UBA2014_4 © NXP B.V. 2008. All rights reserved.
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 V
lamp(fail)
. In the Power-down mode the oscillator will be stopped and
both TR1 and TR2 will be non-conductive. The V
DD
supply is internally clamped. The
circuit is released from the Power-down mode by lowering the low-voltage supply below
V
DD(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 V
CMD
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 f
max
. The frequency behavior is decoupled from
the voltage at pin CSW until C
CSW
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
V
CS
, V
PCS
and V
ACM
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
V
lamp(fail)
level; see Section 8.8.
t
ph
1.8
C
CT
330 10
9–
×
--------------------------
R
IREF
33 10
3
×
--------------------
××=
t
ign
0.26
C
CT
330 10
9–
×
--------------------------
R
IREF
33 10
3
×
--------------------
××=
f
min
40.5 10
3
×
100 10
12–
×
C
CF
----------------------------
33 10
3
×
R
IREF
--------------------
××=
f
max
2.5 f
min
×=
