ML4835CP MICRO-LINEAR [Micro Linear Corporation], ML4835CP Datasheet - Page 11

• Manufacturer Part Number: ML4835CP
• Description: Compact Fluorescent Electronic Dimming Ballast Controller
• Manufacturer: MICRO-LINEAR [Micro Linear Corporation]

FUNCTIONAL DESCRIPTION
Highest lamp power, and lowest output frequency are
attained when voltage at LFB OUT is at its maximum
output voltage (V
In this condition, the minimum operating frequency of the
ballast is set per equation 5 above.
For the IC to be used effectively in dimming ballasts with
higher Q output networks a larger C
value can be used, to yield a smaller frequency excursion
over the control range (voltage at LFB OUT). The
discharge current is set to 5.5mA.
Assuming that I
IC BIAS, UNDER-VOLTAGE LOCKOUT AND
THERMAL SHUTDOWN
The IC includes a shunt clamp which will limit the
voltage at V
a current limited source, typically derived from the
ballast transformer auxiliary winding. When V
V
current and the outputs are off. This allows the IC to start
using a “bleed resistor” from the rectified AC line.
To help reduce ballast cost, the ML4835 includes a
temperature sensor which will inhibit ballast operation if
the IC’s junction temperature exceeds 130°C. In order to
use this sensor in lieu of an external sensor, care should
be taken when placing the IC to ensure that it is sensing
temperature at the physically appropriate point in the
ballast. The ML4835’s die temperature can be estimated
with the following equation:
STARTING, RE-START, PREHEAT AND INTERRUPT
The lamp starting scenario implemented in the ML4835
is designed to maximize lamp life and minimize ballast
heating during lamp out conditions.
CCZ
t
T
DIS VCO
J
– 1.1V, the IC draws less than 0.55mA of quiescent
@
(
T
A
CC
)
+
@
(
P
600
to 15V (V
D
DIS
OH
+
>>I
´
65
).
C
°
RT
T
C W
10
9
CCZ
:
/
R
INTERRUPT
X
/C
). The IC should be fed with
)
R
X
X
C
T
0.625
X
R
value and lower R
SET
Figure 10. Lamp Preheat and Interrupt Timers
(Continued)
1.25/4.75
1.25/6.75
CC
1.0/1.25
is below
(10)
(9)
T
+
–
+
–
+
–
The circuit in Figure 10 controls the lamp starting
scenarios: Filament preheat and lamp out interrupt. C
charged with a current of I
R
up. The time for C
time. During that time, the oscillator charging current
(I
filament preheat, but will not produce sufficient voltage
to ignite the lamp or cause significant glow current.
After cathode heating, the inverter frequency drops to
F
lamp. If lamp current is not detected when the lamp is
supposed to have ignited, the C
off and the inverter is inhibited until C
R
manner prevents the inverter from generating excessive
heat when the lamp fails to strike or is out of socket.
Typically this time is set to be fairly long by choosing a
large value of R
LFB OUT is ignored by the oscillator until INTERRUPT is
above 1.25V The C
Care should also be taken not to turn on the VCCZ clamp
so as not to dissipate excessive power in the IC. This will
cause the temp sensor to become active at a lower
ambient temperature.
A summary of the operating frequencies in the various
operating modes is shown below.
OPERATING MODE
START
CHG
X
X
. The voltage at C
to the 1.25V threshold. Shutting off the inverter in this
) is 2.5/R
Dimming
causing a high voltage to appear to ignite the
Preheat
Preheat
Control
After
SET
X
. This will produce a high frequency for
.
S
R
X
X
HEAT
to rise to 4.75V is the filament preheat
LEA_ENB OR
DIMMING LOCKOUT
X
pin is clamped to about 7.5V.
Q
is initialized to 0.7V (V
R(SET)
INHIBIT
OPERATING FREQUENCY
/4 and discharged through
X
[F(MAX) to F(MIN)]
F(MIN) to F(MAX)
charging current is shut
F(START)
X
is discharged by
2
ML4835
BE
) at power
X
11
is