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UBA2021T View Datasheet(PDF) - NXP Semiconductors.

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Description
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UBA2021T
NXP
NXP Semiconductors. NXP
UBA2021T Datasheet PDF : 16 Pages
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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).
f
(kHz)
bottom
frequency
feed-forward
range
Fig 6. Feed-forward frequency
IRHV (mA)
mgs993
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.
Table 4. Minimum gate-source voltages
FREQUENCY
< 75 kHz
75 kHz to 85 kHz
85 kHz
VOLTAGE
8 V (min)
7 V (min)
6 V (min)
The drive voltage at G2 will exceed the drive voltage of the high side driver.
UBA2021_4
Product data sheet
Rev. 04 — 25 July 2008
© NXP B.V. 2008. All rights reserved.
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