MIC3205 Evaluation Board

MIC3205 Evaluation Board
High-Brightness LED Driver Controller with
Fixed-Frequency Hysteretic Control
General Description
Getting Started
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 optimized for ease of testing, 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 changed as explained in the Application
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 reverse input protection on this board. When
connecting the input sources, make sure that the correct
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 support documentation can be found on
Micrel’s web site at: www.micrel.com.
1. Connect VIN supply to the input terminals VIN
and GND.
Connect a supply 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
crosses 5V, the internal 5V VCC is regulated, 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 MIC3205, a test point is provided for
each of them.
Ordering Information
Part Number
MIC3205YML EV
Description
Evaluation board with
MIC3205YML device
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
Micrel, Inc.
MIC3205 Evaluation Board
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 controlled by varying
the duty cycle, on the DIM input, from 1% to 99%. Do
not leave floating.
LED Current 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 installed as the default value, which
corresponds to an LED current rating of 1A. The
following equation gives the RCS value for required LED
current:
RCS =
200mV
ILED
MIC3205YML EV board comes with a 22µH inductor
installed.
Inductor L is given by:
L=
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 reference 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 inductor values:
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.
FSW
2.22 × 10 -4
=
CT
RCS (Ω)
ILED (A)
VIN (V)
L (µH)
∆VHYS
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
(mV)
Table 1. Inductor for FSW = 400 kHz, VD = 0.4V, 1 LED
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 value can be calculated after average LED
current, operating frequency, and an appropriate
hysteresis ∆VHYS value have been chosen. The
December 2012
(VIN - ILED × RCS - VLED) × (VD + ILED × RCS + VLED) × RCS
Eq. 3
( VIN + VD) × ∆VHYS × FSW
RCS (Ω)
ILED (A)
VIN (V)
L (µH)
∆VHYS
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
(mV)
Table 2. Inductor for FSW = 400 kHz, VD = 0.4V, 4 LEDs
2
M9999-121312-A
Micrel, Inc.
MIC3205 Evaluation Board
RCS (Ω)
ILED (A)
VIN (V)
L (µH)
∆VHYS
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
(mV)
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 recalculated. If LEDs with a current rating other
than 1A need to be evaluated, the RCS value must be
recalculated.
The LED voltage drop depends on the manufacturer
tolerance and number of LEDs. The LED current 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.
December 2012
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M9999-121312-A
Micrel, Inc.
MIC3205 Evaluation Board
Evaluation Board Performance (Typical Characteristics)
Efficiency (ILED = 1A)
vs. Input Voltage
ILED Output Current
vs. Temperature
100
1.03
90
ILED OUTPUT CURRENT (A)
EFFICIENCY (%)
95
4 LED
L = 47µH
85
6 LED
L = 68µH
80
10 LED
L = 33µH
1 LED
L = 22µH
75
70
VIN = 12V
VLED = 3.5V
RCS = 0.2Ω
1.02
1.01
1.00
0.99
65
60
0.98
0
9
18
27
36
45
-50
-25
25
50
75
100
125
Switching Frequency
vs. Temperature
Normalized Switching Frequency
vs. Input Voltage
2
530
ILED = 1A
RCS = 0.2Ω
1 LED
L = 22µH
1
6 LED
L = 68µH
4 LED
L = 47µH
0.5
VIN = 12V
VLED = 3.5V
L = 22µH
CT = 470pF
RCS = 0.2Ω
510
1.5
FREQUENCY (kHz)
NORMALIZED FREQUENCY
0
TEMPERATURE (°C)
INPUT VOLTAGE (V)
10 LED
L = 33µH
490
470
450
0
0
9
18
27
36
430
45
-50
December 2012
-25
0
25
50
75
100
125
TEMPERATURE (°C)
INPUT VOLTAGE (V)
4
M9999-121312-A
Micrel, Inc.
MIC3205 Evaluation Board
Evaluation Board Performance (Functional Characteristics)
December 2012
5
M9999-121312-A
Micrel, Inc.
MIC3205 Evaluation Board
Evaluation Board Schematic
December 2012
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M9999-121312-A
Micrel, Inc.
MIC3205 Evaluation Board
Bill of Materials
Item
Part Number
12105C475KAZ2A
C1, C2,C3,C4,C11
C5
GRM32ER71H475KA88L
C8
C7,C9
(2)
06036D475KAT2A
AVX
Murata
CGA3E1X5R0J475K
TDK
06035C102KAT2A
AVX
SK36-TP
SK36
SK36-7-F
1µF/50V, Ceramic Capacitor, X7R, Size 0805
1
470pF/50V, Ceramic Capacitor, X7R, Size 0603
1
4.7µF/6.3V, Ceramic Capacitor, X5R, Size 0603
1
1nF/50V, Ceramic Capacitor, X7R, Size 0603
2
60V, 3A, SMC, Schottky Diode
1
22µH, 2.1A, 0.0591Ω, SMT, Power Inductor
1
MOSFET, N-CH, 60V, 12A, SO-8
1
0.2Ω Resistor, 1/2W, 1%, Size 1206
1
100kΩ Resistor, 1%, Size 0603
2
AVX
Murata
TDK
GRM188R71H102KA01D
5
TDK
C1608X7R1H471K
GRM188R60J475KE19J
4.7µF/50V, Ceramic Capacitor, X7R, Size 1210
(3)
Murata
C1608X7R1H102K
D1
Murata
GRM21BR71H105KA12L
GRM188R71H471KA01D
Qty.
AVX
TDK
06035C471K4T2A
Description
(1)
CGA6P3X7R1H475K
CGA4J3X7R1H105K
C10
Manufacturer
Murata
TDK
(4)
MCC
Fairchild
(5)
Diodes, Inc.
(6)
L1
SLF10145T-220M1R9-PF
M1
FDS5672
RCS
CSR1206FKR200
R5, R8
CRCW0603100KFKEA
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
High-Brightness LED Driver Controller with
Fixed-Frequency Hysteretic Control
1
U1
MIC3205YML
TDK
Fairchild
Stackpole
(7)
Electronics, Inc.
Vishay Dale
(8)
(9)
Micrel, Inc.
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 Inc.: www.diodes.com.
7. Stackpole Electronics: www.seielect.com.
8. Vishay Dale: www.vishay.com.
9. Micrel, Inc.: www.micrel.com.
December 2012
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Micrel, Inc.
MIC3205 Evaluation Board
PCB Layout Recommendations
Top Layer
Bottom Layer
December 2012
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M9999-121312-A
Micrel, Inc.
MIC3205 Evaluation Board
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 representations or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. This
information is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry,
specifications and descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual
property rights is granted by this document. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no
liability whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or
warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a
product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for
surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury
to the user. A Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and
Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale.
© 2012 Micrel, Incorporated.
December 2012
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M9999-121312-A