ml4832 Microsemi Corporation, ml4832 Datasheet - Page 9

• Manufacturer Part Number: ml4832
• Description: Electronic Dimming Ballast Controller
• Manufacturer: Microsemi Corporation

FUNCTIONAL DESCRIPTION
In running mode, charging current decreases as the V
rises from 0V to V
highest frequency will be attained when I
which is attained when LFB OUT is at 0V:
Highest lamp power, and lowest output frequency are
attained when LFB OUT is at its maximum output voltage
(V
In this condition, the minimum operating frequency of the
ballast is set per (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 (V
set to 5.5mA. Assuming that I
IC BIAS, UNDER-VOLTAGE LOCKOUT AND THERMAL
SHUTDOWN
The IC includes a shunt regulator 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.
CCZ
V
OH
I
CC
CC
0.34mA
the ML4832 is Started with a Bleed Resistor from
).
Figure 6. Typical VCC and ICC Waveforms when
the Rectified AC Line and Bootstrapped from an
5.5mA
– 1.1V, the IC draws less than 0.48mA of quiescent
VCCZ
V
V
OFF
ON
CC
to 15V (V
OH
t
DIS VCO
Auxiliary Winding.
of the LAMP FB amplifier. The
I
CHG
(
CCZ
LFB OUT
( ) 0
)
). The IC should be fed with
DIS
600
R
). The discharge current is
>> I
SET
5
T
RT
C
value and lower R
:
T
CC
CHG
is below
(Continued)
is highest,
t
t
PIN6
(7)
(8)
T
To help reduce ballast cost, the ML4832 includes a
temperature sensor which will inhibit ballast operation if
the IC’s junction temperature exceeds 120°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 ML4832’s die temperature can be estimated
with the following equation:
STARTING, RE-START, PREHEAT AND INTERRUPT
The lamp starting scenario implemented in the ML4832
is designed to maximize lamp life and minimize ballast
heating during lamp out conditions.
The circuit in Figure 7 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.
After cathode heating, the inverter frequency drops to
F
If the voltage does not drop when the lamp is supposed to
have ignited, the lamp voltage feedback coming into pin 9
rises to above V
the inverter is inhibited until C
1.2V threshold. Shutting off the inverter in this manner
prevents the inverter from generating excessive heat when
MIN
R
X
SET
causing a high voltage to appear to ignite the lamp.
C
Figure 7. Lamp Preheat and Interrupt Timers
X
. This will produce a high frequency for filament
X
to rise to 4.8V is the filament preheat time.
X
is initialized to 0.7V (V
10
9
REF
T
R
INT
X
J
RSET
/C
, the C
6.8
V
X
REF
T
/4 and discharged through R
A
X
P
charging current is shut off and
D
–
+
0.625
R
1.2/4.8
1.2/6.8
SET
X
65
is discharged by R
C W
BE
+
+
–
–
/
) at power up. The
X
ML4832
is charged
R
S
CHG
X
X
Q
DIMMING
LOCKOUT
. The
HEAT
to the
INHIBIT
) is
(9)
9