UBA2021 datasheet(6/16 Pages) PHILIPS

6 / 16 page

UBA2021_4

Product data sheet

Rev. 04 — 25 July 2008

6 of 16

NXP Semiconductors

UBA2021

630 V driver IC for CFL and TL lamps

Vin, the ripple is ﬁltered out. The capacitor connected to the CP-pin is used for this

purpose. This pin is also used in the preheat state and the ignition state for timing (tph and

tign).

7.9 Capacitive mode protection

When the preheat mode is completed, the IC will protect the power circuit against losing

the zero voltage switching condition and getting too close to the capacitive mode of

operation. This is detected by monitoring voltage VRS at the RS-pin. If the voltage is below

VRS(cap) at the time of turn-on of T2, the capacitive mode operation is assumed.

Consequently the frequency increases as long as the capacitive mode is detected. The

frequency decreases down to the feed-forward frequency if no capacitive mode is

detected. Frequency modulation is achieved via the CI-pin.

7.10 IC supply

Initially, the IC is supplied from Vin by the current through RRHV. This current charges the

supply capacitor CS9 via an internal diode. As soon as VVS exceeds VVS(start), the circuit

starts oscillating. After the preheat phase is ﬁnished, the pin is connected to an internal

resistor Ri(RHV), prior to this the RHV-pin is internally connected to the VS-pin. The voltage

level at the RHV-pin thus drops from VVS + Vdiode to IRHV × Ri(RHV). The capacitor CS9 at

the VS-pin will now be charged via the snubber capacitor CS7. Excess charge is drained

by an internal clamp that turns on at voltage VVS(clamp).

7.11 Minimum gate-source voltage of T1 and T2

The high side driver is supplied via capacitor Cboot. Capacitor Cboot is charged via the

bootstrap switch during the on periods of T2. The IC stops oscillating at a voltage level

VVS(stop). Given a maximum charge consumption on the load at the G1-pin of 1 nC/V, this

safeguards the minimum drive voltages V(G1-S1) for the high side driver, see Table 1.

The drive voltage at G2 will exceed the drive voltage of the high side driver.

Fig 6.

Feed-forward frequency

mgs993

bottom

frequency

feed-forward

range

(kHz)

IRHV (mA)

Table 4.

Minimum gate-source voltages

FREQUENCY

VOLTAGE

< 75 kHz

8 V (min)

75 kHz to 85 kHz

7 V (min)

≥ 85 kHz

6 V (min)

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