2001-2012 Microchip Technology Inc. DS21444D-page 7
TC642
4.0 SYSTEM BEHAVIOR
The flowcharts describing the TC642’s behavioral
algorithm 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
mode (V
MIN
> V
REL
)…
(2) Turn V
OUT
output on for 32 cycles of the PWM
clock. This ensures that the fan will start from a
dead stop.
(3) During this Start-up Timer, if a fan pulse is
detected, branch to Normal Operation; if none are
received…
(4) Activate the 32-cycle Start-up Timer one more time
and look for a fan pulse; if a fan pulse is detected,
proceed to Normal Operation; if none are
received…
(5) Proceed to Fan Fault.
(6) End.
4.2 Normal Operation
Normal Operation is an endless loop which may only
be exited by entering shutdown mode or Fan Fault. The
loop can be thought of as executing at the frequency of
the oscillator and PWM.
(1) Reset the missing pulse detector.
(2) Is TC642 in shutdown? If so
a. V
OUT
duty cycle goes to zero.
b. FAULT
is disabled.
c. Exit the loop and wait for V
MIN
> V
REL
to
resume operation (indistinguishable from
power-up).
(3) If an over-temperature fault occurs (V
IN
> V
OTF
),
activate FAULT
; release FAULT when V
IN
< V
OTF
.
(4) Drive V
OUT
to a duty cycle proportional to the
greater of V
IN
and V
MIN
on a cycle by cycle basis.
(5) If a fan pulse is detected, branch back to the start
of the loop (1).
(6) If the missing pulse detector times out …
(7) Activate the 3-cycle Diagnostic Timer and look for
pulses; if a fan pulse is detected, branch back to
the start of the loop (1); if none are received…
(8) Activate the 32-cycle Start-up Timer and look for
pulses; if a fan pulse is detected, branch back to
the start of the loop (1); if none are received…
(9) Quit Normal Operation and go to Fan Fault.
(10) End.
4.3 Fan Fault
Fan fault is an infinite loop wherein the TC642 is
latched in shutdown mode. This mode can only be
released by a reset (i.e., V
MIN
being brought below
V
SHDN
, then above V
REL
, or by power-cycling).
(1) While in this state, FAULT
is latched on (low) and
the V
OUT
output is disabled.
(2) A reset sequence applied to the V
MIN
pin will exit
the loop to Power-Up.
(3) End.
TC642
DS21444D-page 8 2001-2012 Microchip Technology Inc.
FIGURE 4-1: TC642 Behavioral Algorithm Flowchart.
FAULT = 0,
V
OUT
= 0
Cycling
Power?
V
MIN
< V
SHDN
?
Yes
Yes
Yes
No
No
Fan Fault
Power-up
V
MIN
> V
REL
?
Fan Fault
Detected?
Fan Pulse
Detected?
V
MIN
< V
SHDN
Shutdown
V
OUT
= 0
Yes
No
No
Yes
Yes
Power-Up
Normal
Operation
Fan Fault
YES
Power-on
Reset
FAULT = 1
V
MIN
>
V
REL
?
No
Fire Start-up
Timer
(1 SEC)
Fire Start-up
Timer
(1 SEC)
V
MIN
> V
REL
Yes
Fan Fault
Clear
Missing Pulse
Detector
V
OUT
Proportional to Greater
of V
IN
or
V
MIN
V
MIN
< V
SHDN
?
V
IN
> V
OTF
?
M.P.D.
Expired?
Fan Pulse
Detected?
No
No
No
No
No
No
Yes
Yes
Yes
Normal
Operaton
Power-up
Yes
FAULT = 0
Yes
Fire Diagnostic
Timer
(100msec)
Fan Pulse
Detected?
Fan Pulse
Detected?
Fire Start-up
Timer
(1 SEC)
Yes
No
Shutdown
V
OUT
= 0
No
Yes
No
2001-2012 Microchip Technology Inc. DS21444D-page 9
TC642
5.0 TYPICAL APPLICATIONS
Designing with the TC642 involves the following:
(1) The temp sensor network must be configured to
deliver 1.25V to 2.65V on V
IN
for 0% to 100% of the
temperature range to be regulated.
(2) The minimum fan speed (V
MIN
) must be set.
(3) The output drive transistor and associated circuitry
must be selected.
(4) The SENSE network, R
SENSE
and C
SENSE
, must
be designed for maximum efficiency, while
delivering adequate signal amplitude.
(5) If shutdown capability is desired, the drive require-
ments 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 TC642 cir-
cuits 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
analysis. At the very least, anyone contemplating a
design using the TC642 should consult the documenta-
tion for both TC642EV (DS21403) and TC642DEMO
(DS21401).
FIGURE 5-1: Typical Application Circuit.
5.1 Temperature Sensor Design
The temperature signal connected to V
IN
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.
Figure 5-2 shows a simple temperature dependent
voltage divider circuit. RT
1
is a conventional NTC
thermistor while R
1
and R
2
are standard resistors. The
supply voltage, V
DD
, is divided between R
2
and the par-
allel combination of RT
1
and R
1
(for convenience, the
parallel combination of RT
1
and R
1
will be referred to as
R
TEMP
). The resistance of the thermistor at various
temperatures is obtained from the manufacturers
specifications. Thermistors are often referred to in
terms of their resistance at 25°C.
FAULT
SENSE
NTC
R
1
R
2
R
3
R
4
GND
Thermal
Shutdown
Shutdown
(Optional)
Note: *See cautions re
g
ardin
g
latch-up considerations in Section 5.0, "T
y
pical Applications".
Q
1
+12V
+5V*
V
DD
V
IN
V
MIN
V
OUT
R
BASE
R
SENSE
C
SENSE
C
F
1 µF
C
F
TC642
Fan
C
B
1 µF
C
B
0.01 µF
C
B
0.01 µF
1
8
6
7
5
4
2
3

TC642CPA

Mfr. #:
Manufacturer:
Microchip Technology
Description:
Motor / Motion / Ignition Controllers & Drivers w/Fault Dtct
Lifecycle:
New from this manufacturer.
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