Microchip MIC3223TE-BOOST Manual

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Side 1/8

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

OVP −

On the evaluation board, these values have been set as

follows: R4 = 3.24kΩ and R3 = 100kΩ and V OVP = 40V.

Produkt Specifikationer

Mærke:	Microchip
Kategori:	Ikke kategoriseret
Model:	MIC3223TE-BOOST

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