mic3230 Micrel Semiconductor, mic3230 Datasheet - Page 11

• Manufacturer Part Number: mic3230
• Description: Constant Current Boost Controller For Driving High Power Leds
• Manufacturer: Micrel Semiconductor

Leading Edge Blanking
Large transient spikes due to the reverse recovery of the
diode may be present at the leading edge of the current
sense signal. (Note: drive current can also cause such
spikes) For this reason a switch is employed to blank the
first 100ns of the current sense signal. See Figure 6.
Eq. (9)
Micrel, Inc.
January 2009
I
IN
_
RMS
=
V
OUT
eff
×
×
V
I
Clock
Clock
OUT
IN
PWM
I
Figure 4. Current sense circuit (An explanation of the IS pin)
DIODE
I
FET
I
L
R
V
V
V
COMP
0
0
0
C
C
C
PWM Comparator
COMP
= 10k
V
DT
C
m1
T
(1-D)T
C
COMP
S
R
Current Limit
m2
Figure 5. Current Waveforms
Q
0.45V
IADJ
Ai
0.45V
11
Eq. (10)
Eq. (11)
Note: If I
DRV
IS
250µa/T
I
I
I
I
I
L_PK
L_AVE
L_AVE
FET_RMS
OUT
V
= I
A
= I
= I
= I
+RSLC–
RAMP
L_AVE
IN_PP
IN_AVE
IN_AVE
V
A
× R
I
I
IN
IN
+ 1/2 I
SLP
_
_
is small then I
VIN
PEAK
AVE
+
R
–
L_PP
L1
V
CS
CS
IL
D1
=
V
CS
=
= IL × R
I
I
L_PP
(
IN
I
IN
CS
_
_
AVE
RMS
IN_AVE
+
) (
2
I
IN
−
nearly equals I
_
2
I
IN
PP
_
12
M9999-011409-A
PP
MIC3230/1/2
)
2
IN_RMS