mic3230 Micrel Semiconductor, mic3230 Datasheet - Page 16
mic3230
Manufacturer Part Number
mic3230
Description
Constant Current Boost Controller For Driving High Power Leds
Manufacturer
Micrel Semiconductor
Datasheet
1.MIC3230.pdf
(20 pages)
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Company:
Part Number:
mic3230YTSE
Manufacturer:
Micrel Inc
Quantity:
135
The switching losses occur during the switching
transitions of the FET. The transition times, t
the times when the FET is turning off and on. Th
two transition times per period, T. It is important not to
confuse T (the period) with the transition time, t
Eq. (24)
Eq. (25)
Eq. (26)
where Qg
MOSFET provided by the MOSFET manufacturer and
the Qg
exact value, but is more of an estimate of
The FET manufacturers’ provide a gate
specified V
This is the FET’s input capacitance. Select a FET with
R
about 0.7W for a SO-8 or about 1W for a PowerPak
(FET package).
PowerPak SO-8 package is one good choice. The
internal gate driver in the MIC3230/1/2 is 2A. From the
Si7148DP data sheet:
The
temp
To find
double the
Eq. (27)
The
From Equ
P
Micrel, Inc.
To find
January 2009
FET
DS(on)
R
erature
_
R
R
SWITCH
DS
DSon
DS
and Q
t
(
sh
(
R
I
transition
R
on
ation 23:
on
t
transition
FET
GS
(
DS
DS
R
is the total gate c
ould chosen at a V
125
Total gate C
)
)
(
in the FET increases so does the
(
_
DS
(
temp
voltage:
temp
(
on
_
G
max
on
o
RMS
(
)
C
T
such that the external power is below
on
(
)
_
temp
(
)
_
R
=
temp
The Vishay Siliconix Si7148DP in a
)
)
=
max
) is a function of tem
max
C
=
(
=
P
DS(on)_25°C
I
25
at 125°C is:
Fsw
FET
In
. 0
FET
)
1
0145
_
:
≈
o
=
D
)
FET
C
harge=68nC (typical)
_
_
Igatedrv
R
COND
⎛
⎜
⎜
⎝
) for
AVE
use Equation 27, or simply
DS
I
Qg
×
IN
=
=0.0145Ω
(
(on
_
. 1
_
@
max
R
00
=
AVE
)
Q
(
GS
DS
V
. 1
ha
25
7
G
×
GS
2
64
≈10V. This is not an
(
(
125
rge of the external
o
V
on
+
C
OUT
2
)
)
∗
I
−
×
(
×
125
25
L
30
perature. As the
12
(
_
_
. 1
o
PP
max
t
)
m
transition
007
)
o
2
charge at a
Ω
≈
C
transition
×
⎞
⎟
⎟
⎠
30
)
R
(
=
Temp
transition
t
.
transition
DS(on)
62
m
ere are
Ω
mW
_
, are
−
max
25
.
.
o
)
_
)
.
max
16
×
F
SW
From Equation 26:
From Equation 25:
From Equation 22
This about the limit for a part on a circuit board without
having to use any additional heat sinks.
Rectifier Diode
A Schottky Diode
forward voltage an
voltage stress on the diode is the max V
therefore a diode with a higher rating than max V
should be used.
here as well.
Eq (28)
Eq. (29)
MIC3230 power losses
The power losses in the M
Eq.(30)
where
MOSFE
MIC3230. F is the switching frequency.
quiescent cu rent of the MIC3230 found in th
characteriz on table.
the V
P
P
FET
MIC
3230
_
IN
SWITCH
pin of the MIC3230 . From Eq.(30)
Q
T.
gat
=
I
ati
diode
P
68
P
e
MIC
r
_
FET
P
P
max
nF
V
_
is the total gate charge of the
diode
diode
RMS
gate
3230
I
FET
×
=
is best used here because of the lower
=
d the low reverse recovery time. The
_
12
≈
≈
V
62
An 80% de-rating is recommended
max
t
. 1
transition
OUT
_
V
. 0
=
is the gate drive voltage of the
64
×
mW
AVE
SCHOTTKY
=
Q
81
I
500
Q
A
gate
_
1 (
W
×
IC3230are:
=
max
_
−
+
kHz
28
≈
max
D
3
. 0
×
Igatedrv
)
2 .
V
⎛
⎜
⎜
⎝
V
I
78
=
IN
mA
Qg
×
+
×
gate
=
_
28
W
34
3
I
AVE
. 1
2 .
diode
. V
V
ns
=
64
×
mA
_
=
max
. 0
F
IN
×
_
A
68
RMS
500
84
+
M9999-011409-A
2
×
2
is the voltage at
nC
A
+
I
14
W
Q
MIC3230/1/2
I
kHz
_
L
max
_
×
12
=
=
PP
Vin
e e
I
34
. 0
Q
2
=
ns
OUT
⎞
⎟
⎟
⎠
45
external
. 0
lectrical
is the
78
W
Watts
and
OUT