Datasheet

UBA20260 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Product data sheet Rev. 2 — 10 October 2011 8 of 30
NXP Semiconductors
UBA20260
600 V driver IC for step dimmable CFLs
7.2.5 Boost state and transition to burn state
When ignition is detected, by measuring lamp current on the CSI pin, the circuit enters the
boost state. Figure 7
shows the boost and burn state in more detail. In the boost state, the
nominal burn state lamp current can be increased with a fixed boost ratio of 1.5. This ratio
boosts the slow luminescence increase of a cold amalgam CFL lamp, provided the IC is in
the DIM_1 mode. If the IC is at a temperature (T
j(bp)bst
) before entering the boost state, the
burn state is bypassed.
A boost timing circuit is included to determine the boost time and transition to burn time.
The circuit consists of a clock generator comprising C
CB
, R
ext(RREF)
and a 64-step counter.
When the timer is not operating, C
CB
is discharged below the V
th(CB)min
level of 1.1 V. This
voltage, about 0.6 V, is still higher than the level at which the comparator on C
CB
detects if
the CB pin is shorted to ground.
The boost time consists of 63 saw-tooth pulses on the CB pin, automatically followed by
the transition time at the CP pin. The 32 saw-tooth pulses form the transition time from
boost to burn and enables a smooth transition between the current controlled boost and
burn state. The total transition time is approximately four times the preheat time (see
Figure 6
).
Fig 5. Retry cycle
001aan537
voltage
(V)
V
CP
V
th(CP)max
5 V
0 V
V
th(CP)min
V
th(rel)CP
t
ph
t
ph
restart
delay time
startup
time
t
en(ign)
t
en(ign)
2
nd
startup
t
d(restart)
discharge
to 0 V
time (s)
1
st
preheat
time
1
st
ignition
enabling time
2
nd
ignition
enabling time
2
nd
preheat
time
2
nd
failed
ignition
attempt
1
st
failed
ignition
attempt
POWER DOWN STATE
HOLD STATE