UBA2014P datasheet(7/19 Pages) NXP

7 / 19 page

UBA2014_4

Product data sheet

Rev. 04 — 16 October 2008

7 of 19

NXP Semiconductors

UBA2014

600 V driver IV for HF ﬂuorescent lamps

8.9 Power-down mode

The Power-down mode 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 mode by lowering the low-voltage supply below

VDD(reset).

8.10 Capacitive mode protection

The signal across R16 also gives information about the switching behavior 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 (CMD)

circuit assumes that the circuit is in the capacitive mode of operation. As a consequence

the frequency will directly be increased to fmax. The frequency behavior is decoupled from

the voltage at pin CSW until CCSW has been discharged to zero.

8.11 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 approximately 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.

8.12 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.

(1)

(2)

(3)

(4)

Start of ignition is deﬁned as the moment at which the measured lamp voltage crosses the

Vlamp(fail) level; see Section 8.8.

1.8

330

–

--------------------------

IREF

--------------------

ign

0.26

330

–

--------------------------

IREF

--------------------

min

40.5

100

–

----------------------------

IREF

--------------------

max

2.5

min

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