments about this document.
To:
Technical Publications Manager
RE:
Reader Response
Total Pages Sent ________
From: Name
Company
Address
City / State / ZIP / Country
Telephone: (_______) _________ - _________
FAX: (______) _________ - _________
Application (optional):
Would you like a reply?
Device: TC648
Y
N
Literature Number: DS21448C
Questions:
1. What are the best features of this document?
2. How does this document meet your hardware and software development needs?
3. Do you find the organization of this document easy to follow? If not, why?
4. What additions to the document do you think would enhance the structure and subject?
5. What deletions from the document could be made without affecting the overall usefulness?
6. Is there any incorrect or misleading information (what and where)?
7. How would you improve this document?
DS21448C-page24
 2002 Microchip Technology Inc.
TC648
PRODUCT IDENTIFICATION SYSTEM
To order or obtain information, e.g., on pricing or delivery, refer to the factory or the listed sales office.
PART NO.
Device
X
/XX
Temperature
Range
Package
Device:
TC648:
PWM Fan Speed Controller w/Auto Shutdown
and Overtemperature Alert
Temperature Range:
V
E
Package:
PA = Plastic DIP (300 mil Body), 8-lead
OA = Plastic SOIC, (150 mil Body), 8-lead
UA = Plastic Micro Small Outline (MSOP), 8-lead
Examples:
a)
TC648VOA:
PWM Fan Speed Controller
w/Auto Shutdown and Over-Temperature Alert,
SOIC package.
b)
PWM Fan Speed Controller
TC648VUA:
w/Auto Shutdown and Over-Temperature Alert,
MSOP package.
c)
PWM Fan Speed Controller
TC648VPA:
w/Auto Shutdown and Over-Temperature Alert,
PDIP package.
d)
TC648EOA713: PWM Fan Speed Controller
w/Auto Shutdown and Over-Temperature Alert,
SOIC package, Tape and Reel.
= 0°C to +85°C
= -40°C to +85°C
* PDIP package is only offered in the V temp range
Sales and Support
Data Sheets
Products supported by a preliminary Data Sheet may have an errata sheet describing minor operational differences and recommended workarounds. To determine if an errata sheet exists for a particular device, please contact one of the following:
1.
2.
3.
Your local Microchip sales office
The Microchip Corporate Literature Center U.S. FAX: (480) 792-7277
The Microchip Worldwide Site (www.microchip.com)
Please specify which device, revision of silicon and Data Sheet (include Literature #) you are using.
New Customer Notification System
Register on our web site (www.microchip.com/cn) to receive the most current information on our products.
 2002 Microchip Technology Inc.
DS21448C-page25
TC648
NOTES:
DS21448C-page 26
 2002 Microchip Technology Inc.
Information contained in this publication regarding device
applications and the like is intended through suggestion only
and may be superseded by updates. It is your responsibility to
ensure that your application meets with your specifications.
No representation or warranty is given and no liability is
assumed by Microchip Technology Incorporated with respect
to the accuracy or use of such information, or infringement of
patents or other intellectual property rights arising from such
use or otherwise. Use of Microchip’s products as critical components in life support systems is not authorized except with
express written approval by Microchip. No licenses are conveyed, implicitly or otherwise, under any intellectual property
rights.
Trademarks
The Microchip name and logo, the Microchip logo, K EELOQ,
MPLAB, PIC, PICmicro, PICSTART and PRO MATE are
registered trademarks of Microchip Technology Incorporated
in the U.S.A. and other countries.
FilterLab, microID, MXDEV, MXLAB, PICMASTER, SEEVAL
and The Embedded Control Solutions Company are
registered trademarks of Microchip Technology Incorporated
in the U.S.A.
dsPIC, dsPICDEM.net, ECONOMONITOR, FanSense,
FlexROM, fuzzyLAB, In-Circuit Serial Programming, ICSP,
ICEPIC, microPort, Migratable Memory, MPASM, MPLIB,
MPLINK, MPSIM, PICC, PICDEM, PICDEM.net, rfPIC, Select
Mode and Total Endurance are trademarks of Microchip
Technology Incorporated in the U.S.A. and other countries.
Serialized Quick Turn Programming (SQTP) is a service mark
of Microchip Technology Incorporated in the U.S.A.
All other trademarks mentioned herein are property of their
respective companies.
© 2002, Microchip Technology Incorporated, Printed in the
U.S.A., All Rights Reserved.
Printed on recycled paper.
Microchip received QS-9000 quality system
certification for its worldwide headquarters,
design and wafer fabrication facilities in
Chandler and Tempe, Arizona in July 1999
and Mountain View, California in March 2002.
The Company’s quality system processes and
procedures are QS-9000 compliant for its
PICmicro ® 8-bit MCUs, KEELOQ® code hopping
devices, Serial EEPROMs, microperipherals,
non-volatile memory and analog products. In
addition, Microchip’s quality system for the
design and manufacture of development
systems is ISO 9001 certified.
 2002 Microchip Technology Inc.
DS21448C - page 27
M
WORLDWIDE SALES AND SERVICE
AMERICAS
ASIA/PACIFIC
Corporate Office
Australia
2355 West Chandler Blvd.
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Tel: 480-792-7200 Fax: 480-792-7277
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2107 North First Street, Suite 590
San Jose, CA 95131
Tel: 408-436-7950 Fax: 408-436-7955
Microchip Technology Hongkong Ltd.
Unit 901-6, Tower 2, Metroplaza
223 Hing Fong Road
Kwai Fong, N.T., Hong Kong
Tel: 852-2401-1200 Fax: 852-2401-3431
New York
Toronto
6285 Northam Drive, Suite 108
Mississauga, Ontario L4V 1X5, Canada
Tel: 905-673-0699 Fax: 905-673-6509
India
Microchip Technology Inc.
India Liaison Office
Divyasree Chambers
1 Floor, Wing A (A3/A4)
No. 11, O’Shaugnessey Road
Bangalore, 560 025, India
Tel: 91-80-2290061 Fax: 91-80-2290062
Japan
Microchip Technology Japan K.K.
Benex S-1 6F
3-18-20, Shinyokohama
Kohoku-Ku, Yokohama-shi
Kanagawa, 222-0033, Japan
Tel: 81-45-471- 6166 Fax: 81-45-471-6122
Korea
Microchip Technology Korea
168-1, Youngbo Bldg. 3 Floor
Samsung-Dong, Kangnam-Ku
Seoul, Korea 135-882
Tel: 82-2-554-7200 Fax: 82-2-558-5934
Singapore
Microchip Technology Singapore Pte Ltd.
200 Middle Road
#07-02 Prime Centre
Singapore, 188980
Tel: 65-6334-8870 Fax: 65-6334-8850
Taiwan
Microchip Technology (Barbados) Inc.,
Taiwan Branch
11F-3, No. 207
Tung Hua North Road
Taipei, 105, Taiwan
Tel: 886-2-2717-7175 Fax: 886-2-2545-0139
EUROPE
Austria
Microchip Technology Austria GmbH
Durisolstrasse 2
A-4600 Wels
Austria
Tel: 43-7242-2244-399
Fax: 43-7242-2244-393
Denmark
Microchip Technology Nordic ApS
Regus Business Centre
Lautrup hoj 1-3
Ballerup DK-2750 Denmark
Tel: 45 4420 9895 Fax: 45 4420 9910
France
Microchip Technology SARL
Parc d’Activite du Moulin de Massy
43 Rue du Saule Trapu
Batiment A - ler Etage
91300 Massy, France
Tel: 33-1-69-53-63-20 Fax: 33-1-69-30-90-79
Germany
Microchip Technology GmbH
Steinheilstrasse 10
D-85737 Ismaning, Germany
Tel: 49-89-627-144 0 Fax: 49-89-627-144-44
Italy
Microchip Technology SRL
Centro Direzionale Colleoni
Palazzo Taurus 1 V. Le Colleoni 1
20041 Agrate Brianza
Milan, Italy
Tel: 39-039-65791-1 Fax: 39-039-6899883
United Kingdom
Microchip Ltd.
505 Eskdale Road
Winnersh Triangle
Wokingham
Berkshire, England RG41 5TU
Tel: 44 118 921 5869 Fax: 44-118 921-5820
08/01/02
DS21448C-page 28
 2002 Microchip Technology Inc.