Datasheet

UBA20260 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Product data sheet Rev. 2 — 10 October 2011 11 of 30
NXP Semiconductors
UBA20260
600 V driver IC for step dimmable CFLs
the supply voltage V
DD
rises between V
DD(stop)
and V
DD(start)
. Typically, the supply current
is 2 mA when V
DD
falls between V
DD(start)
and V
DD(stop)
. More current is drawn during the
fall in V
DD
because the internal analog supply is turned on when V
DD
>V
DD(start)
. This
function enables the comparators to monitor the voltage on the CP pin and if the supply
voltage V
DD
falls below V
DD(stop)
.
7.3 Oscillation and timing
7.3.1 Oscillator control
The internal oscillator is a VCO which generates a saw-tooth waveform between the
V
th(CF)max
level and 0 V. Capacitor C
CF
, resistor R
ext(RREF)
and the voltage on the CI pin
determine the saw-tooth frequency. R
ext(RREF)
and C
CF
determine the minimum and
maximum switching frequencies. Their ratio is internally fixed. Two ratios are available,
the ratio between f
bridge(max)
and f
bridge(min)
is 2.5 and the ratio between f
bridge(max)
and
f
bridge(bst)min
is 4.6. The saw-tooth frequency is twice the half-bridge frequency.
Transistors HS (Q1) and LS (Q2) are switched to conducting at a duty cycle of
approximately 50 %. An overview of the oscillator signal and driver signals is shown in
Figure 8
. The oscillator starts oscillating at f
bridge(max)
. The non-overlap time between the
gate driver signals V
GLS
and V
GHS
is t
no
.
Fig 8. Saw-tooth, gate driver and half-bridge output signals
001aam766
0
t
dch
0
0
0
V
CF
voltage
(V)
V
(GHS-HBO)
V
GLS
V
HBO
t
no
time (s)
t
no