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UBA2016A_15_15A

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Objective data sheet

Rev. 1 — 20 May 2011

15 of 42

NXP Semiconductors

UBA2016A/15/15A

600 V fluorescent lamp driver

7.4.7.1

Lamp current control and dimming

The AC lamp current is sensed by an external resistor connected to pin IFB. The resulting

AC voltage on pin IFB is internally Double-Side Rectified (DSR), and compared to a

reference level by an OTA. This reference level is determined by the internal reference

regulation level Vreg(ref) and the voltage on the DIM input (UBA2015A and UBA2016A

only), as shown in Figure 12 “Lamp current control”.

Definition: the regulation voltage on pin IFB (Vreg(IFB)) is the level seen from outside the IC

to which the IC will try to regulate the average absolute voltage on pin IFB.

If the DIM input is not present or not connected or VDIM >Vreg(ref) then Vreg(IFB) is

Vreg(ref) + non-idealities from the OTA and the DSR else Vreg(IFB) =VDIM + non-idealities

from OTA and DSR.

For the UBA2016A Vreg(IFB) also depends on the input current on pin BOOST (IBOOST).

The boost current is multiplied and added to the OTA output current which translates to an

extra voltage being added to Vreg(ref). See Section 7.4.7.3 “Boost” for further detail about

the boost function. For the remainder of this Section we will assume IBOOST =0.

For the UBA2015A and UBA2016A the DIM input controls the lamp current set point. The

DIM input level is internally clamped to Vreg(ref). The lowest possible DIM input level is set

by the bias current on pin DIM Ibias(DIM) and the external resistance on the pin. If no

dimming is required, pin DIM can be left open or connected via a capacitor to ground. The

internal current source Ibias(DIM) will then charge the pin until it is internally clamped to

Vreg(ref).

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