LM3555TLE Datasheet, PDF (17/33 Pages) Texas Instruments – LM3555 Synchronous Boost Converter with 500 mA High Side LED Driver and Dual-Mode Control Interface

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
pin is only functional when the LM3555 is placed into I²C Control Mode (I2C/EN = '1') and the Output On (OEN in
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
falling edge transition ('1' to '0') or the internal flash timer, which ever occurs first, will terminate the event. In I²C
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
Mode without having to write the command through the I²C bus or through toggling the EN1 and EN2 pins. In
simple mode, the LM3555 will drive 60 mA of LED current if two series LEDs are present and 80mA is one LED
is present. In I²C mode, the external torch mode bit (TEN in register 0x04) must be set to a '1' to allow an
external torch (default value = '1'). In I²C mode, the torch mode current is equal to the Assist mode current level
stored in register 0x03. The Torch pin has an internal pull-down resistor enabled in both Simple Mode and I²C
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
current is 2.5mA, and in I²C Mode, the indicator LED current can be adjusted to 2.5 mA, 5.0 mA, 7.5 mA or 10
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)
I²C-Compatible Interface
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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