UBA2071ATS datasheet(21/35 Pages) NXP

21 / 35 page

UBA2071_A_1

Product data sheet

Rev. 01 — 23 June 2008

21 of 35

NXP Semiconductors

UBA2071; UBA2071A

Half bridge control IC for CCFL backlighting

times in case overvoltage and overvoltage extra are detected at the same moment (curve

(1)) and if overvoltage, overvoltage extra and hard switching are detected at the same

moment (curve (2)). The ﬁrst parts of the curves are dashed because an internal ﬁlter

makes that VFB needs to be above Vth(ovextra)(VFB) for at least about 1 µs for the

overvoltage extra to react at all.

If a normal overvoltage fault was already present for more than about 840

µs before

overvoltage extra detection started or hard switching was already detected for more than

about 55

µs before overvoltage extra detection started, then the IC will shut down about

µs after overvoltage extra is detected.

8.14.5 Current feedback open or short protection

If the IFB pin is left open or shorted to SGND, the peak of the absolute value of the voltage

at the IFB pin will be below the IFB open/short protection threshold Vth(osp)(IFB) and the

fault timer is started.

The IFB open/short protection looks only at the IFB pin voltage if the voltage at the CSWP

pin is equal to the voltage at the CVFB pin. During PWM dimming this is when the lamps

are on and in current regulation or voltage regulation (so not during PWM lamps-off period

and not during the re-ignition frequency sweep).

8.14.6 Overcurrent detection

When the peak of the absolute value of the voltage across the current sense resistor

(connected to the IFB pin) exceeds the OC reference level Vth(ocd)(IFB) and the IC is

oscillating at fsw(max), overcurrent is detected. As result PWM dimming is disabled and the

fault timer is started.

8.14.7 Arcing detection

If arcing occurs, for instance due to a bad lamp connection, it causes repetitive short

current spikes that can be seen as voltage spikes at the IFB input. The arcing detection

circuit is directly connected to the IFB pin, so it can only see spikes with a positive polarity.

Usually that will be sufﬁcient. It can detect spikes with amplitude above Vth(det)arc(IFB) and a

Fig 16. Shutdown time at over voltage extra detection

VFB above OVE (%)

100

014aaa112

200

300

100

400

500

stop time

(

µs)

(1)

(2)

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