MIC3263 datasheet(11/32 Pages) MICREL

11 / 32 page

Micrel, Inc.

MIC3263

January 2010

M9999-012110

A constant

d for driving

operate as

nt in all six

ed in each

vidually and

R) on-time.

ed off. The

ightness of

as a boost

er than the

e design of

or a

e boost

st converter

range of 6V

nge of input

rent can be

nal resistor

djusting the

IC3263 can

M dimming

dimming signal (up to 40kHz)

ness of the

s a boost stage that boosts the VIN to a high

rd bias the LED channels. The

t current controller. The controller

nnels at

value. Each channel has an independent curren

The MIC3263 uses three main control loops

control loops):

1) Current Amp loop (Fastest)

2) Booster loop (Fast)

3) Capacitor Reference Voltage (CRV) loop (Slo

The current Amplifier Loop is faster than the Boost Loop

and CRV Loop. CRV is the reference voltage for the boost

error amp.

Functional Description

The MIC3263 is a six-channel LED driver.

output current converter is the preferred metho

LEDs. The MIC3263 is specifically designed to

a constant-current LED driver to keep the curre

channels constant. PWM dimming is employ

channel. Each channel of LED current is indi

tightly regulated during each Duty Ratios (D

During the DR off-time the LED current is turn

duty cycle of the DR pulse determines the br

the LEDs. The MIC3263 is designed to operate

controller in which the output voltage is high

input voltage. This configuration allows for th

multiple LEDs in series to help maintain

brightness. During each DR pulse off-time

converter is turned off (not switching). The boo

is on (switching) during each DR pulse on-time.

The MIC3263 has a very-wide input voltage

and 40V to help accommodate for a diverse ra

voltage applications. In addition, the LED cur

programmed through the use of an exter

(RISET). This provides design flexibility in a

current for a particular application. The M

control the brightness of the LEDs via its PW

capability. Applying a PWM

col

to the DRC pin allows for control of the bright

LED. It ha

enough voltage to forwa

onstan

MIC3263 is a c

keeps the current in each of the six cha

a constant

t regulator

t in each

(Figure 1

in series with each LED channel. The curr

channel is within 3% of the others.

Figure 1. Constant-Current Control Loops

Figure 2. Simplified C

The objective of these loops is t

constant.

ontrol Loop

o keep the LED current

The boost output voltage VOUT will vary when

CRV changes. VOUT will be what it needs to be to keep

ILEDs constant. The current amp loop is so fast the other

loops can be viewed as static DC values. On a pulse to

pulse basis the boost loop is fast enough that CRV is a

constant value.

The goal of the CRV loop is to keep the collector’s voltage

V(IO1–IO6) at or about 1.2V, thereby keeping the bipolar

transistor in the linear region and also keep the power loss

across the bipolar as low as possible. Keeping the bipolar

in the linear region allows the current amp loop to be able

to regulate the LED current.

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