MIC3232YMM Evaluation Board User Guide

MIC3232 Evaluation Board
High Voltage Boost HBLED Driver with
PWM Dimming Control
Bringing the Power to Light™
General Description
The MIC3232 is a constant current boost switching
controller specifically designed to power one or more
strings of high power LEDs. The MIC3232 has an input
voltage range from 6V to 45V and is ideal for a variety of
applications. The MIC3232 is the fixed 400kHz version of
the MIC3230, in a 10-pin MSOP package.
The MIC3232 utilizes an external power device which
offers a cost conscious solution for driving high power LED
applications. Power consumption has been minimized
through the implementation of a 250mV feedback voltage
reference providing an accuracy of ±3%. The MIC3232 is
dimmable via a PWM input signal and also features an
enable pin for low power shutdown.
The LED current is regulated by keeping the voltage drop
across the current sense resistor (R7) constant. The LED
current can be set by selecting the value of R7. In this
version of the eval board, the output current is limited to
1A.
Table 1 provides a summary of the eval board
specifications. The evaluation board schematic is shown in
Figure 1 and the parts list is shown in the Bill of Materials
table.
Requirements
1. Voltage source capable of supplying 50 Watts
2. Load: LED, resistive or electronic load
3. Scope
4. Voltage meter
5. (Optional) Function generator for PWM Dimming
How it works
The MIC3232 evaluation board is set to operate as a boost
converter, which requires the output voltage to be greater
than the input voltage. It is important to have the series
LED forward voltage drops be greater than the input
voltage because when the MIC3232 is off, the input is
connected to the output through the inductor (L1) and
diode (D1). The input voltage (VIN) is effectively applied
across the LEDs and will turn on if VIN is greater than the
sum of the forward voltage drops across the LED string.
For 100% duty cycle, simply pull PWMD high or leave
open. For a different LED current change R7 using the
following equation. When R7 is 0.62Ω the LED current is
to 0.4A. The evaluation board is currently set to this
output current value.
ILED =
VREF
R7
Where VREF = 0.25
PWM Dimming
A PWM signal applied to the PWMD pin turns the current
to the LEDs on and off. When PWMD is high, the MIC3232
is enabled and the boost converter regulates the LED
current by keeping the voltage drop across the R7 resistor
constant. When PWMD is low the converter turns off and
the LED current discharges the output capacitors and the
LED current stops.
Ordering Information
Part Number
Description
MIC3232YMM EV
Evaluation board for the MIC3232YML
IC
Precautions
The evaluation board does not have input reverse polarity
protection. Applying a negative voltage at the VIN terminal
may damage the board. When the controller is off there is
a current path through the inductor and the flyback diode
to the output. No current limit exists for this current path so
care must be taken not to short circuit the output.
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
July 2009
M9999-071609-A
(408) 944-0800
Micrel, Inc.
MIC3232 Evaluation Board
Quick-Start Guide
1. Connect a load (LED series string or resistive load)
between VOUT and LED RTN (this is not the same as
ground).
2. Connect 12V (or other input voltage) to VIN and
GND.
3. Use a current probe to measure the load current.
and Monitor the Switch node with a scope to view
the switch waveform
4. PWM Dimming:
a. For no PWM dimming, leave the PWMD
terminal open
b. For PWM DIMMING connect a function
generator to the PWM DIM input and GND
(not RTN). Set the output at 0-5V square
wave pulse at 300Hz. Make sure the pulse
goes all the way to 0V.
RSET – Current Limit Sensing
The MIC3232 features current limit sensing. Current limit
is set through the external resistor, R6, by the following
equation:
IS=0.5V = R6 × IQ1
Where, IQ1 is the peak FET current that will trigger the
current limit, the Default setting for the evaluation board
is R6 = 75mΩ with the current limit set at 6.7A.
OVP – Setting the over voltage protection
OVP is set with the R9 resistor, according to equation:
OVP = 1.245 V =
(R8 + R9)
On the evaluation board, these values have been set to:
R9=2kΩ and R8=100kΩ and VO,MAX = 64V.
C3
1000pF
100V
R4
1/2 W
L1
47µH
J1
VIN
C1
4.7uF
50V
R1
J3
EN
J4
PWMD Dim
VIN
2
EN
OVP
7
3
PWMD
DRV
9
IS
6
IADJ
5
C5
10uF
6.3V
COMP
VDD
Q1
SI7148DP
C6
2.2uF
100V
R5
C7
2.2uF
100V
R10
OPEN
R9
Vfb=0.25V
R7
R6
1/4W
1/2 W
PGND
C4
10nF
R8
1
10
J6
+Vout to LED
D1
SS5P10-E3
MIC3232YMM
MSOP-10
4
R3
J2
GND
(R9 × VO,MAX )
8
J7
LED RTN
Figure 1. Schematic Diagram
July 2009
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M9999-071609-A
(408) 944-0800
Micrel, Inc.
MIC3232 Evaluation Board
Evaluation Board Design Specifications
MIN
TYP
MAX
VIN
6V
12-24
45V
Output Voltage
Vin
12-24 Series
LEDs
90V*
LED Current
0
0.2-.5
0.70A
Power Out
0
20W
70W
Efficiency
90%
Switching Frequency
100kHz
400kHz
1MHz
PWM Dim Frequency
0
300Hz
500Hz
Line Regulation
<3%
Load Regulation
<3%
Ambient Temperature
–40°C
+25°C
+85°C
*Evaluation Board parts are rated to 75V
Table 1. Evaluation Board Design Specifications
LED current selection
R7 (ohms)
I_LED
5
50mA
2
125mA
1
250mA
0.62
404mA
0.5
500mA
0.4
625mA
.35
0.7A
Table 2. LED current selection
July 2009
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MIC3232 Evaluation Board
Bill of Materials
Item
Part number
U1
MIC3232-YMM
Q1
Si7148DP-T1
D1
SS5P10-E3
L1
MSD1278-473ML
Coilcraft
47µH, rate 5.2A inductor
1
C1
GRM32ER71H475KA88L
Murata
4.7µF/50V, 1210, Ceramic capacitor
1
C5
GRM21BR61A106KE19L
Murata
10uF/10V, 0805, ceramic capacitor
1
LMK212BJ106KD-T
C0805C106K8PACTU
C3
VJ0805Y102KXBAT.
OR
GRM2195C2A102JA01B.
Manufacturer
Micrel.Inc
Part Description
Quant
Constant Current Boost control for Hi Power LED
1
Vishay Siliconix.
N Channel 75V MOSFET
1
Vishay corp
5A, 100V schottky diode
1
Taiyo Yuden
OR
Kemet
OR
Vishay Vitramon
1nF/100V,0805, Ceramic capacitor
1
Murata
C2012X7R2A102K
TDK
C6,C7
C4532X7R2A225K
TDK
2.2µF/100V,1812, Ceramic capacitor
OR
GRM32ER72A225KA35L.
Murata
2.2uF/100V, 2220, Ceramic capacitor
C4
VJ0603Y103KXBAT.
OR
GRM188R71H103KA01D.
R1,R8
CRCW0603100KFKEA.
Vishay Dale
100kΩ, 0603, 1%
2
R3
CRCW06030000FKEA.
Vishay Dale
0Ω, 0603
1
R4
CRCW20102R00FKEF
Vishay Dale
2Ω, 1/2W, 2010
1
R9
CRCW06032K00FKEA.
Vishay Dale
2kΩ, 0805
1
R5
CRCW12064990FKEA.
Vishay Dale
499Ω, 1206
1
R6
WSL2010-R0750-FKEA
Vishay Dale
0.075Ω, 1/2W, 1812
1
R7
CRCW1206R620JNTALR.
Vishay Dale
0.620Ω, 1/4W, 1206
1
Open
1
Vishay Vitramon
10nF/50V, 0603, Ceramic capacitor
Murata
R10
2
1
Notes:
1. DigiKey: www.digikey.com
2. Murata: www.murata.com
3. Vishay: www.vishay.com
4. AVX: www.avx.com
5. TDK: www.tdk.com
6. Diodes, Inc.: www.diodes.com
7. Sumida: www.sumida.com
8. International Rectifier: www.irf.com
9. Micrel, Inc: www.micrel.com
July 2009
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M9999-071609-A
(408) 944-0800
Micrel, Inc.
MIC3232 Evaluation Board
Top Layer
July 2009
5
M9999-071609-A
(408) 944-0800
Micrel, Inc.
MIC3232 Evaluation Board
Bottom Layer
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its
use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
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.
© 2009 Micrel, Incorporated.
July 2009
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