TC642 Microchip, TC642 Datasheet - Page 7

• Manufacturer Part Number: TC642
• Description: PWM Fan Speed Controller
• Manufacturer: Microchip

4.0
The flowcharts describing the TC642’s behavioral
algorithm are shown in Figure 4-1. They can be
summarized as follows:
4.1
(1) Assuming the device is not being held in shutdown
(2) Turn V
(3) During this Start-up Timer, if a fan pulse is
(4) Activate the 32-cycle Start-up Timer one more
(5) Proceed to Fan Fault.
(6) End.
4.2
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…
(3) If an over-temperature fault occurs (V
(4) Drive V
(5) If a fan pulse is detected, branch back to the start
(6) If the missing pulse detector times out …
(7) Activate the 3-cycle Diagnostic Timer and look for
(8) Activate the 32-cycle Start-up Timer and look for
(9) Quit Normal Operation and go to Fan Fault.
(10) End.
2002 Microchip Technology Inc.
of the loop (1).
pulses; if a fan pulse is detected, branch back to
the start of the loop (1); if none are received…
pulses; if a fan pulse is detected, branch back to
the start of the loop (1); if none are received…
greater of V
mode (V
clock. This ensures that the fan will start from a
dead stop.
detected, branch to Normal Operation; if none are
received…
time and look for a fan pulse; if a fan pulse is
detected, proceed to Normal Operation; if none
are received…
activate FAULT; release FAULT when V
a. V
b. FAULT is disabled.
c. Exit the loop and wait for V
resume
power-up).
OUT
SYSTEM BEHAVIOR
Power-Up
Normal Operation
OUT
OUT
MIN
duty cycle goes to zero.
output on for 32 cycles of the PWM
IN
> V
to a duty cycle proportional to the
operation
and V
REL
)…
MIN
on a cycle by cycle basis.
(indistinguishable
MIN
> V
REL
IN
IN
to
> V
< V
OTF
from
OTF
),
.
4.3
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
V
(1) While in this state, FAULT is latched on (low) and
(2) A reset sequence applied to the V
(3) End.
SHDN
the V
the loop to Power-Up.
, then above V
Fan Fault
OUT
output is disabled.
REL
, or by power-cycling).
MIN
being brought below
DS21444C-page 7
TC642
MIN
pin will exit