UCC2975, UCC2976, UCC2977

UCC3975, UCC3976, UCC3977

SLUS499A – NOVEMBER 2001 – REVISED JANUARY 2002

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state diagram

A logic state diagram for the UCC397x family of controllers is shown in Figure 5. During power-up the controller

transitions from UVLO to the momentary startup state. During startup, the COMP pin is preconditioned at

maximum frequency and the OPEN/SD capacitor is discharged before beginning normal operation. In the

normal operating state, the frequency is swept from high to low allowing the lamp to be struck and the current

in the lamp to be regulated.

STARTUP *

OPEN/SD = 0V

COMP = 0V

OSC, OUT active

NORMAL OPERATION

OPEN/SD < 1.5V

COMP < 2.5V

OSC, OUT active

OPEN LAMP *

1.5V < OPEN/SD <2.5V

COMP < 2.5V

OSC, OUT active

NO–LOCK *

COMP > 2.5V

OPEN/SD < 1.5V

OSC, OUT active

COUNT=7?

ERROR

SHUTDOWN

OSC active

OUT off state

UVLO

VDD < 3.0V

OSC inactive

OUT off state

COUNT=0

SHUTDOWN

OPEN/SD > 2.5V

COUNT =0

OSC inactive

OUT off state

Low current VDD,

OPEN/SD

VDD>3.0V

OPEN/SD

< 0.5V

NO

YES

Increment COUNT

OUT off state

UCC3975: OUT1 low, OUT2 low

UCC3976: OUTP high, OUTN high

UCC3977: OUT1 low, OUT2 low

* Momentary states

UDG–01102

Figure 5. State Diagram

The normal operating state can be exited in one of four ways:

The latter two conditions cause an internal retry counter to increment before attempting another startup. If the

application does not operate normally after seven retrys, the controller enters an error induced shutdown state

user commanded shutdown.