Instrukcja obsługi Microchip MIC3203YM

Microchip nieskategoryzowany MIC3203YM

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MIC3203/MIC3203-1
Evaluation Board
High Brightness LED Driver Controller
with High-Side Current Sense
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (
408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
January 2011 M9999-011311-B
General Description
The MIC3203/MIC3203-1 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
MIC3203/MIC3203-1 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 4.5V to 42V
input voltage range, and controls an external power
MOSFET to drive high current LEDs. When the input
voltage approaches and crosses UVLO threshold, the
internal 5V VCC is regulated and the external 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 VCS(MAX) with respect to VIN, the external MOSFET is
turned off and the Schottky diode takes over and returns
the current to VIN. Then the current through inductor and
LEDs starts decreasing. When CS pin hits VCS(MIN), the
external 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.
Requirements
This board needs a single bench power source
adjustable over the input voltage of 4.5V < VIN < 42V 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, ensure 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 over voltage damage to the IC.
Getting Started
1. Connect VIN supply to the input terminals VIN
and GND. With the output of this supply
disabled, set its voltage to the desired input test
voltage (4.5V < VIN
< 42V). 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.
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 current sense resistor RCS i.e.,
200mΩ.
Selecting the sense resistor refers to the table
given in data sheet application sub-section.
2. Enable the input supply. By default, the
controller is enabled when the input voltage
approaches UVLO threshold and crosses 5V,
the internal 5V VCC is regulated and the
external MOSFET is turned on if EN pin and
DIM pin are high. To use the EN and DIM
functions of the MIC3203/MIC3203-1, a test
point is provided for each of them.
Ordering Information
Part Number Description
MIC3203YM EV Evaluation board with
MIC3203YM device
MIC3203-1YM EV Evaluation board with
MIC3203-1YM device
Micrel, Inc. MIC3203/3203-1 Evaluation Board
January 2011 2 M9999-011311-B
Other Features RCS is given by
)
I
V+V
(x
2
1
=R
LED
)MIN(CS)MAX(CS
CS Error! Bookmark not
defined.
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. In the off state, the output drive is placed
in a "tri-state" condition, where MOSFET is in an “off” or
non-conducting state. Do not drive the EN pin above the
supply voltage.
ILED is LED current required to set.
For VCS(MAX) and VCS(MIN) , refers to electrical
characteristics table in the data sheet.
To calculate the frequency spread across input supply:
)V+V(×IΔ×L
)VR×IV(×)V+R×I+V(
=F
INDL
LEDCSLEDINLEDCSLEDD
SW
--
CS
)MIN(CS)MAX(CS
LR
VV
=IΔ
-
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.
where : VD is Schottky diode forward drop
VLED is total LEDs voltage drop
VIN is input voltage
ILED is average LED current
Current Sense Input According to the above equation, choose the inductor to
make the operating frequency no higher than 1.5MHz.
The CS pin provides the high-side current sense to set
the LED current with an external sense resistor. Refer to the datasheet “Application Information” for more
information on components selection guidelines.
A sense resistor RCS is placed between VIN and LED+
terminal.
Frequency Dithering
The current flowing through LED is sensed and current
feedback is provided to the hysteretic step-down
regulator.
The MIC3203 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
to spread the frequency spectrum over a wider range
and reduce the EMI noise peaks
The MIC3203-1 is non-dithering version of the MIC3203.
Micrel, Inc. MIC3203/3203-1 Evaluation Board
January 2011 3 M9999-011311-B
Evaluation Board Performance
Efficiency
vs. Input Voltage
60
70
80
90
100
0 5 10 15 20 25 30 35 40 45
INPUT VOLTAGE (V)
EFFICIENCY (%)
L=150µH
ILED=1A
4LED
6LED
8LED
10LED
Efficiency
vs Input Voltage
60
70
80
90
100
0 5 10 15 20 25 30 35 40 45
INPUT VOLTAGE (V)
EFFICIENCY (%)
L=68µH
ILED=1A
4LED
6LED
8LED
10LED
Normalized LED Currents
vs. Input Voltage
0.97
0.98
0.99
1
1.01
1.02
1.03
0 5 10 15 20 25 30 35 40 45
INPUT VOLTAGE (V)
NORMALIZED LED CURRENTS (A)
L=150µH
ILED=1A
1LED 2LED 4LED 6LED 8LED
10LED
Normalized LED Currents
vs Input Voltage
0.97
0.98
0.99
1
1.01
1.02
1.03
0 5 10 15 20 25 30 35 40 45
INPUT VOLTAGE (V)
NORMALIZED LED CURRENTS (A)
L=68µH
ILED=1A
1LED
2LED
4LED
6LED 8LED 10LED
* With regards to VIN

Specyfikacje produktu

Marka: Microchip
Kategoria: nieskategoryzowany
Model: MIC3203YM

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