uba20271 NXP Semiconductors, uba20271 Datasheet - Page 13

• Manufacturer Part Number: uba20271
• Description: 350 V And 600 V Power Ics For Dimmable Compact Fluorescent Lamps
• Manufacturer: NXP Semiconductors

NXP Semiconductors
UBA20271_UBA20272
Product data sheet
Fig 9.
Timing diagram preheat, ignition and overcurrent
V
V
th(CP)max
th(CP)min
5 V
0 V
7.3 Natural linear dimming
voltage
(V)
4.5 V
3.8 V
startup
time
What determines the actual internal set point level used for the current control feedback
loop is an external level applied via the DCI pin for dimming. The DCI voltage is a function
of the phase cut angle of the applied dimmer. To ensure that the external input for the
control on the DCI pin internally stays within a certain range, this input signal passes an
internal linear to logarithmic conversion circuit followed by a limiting circuit.
The linear to logarithmic conversion circuit is designed to improve dimming control by
correcting for the higher sensitivity of the human eye to small changes in low light levels.
See
adjustment of the lamp.
The limiting circuit prevents the signal falling below the MDL or rising above the 100 %
reference level of V
the actual reference voltage for the lamp current control loop. See signal V
(dimmer control block). When the IC is in the burn state, the voltage is equal to the RMS
voltage on the CSI pin. When the control loop is regulating correctly, the upper limit is
clamped at the 100 % reference level. This condition prevents lamp current values that
are too high in mains overvoltage situations. See
The MDL level presets a minimum to which the lamp current clips at low dim levels and is
adjustable via the MDL pin. An accurate minimum dimming voltage level is set by using an
internal reference current (derived from the internal band gap reference circuit and
resistor R
Figure
ext(RREF)
10. The conversion circuit also provides a natural perceived linear brightness
V
CP
All information provided in this document is subject to legal disclaimers.
350 V and 600 V Power ICs for dimmable compact fluorescent lamps
) and an applied external resistor R
clamp(CSI).
preheat time
Rev. 2 — 8 September 2011
The output of the linear to logarithmic conversion circuit is
ignition
time
enabling time
Figure
ignition
CFL ignition
MDL
boost-burn
10.
on the MDL pin.
overcurrent
fault time
UBA20271/2
power down
© NXP B.V. 2011. All rights reserved.
001aam768
time (s)
LD
in
Figure 1
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