Datasheet

UBA2071_A_1 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 01 — 23 June 2008 22 of 35
NXP Semiconductors
UBA2071; UBA2071A
Half bridge control IC for CCFL backlighting
duration longer than t
spike(min)
. Each spike will trigger an internal one-shot, which signals to
the control circuits that arcing has been detected. When arcing is detected, PWM dimming
is disabled and the fault timer is started.
8.14.8 Ignition Failure (IF)
When the current control loop comes close to its regulation point, the lamps are assumed
to be on (ignited). This is when the average absolute voltage on the IFB pin is above
V
th(lod)(IFB)
. If the lamps are not on when the ignition sweep is finished, (switching
frequency has reached f
sw(min)
), then an ignition failure is detected, PWM dimming is
disabled and the fault timer is started.
8.14.9 The NONFAULT pin
The NONFAULT pin provides bidirectional signalling of the fault status between the IC and
any external circuit. When no fault is detected, the voltage on the pin is pulled high to
V
oc(NONFAULT)
by an internal current source.
An external circuit can signal to the IC that a fault has been detected by pulling a current
larger than I
trig(I)NONFAULT
from the NONFAULT pin. The IC will detect the current drawn
from the pin and start the fault timer. To prevent interference with the PWM dimming, the
IC will only look at the NONFAULT pin during the period when the lamp current regulation
loop is closed (when ).
When the IC detects an internal fault, see Section 8.14.2 to Section 8.14.8), it signals this
via the NONFAULT pin by pulling the pin down (after the fault output delay time t
d(o)fault)
).
At this point the IC can no longer detect the external fault. However, by then the fault timer
is already running.
Fig 17. Input and output levels at the NONFAULT pin
V
CSWP
V
CVFB
=
I
sink(NONFAULT)
NONFAULT
pin current
NONFAULT
pin voltage
0
V
trig(I)NONFAULT
V
oc(NONFAULT)
in: low (active)
out: high (inactive)
in: unknown
out: low (active)
I
trig(I)NONFAULT
I
sc(NONFAULT)
in: high (inactive)
out: high (inactive)
load line
014aaa113
1 V