UBA20270 Просмотр технического описания (PDF) - NXP Semiconductors.

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UBA20270

600 V Driver IC for dimmable compact fluorescent lamps

NXP Semiconductors. 

NXP Semiconductors

UBA20270

600 V Driver IC for dimmable compact fluorescent lamps

7.1 Lamp start-up cycle

7.1.1 Reset state

The UBA20270 is in a reset state while the supply voltage on the VDD pin is below the

VDD(rst) level. In the reset state, a part of the internal supply is turned off, all registers,

counters and timers are undefined. In addition, the hold state latch is reset and both the

applied external high and low-side transistor (Q1, Q2) are non-conductive. During

power-up, the low voltage supply capacitor on the VDD pin is charged via an external

start-up resistor. When the voltage on the VDD pin is above the VDD(rst) level, the start-up

state is entered. The UBA20270 enters the reset state when the supply voltage on the

VDD pin drops lower than VDD(rst).

7.1.2 Start-up state

Start-up is achieved by charging the low voltage supply capacitor on the VDD pin via an

external start-up resistor. At start-up the High-Side (HS) transistor is non-conductive and

the Low-Side (LS) is conductive to enable charging of the bootstrap capacitor. This

capacitor supplies the HS driver and level shifter circuit connected between the FS and

HBO pin. A DC reset circuit is incorporated in the ICs HS driver. This circuit ensures that

lower than the lockout voltage on the FS pin the output voltage (VGHS - VHBO) is zero.

As the start-up state is entered, the circuit only starts oscillating when the low voltage

supply (VDD) reaches the value of VDD(start) AND Vi(DCI) > Vth(start)DCI. The circuit starts

oscillating at fbridge(max).

The circuit enters the preheat state as soon as the capacitor on the CP pin is charged to a

voltage level above Vth(CP)max. To remain oscillating, the VDD voltage must remain higher

than VDD(stop) and lower than the upper limit VDD(clamp). In addition, the typical voltage level

on the DCI pin must be higher than Vth(start)DCI  Vth(hys)DCI = 0.24 V.

An UnderVoltage LockOut (UVLO) is implemented on the DCI pin to create a guaranteed

turn-off for multiple lamps when the lamps are at low dim levels. The UVLO also

guarantees that there is a preheat phase when the dim level is turned up again.

The typical turn-on level on the DCI pin is set to lower than Vth(start)DCI = 0.36 V, else it

increases the turn-on hysteresis of the lamp. This level enables the UBA20270 to perform

a stable ignition of the lamp when there is already sufficient power from the dimmer at

lower dim levels.

During the start-up state, the voltage on the CF pin is at zero and the CB pin is close to

zero. The voltage on the CP pin rises to higher than Vth(CP)max level during the start-up

state. See Figure 9.

7.1.3 Preheat state

Starting at fbridge(max), the frequency decreases by charging capacitor CCI via an output

current circuit controlled by the preheat current sensor circuit. This state continues until

the momentary value of the voltage across sense resistor RSLS reaches the internally

fixed preheat voltage level (SLS pin). At this level, the current of the preheat current

sensor reaches a charge and discharge balanced state on capacitor CCI to set the

frequency.

UBA20270

Product data sheet

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

Rev. 2 — 8 September 2011

© NXP B.V. 2011. All rights reserved.

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