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UBA2016A_15_15A

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Objective data sheet

Rev. 1 — 20 May 2011

20 of 42

NXP Semiconductors

UBA2016A/15/15A

600 V fluorescent lamp driver

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 Figure 14 “Switching”.

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 VSHHB did rise before going down again. The backgate diode of one switch is

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.

7.6.4 Hard switching regulation (UBA2016A)

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 tno(LH) (Vstep(SHHB) in Figure 14 “Switching”) and increases the switching

frequency by discharging pin CIFB with a current according to the formula:

Idch(hswr)CIFB =(Vstep(SHHB) − Vth(hswr)SHHB)× gm(hswr)

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 Figure 14 “Switching” shows, hard switching also occurs when the amplitude of the

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

fhigh the hard switching regulation is disabled until zero voltage switching has been

observed, that is if Vstep(SHHB) <Vth(zvs)SHHB.

7.6.5 Hard switching protection

The hard switching level Vstep(SHHB) step is measured via pin SHHB. The hard switching

level is determined by measuring the voltage step on pin SHHB on the rising edge of pin

GHHB; see Figure 14 “Switching”. When Vstep(SHHB) is above the hard switching

protection threshold voltage on pin SHHB (Vth(hswp)SHHB) the fault timer is activated.

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