Microchip MIC3203YM Manual

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Side 1/7

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

)

V+V

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(

INDL

LEDCSLEDINLEDCSLEDD

)MIN(CS)MAX(CS

=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.

Produkt Specifikationer

Mærke:	Microchip
Kategori:	Ikke kategoriseret
Model:	MIC3203YM

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