Microchip MIC3231 Manual

Microchip Ikke kategoriseret MIC3231

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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

General Description

The MIC3230/1 are constant current boost switching

controllers specifically designed to power one or more

strings of high power LEDs. The MIC3230/1 have an input

voltage range from 6V to 45V and are ideal for a variety of

applications.

The MIC3230/1 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 MIC3230/1

are 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

750mA.

Multiple MIC3230 ICs can be synchronized to a common

operating frequency by connecting the ICs together

through the SYNC pin. This feature is only good on the

MIC3230. The clocks of these synchronized devices can

be used together which help reduce noise and errors in a

system.

The MIC3231 offers a dither feature to assist in the

reduction of EMI. This is particularly useful in sensitive

EMI applications, and provides for a reduction in emissions

by approximately 10dB.

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.

The switching frequency is determined by the selection of

R1. The chart in Figure 2 can be used to select the

desired frequency. The board is set at approximately

500kHz.

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

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.

How it works

The MIC3230/1 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% 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 equal to 0.4A. The evaluation

board is currently set to this output current value.

IREF

LED = Where VREF = 0.25V

PWM Dimming

A PWM signal applied to the PWMD pin turns the current

to the load LEDs on and off. When PWMD is high the

MIC3230/1 is enabled and the boost converter regulates

the LED current by keeping the voltage drop across R7

constant. When PWMD is low the converter turns off and

the LED current discharges the output caps and LED

current stops.

Ordering Information

Part Number Description

MIC3230ML

BOOST EV

Boost evaluation board for the

MIC3230YML IC

MIC3231ML

BOOST EV

Boost evaluation board for the

MIC3231YML IC

Micrel, Inc. MIC3230/1 Evaluation Board

July 2009 2 M9999-071609-A

(408) 944-0800

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 LED 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 MIC3230/1 features current limit sensing. Current

limit is set by an external resistor 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 R9 according to this equation;

(

)

( )

9R8R

V9R

V245.1OVP MAX,O

On the evaluation board, these values have been set to:

R9 = 2kΩ and R8 = 100kΩ and VO,MAX = 64V.

VFB=0.25V

100k

10uF/10V

10nF

4.7µH

0.075

1/2W

/2W

4.7µF

50V

4.7µF

50V

SS5P10-E3

+VIN

PWM Dim

SYNCH

GND

LED RTN

1J6

+VOUT LED

SI7148DP

COMP

PWMD

VDD GND

EPAD

12 10

IS 8

OVP 9

DRV 11

VIN

IADJ 5

SYNC

MIC3230-YML

100pF /100V

2.2µF

100V

2.2µF

100V R10

TBD/OPEN

Figure 1. Schematic Diagram

Produkt Specifikationer

Mærke:	Microchip
Kategori:	Ikke kategoriseret
Model:	MIC3231

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