MIC3263 datasheet(13/32 Pages) MICREL

13 / 32 page

Micrel, Inc.

MIC3263

January 2010

M9999-012110

stor harder and

ntrol loop will increase CR

n external pulse

the DRC pin. The duty cycle of the external puls

DRC) is converted to one of 16 levels called Duty Ratio

(DR) (see Table 2 for DR ratios). It is this inte

(DR) that is used to PWM dim the LEDs.

Case 2

If 29.3V is not high enough to properly forwa

LED channel at the ISET current level, the

loop will drive the bipolar transi

d bias the

rrent amp

V(IO) will

V and the

drop and the CRV co

boost output voltage (VOUT) will increase.

Internal Dimming Control

In the internal dimming mode, the dimming is

by the DFS and MODE pins. A

etermined

is tied to

e (pulse at

rnal pulse

Figure 3. Internal Dimming Control

External Dimming Control

In external dimming mode, connect the DFS pin

apply a PWM dimming pulse to the MODE

external pulse directly controls the LED curre

(see Figure 4).

to VDD and

pin. The

nt drivers

Figure 4. External Dimming Control

lts

pen, the voltage on the

sistor (IO1-IO6) will go

rs the IO pins will detect less

to the transistor. A flip-

nd a power down and

eset that channel.

r, the channel of LEDs

e will be present at the

r five channels will continue

ting normally. This fault sequence is identical if up to

ur channels fail open or

D channels will stay on

shorted, the voltage on

stor (IO1–IO6) will go

at monitors the current

ore than 7.5V at the

to the transistor will turn

ondition. A power-down

ed to reset that channel.

tolerate a two LED difference before a fault

is detected.

e drive to the transistor, the channel of LEDs

ce is present at the

channels will continue

ce is identical if more

r channels fail open

ED channels will stay on

tors the current amp bipolar

transistor detects less than 0.5V at the collector (IO), then

the base drive to the transistor will turn off. A flip-flop

latches the fault condition. A power-down and power-up

sequence is required to reset that channel.

Without base drive to the transistor, the channel of LEDs

will turn off and a high impedance is present at the

collector (IO). The other five channels will continue

operating normally. This fault sequence is identical if more

than one LED channel fails open. If four channels fail open

or short, then the remaining two LED channels will stay on

and no more faults will be detected.

Fau

Open LED in Channel

If any LED in a channel fails o

collector of the current amp tran

low. The circuitry that monito

than 0.5V and turn off base drive

flop latches the fault condition a

power up sequence is required to r

Without base drive to the transisto

will turn off and a high impedanc

collector (IO). The othe

opera

three LED channels fail open. If fo

short, then the remaining two LE

and no more faults will be detected.

Short LED in Channel

If any LED in a channel fails

collector of the current amp transi

high in voltage. If the circuitry th

amp bipolar transistor detects m

collector (IO), then the base drive

off. A flip-flop latches the fault c

and power-up sequence is requir

A channel can

Without bas

will turn off and a high impedan

collector (IO). The other five

operating normally. This fault sequen

than one LED channel fails open. If fou

or short, then the remaining two L

and no more faults will be detected.

Shorted Cathode (or IO Short)

If the circuitry that moni

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