Shutdown

External

Torch

Standby

Output On

Strobe Flash

Level

Strobe Flash

Edge

Internal

Flash

External

Torch

Assist Light

Red

Indicator

LM3555

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SNVS594E – JANUARY 2009 – REVISED NOVEMBER 2011

I

OEN

OM1

OM0

TEN

SEN

TORCH

STROBE

Mode

0

0

0

0

X

X

X

Standby

0

0

0

1

X

0

X

Standby

0

0

0

1

X

1

X

Ext Torch

0

0

1

X

X

X

X

Standby

0

1

0

X

X

X

X

Standby

0

1

1

X

X

X

X

Standby

1

0

0

X

X

0

X

Standby

1

0

0

X

X

1

X

Ext Torch

1

0

1

X

X

X

X

Indicator

1

1

0

X

X

X

X

Assist

1

1

1

X

0

X

X

Internal Flash

1

1

1

X

1

X

0

Standby

1

1

1

X

1

X

1

Strobe Flash

Application Information

INTERNAL DIODE DETECTION

During the LM3555's startup sequence, an internal voltage comparator on the VLED pin monitors the forward

voltage of the LED or LEDs. This measurement occurs when the ramp-up current reaches 80 mA. If at this time

the diode voltage exceeds the user-selectable diode detect threshold (Register 0x02 bits VO1 and VO0), the

LM3555 will assume two series LEDs are present and will limit the maximum flash current to 400 mA. The four

adjustable levels are; '00' = 4.35V, '01' = 4.65V, '10' = 4.05V and '11' = 4.95V. This detection feature can be

disabled by setting the Diode Detect Enable bit (DEN) in the Current Set Register (address 0x03) to a '0'. The

DEN bit is set to a '1' (Enabled) by default.

Copyright © 2009–2011, Texas Instruments Incorporated

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