UBA2014 datasheet(7/20 Pages) PHILIPS

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2002 May 16

Philips Semiconductors

Product speciﬁcation

600 V driver IC for HF ﬂuorescent lamps

UBA2014

Lamp failure mode

DURING IGNITION STATE

If the lamp does not ignite, the voltage level increases.

When the lamp voltage exceeds the Vlamp(max) level, the

voltage will be regulated at the Vlamp(max) level; see Fig.6.

At crossing the Vlamp(fail) level the ignition timer was

already started. If the voltage at pin LVS is above the

Vlamp(fail) level at the end of the ignition time the circuit

stops oscillating and is forced in a Power-down mode. The

circuit will be reset only when the supply voltage is

powered-down.

DURING BURN STATE

If the lamp fails during normal operation, the voltage

across the lamp will increase and the lamp voltage will

exceed the Vlamp(fail) level; see Fig.7. At that moment the

ignition timer is started. If the lamp voltage increases

further it will reach the Vlamp(max) level. This forces the

circuit to re-enter the ignition state and results in an

attempt to re-ignite the lamp. If during restart the lamp still

fails, the voltage remains high until the end of the ignition

time. At the end of the ignition time the circuit stops

oscillating and the circuit will enter in the Power-down

mode.

Power-down state

The Power-down state will be entered if, at the end of the

ignition time, the voltage at pin LVS is above Vlamp(fail).

In the Power-down mode the oscillator will be stopped and

both TR1 and TR2 will be non-conductive. The VDD supply

is internally clamped. The circuit is released from the

Power-down state by lowering the low voltage supply

below VDD(reset).

Capacitive mode protection

The signal across R16 also gives information about the

switching behaviour of the half bridge.

If, after the preheat state, the voltage across the ACM

resistor (R16) does not exceed the VCMD level during the

non-overlap time, the Capacitive Mode Detection circuit

(CMD) assumes that the circuit is in the capacitive mode

of operation. As a consequence the frequency will directly

be increased to fmax. The frequency behaviour is

decoupled from the voltage at pin CSW until CCSW has

been discharged to zero.

Charge coupling

Due to parasitic capacitive coupling to the high voltage

circuitry all pins are burdened with a repetitive charge

injection. Given the typical application the pins IREF and

CF are sensitive to this charge injection. For charge

coupling of

±8 pC, a safe functional operation of the IC is

guaranteed, independent of the current level.

Charge coupling at current levels below 50

µA will not

interfere with the accuracy of the VCS, VPCS and VACM

levels.

Charge coupling at current levels below 20

µA will not

interfere with the accuracy of any parameter.

Design equations

The following design equations are used to calculate the

desired preheat time, the maximum ignition time, and the

minimum and the maximum switching frequency.

tph = 1.7 × 10−4 × CCT × RIREF (s)

tign = 3.1 × 10−5 × CCT × RIREF (s)

in kHz

fmax = 2.5 × fmin (kHz)

with CCT in nF, RIREF in kΩ, and CCF in pF. Start of ignition

is defined as the moment at which the measured lamp

voltage crosses the Vlamp(fail) level; see Section “Lamp

failure mode”.

min

125

IREF

()

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