TC647 Microchip, TC647 Datasheet - Page 14

• Manufacturer Part Number: TC647
• Description: PWM Fan Speed Controller
• Manufacturer: Microchip

TC647
FIGURE 5-7:
FIGURE 5-8:
-12V Supply.
5.6
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
powered by a supply different from that of the TC647.
Care should be taken to ensure that the TC647’s V
supply powers up first. If possible, the networks
attached to V
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 connect-
DS21447C-page 14
*Note: Value depends on the specific application and is shown for example only.
V
OUT
Latch-Up Considerations
TC647
GND
+5V
V
DD
IN
R
a) Single Bipolar Transistor
V
BASE
OUT
and V
MIN
12.0V
Zener
Output Drive Transistor Circuit Topologies.
Powering the Fan from a
D 1
MIN
divider or shutdown circuit) is
GND
V
R 2 *
2.2 k
Fan
should connect to the V
DD
Q 1
R
SENSE
R 4 *
10 k
-12V
V
Fan
OUT
Q 1 *
R 3 *
2.2
R
BASE
DD
DD
b) Darlington Transistor Pair
ing points can result in enough parasitic capacitance
and/or inductance in the power supply connections to
delay one power supply “routing” versus another.
5.7
Noise present on the V
erroneous operation of the FAULT output. As a result,
these inputs should be bypassed with a 0.01 µF capac-
itor mounted as close to the package as possible. This
is particularly true of V
high impedance source (such as a thermistor). In addi-
tion, the V
capacitor. Ground should be kept as short as possible.
To keep fan noise off the TC647 ground pin, individual
ground returns for the TC647 and the low side of the
fan current sense resistor should be used.
Design Example
Step 1. Calculate R
Step 2. Set minimum fan speed V
Step 3. Design the output circuit.
Q 1
GND
V
Fan
DD
R
Q 2
SENSE
having a resistance of 10 k
and 4.65 k at T
R
Limit the divider current to 100 µA from which
R
Q
R
Power Supply Routing and
Bypassing
R
Maximum fan motor current = 250 mA.
2
5
7
1
1
DD
= 3.83 k
= 33 k
= 800
= 20.5 k
beta is chosen at 50 from which
input should be bypassed with a 1 µF
V
1
and R
OUT
IN
and R
IN
, which is usually driven from a
MAX
2002 Microchip Technology Inc.
and V
6
= 18 k
2
based on using an NTC
(45°C) (see Figure 5-9).
C) N-Channel MOSFET
MIN
MIN
inputs may cause
= 1.8V.
at T
V
GND
Fan
DD
MIN
R
Q 1
SENSE
(25°C)