TC649 datasheet(6/28 Pages) MICROCHIP

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TC649

DS21449C-page 6

 2002 Microchip Technology Inc.

FIGURE 3-1:

TC649 Nominal Operation.

3.7

Shutdown Mode (RESET)

If an unconditional shutdown and/or device reset is

desired, the TC649 may be placed in shutdown mode

by forcing VIN to a logic low (i.e., VIN < VSHDN) (see

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 VIN becomes greater than VREL,

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 (VIN > VREL), the Start-up Timer will be triggered

and normal operation will resume, assuming no fault

conditions exist and VIN > (VAS + VHAS).

If a fan fault has occurred and the device has latched

itself into shutdown mode, performing a reset will not

clear the fault unless VIN > (VAS + VHAS). If VIN is not

greater than VAS + VHAS upon exiting shutdown mode,

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 VIN > (VAS + VHAS) when the device

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 VDD (50mV at VDD

= 5.0V), is designed into the VSHDN/VREL threshold.

The levels specified for VSHDN and VREL 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.

2.6V

VAS + VHAS

VIN

tRESET

VREL

VSHDN

VAS

1.2V

TC649

Status

Normal

Operation

Auto-Shutdown

Mode

Normal

Operation

Shut-

Down

Normal

Operation

GND

TIME

TEMP.

Note:

If VIN < VAS when the device exits shut-

down mode, the fan will not restart, but will

be in auto-shutdown mode.

CAUTION: The fan will remain off as long as the VIN

pin is being held low or VIN < VAS+ VHAS.

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