UBA2025T データシートの表示（PDF） - NXP Semiconductors.

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UBA2025T

CFL power IC

NXP Semiconductors. 

NXP Semiconductors

UBA2025

CFL power IC

7.8 Feed forward frequency

Above a defined voltage level at pin VDC the oscillation frequency also depends on the

supply voltage of the half bridge (see Figure 5). The current for the current controlled

oscillator is in this feed forward range and is derived from the current through RHV (this is

similar to pin RHV current). The feed forward frequency is proportional to the average

value of the current (within its operating range) through RHV. The feed forward frequency

is clamped for currents beyond the operating range (i.e. between 1.0 mA and 1.6 mA). In

order to prevent feed forward of the ripple on the input voltage on pin VDC, the ripple is

filtered out. The capacitor connected to pin CPAV 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 5. Feed forward frequency

IRHV (mA)

mgs993

7.9 Capacitive mode

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 the voltage across RSHUNT. If the voltage at

pin RS is below Vth(capm) the capacitive mode threshold voltage at the time of turn-on

of T2, then capacitive mode operation is assumed. Consequently, the frequency will be

increased 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 pin CI.

7.10 IC supply

Initially, the IC is supplied from the bus voltage VDC by the current through RHV. This

current charges the supply capacitor CS9 via an internal diode. As soon as VS exceeds

Vstartup, the circuit starts oscillating. After the preheat phase is finished, pin RHV is

connected to an internal resistor (RRHV); prior to this the pin is internally connected to

pin VS. The voltage level at pin RHV thus drops from (VS + Vd) to a voltage equal to the

RHV pin current × RRHV. The capacitor CS9 at pin VS will now be charged via the snubber

capacitor CS7. Excess charge is drained by an internal clamp that turns on at the clamp

voltage (Vclamp) on pin VS.

7.11 Minimum gate source voltage of T1 and T2

The high side driver is supplied via capacitor CBOOT. CBOOT is charged via the bootstrap

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

a maximum charge consumption on the gate of T1 (G1) of 1 nC/V, this safeguards the

minimum drive voltages V(G1-S1) for the high side driver; see Table 3.

UBA2025_1

Product data sheet

Rev. 01 — 16 October 2009

© NXP B.V. 2009. All rights reserved.

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