UM10561 Datasheet, PDF(11/24 Page) NXP Semiconductors – UBA2017AT reference design for 420 V (DC)

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UM10561 Datasheet, PDF (11/24 Pages) NXP Semiconductors – UBA2017AT reference design for 420 V (DC)

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NXP Semiconductors

UM10561

UBA2017AT reference design for 420 V (DC)

5.3 Functional description

The DC supply voltage is applied to the board and current flows through R3 and R4 to the

supply of the controller (VDD pin). When the current through R3 and R4 is higher than

240 ïA (Istb(VDD)) of the controller the VDD voltage rises. When the VDD voltage is above

4.2 V (Vrst(VDD)), the half-bridge circuit low-side MOSFET switches on and the floating

supply capacitor C32 is pre-charged.

The controller starts oscillating when the VDD voltage is above the 12.4 V (Vstartup(VDD)).

The HB gate drivers start oscillating at 100 kHz (fsw(high)). The dV/dt supply using

capacitor C8 takes over the VDD supply to supply the IC with enough energy for the gate

drivers. The preheat timer starts and the controller sweeps down the frequency from 100

kHz to the preheat frequency. The PH/EN pin sets the preheat frequency level. The

oscillator remains at the preheat frequency until the preheat timer has ended.

When the preheat ends, the controller sweeps down the half-bridge switching frequency.

The lamp ignites when the LC tank voltage reaches the lamp ignition voltage. The ignition

frequency is typically 60 kHz. The lamp current increases and the LC tank voltage

decreases. The controller senses the lamp current and LC tank voltage. The controller

assumes that the lamp is on when the lamp current is high enough and the LC tank

voltage is low enough for 3 ms. The representation of the states is VIFB > Vth(lod)IFB and

VVFB < Vth(lod)VFB for td(lod). The controller enters burn state.

In burn state, all the protective features are activated. The controller closes the lamp

current control loop and the oscillator regulates the half-bridge switching frequency. The

half-bridge frequency is controlled. It reaches the set point when the average absolute IFB

pin voltage equals the DIM pin voltage.

5.3.1 Start-up current and relamp function

The VDD supply of the IC is charged using a start-up current derived from the rectified

mains voltage. Resistors R3 and R4 provide the current path and determines the start-up

voltage level.

When the lamp is removed while set to deep dimming, the protection must trigger the

controller to shut down. In this board, transistor Q7 pulls down the VDD voltage. The

signals Lamp1 and Lamp2 sense the filaments of the lamps and control transistor Q7. The

pull down by Q7 is released when all lamps are inserted.

UM10561

User manual

All information provided in this document is subject to legal disclaimers.

Rev. 1 â 13 August 2012

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