MIC3263 datasheet(14/32 Pages) MICREL

14 / 32 page

Micrel, Inc.

MIC3263

January 2010

M9999-012110

OVP. OVP

ccurs

turns

o, o

. Fou

e on an

chan

open), then

rmal for those three chann

t having to go through a po

pening (four or more ch

ost output

VOUT_MA

= 2.4*

5. Feedback VOVP will reach 2.4V and

comparator will trip and turn off the boos

6. With the booster off, VOUT and VOVP will

When feedback reduces to 1.7V the

turned back on.

7. The OVP circuit will switch 1.8V onto CR

8. If the load is still open the cycle will co

Result

OVP

An open LED in a channel will not trigger an

monitors the boost output voltage. If an open o

load (all channels open) an OVP fault will trigger

voltage condition. When the OVP triggers, it

boost and starts an OVP cycle. If one, tw

channels open, they will not trigger an OVP

channels will trigger an OVP fault and will cycl

at about 2Hz as long as there are four open

on the

n over-

off the

r three

r open

d off

nels. If

one of the LED channels is reconnected (not

operation returns to no

els th

wer on

are reconnected with ou

reset.

he even

In t

t of a load o

annels

open) the following will occur:

1. VIO will drop below 1V

. Charge

pump will raise CRV during each DR pulse

on-time

3. CRV will increase to 2.4V

4. When CRV reaches 2.4V the bo

maximum voltage will be;

(R2+R2)/R1.

the OVP

ter.

discharge.

booster is

ntinue.

C ndition

Fault

Monitor

1 L

> 1.2V

All Channels

ED Shorts

in Same

Channel

< IO < 7.5

All Channels

EDs Shor

1.2

LEDs Short

in Same

> 7.5V

1 Channel

Off; 5

Channels On

re Than 2

C annels

YES

1 LED Opens

< 0.5V

1 Channel

Off; 5

Channels On

in hannel 1

YES

2 or 3

< 0.5V

3 Channels

Off; 3

Channels On

C annels

en LEDs

YES

4 o

Open

< 0.5V

4 Channels

Off; 2

Channels On

r More

annels

YES

All Channels

Open

YES

OVP

Threshold

Exceeded

OVP

Triggered

VOUT Shorted

YES

Curren

Exceed

t Limit

Output

Current is

Limited

Table 1. Fault Summary

n Sequence

o be present before PWM pulses are applied to

DRC pin. Some channels may not turn on if the power

up sequence isn’t followed. This is because the circuits

that monitor the IO pins may see transients during the turn

on-time and may interpret voltage spikes during turn on as

a fault, preventing that channel from turning on. When a

channel is off, its IO pin is at high impedance.

It is best to follow the sequence:

1. VIN

2. PWM dimming at DRC

3. Enable high

Power-O

VIN needs t

the

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