TC649 Microchip, TC649 Datasheet - Page 7

• Manufacturer Part Number: TC649
• Description: PWM Fan Speed Controller
• Manufacturer: Microchip

4.0
The flowcharts describing the TC649’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, auto-shutdown
mode or Fan Fault. The loop can be thought of as exe-
cuting at the frequency of the oscillator and PWM.
(1) Reset the missing pulse detector.
(2) Is TC649 in shutdown or auto-shutdown mode? If
(3) Drive V
(4) If a fan pulse is detected, branch back to the start
(5) If the missing pulse detector times out …
(6) Activate the 3-cycle Diagnostic Timer and look for
(7) Activate the 32-cycle Start-up Timer and look for
(8) Quit Normal Operation and go to Fan Fault.
(9) End.
2002 Microchip Technology Inc.
pulses; if a fan pulse is detected, branch back to
the start of the loop (1); if none are received…
a. V
b. FAULT is disabled.
c. Exit the loop and wait for V
cycle by cycle basis.
of the loop (1).
pulses; if a fan pulse is detected, branch back to
the start of the loop (1); if none are received…
or auto-shutdown 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 fan pulse; if a fan pulse is
detected, proceed to Normal Operation; if none
are received…
so…
resume operation.
OUT
SYSTEM BEHAVIOR
Power-Up
Normal Operation
OUT
OUT
duty cycle goes to zero.
output on for 32 cycles of the PWM
to a duty cycle proportional to V
IN
> V
IN
> (V
AS
)...
AS
+ V
HAS
IN
on a
) to
4.3
Fan Fault is an infinite loop wherein the TC649 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
loop to Power-up.
, then above (V
Fan Fault
OUT
output is disabled.
AS
+ V
HAS
IN
) or by power-cycling).
being brought below
DS21449C-page 7
TC649
IN
pin will exit the