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MIC3202 Datasheet(PDF) 10 Page - Micrel Semiconductor

Part # MIC3202
Description  High-Brightness LED Driver with Integrated MOSFET and High-Side Current Sense
PDF  19 Pages
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Manufacturer  MICREL [Micrel Semiconductor]
Direct Link  http://www.micrel.com
Logo MICREL - Micrel Semiconductor

MIC3202 Datasheet(HTML) 10 Page - Micrel Semiconductor

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Micrel, Inc.
MIC3202
September 2010
10
M9999-091710-A
Application Information
The internal block diagram of the MIC3202 is shown in
Figure 1. The MIC3202 is composed of a current-sense
comparator, voltage and current reference, 5V regulator
and MOSFET. Hysteretic mode control, also called
bang-bang control, is a topology that does not employ an
error amplifier, using an error comparator instead.
The inductor current is controlled within a hysteretic
window. If the inductor current is too small, the power
MOSFET is turned on; if the inductor current is large
enough, the power MOSFET is turned off. It is a simple
control scheme with no oscillator and no loop
compensation. Since the control scheme does not need
loop compensation, it simplifies design and avoids
problems of instability.
Transient response to load and line variation is very fast
and only depends on propagation delay. This makes the
control scheme very popular to achieve low dimming
duty cycles.
LED Current and RCS
The main function of the MIC3202 is to control the LED
current accurately within
±5% of the set current. A high-
side RCS resistor sets LED current. The following
equation gives the RCS value:
)
I
V
+
V
(
x
2
1
=
R
LED
)
MIN
(
CS
)
MAX
(
CS
CS
RCS (Ω)
ILED (A)
I
2R (W)
Size (SMD)
1.33
0.15
0.03
0603
0.56
0.35
0.07
0805
0.4
0.5
0.1
0805
0.28
0.7
0.137
0805
0.2
1.0
0.2
1206
Table 1. RCS Values for Various LED Currents
For VCS(MAX) and VCS(MIN), refer to the Electrical
Characteristic table.
Frequency of Operation
To calculate the frequency spread across input supply:
t
Δ
I
Δ
L
=
V
L
L
L is the inductance, ∆IL is fixed (the value of the hysteresis):
CS
)
MIN
(
CS
)
MAX
(
CS
L
R
V
V
=
I
Δ
-
VL is the voltage across inductor L which varies by supply.
For current rising (MOSFET is ON):
RISE
_
L
L
r
V
I
Δ
L
=
t
where:
VL_RISE = VIN − ILED × RCS − VLED.
For current falling (MOSFET is OFF):
FALL
_
L
L
f
V
I
Δ
L
=
t
where:
VL_FALL = VD + ILED × RCS + VLED
f
r
t
+
t
=
T
,
T
1
f
SW =
)
IN
V
D
(V
L
ΔI
L
)
LED
V
-
CS
R
LED
I
-
IN
(V
)
LED
V
CS
R
LED
I
D
(V
f
SW
+
×
×
×
×
+
×
+
=
where:
VD is Schottky diode forward drop.
VLED is total LEDs voltage drop.
VIN is input voltage.
ILED is average LED current.



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