Datasheet

Evaluates: MAX4990
Soft-Start (R
DIM
, C
DIM
)
Subject to the constraint that R
DIM
/R
SLEW
≤ 1.3, the
gradual turn-on/turn-off time is set by R
DIM
and C
DIM
(see Table 4) by the equations:
Lamp Output Frequency (R
SLEW
, C
EL
)
Lamp output frequency can be set by an external
capacitor, C
EL
(see Table 5):
f
RC
EL
SLEW EL
=
×
0 0817.
tRC
tRC
ON DIM DIM
OFF DIM DIM
=× ×
=× ×
26
12
.
.
MAX4990 Evaluation Kit
4 _______________________________________________________________________________________
C
DIM
(µF)
JU3 SHUNT
POSITION
VR2 TRIMMER
R
DIM
(MΩ)
t
ON
(S)
t
OFF
(S)
2-3 — R4 = 0.374 0.972 0.449
7% CW VR2 = 0.152 0.395 0.182
10% CW VR2 = 0.211 0.549 0.253
18% CW VR2 = 0.374 0.972 0.449
25% CW VR2 = 0.496 1.290 0.595
35% CW VR2 = 0.700 1.820 0.840
50% CW VR2 = 1.000 2.600 1.200
C1 = 1.0
1-2
70% CW VR2 = 1.398 3.635 1.678
Table 4. Soft-Start Configuration
CW = Clockwise. Approximate trimmer values provided for initial guidance only.
C
EL
(pF) JU1 SHUNT POSITION VR1 TRIMMER
R
SLEW
(MΩ)
f
EL
(Hz)
1-2 — R2 = 0.374 390
25% CW VR1 + R1 = 0.560 260
C2 = 560
2-3
50% CW VR1 + R1 = 0.997 150
1-2 — R2 = 0.374 218
25% CW VR1 + R1 = 0.560 146C2 = 1000
2-3
50% CW VR1 + R1 = 0.997 82
Table 5. Lamp Output Frequency When JU4 = Open (Internal f
EL
)
CW = Clockwise. Approximate trimmer values provided for initial guidance only.