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 15 of 30
NXP Semiconductors
UBA20260
600 V driver IC for step dimmable CFLs
switching cycle. The injected current is maintained until the end of the switching cycle.
This action immediately increases the half-bridge switching frequency. Additionally, for
each successive cycle that coil saturation is detected, capacitor C
CI
discharges enabling
ignition time-out detection in the ignition state.
CSP is triggered when the voltage on the SLS pin exceeds V
th(sat)SLS
(typically 2.5 V). The
voltage V
i(SLS)
on the SLS pin is determined by the external resistor R
SLS
value and also
sets the preheat current.
7.5.2 Overcurrent protection
OCP is active in both the burn and boost states but not during boost transition.
Overcurrent is detected, when the peak voltage of the absolute value across the current
sense resistor connected to the SLS pin exceeds the OCP reference level V
th(ocp)SLS
. A
current I
o(CP)
is then sunk from the capacitor connected to the CP pin for the next full
cycle.
If overcurrent is not present at the end of this cycle, the current is disabled. A current,
equal to I
o(CP)
is sourced to the CP pin instead. If overcurrent occurs in more than half the
number of cycles, a net discharging of the capacitor connected to the CP pin occurs.
When the voltage on the CP pin drops below V
th(CP)min
, the IC enters Power-down mode.
During a continuous overcurrent condition, the overcurrent fault time of t
fault(oc)
takes
1
⁄
9
t
ph
after which the IC enters Power-down mode. The V
th(ocp)SLS
level is the same as
the V
th(sat)SLS
level during the ignition state.
7.5.3 Overpower protection
OPP is active in the boost and burn state. The lamp current is limited and regulated in all
dim step states to the internal dim step reference voltage levels. These reference voltage
levels are derived from an internal reference voltage. Consequently, supply voltage
fluctuations in the mains supply voltage during overvoltage situations do not affect these
reference voltage levels.
When the lamp is in the first dim mode (no dimming), the current is limited and regulated
to the nominal lamp current. In addition, in the boost state the first dim mode boosted by a
factor of 1.5.
7.5.4 Capacitive mode protection
CMP is active in the ignition, burn and boost states and during boost transition. The signal
across resistor R
SLS
also provides information about the half-bridge switching behavior.
When conditions are normal, the current flows from the LS transistor source to the
half-bridge when the LS transistor is switched on. This results in a negative voltage on the
SLS pin.
As the circuit yields to capacitive mode, the voltage becomes smaller and eventually
reverses polarity. CMP prevents this action by checking if the voltage on the SLS pin is
above the V
th(capm)SLS
level.
If the voltage across resistor R
SLS
is above the V
th(capm)SLS
threshold when the LS
transistor is switched on, the circuit recognizes it as capacitive mode. When capacitive
mode is detected, the currents from the OTA, which normally regulate the lamp current,
are disabled. Then the capacitive mode sink current I
o(CI)
is enabled.
