MIC3202/MIC3202-1
Evaluation Board
High-Brightness LED Driver with Integrated
MOSFET and High-Side Current Sense
General Description
The MIC3202/MIC3202-1 is a hysteretic step-down,
constant-current, High-Brightness LED (HB LED) driver.
It provides an ideal solution for interior/exterior lighting,
architectural and ambient lighting, LED bulbs, and other
general illumination applications.
This board enables the evaluation of the
MIC3202/MIC3202-1 for 1A LED current. The board is
optimized for ease of testing, with all the components on
a single side. The device operates from a 6V to 37V
input voltage range, and includes an integrated 1.0A
MOSFET. When the input voltage approaches and
crosses UVLO threshold, the internal 5V V
CC
is
regulated and the integrated MOSFET is turned on if EN
pin and DIM pin are high. The inductor current builds up
linearly. When the CS pin voltage hits the V
CS(MAX)
with
respect to V
IN
, the internal MOSFET is turned off and the
Schottky diode takes over and returns the current to V
IN
.
Then the current through inductor and LEDs starts
decreasing. When CS pin hits V
CS(MIN)
, the internal
MOSFET is turned on and the cycle repeats.
Since the control scheme does not need loop
compensation, it makes for a very simple design and
avoids problems of instability.
Datasheets and support documentation can be found on
Micrel’s web site at:
www.micrel.com.
Requirements
This board needs a single-bench power source
adjustable over the input voltage of 6V < V
IN
< 37V that
can provide at least 1A of current. The loads can either
be active (electronic load in CV mode) or passive
(LEDs) with the ability to dissipate the maximum load
power while keeping accessible surfaces ideally <70°C.
Precautions
There is no reverse input protection on this board. When
connecting the input sources, ensure that the correct
polarity is observed.
In the line transient condition, such as hot plug-in, an
electrolytic capacitor may be required at the VIN and
GND terminals in order to prevent IC damage from a
surge voltage.
Getting Started
1.
Connect V
IN
supply to the input VIN and GND
terminals.
With the output of this supply disabled,
set the supply voltage to the desired input test
voltage (6V < V
IN
< 37V). This supply voltage should
be monitored at the test boards input terminals to
allow voltage drops in the test cables (and ammeter
if used) to be accounted for. An ammeter can be
added inline with the +VIN input terminal to
accurately measure input current.
2.
Connect the LEDs to the output terminals
between LED+ and LED−.
This LED voltage drop
depends on manufacturer tolerance and number of
LEDs. The LED current can be measured using an
ammeter or current probe. A 4.7µF ceramic
capacitor helps to reduce the current ripple through
the LED. The LED current is set to 1A by a 200mΩ
current-sense resistor (R
CS
).
3.
Enable the input supply.
By default, the IC is
enabled when the input voltage crosses the VIN
threshold (4V) and the internal VCC regulator and
internal MOSFET are turned on with the EN and
DIM pins are high. To use the EN and DIM functions
of the MIC3202/MIC3202-1, a test point is provided
for each of them.
Ordering Information
Part Number
MIC3202YME EV
Description
MIC3202YME Evaluation Board
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 •
http://www.micrel.com
October 2010
M9999-102810
Micrel, Inc.
MIC3202/MIC3202-1 Evaluation Board
Other Features
EN Input
The EN pin provides a logic level control of the output
and the voltage has to be 2.0V or higher to enable the
current regulator. The output stage is gated by the DIM
pin. When the EN pin is pulled low, the regulator goes to
off-state and the supply current of the device is reduced
to below 1µA. Do not drive the EN pin above the supply
voltage.
DIM Input
The DIM pin provides a logic level control for brightness
of the LED. A PWM input can be used to control the
brightness of LED. DIM high enables the output and its
voltage has to be 2.0V or higher. DIM low disables the
output, regardless of EN high-state.
Current-Sense Input
The CS pin provides the high-side current sense to set
the LED current with an external sense resistor.
A sense resistor R
CS
is placed between V
IN
and LED+
terminals.
The current through LED is sensed by the sense resistor
(R
CS
). The sensed voltage is fed back to the MIC3202 to
regulate the LED current
R
CS
is given by:
Frequency of Operation
To calculate the frequency spread across input supply:
(V
D
+I
LED
×R
CS
+ V
LED
) ×(V
IN
-
I
LED
×R
CS
-
V
LED
)
L ×
Δ
I
L
×(V
D
+ V
IN
)
F
SW
=
Δ
I
L
=
V
CS(MAX )
-
V
CS(MIN)
R
CS
where:
V
D
is Schottky diode forward drop
V
LED
is total LEDs voltage drop
V
IN
is input voltage
I
LED
is average LED current
According to the above equation, choose the inductor to
make the operating frequency no higher than 1MHz.
Refer to the datasheet
Application Information
for more
information on components selection guidelines.
Frequency Dithering
The MIC3202 is designed to modulate the V
CS(MAX)
with
amplitude ±6mV by a pseudo random generator to
generate the ±12% of the switching frequency dithering.
This spreads the frequency spectrum over a wider range
and reduce the EMI noise peaks.
The MIC3202-1 is non-dithering version of the MIC3202.
1 V
CS(MAX)
+ V
CS(MIN)
x(
)
2
I
LED
Bookmark not defined.
R
CS
=
I
LED
is LED current required to set.
R
CS
(Ω)
1.33
0.56
0.4
0.28
0.2
I
LED
(A)
0.15
0.35
0.5
0.7
1.0
I
2
R (W)
0.03
0.07
0.1
0.137
0.2
Error!
Size (SMD)
0603
0805
0805
0805
1206
For V
CS(MAX)
and V
CS(MIN)
refers to the Electrical
Characteristics table.
October 2010
2
M9999-102810
Micrel, Inc.
MIC3202/MIC3202-1 Evaluation Board
Evaluation Board Performance
October 2010
3
M9999-102810
Micrel, Inc.
MIC3202/MIC3202-1 Evaluation Board
Evaluation Board Schematic
Notes:
1. If bulk capacitor on input rail is away (4 inches or more) from the MIC3202/MIC3202-1, install the 100µF bulk capacitor near V
IN
.
2. Source impedance should be as low as 10mΩ.
October 2010
4
M9999-102810
Micrel, Inc.
MIC3202/MIC3202-1 Evaluation Board
Bill of Materials
Item
C1, C2, C8
Part Number
12105C475KAZ2A
GRM32ER71H475KA88L
08053D105KAT2A
C3, C9
GRM21BR71E105KA99L
C2012X7R1E105K
C4, C7
06035C271KAT2A
GRM188R71H271KA01D
06035C104MAT
C5, C6
GRM188R71H104KA93D
C1608X7R1H104K
D1
D2, D3
L1
R1
R2, R3
R4
R5
R6
R7, R8
R9
RV1
U1
U2
SS24-TP
SS24
B0530WS-TP
SLF10145T-470M1R4
CSR 1/2 0.2 1% I
CRCW06031003FKEA
CRCW08052R20FKEA
CRCW080510R0FKEA
CRCW060310K0FKEA
CRCW06030000FKEA
CRCW060349R9FKEA
3386P-1-104TLF
MIC3202YME
MIC1557YM5
Manufacturer
AVX
(1)
Description
4.7µF/50V, Ceramic Capacitor, X7R, Size 1210
1µF/25V, Ceramic Capacitor, X5R, Size 0805
1µF/25V, Ceramic Capacitor, X7R, Size 0805
270pF/50V, Ceramic Capacitor NPO, Size 0603
Qty.
2
1
1
2
Murata
(2)
AVX
(1)
Murata
(2)
TDK
(3)
AVX
(1)
Murata
(2)
AVX
(1)
Murata
(2)
TDK
(3)
MCC
(4)
Fairchild
(5)
MCC
(4)
TDK
(3)
0.1µF/50V, Ceramic Capacitor, X7R, Size 0603
2
60V, 2A, SMA, Schottky Diode
30V, 200mA, Schottky diode, SOD-323
47µH, 1.4A, SMT, Power Inductor
0.2Ω Resistor, 1/2W, 1%, Size 1206
100kΩ Resistor, 1%, Size 0603
2.2Ω Resistor, 1%, Size 0805
10Ω Resistor, 1%, Size 0805
10kΩ Resistor, 1%, Size 0603
0Ω Resistor, 1%, Size 0603
49.9Ω Resistor, 1%, Size 0603
POT 100kΩ 3/8" SQ CERM SL ST
High Brightness LED Driver with High-Side
Current Sense
RC Time/Oscillator (SOT-23-5)
1
2
1
1
2
1
1
1
2
1
Stackpole
Electronics,
(7)
Inc
Vishay
(8)
Vishay
(8)
Vishay
(8)
(8)
(8)
Vishay
Vishay
Vishay
(8)
Bourns
(9)
Micrel, Inc.
(10)
Micrel, Inc.
(10)
1
1
1
Notes:
1. AVX:
www.avx.com.
2.
3.
4.
5.
6.
7.
8.
9.
Murata:
www.murata.com.
TDK:
www.tdk.com.
MCC:
www.mccsemi.com.
Fairchild:
www.fairchildsemi.com.
Diodes Inc. :
www.diodes.com.
Stackpole Electronics:
www.seielect.com.
Vishay:
www.vishay.com.
Bourns Inc :
www.bourns.com.
10.
Micrel, Inc.:
www.micrel.com.
October 2010
5
M9999-102810
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