uba2015t/n1 NXP Semiconductors, uba2015t/n1 Datasheet - Page 20

• Manufacturer Part Number: uba2015t/n1
• Description: 600 V Fluorescent Lamp Driver With Pfc, Linear Dimming And Boost Function
• Manufacturer: NXP Semiconductors

NXP Semiconductors
UBA2016A_15_15A
Objective data sheet
7.6.4 Hard switching regulation (UBA2016A)
7.6.5 Hard switching protection
During ignition a situation may occur where the amplitude of the load current is high and
the half-bridge is at the boundary of capacitive mode switching; see
The load current crosses zero during the non-overlap time. If the amplitude of the load
current is large enough, the UBA2015 and UBA2015A might not detect capacitive mode
because V
conducting again when the other switch switches on. Since this can only happen if the
load current crosses zero during the non-overlap time, the momentary value of the load
current at the end of the non-overlap time will be not so big, and will not necessarily
damage the switches.
Depending on the topology used, the DC blocking capacitor might be charged via the
lamp(s) at the moment the lamp(s) ignite. This will cause a temporary DC current addition
to the load current that might be interpreted by the UBA2015 and UBA2015A as
capacitive mode switching. If this happens the DC blocking capacitor must be reduced or
pre-charged. The UBA2016A does not have this problem.
In Ignition state the UBA2016A capacitive mode detection is disabled and replaced by
hard switching regulation. This enables ignition without voltage feedback.
The hard switching regulation measures the voltage step on pin SHHB at the end of the
non-overlap time t
frequency by discharging pin CIFB with a current according to the formula:
I
In this way the IC keeps the switching frequency during ignition at the point where there is
still a small phase difference between the load current and the half-bridge voltage, and the
switching losses due to hard switching are limited. This is assuming that it is not already
held at the higher frequency by the overvoltage protection or coil saturation protection.
As
load current is to small. This might happen when the IC enters Ignition state at the end of
preheat and the frequency is still relatively high. To prevent the IC from getting stuck at
f
observed, that is if V
The hard switching level V
level is determined by measuring the voltage step on pin SHHB on the rising edge of pin
GHHB; see
protection threshold voltage on pin SHHB (V
dch(hswr)CIFB
high
Figure 14 “Switching”
the hard switching regulation is disabled until zero voltage switching has been
SHHB
Figure 14
= (V
All information provided in this document is subject to legal disclaimers.
did rise before going down again. The backgate diode of one switch is
step(SHHB)
no(LH)
step(SHHB)
“Switching”. When V
(V
Rev. 1 — 20 May 2011
shows, hard switching also occurs when the amplitude of the
step(SHHB)
step(SHHB)
− V
th(hswr)SHHB
< V
th(zvs)SHHB
in
step is measured via pin SHHB. The hard switching
Figure 14
) × g
step(SHHB)
.
th(hswp)SHHB
m(hswr)
“Switching”) and increases the switching
UBA2016A/15/15A
is above the hard switching
) the fault timer is activated.
600 V fluorescent lamp driver
Figure 14
© NXP B.V. 2011. All rights reserved.
“Switching”.
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