LM3555

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SNVS594E – JANUARY 2009 – REVISED NOVEMBER 2011

STROBE Pin

The Strobe pin of the LM3555 provides an external method for initiating a flash event. In most cases, the Strobe

pin is connected to an imaging module so that the image capture and flash event are synchronized. The Strobe

0x04) and Strobe Signal Mode (SEN in 0x04) bits are set ('1'). The Strobe pin can be configured to be an edge

sensitive or level sensitive input by setting the Strobe Signal Usage bit (SSU in 0x04. '1' = Level, '0' = Edge). In

Edge Sensitive mode, a rising edge transition ('0' to '1') will start the flash event and the internal flash timer will

terminate the event. In Level Sensitive mode, a rising edge transition ('0' to '1') will start the flash event and a

Mode, there is an internal pull-down resistor that becomes enabled on this pin.

In Simple Control mode, the Strobe pin functions as a output when a pullup resistor is connected, alerting the

user to the number of flash LEDs present in the system. If the Strobe pin is outputting a '1', two LEDs are

present, whereas a '0' indicates a single LED is present.

TORCH Pin

The Torch pin of the LM3555, depending on the state and configuration, allows the user to enable Torch/Assist

simple mode, the LM3555 will drive 60 mA of LED current if two series LEDs are present and 80mA is one LED

Mode.

Indicator LED Pin (IND)

The Indicator LED current source pin (IND) is able to drive a single red indicator LED when the Anode is

connected to the LM3555 and the Cathode is connected to Ground. In Simple Logic Mode, the default indicator

mA.

Fault Protections

The LM3555 has numerous internal fault protection mechanisms to help prevent damage to the LM3555 as well

as the system in the event of a fault. In the event of a fault, the LM3555 will enter shutdown mode and will report

a fault to the fault register (0x05). The faults that can be detected are as follows:

•

Over-Voltage Protection (VOUT)

•

Short-Circuit Protection (VOUT and VLED)

•

Over-Temperature Protection

•

Flash Timeout

•

Indicator LED Protection (Open and Short)

•

Broken Inductor Protection

•

Under-Voltage Lock-Out (not reported)

•

Inductor Current Limit (not reported)

DATA VALIDITY

The data on SDA line must be stable during the HIGH period of the clock signal (SCL). In other words, the state

of the data line can only be changed when CLK is LOW.

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