UBA2014P PHILIPS [NXP Semiconductors], UBA2014P Datasheet - Page 6

• Manufacturer Part Number: UBA2014P
• Description: 600 V driver IC for HF fluorescent lamps
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
FUNCTIONAL DESCRIPTION
Start-up state
Initial start-up can be achieved by charging the low voltage
supply capacitor C7 (see Fig.8) via an external start-up
resistor. Start-up of the circuit is achieved under the
condition that both half-bridge transistors TR1 and TR2
are non-conductive. The circuit will be reset in the start-up
state. If the low voltage supply (V
V
incorporated in the High-Side (HS) driver. Below the
lock-out voltage at the F
(V
zero during the start-up state.
Oscillation
The internal oscillator is a Voltage-Controlled Oscillator
circuit (VCO) which generates a sawtooth waveform
between the CF
sawtooth is determined by capacitor C
and the voltage at pin CSW. The minimum and maximum
switching frequencies are determined by R
their ratio is internally fixed. The sawtooth frequency is
twice the half-bridge frequency. The UBA2014 brings the
transistors TR1 and TR2 into conduction alternately with a
duty cycle of approximately 50%. An overview of the
oscillator signal and driver signals is illustrated in Fig.4.
The oscillator starts oscillating at f
switching cycle the Low-Side (LS) transistor is switched
on. The first conducting time is made extra long to enable
the bootstrap capacitor to charge.
Adaptive non-overlap
The non-overlap time is realized with an adaptive
non-overlap circuit (ANT). By using an adaptive
non-overlap circuit, the application can determine the
duration of the non-overlap time and make it optimum for
each frequency (see Fig.4). The non-overlap time is
determined by the slope of the half-bridge voltage, and is
detected by the signal across resistor R16 which is
connected directly to pin ACM. The minimum non-overlap
time is internally fixed. The maximum non-overlap time is
internally fixed at approximately 25% of the bridge period
time. An internal filter of 30 ns is included at the ACM pin
to increase the noise immunity.
Timing circuit
A timing circuit is included to determine the preheat time
and the ignition time. The circuit consists of a clock
generator and a counter.
2002 May 16
DD(H)
GH
600 V driver IC for HF fluorescent lamps
the circuit will start oscillating. A DC reset circuit is
V
SH
) is zero. The voltages at pins CF and CT are
high
level and 0 V. The frequency of the
VDD
pin the output voltage
DD
max
) reaches the value of
. During the first
CF
, resistor R
IREF
and C
IREF
CF
,
;
6
The preheat time is defined by C
of 7 pulses at C
C
state, as soon as the low supply voltage (V
V
(V
C
Preheat state
After starting at f
momentary value of the voltage across sense resistor R14
reaches the internally fixed preheat voltage level (pin
PCS). At crossing the preheat voltage level, the output
current of the Preheat Current Sensor circuit (PCS)
discharges the capacitor C
The preheat time begins at the moment that the circuit
starts oscillating. During the preheat time the Average
Current Sensor circuit (ACS) is disabled. An internal filter
of 30 ns is included at pin PCS to increase the noise
immunity.
Ignition state
After the preheat time the ignition state is entered and the
frequency will sweep down due to charging of the
capacitor at pin CSW with an internally fixed current; see
Fig.5. During this continuous decrease in frequency, the
circuit approaches the resonant frequency of the load. This
will cause a high voltage across the load, which normally
ignites the lamp. The ignition voltage of a lamp is designed
above the V
V
Burn state
If the lamp voltage does not exceed the V
voltage at pin CSW will continue to increase until the clamp
level at pin CSW is reached; see Fig.5. As a consequence
the frequency will decrease until the minimum frequency is
reached.
When the frequency reaches its minimum level it is
assumed that the lamp has ignited and the circuit enters
the burn state. The Average Current Sensor circuit (ACS)
will be enabled. As soon as the averaged voltage across
sense resistor R14, measured at pin CS , reaches the
reference level at pin CS+, the average current sensor
circuit will take over the control of the lamp current. The
average current through R14 is transferred to a voltage at
the voltage controlled oscillator and regulates the
frequency and, as a result, the lamp current.
DD(H)
lamp(fail)
CT
CT
lamp(fail)
. The timing circuit starts operating after the start-up
is discharged to 0 V at 1 mA.
or when a critical value of the lamp voltage
level the ignition timer is started.
) is exceeded. When the timer is not operating
lamp(fail)
CT
max
; the maximum ignition time is 1 pulse at
level. If the lamp voltage exceeds the
, the frequency decreases until the
CSW
, thus raising the frequency.
CT
and R
Product specification
IREF
lamp(max)
UBA2014
DD
) has reached
and consists
level the