TC646
TC646
Status
2.6V
Normal
Operation
Auto-Shutdown
Mode
Normal
Operation
Shut-
Down
Normal
Operation
HI
V
AS
+ V
HAS
V
AS
TEMP.
1.2V
V
IN
V
REL
V
SHDN
t
RESET
LO
GND
Time
FIGURE 3-1:
TC646 Nominal Operation.
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
IN
> (V
AS
+ V
HAS
). If V
IN
is not
greater than (V
AS
+ V
HAS
) upon exiting shutdown
mode, the fan will not be restarted. Consequently, there
is 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
IN
> (V
AS
+ V
HAS
)
when the device is released from shutdown mode. A
recommended algorithm for management of the TC646
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
DD
(50 mV at V
DD
= 5.0V), is designed into the V
SHDN
/
V
REL
threshold. The levels specified for V
SHDN
and
V
REL
in Section 1.0, “Electrical Characteristics”,
include this hysteresis plus adequate margin to
account for normal variations in the absolute value of
the threshold and hysteresis.
3.7
Shutdown Mode (Reset)
If an unconditional shutdown and/or device reset is
desired, the TC646 may be placed in shutdown mode
by forcing V
IN
to a logic low (i.e., V
IN
< V
SHDN
) (see
FAULT output is unconditionally inactive. The TC646
should not be shut down unless all heat producing
activity in the system is at a negligible level. The TC646
exits shutdown mode when V
IN
becomes greater than
V
REL
, the release voltage.
Entering shutdown mode also performs a complete
device reset. Shutdown mode resets the TC646 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
IN
> V
REL
), the Start-up Timer will be triggered
and normal operation will resume, assuming no fault
conditions exist and V
IN
> V
AS
+ V
HAS
Note:
If V
IN
< V
AS
when the device exits shutdown
mode, the fan will not restart as it will be in auto-shut-
down mode.
CAUTION:
Shutdown mode is unconditional. That is,
the fan will remain off as long as the V
IN
pin is being
held low or V
IN
< V
AS
+ V
HAS
.
2002 Microchip Technology Inc.
DS21446C-page 7
MICROCHIP [ MICROCHIP TECHNOLOGY ]
