DTC646 datasheet(7/30 Pages) MICROCHIP

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 2002-2012 Microchip Technology Inc.

DS21446D-page 7

TC646

FIGURE 3-1:

TC646 Nominal Operation.

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 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 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 VIN becomes greater than

VREL, 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 (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. 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 VIN > (VAS + VHAS)

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 VDD

(50 mV 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

TC646

Status

Normal

Operation

Auto-Shutdown

Mode

Normal

Operation

Shut-

Down

Normal

Operation

GND

Time

TEMP.

Note: If VIN < VAS 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 VIN pin is being

held low or VIN < VAS + VHAS.

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