UBA2015AP datasheet(19/42 Pages) PHILIPS

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UBA2016A_15_15A

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Objective data sheet

Rev. 1 — 20 May 2011

19 of 42

NXP Semiconductors

UBA2016A/15/15A

600 V fluorescent lamp driver

A programmable end-of-life window is achieved by the internal bias current sink Ibias(EOL).

The effective relative size of the EOL window will decrease in line with the increasing

series resistance connected to pin EOL.

The end-of-life lamp rectifying detection is only active during the Burn state.

7.6.2 End-of-life overvoltage detection

This protection is intended to protect against symmetrical lamp aging. When in Burn state

the voltage on pin VFB exceeds the overvoltage end-of-life threshold voltage Vth(oveol)(VFB)

by more then 50 % of each switching cycle the fault timer will start. Vth(oveol)(VFB) is related

to the regulation voltage on pin IFB Vreg(IFB) that itself is dependent on the voltage on pin

DIM (see Section 7.4.7.1 “Lamp current control and dimming”) according to the formula:

Vth(oveol)(VFB) =a − b × Vreg(IFB)

Parameters a and b can be calculated from the Vth(oveol)(VFB) values given in Table 6.

The end-of-life overvoltage protection is only active during Burn state and (for UBA2015A

and UBA2016A) if the voltage at pin DIM is above the overvoltage end-of-life enable

voltage Ven(oveol)(DIM).

7.6.3 Capacitive mode detection

Under all normal operating conditions the half-bridge switching frequency should be

higher than the load resonance frequency. The load then shows an inductive behavior in

that the load current Iload lags behind the half-bridge voltage VSHHB. If the amplitude and

the phase difference are large enough, the load current will charge any capacitance on pin

SHHB during the non-overlap time tno(LH), and discharge it during the other non-overlap

time tno(HL). As a result the voltage across the switches is almost zero at the moment they

turn on. This is called zero voltage switching; see Figure 14 “Switching”. Zero voltage

switching provides the highest switching efficiency and the least Electromagnetic

Emission (EME).

Capacitive mode switching can occur when, due to any abnormal condition, the switching

frequency is below the load resonance frequency. This can happen when the lamp is

removed. The load current will then keep the backgate diode of the switch that is switched

off conducting during the non-overlap time, and if the other switch is turned on, a sudden

step of the half-bridge voltage to the other supply rail takes place (which causes huge

current spikes). Also cross conduction between the switches can occur during the reverse

recovery of the backgate diode. These effects put huge stress on the power switches,

most of which can only handle capacitive mode switching a few times before they break

down.

To protect against capacitive mode switching the IC monitors pin SHHB during the

non-overlap time tno(LH) between switching off of the low-side switch and switching on of

the high-side switch. If a rise of VSHHB (dVSHHB/dt > Vth(cm)(SHHB)) during tno(LH) is not

detected then the IC will conclude that capacitive mode switching is occurring during the

next full cycle. If capacitive mode is detected longer than the fault activation delay time

tdet(fault) then the IC will enter Stop state.

Capacitive mode detection is active in all oscillating states for all ICs except in the Ignition

state of the UBA2016A if zero voltage switching has been observed. In that case the

UBA2016A switches to hard switching regulation, see Section 7.6.4 “Hard switching

regulation (UBA2016A)”.

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