ml4836 Microsemi Corporation, ml4836 Datasheet - Page 10

• Manufacturer Part Number: ml4836
• Description: Compact Fluorescent Electronic Dimming Ballast Controller
• Manufacturer: Microsemi Corporation

ML4836
FUNCTIONAL DESCRIPTION
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 7.5mA. The operation of the oscillator is
hown in Figure 7.
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. The ICC
start-up condition is shown in Figure 7. To help reduce
10
CCZ
CC
t
DIS VCO
– 1.1V, the IC draws less than 0.55mA of quiescent
to 14.5V (V
(
)
@
600
DIS
CCZ
>>I
´
C
). The IC should be fed with
RT
T
10
9
:
R
INTERRUPT
X
/C
R
X
X
T
C
X
0.625
value and lower R
R
CC
SET
Figure 9. Lamp Preheat and Interrupt Timers
is below
(Continued)
1.75/4.65
1.25/6.65
1.0/1.20
(9)
T
+
+
+
–
–
–
ballast cost, the ML4836 includes a temperature sensor
which will inhibit ballast operation if the IC’s junction
temperature exceeds 140°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
ML4836’s die temperature can be estimated with the
following equation:
STARTING, RE-START, PREHEAT AND INTERRUPT
The lamp starting scenario implemented in the ML4836
is designed to maximize lamp life and minimize ballast
heating during lamp out conditions.
The circuit in Figure 9 controls the lamp starting scenarios:
Filament preheat and lamp out interrupt. C
with a current of I
voltage at C
time for C
During that time, the oscillator charging current (I
2.5/R
preheat, but will not produce sufficient voltage to ignite
the lamp or cause significant glow current.
T
SET
J
@
. This will produce a high frequency for filament
T
X
A
to rise to 4.65V is the filament preheat time.
X
+
is initialized to 0.7V (V
(
P
D
+
R(SET)
R
S
65
HEAT
LEA_ENB OR
DIMMING LOCKOUT
°
Q
/4 and discharged through R
C W
/
INHIBIT
)
BE
) at power up. The
X
is charged
CHG
X
. The
(10)
) is