MIC3263 datasheet(16/32 Pages) MICREL

16 / 32 page

Micrel, Inc.

MIC3263

January 2010

M9999-012110

ill be

nnect DFS to VD

n for the input dimming pulse. This

ing

tput of a transconductance differential am

efore, a RC filter is required to compensa

, a phase lead at the DFS pin. U

stor in series with a 2.2nF ceramic capac

nect a capacitor and resistor to ground to co

g Ratio Control (DRC) is an input PWM

ming

CINT integrates the DRC input pulse. For a PWM frequency

range of around 1kHz use 100nF. For a PWM frequen

range of around 20kHz pulse, use 10nF. Fo

frequency range of around 100Hz pulse use 1μF.

ISET

Set the LED current of all six channels by this resistor. Use

2kΩ for 30mA and 3kΩ for 20mA. The RISET is inversely

proportional to ILED. Use the following equation to find

RISET:

The input frequency to the DRC pin can be 100Hz to

40kHz and the internal dimming frequency

determined by RDFS.

R w

The duty cycle of the input frequency at DRC

according to Table 2 for the actual dimming duty

For direct dimming control, co

converted

cycle.

D and use

method by

the MODE pi

passes the internal dimming control and

dimming control by the external PWM.

DFS Filter

In addition to the R

resistor-to-gro

allows f

DFS

d at th

series RC filter is required when operating

frequencies below 1kHz. The reason is that the

the ou

DFS pin, a

t dimm

DFS pin is

plifier. The

DFS is high

differential amplifier has a high-frequency pole.

At low dimming frequencies of around 1kHz

around 100kΩ and the differential amplifier po

a phase shift that can cause instabilities

control.

produces

the DFS

te for the

ing a zero

se a 4kΩ

itor. When

e filter has

mpensate

Ther

lagging phase shift created by the pole by ad

and therefore

resi

using a dimming frequency of 2 kHz or less. T

no ill effect at higher dimming frequencies.

COMP

Con

the boost stage.

DRC

Dimmin

con

dim

trol. The MIC3263 converts this to one

dimming ratios that is used to dim the LEDs. T

ratio is built on a log scale.

CINT

of sixteen

e dimming

r a PWM

LED

ISET

Ω

best current matching accuracy design for an ILED

current of 15mA to 30mA.

pin. This is used as the

ge. The CRV capacitor is

continually being charged or discharged in order to keep

VOUT at the right level (refer to Functional Diagram

o keep the IO’s at about

e linear-mode current

t the cathode end of the

control loop will keep this

he current amplifier is in

can regulate the LED

ent number of LEDs in a

ith the fewest LEDs will

as high as 7.5V before

as a

er of LEDs in a channel

nnels that have less

Ds biased correctly. A

en channels can occur

at monitors the IO pins

off and that channel’s IO

off channel’s IO pin will

ut voltage. On a channel

hannel’s IO voltage will

increase to keep correct voltage drops on the other series

LEDs. It is best to use equal number of LEDs in each

rences in the LEDs

ge drops so all IOs will not have the exact same

voltage. Each channel has its own monitoring circuit

any V(IO) drops below

an LED opens), that channel is turned off and the

other channels are unaffected. If any IO goes about 7.5V

short to VOUT), that channel is turned off

and the other channels are unaffected.

VSW

This is the boost-stage switch node, the collector of the

internal power switch.

Connect EN high to enable the part, low to disable. Do not

leave the EN pin floating.

VIN

Supply voltage to the part (6V–40V).

For the

CRV

Use a 2.2μF capacitor at the CRV

reference voltage of the boost sta

illustration). CRV will be charged t

1.2V.

IO1─IO6

These are the connections to th

amplifier in each channel. Connec

LED channels to these pins. The

at about 1.2V. 1.2V insures that t

the linear region and therefore

current.

In cases where there are a differ

channel, the V(IO) of the channel w

have a higher V(IO). V(IO) can be

the fault monitoring circuits will sense that channel

short to VOUT.

When there are a different numb

the IO voltage will be higher in the cha

LEDs in order to keep the LE

difference of up to 7.5V betwe

because of this. If the circuits th

sees a fault, that channel will turn

pin will be at high impedance. An

be near or below the booster outp

that has a shorted LED, that c

channel but there will always be diffe

volta

monitoring the IO1─IO6 pins. If

0.5V (if

(if several LEDs

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