ML4836CS View Datasheet(PDF) - Micro Linear Corporation
Part Name
Description
MFG CO.
'ML4836CS' PDF : 15 Pages View PDF
FUNCTIONAL DESCRIPTION (Continued)
FOSC
=
1
t CHG +
t DIS
(3)
and
t CHG = RTCT In
VREF + ICHG ´ RT - VTL
VREF + IICHG ´ RT - VTH
(4)
The oscillator’s minimum frequency is set when ICHG = 0
where:
FMIN
≅
1
0.54 × RT CT
(5)
The oscillator's start frequency can be expressed by:
2 7 FSTART = 0.54 ×
1
RT RT2
× CT
(5a)
Both equations assume that tCHG >> tDIS.
When LFB OUT is high, ICHG = 0 and the minimum
frequency occurs. The charging current varies according to
two control inputs to the oscillator:
1. The output of the preheat timer
ML4836
2. The voltage at LFB OUT (lamp feedback amplifier
output)
In preheat condition, charging current is fixed at
ICHG(PREHEAT)
=
2.5
R SET
(6)
In running mode, charging current decreases as the
voltage rises from 0V to VOH at the LAMP FB amplifier.
The charging current behavior can be expressed as:
ICHG
= 5V
R SET
-
LEAO
8k ± 25%
(7)
The highest frequency is attained when ICHG is highest,
which is attained when voltage at LFB OUT is at 0V:
ICHG(0)
=
5
R SET
(8)
Highest lamp power, and lowest output frequency are
attained when voltage at LFB OUT is at its maximum
output voltage (VOH).
VCC VCCZ
V(ON)
V(OFF)
ICC
t
5.5mA
0.34mA
t
Figure 8. Typical VCC and ICC Waveforms when the ML4836 is Started with a Bleed Resistor from
the Rectified AC Line and Bootstrapped from an Auxiliary Winding.
9
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