Electronic Components Datasheet Search
  English  ▼

X  

Preview PDF HTML

MIC3232 Datasheet(PDF) 15 Page - Micrel Semiconductor

Part # MIC3232
Description  Constant Current Boost Controller for Driving High Power LEDs
PDF  19 Pages
Scroll/Zoom Zoom In 100%  Zoom Out
Manufacturer  MICREL [Micrel Semiconductor]
Direct Link  http://www.micrel.com
Logo MICREL - Micrel Semiconductor

MIC3232 Datasheet(HTML) 15 Page - Micrel Semiconductor

Back Button MIC3232 Datasheet HTML 11Page - Micrel Semiconductor MIC3232 Datasheet HTML 12Page - Micrel Semiconductor MIC3232 Datasheet HTML 13Page - Micrel Semiconductor MIC3232 Datasheet HTML 14Page - Micrel Semiconductor MIC3232 Datasheet HTML 15Page - Micrel Semiconductor MIC3232 Datasheet HTML 16Page - Micrel Semiconductor MIC3232 Datasheet HTML 17Page - Micrel Semiconductor MIC3232 Datasheet HTML 18Page - Micrel Semiconductor MIC3232 Datasheet HTML 19Page - Micrel Semiconductor  
Zoom Inzoom in Zoom Outzoom out
 15 / 19 page
background image
Micrel, Inc.
MIC3230/1/2
November 2009
15
M9999-113009-B
Maximum Power dissipated in RCS is;
Eq. (17)
CS
R
R
R
I
P
RMS
CS
CS
×
=
2
_
Eq. (18)
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
+
=
=
12
2
_
2
max
_
_
max
_
_
max
_
_
PP
L
AVE
IN
RMS
FET
R
I
I
D
I
I
RMS
CS
rms
A
I
RMS
CS
R
_
44
.
1
12
26
.
0
64
.
1
78
.
0
2
2
_
=
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
+
=
watt
P
CS
R
31
.
0
15
.
25
.
1
2
=
×
=
Use a 1/2 Watt resistor for RCS.
Output Capacitor
In this LED driver application, the ILED ripple current is a
more important factor compared to that of the output
ripple voltage (although the two are directly related). To
find the COUT for a required ILED ripple use the following
calculation:
For an output ripple
=
ripple
ILED
20% of
nom
ILED
mA
ILEDripple
70
35
.
0
2
.
0
=
×
=
Eq. (19)
)
(
*
*
*
_ total
LED
adj
ripple
nom
nom
out
R
R
ILED
T
D
ILED
C
+
=
Find the equivalent ac resistance
ac
LED
R
_
from the
datasheet of the LED. This is the inverse slope of the
ILED vs. VF curve i.e.:
Eq. (20)
ILED
V
R
F
ac
LED
Δ
Δ
=
_
In this example, use
Ω
= 1
.
0
_ ac
LED
R
for each LED.
If the LEDs are connected in series, multiply
Ω
= 1
.
0
_ ac
LED
R
by the total number of LEDs. In this
example of 6 LEDs, we obtain the following:
Ω
=
Ω
×
=
6
.
0
1
.
0
6
_ total
LED
R
uF
R
R
ILED
T
D
ILED
C
total
LED
adj
ripple
nom
nom
out
1
.
4
)
(
*
*
*
_
=
+
=
Use the next highest standard value, which is 4.7uF.
There is a trade off between the output ripple and the
rising edge of the PWMD pulse.
This is because
between PWM dimming pulses, the converter stops
pulsing and COUT will start to discharge. The amount that
COUT will discharge depends on the time between PWM
Dimming pluses. At the next PWMD pulse COUT has to
be charged up to the full output voltage VOUT before the
desired LED current flows.
Input Capacitor
The input current is shown in Figure 5. For superior
performance, ceramic capacitors should be used because of
their low equivalent series resistance (ESR). The input ripple
current is equal to the ripple in the inductor plus the ripple
voltage across the input capacitor, which is the ESR of CIN
times the inductor ripple.
The input capacitor will also
bypass the EMI generated by the converter as well as any
voltage spikes generated by the inductance of the input line.
For a required VIN_RIPPLE:
Eq. (21)
()
F
kHz
mV
A
F
V
I
C
SW
RIPPLE
IN
PP
IN
IN
μ
4
.
1
500
50
8
28
.
0
8
_
_
=
×
×
=
×
×
=
T
his is the minimum value that should be used. The input
capacitor should also be rated for the maximum RMS input
current.
To protect the IC from inductive spikes or any
overshoot, a larger value of input capacitance may be
required and it is recommended that ceramic capacitors be
used. In this design example a value of 4.7µF ceramic
capacitor was selected.
MOSFET Selection
In this design example, the FET has to hold off an output
voltage maximum of 30V. It is recommended to use an 80%
de-rating value on switching FETs, so a minimum of a 38V
FET should be selected. In this design example, a 75V FET
has been selected.
The switching FET power losses are the sum of the
conduction loss and the switching loss:
Eq. (22)
SWITCH
FET
COND
FET
FET
P
P
P
_
_
+
=
The conduction loss of the FET is when the FET is turned
on. The conduction power loss of the FET is found by the
following equation:
Eq. (23)
DSON
RMS
FET
COND
FET
R
I
P
×
=
2
_
_
, where
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
+
=
12
2
_
2
_
_
PP
L
AVE
IN
RMS
FET
I
I
D
I
The switching losses occur during the switching transitions
of the FET. The transition times, ttransition, are the times when
the FET is turning off and on. There are two transition times
per period, T. It is important not to confuse T (the period)
with the transition time, ttransition.
Eq. (24)
Fsw
T
1
=
Eq. (25)
SW
transition
OUT
AVE
FET
SWITCH
FET
F
t
V
I
P
×
×
×
=
max
_
max
_
max
_
_
max
_
_
To find
max
_
transition
t
:
Eq. (26)
Igatedrv
Qg
ttransition
≈
max
_
where Qg is the total gate charge of the external MOSFET



Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19


Datasheet Download

Go To PDF Page


Link URL



Does ALLDATASHEET help your business so far?  [ DONATE ] 

About Alldatasheet   |   Advertisement   |   Contact us   |   Privacy Policy   |   Link to Datasheet    |   Link Exchange   |   Manufacturer List
All Rights Reserved©Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn
Indian : Alldatasheet.in  |   Mexican : Alldatasheet.com.mx  |   British : Alldatasheet.co.uk  |   New Zealand : Alldatasheet.co.nz
Family Site : ic2ic.com  |   icmetro.com