MIC3205 Evaluation Board
High-Brightness LED Driver Controller wi th
Fixed-Frequency Hysteretic Control
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
December 2012 M9999-121312-A
General Description
The MIC3205 is a hysteretic, step-down, high-brightness
LED (HB LED) driver with a patent pending frequency
regulation scheme that maintains a constant operating
frequency over input voltage range. It provides an ideal
solution for interior/exterior lighting, architectural and
ambient lighting, LED bulbs, and other general
illumination applications.
The board is o ptim ized for ease of test ing, with all of the
components on a single side. The device operates from
a 4.5V to 40V input voltage range, and controls an
external power MOSFET to drive high-current LEDs.
On-board components are set up to evaluate one 1A
current rating LED, at a switching frequency of
approximately 400 kHz. To evaluate a different number
of LEDs or different current rating LEDs, component
values must be change d as explaine d in the Applic ation
Information section of the MIC3205 data sheet.
Requirements
This board needs a single bench power source
adjustable over the input voltage of 4.5V < VIN < 40V
that can provide at least 1A of current. The loads can
either be active (electronic load) or passive (LEDs) with
the ability to dissipate the maximum load power while
keeping accessible surfaces ideally < 70°C.
Precautions
There is no revers e in put protecti on on t his bo ar d. When
connecti ng the i nput s ourc e s , make s ure that the c orr ect
polarity is observed.
Under extreme load conditions, input transients can be
quite large if long test leads are used. In such cases, a
100µF, 63V electrolytic capacitor is needed at the VIN
terminals to prevent overvoltage damage to the IC.
Datasheets and supp ort do cumentati on can be f ound on
Micrel’s web site at: www.micrel.com.
Getting Started
1. Connect VIN supply to the input terminals VIN
and GND.
Connect a s upply between the VIN terminal (J1) and
the GND terminal (J2), paying careful attention to
polarity and supply range (4.5V < VIN < 40V).
Monitor IIN with a current meter and VIN at the VIN
and GND terminals with a voltmeter. Don’t apply
power until step 4.
2. Connect the load to the output terminals, LED+
and LED
−
.
Connect a load between the LED+ (J5) and LED–
(J6) terminals. The load can be either one 1A rated
LED or an active, electronic load. Make sure to
connect the anode of the 1A LED to the LED+
terminal and the cathode to the LED– terminal.
3. Enable input.
The MIC3205YML EV board comes with a 100kΩ
pull-up resistor to VIN. A jumper (JP6) is provided
on board for users to easily access the enable
feature. Applying an external logic signal on the EN
pin to pull it low or using a jumper to short the EN
pin to GND shuts off the output of the evaluation
board.
4. Turn ON the input supply.
By default, the controller is enabled when the input
voltage approaches the UVLO threshold and
cross es 5V, the intern al 5 V VCC is regul ate d, and the
external MOSFET is turned ON if the EN pin and
the DIM pin are high. To use the EN and DIM
functions of the M IC3 205, a tes t po int is pr o vided f or
each of them.
Ordering Information
Part Number Description
MIC3205YML EV Evaluation board with
MIC3205YML device
Micrel, Inc.
MIC3205 Evaluation Board
December 2012
2
Evaluation Board Features
EN Input
The EN pin provides a logic level control of the output.
The voltage must 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
into an off state and the supply current of the device is
reduced to 1µA. A logic low pulls down the DRV pin,
turning off the external MOSFET. Do not drive the EN
pin above the supply voltage. Do not leave floating. R8
is provided for default “ON.”
DIM Input
The DIM pin provides logic level control for the
brightness of the LED. The DIM pin can turn the LEDs
on and off if EN is in an active-high state. The
MIC3205YML EV board comes with a 100kΩ pull-up
resistor installed (R5). R5 provides default 100%
brightness. LED brightness can be c ontrolled b y varying
the duty cycle, on the DIM input, from 1% to 99%. Do
not leave floating.
LED Curren t and RCS
The CS and VINS pins provide the high-side current
sense to set the LED current with an external sense
resistor RCS. The MIC3205YML EV board comes with a
200mΩ RCS resistor ins talled as th e default value, which
corresponds to an LED current rating of 1A. The
following equation gives the RCS value for required LED
current:
LED
CS I
200mV
R=
Eq. 1
For more information, please see the LED Current and
RCS subsection in the Application Information section of
the MIC3205 data sheet.
Operating Frequency
The operating switching frequency can be programmed
by installing an external capacitor from the CTIMER pin
to AGND.
T
-4
SW C 1022.2
F×
=
Eq. 2
The MIC3205YML EV board comes with a 470pF CT
capacitor (C10) installed for default 400kHz frequency.
For more information, please see the Frequency of
Operation subsection in the Application Information
section of the MIC3205 datasheet.
Inductor
The inductor valu e can be calculated after average L ED
current, operating frequency, and an appropriate
hysteresis ∆VHYS value have been chosen. The
MIC3205YML EV board comes with a 22µH inductor
installed.
Inductor L is given by:
SWHYSDIN
CSLEDCSLEDDLEDCSLEDIN
F V ) V V( R) V RI (V) V- RI - (V
L×∆×+
×+×+××
=
Eq. 3
where:
VLED is the total voltage drop of the LED string
VIN is the input voltage
RCS is the current sense resistor
ILED is the average LED current
VD is the freewheeling diode forward drop
FSW is the operating switching frequency
∆VHYS is the hysteresis on the CS pin
L is the inductor value
Tables 1, 2, and 3 give ref erence inductor values for an
operating frequency of 400 kHz, for a given LED current,
freewheeling diode forward drop, and number of LEDs.
By selecting ∆VHYS in the 55mV to 75mV range, we get
the following in duc tor va lue s:
RCS (Ω) ILED (A) VIN (V) L (µH)
∆V
HYS
(mV)
0.56
0.35
5
22
64.1
0.56
0.35
12
68
57.7
0.28
0.7
5
10
70.5
0.28
0.7
12
33
59.4
0.2
1.0
5
6.8
72.6
0.2
1.0
12
22
62.4
0.1
2.0
5
3.6
68.5
0.1
2.0
12
10
68.6
Table 1. Inductor for FSW = 400 kHz, VD = 0.4V, 1 LED
RCS (Ω) ILED (A) VIN (V) L (µH)
∆V
HYS
(mV)
0.56
0.35
24
150
55.8
0.56
0.35
36
220
56.8
0.28
0.7
24
68
61.6
0.28
0.7
36
100
62.5
0.2
1.0
24
47
62.4
0.2
1.0
36
68
64.3
0.1
2.0
24
22
66.6
0.1
2.0
36
33
66.2
Table 2. Inductor for FSW = 400 kHz, VD = 0.4V, 4 LEDs
Micrel, Inc.
MIC3205 Evaluation Board
December 2012
3
RCS (Ω) ILED (A) VIN (V) L (µH)
∆V
HYS
(mV)
0.56
0.35
36
150
58.4
0.56
0.35
40
220
54.3
0.28
0.7
36
68
64.4
0.28
0.7
40
100
59.6
0.2
1.0
36
47
65.2
0.2
1.0
40
68
61.4
0.1
2.0
36
22
69.6
0.1
2.0
40
33
63.3
Table 3. Inductor for FSW = 400 kHz, VD = 0.4V, 8 LEDs
The MIC3205YML EV board is set up for evaluation for
one 1A LED. If more LEDs are required, the inductor
value must be recalculated. If a different operating
switching frequency is desired, the CT capacitor value
must be r ecalcula ted. If LE Ds with a c urrent rat ing oth er
than 1A need to be evaluated, the RCS value must be
recalculated.
The LED voltage drop depends on the manufacturer
tolerance an d number of LEDs. The LED c urrent can be
measured using an ammeter or current probe. The
4.7µF ceramic capacitor between the LED+ and LED–
terminals is highly recommended, as it helps to reduce
the current ripple through the LED.
Micrel, Inc.
MIC3205 Evaluation Board
December 2012
4
Evaluation Board Performance (Typical Characteristics)
60
65
70
75
80
85
90
95
100
0 9 18 27 36 45
EFFICIENCY (%)
INPUT VOLTAGE (V)
Efficiency (I
LED
= 1A)
vs. Input Voltage
1 LED
L = 22µH
4 LED
L = 47µH
6 LED
L = 68µH
10 LED
L = 33µH
0.98
0.99
1.00
1.01
1.02
1.03
-50 -25 025 50 75 100 125
I
LED
OUTPUT CURRENT (A)
TEMPERATURE (°C)
ILED Output Curr e nt
vs. Temperature
V
IN
= 12V
V
LED
= 3.5V
R
CS
= 0.2Ω
0
0.5
1
1.5
2
0 9 18 27 36 45
NORMALIZED FREQUENCY
INPUT VOLTAGE (V)
Normalized Switching Frequency
vs. Input Voltage
1 LED
L = 22µH
I
LED
= 1A
R
CS
= 0.2Ω
4 LED
L = 47µH
6 LED
L = 68µH
10 LED
L = 33µH
430
450
470
490
510
530
-50 -25 025 50 75 100 125
FREQUENCY (kHz)
TEMPERATURE (°C)
Switching Frequency
vs. Temperature
V
IN
= 12V
VLED = 3.5V
L = 22µH
CT = 470pF
RCS = 0.2Ω
Micrel, Inc.
MIC3205 Evaluation Board
December 2012
5
Evaluation Board Performance (Functional Characteristics)
Micrel, Inc.
MIC3205 Evaluation Board
December 2012
6
Evaluation Board Schematic
Micrel, Inc.
MIC3205 Evaluation Board
December 2012
7
Bill of Materials
Item Part Number Manufacturer Description Qty.
C1, C2,C3,C4,C11
12105C475KAZ2A AVX
(1)
4.7µF/50V, Ceramic Capacitor, X7R, Size 1210 5
GRM32ER71H475KA88L Murata(2)
CGA6P3X7R1H475K TDK
(3)
C5 GRM21BR71H105KA12L Murata 1µF/50V, Ceramic Capacitor, X7R, Size 0805 1
CGA4J3X7R1H105K TDK
C10 06035C471K4T2A AVX 470pF/50V, Ceramic Capacitor, X7R, Size 0603 1 GRM188R71H471KA01D Murata
C1608X7R1H471K TDK
C8 06036D475KAT2A AVX 4.7µF/6.3V, Ceramic Capacitor, X5R, Size 0603 1 GRM188R60J475KE19J Murata
CGA3E1X5R0J475K TDK
C7,C9 06035C102KAT2A AVX 1nF/50V, Ceramic Capacitor, X7R, Size 0603 2 GRM188R71H102KA01D Murata
C1608X7R1H102K TDK
D1 SK36-TP MCC
(4)
60V, 3A, SMC, Schottky Diode 1 SK36 Fairchild
(5)
SK36-7-F Diodes , Inc.
(6)
L1 SLF10145T-220M1R9-PF TDK 22µH, 2.1A, 0.0591Ω, SMT, Power Inductor 1
M1 FDS5672 Fairchild MOSFET, N-CH, 60V, 12A, SO-8 1
RCS CSR1206FKR200 Stackpole
Electronics, Inc.(7) 0.2Ω Resistor, 1/2W, 1%, Size 1206 1
R5, R8 CRCW0603100KFKEA Vishay Dale
(8)
100kΩ Resistor, 1%, Size 0603 2
R2, R3 CRCW060330R0FKEA Vishay Dale 30Ω Resistor, 1%, Size 0603 2
R1, R9 CRCW06032R00FKEA Vishay Dale 2Ω Resistor, 1%, Size 0603 2
R4 CRCW060310K0FKEA Vishay Dale 10kΩ Resistor, 1%, Size 0603 1
R6 CRCW060351R0FKEA Vishay Dale 51Ω Resistor, 1%, Size 0603 1
R7 CRCW06030000Z0EA Vishay Dale 0Ω Resistor, Size 0603 1
U1 MIC3205YML Micrel, Inc.(9) High-Brightness LED Driver Controller with
Fixed-Frequency Hysteretic Control 1
Notes:
1. AVX: www.avx.com.
2. Murata: www.murata.com.
3. TDK: www.tdk.com.
4. MCC: www.mccsemi.com.
5. Fairchild: www.fairchildsemi.com.
6. Diodes I nc.: www.diodes.com.
7. Stack pol e Electronics : www.seielect.com.
8. Vis hay Dale: www.vishay.com.
9. Micrel, Inc.: www.micrel.com.
Micrel, Inc.
MIC3205 Evaluation Board
December 2012
8
PCB Layout Recommendations
Top Layer
Bottom Layer
Micrel, Inc.
MIC3205 Evaluation Board
December 2012
9
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB www.micrel.com
Micrel makes no representati ons or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. This
informat i on is not intended as a warranty and Micrel does not assume responsibilit y for its use. Micrel reserves the right to change circuitry,
specificat i ons and descript i ons at any time without notice.
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liability whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products includi ng liabi l ity or
warranties relating to fitness for a particul ar purpose, merchant abili ty, or infringement of any patent, copyright or other intellectual property right.
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product can reasonably be expected to result in personal i nj ury. Lif e support devices or systems are devices or systems that (a) are intended for
surgical implant int o the body or (b) support or sustain life,
and whose failure to perform can be reasonably expected to result in a significant injury
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© 2012 Micrel, Incorporated.