TC649 Microchip, TC649 Datasheet - Page 6

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

TC649
FIGURE 3-1:
3.7
If an unconditional shutdown and/or device reset is
desired, the TC649 may be placed in shutdown mode
by forcing V
Figure 3-1). In this mode, all functions cease and the
FAULT output is unconditionally inactive. The TC649
should not be shut down unless all heat producing activ-
ity in the system is at a negligible level. The TC649 exits
shutdown mode when V
the release voltage.
Entering shutdown mode also performs a complete
device reset. Shutdown mode resets the TC649 into its
power-up state. The Start-up and Fault Timers and any
current faults are cleared. FAULT is unconditionally
inactive in shutdown mode. Upon exiting shutdown
mode (V
and normal operation will resume, assuming no fault
conditions exist and V
DS21449C-page 6
Note:
V
V
AS
IN
V
TC649
Status
+ V
V
SHDN
GND
REL
V
2.6V
IN
Shutdown Mode (RESET)
1.2V
HAS
AS
> V
If V
down mode, the fan will not restart, but will
be in auto-shutdown mode.
IN
REL
IN
to a logic low (i.e., V
), the Start-up Timer will be triggered
< V
Operation
AS
Normal
IN
TC649 Nominal Operation.
IN
> (V
when the device exits shut-
becomes greater than V
AS
+ V
HAS
IN
).
< V
Auto-Shutdown
SHDN
Mode
) (see
REL
,
TIME
If a fan fault has occurred and the device has latched
itself into shutdown mode, performing a reset will not
clear the fault unless V
greater than V
the fan will not be restarted, and there will be no way to
establish that the fan fault has been cleared. To ensure
that a complete reset takes place, the user’s circuitry
must ensure that V
is released from shutdown mode. A recommended
algorithm for management of the TC649 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 V
= 5.0V), is designed into the V
The levels specified for V
“Electrical Characteristics”, include this hysteresis plus
adequate margin to account for normal variations in the
absolute value of the threshold and hysteresis.
CAUTION: The fan will remain off as long as the V
pin is being held low or V
Operation
Normal
AS
t
RESET
Down
Shut-
+ V
IN
HAS
> (V
IN
SHDN
upon exiting shutdown mode,
> (V
AS
IN
2002 Microchip Technology Inc.
< V
Operation
+ V
Normal
AS
and V
AS
HAS
SHDN
+ V
+ V
REL
) when the device
HAS
DD
HAS
/V
REL
in Section 1.0,
(50mV at V
). If V
.
threshold.
TEMP.
LO
IN
HI
is not
DD
IN