Instrukcja obsługi Microchip MIC3223TE-BOOST

Microchip nieskategoryzowany MIC3223TE-BOOST

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MIC3223 Evaluation Board
High-Power Boost LED Driver with
Integrated FET
Bringing the Power to Light™
MLF and MicroLeadFrame are registered trademarks of Amkor Technology, Inc.
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
General Description
The MIC3223 is a constant-current boost switching
controller specifically designed to power a string of high-
power LEDs. The MIC3223 has an input voltage range
from 4.5V to 20V and is ideal for a variety of applications.
The MIC3223 evaluation board is designed to
accommodate for a VIN of 6V to 20V.
The MIC3223 utilizes an internal power device which
offers a cost-conscious solution for driving high-power LED
applications. Power consumption has been minimized
through the implementation of a 200mV feedback-voltage
reference providing an initial accuracy of ±5%. The
MIC3223 controller is dimmable via a PWM input signal.
An external FET (Q1) is in series with the LED string and
is used to PWM Dim the LEDs. The MIC3223 also features
an enable pin for low-power shutdown.
The LED current is regulated by keeping the voltage drop
across the current-sense resistor (R5) constant. The LED
current can be set by selecting the value of R5. In this
version of the evaluation board, the output current is
limited to 700mA. Table 1 provides a summary of the
evaluation board specifications. The evaluation board
schematic is shown in Figure 1 and the parts list is shown
in the Bill of Materials table.
The switching frequency is fixed to 1MHz ±30%.
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 MIC3223 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 converter is off the input is
connected to the output through the inductor (L1) and
diode (D1). VIN is effectively applied across the LEDs and
will turn on if the series sum of their forward voltage drop is
not greater than VIN. For 100% dimming duty-cycle, simply
pull DIM IN to 5V. For a different LED current, change R5
using the following equation (when R5 is 0.56Ω and the
LED current is equal to 0.35A):
FB REF LED
V = V = I ×R5
where VREF = 0.2V
PWM Dimming
The PWM DIM signal applied to the DIM IN pin switches
the current to the LEDs on and off. When DIM IN is high,
the MIC3223 is enabled and the boost converter regulates
the LED current by keeping the voltage drop across R5
constant. DIM IN also controls the DIM OUT pin. DIM OUT
drives the gate of the external dimming FET (Q1). When
DIM IN is high, DIM OUT is also high. When DIM IN is low,
the converter turns off and the DIM OUT pin is low while
driving the gate of Q1 low. When the gate of Q1 is low, Q1
turns off and the LED current stops.
Ordering Information
Order Part Number Description
MIC3223TE BOOST EV Boost Evaluation Board
March 2010 M9999-030210
Micrel, Inc. MIC3223 Evaluation Board
March 2010 2 M9999-030210
Quick-Start Guide
1. Connect a load (LED series string or resistive)
between VOUT and LED RTN (note that this is not the
same as GND).
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, connect the DIM IN
terminal to the EN terminal. This is a
convenient way to turn on and off the
converter.
b. For PWM DIMMING, connect a function
generator to the DIM IN input and GND (not
LED RTN). Set the output at 0V − 5V square
wave pulse at 100Hz − 20kHz. Make sure
the pulse goes all the way to 0V.
Output Over-Voltage Protection (OVP)
The MIC3223 provides over-voltage protection (OVP)
circuitry in order to protect the system from an over-
voltage fault condition. This OVP threshold can be
programmed through the use of external resistors (R3
and R4). A reference value of 1.245V is used for the
OVP. The following equation can be used to calculate
the resistor value for R3 to set the OVP point. Normally
use 100k for R3:
1/1.245)(V
R3
R4
OVP −
=
On the evaluation board, these values have been set as
follows: R4 = 3.24kΩ and R3 = 100kΩ and V OVP = 40V.
Micrel, Inc. MIC3223 Evaluation Board
March 2010 3 M9999-030210
Evaluation Board Design Specifications
Parameter Minimum Typical Maximum
VIN 6V 12 20V
Output Voltage V
IN 18-25 37V
Number of LEDs 7 9
LED Current 0 0.2 − 0.5 .7A
Power Out 0 20W 15W
Efficiency 90%
Switching Frequency (FIXED) 1MHz
PWM Dim Frequency 0 300Hz 500Hz
Line Regulation <5%
Load Regulation <5%
Ambient Temperature –40°C +25°C +85°C
Table 1. Evaluation Board Design Specifications
LED Current Selection
R5 (Ω) I_LED
5 40mA
2 100mA
1 200mA
0.62 320mA
0.5 400mA
0.56 350mA
0.4 500mA
0.28 700mA
Table 2. LED Current Selection

Specyfikacje produktu

Marka: Microchip
Kategoria: nieskategoryzowany
Model: MIC3223TE-BOOST

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