TC649VUATR View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

TC649VUATR

PWM Fan Speed Controller with Auto-Shutdown and FanSense™ Technology

Microchip Technology 

4.0 SYSTEM BEHAVIOR

The flowcharts describing the TC649’s behavioral

algorithm are shown in Figure 4-1. They can be

summarized as follows:

4.1 Power-Up

(1) Assuming the device is not being held in shutdown

or auto-shutdown mode (VIN > VAS)...

(2) Turn VOUT output on for 32 cycles of the PWM

clock. This ensures that the fan will start from a

dead stop.

(3) During this Start-up Timer, if a fan pulse is

detected, branch to Normal Operation; if none are

received…

(4) Activate the 32-cycle Start-up Timer one more

time and look for fan pulse; if a fan pulse is

detected, proceed to Normal Operation; if none

are received…

(5) Proceed to Fan Fault.

(6) End.

4.2 Normal Operation

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

so…

a. VOUT duty cycle goes to zero.

b. FAULT is disabled.

c. Exit the loop and wait for VIN > (VAS + VHAS) to

resume operation.

(3) Drive VOUT to a duty cycle proportional to VIN on a

cycle by cycle basis.

(4) If a fan pulse is detected, branch back to the start

of the loop (1).

(5) If the missing pulse detector times out …

(6) Activate the 3-cycle Diagnostic Timer and look for

pulses; if a fan pulse is detected, branch back to

the start of the loop (1); if none are received…

(7) Activate the 32-cycle Start-up Timer and look for

pulses; if a fan pulse is detected, branch back to

the start of the loop (1); if none are received…

(8) Quit Normal Operation and go to Fan Fault.

(9) End.

TC649

4.3 Fan Fault

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., VIN being brought below

VSHDN, then above (VAS + VHAS) or by power-cycling).

(1) While in this state, FAULT is latched on (low) and

the VOUT output is disabled.

(2) A reset sequence applied to the VIN pin will exit the

loop to Power-up.

(3) End.

 2002 Microchip Technology Inc.

DS21449C-page 7

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