Datasheet

UBA2071_A_1 © NXP B.V. 2008. All rights reserved.
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 V
th(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
1 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 V
th(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 V
th(ocd)(IFB)
and the IC is
oscillating at f
sw(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 V
th(det)arc(IFB)
and a
Fig 16. Shutdown time at over voltage extra detection
VFB above OVE (%)
0 1008040 6020
014aaa112
200
300
100
400
500
stop time
(µs)
0
(1)
(2)