mic3202 Micrel Semiconductor, mic3202 Datasheet - Page 10

• Manufacturer Part Number: mic3202
• Description: High-brightness Led Driver With Integrated Mosfet And High-side Current Sense
• Manufacturer: Micrel Semiconductor

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 R
The main function of the MIC3202 is to control the LED
current accurately within ±5% of the set current. A high-
side R
equation gives the R
For V
Characteristic table.
Micrel, Inc.
September 2010
R
CS
1.33
0.56
0.28
0.4
0.2
Table 1. R
CS(MAX)
(Ω)
CS
R
CS
resistor sets LED current. The following
=
2
1
and V
CS
( x
I
LED
0.15
0.35
Values for Various LED Currents
V
0.5
0.7
1.0
CS
CS
CS
(A)
(
value:
CS(MIN),
MAX
I
)
LED
+
V
CS
I
refer to the Electrical
2
0.137
R (W)
0.03
0.07
0.1
0.2
(
MIN
)
)
Size (SMD)
0603
0805
0805
0805
1206
10
Frequency of Operation
To calculate the frequency spread across input supply:
L is the inductance, ∆I
V
For current rising (MOSFET is ON):
where:
V
For current falling (MOSFET is OFF):
where:
V
where:
V
V
V
I
T
f
LED
SW
L
L_RISE
L_FALL
D
LED
IN
=
is the voltage across inductor L which varies by supply.
is Schottky diode forward drop.
is input voltage.
is average LED current.
t
=
is total LEDs voltage drop.
r
(V
t +
= V
= V
D
V
I Δ
t
t
f
r
+
f
,
L
IN
D
L
=
I
LED
=
f
=
=
+ I
L
− I
SW
L
L
V
V
V
LED
LED
×
L
I Δ
CS
L
t Δ
R
I Δ
=
_
I Δ
_
CS
(
RISE
L
× R
× R
MAX
L
FALL
T
1
L
L
+
R
CS
×
)
CS
L
V
CS
ΔI
-
LED
is fixed (the value of the hysteresis):
V
− V
+ V
L
CS
×
)
(V
LED
LED
×
(
MIN
(V
D
.
IN
+
)
V
I -
IN
LED
)
×
R
CS
-
M9999-091710-A
V
LED
)
MIC3202