UBA2015AP datasheet(17/42 Pages) PHILIPS

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UBA2016A_15_15A

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Objective data sheet

Rev. 1 — 20 May 2011

17 of 42

NXP Semiconductors

UBA2016A/15/15A

600 V fluorescent lamp driver

However, the switching frequency can never go below fsw(low) (unless for UBA2016A when

the boost function is active, see Section 7.4.7.3). If the regulation level is not reached at

fsw(low) the IC will stay at fsw(low) (point E in Figure 10 and Figure 11).

7.4.7.2

Operation without lamp current control

To operate the lamp without current control the lamp current sense pin IFB must be

connected to ground. The lamp now operates at the lowest frequency fsw(low) (point E in

Figure 10 or Figure 11). Dimming is not supported in this case.

7.4.7.3

Boost

The boost feature is available only in the UBA2016A to support shorter run up times. The

boost function changes the half-bridge switching frequency by lowering the lowest

possible switching frequency from fsw(low) to fsw(bst)(low) and increasing the lamp current set

point Vreg(IFB) by adding a multiple of the boost current to the OTA output current which

translates to an extra voltage being added to Vreg(ref). During boost time, the frequency is

lowered, and as a consequence of the inductive load the lamp current is increased.

The implementation of the boost function is shown in Figure 12 “Lamp current control”.

The boost input is a current input with an input range of 0 to Isat(BOOST). The input current

is internally clamped at Isat(BOOST). If the input current at the pin is above Isat(BOOST) the

effect will not become bigger. The voltage on the pin is determined by the voltage drop

across the internal current mirror input and limited by an internal clamp circuit if the input

current at the pin rises above Isat(BOOST). For maximum current allowed into the pin; see

Table 4. An example of how boost function can be implemented is shown in Figure 13.

The boost current is determined by resistor RBOOST. Rbias provides a small threshold for

the boost function and with capacitor CBOOST keeps the BOOST pin at a defined (inactive)

level (0 V) during normal lamp operation (after the boost period). The boost time constant

is reflected by the sum of capacitors Chv and CBOOST and RBOOST. Resistor Rhv and

capacitor CBOOST filter out the ripple on Vo(PFC).

An example of component values for Vo(PFC) =430 V is:

Rhv =22 MΩ (500 V); Chv = 100 nF (500 V); Dreset = 1N4148; CBOOST = 150 nF (63 V);

RBOOST =10MΩ and Rbias =10MΩ.

Fig 13. Boost application example; UBA2016A

001aam539

Dreset

Cboost

CBUS

Vo(PFC)

Chv

BOOST

RBOOST

Rhv

Rbias

UBA2016A

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