TC646
Power-Up
Normal
Operation
Power-on
Reset
FAULT = 1
Clear Missing
Pulse Detector
Yes
V
IN
< V
SHDN
?
No
Shutdown
V
OUT
= 0
V
IN
> V
REL
?
No
VIN < V
SHDN
?
No
Yes
Yes
Shutdown
V
OUT
= 0
No
Yes
Yes
Auto-
Shutdown
VOUT = 0
V
IN
> V
REL
Auto
Shutdown
V
OUT
= 0
No
V
IN
>
(V
AS
+ V
HAS
)
Yes
FAULT = 0
V
IN
< V
AS
?
No
Yes
Yes
Power-Up
V
IN
< V
AS
?
No
V
IN
>
No
(V
AS
+ V
HAS
)
Hot Start
Fire Start-up
Timer
(1 SEC)
V
IN
> V
OTF
?
No
Yes
Hot Start
V
OUT
Proportional
to V
IN
Fan Pulse
Detected?
Yes
No
Fire Start-up
YES
Timer
(1 SEC)
Yes
Fan Pulse
Detected?
No
No
M.P.D.
Expired?
Yes
Fire
Diagnostic
Timer
(100msec)
Yes
Fan Pulse
Detected?
No
Fan Fault
Yes
Normal
Operation
No
Fan Pulse
Detected?
Fire Start-up
Timer
(1 sec)
Fan Fault
Yes
Fan Pulse
Detected?
No
FAULT = 0,
V
OUT
= 0
No
Fan Fault
Auto-Shutdown
FAULT = 1
V
OUT
= 0
Yes
V
IN
> V
REL
?
V
IN
< V
SHDN
?
Yes
No
Cycling
Power
Yes
No
V
IN
> (V
AS
+ V
HAS
)?
No
Yes
Power-Up
FIGURE 4-1:
TC646 Behavioral Algorithm Flowchart.
2002 Microchip Technology Inc.
DS21446C-page 9
MICROCHIP [ MICROCHIP TECHNOLOGY ]
