LM3554 datasheet(27/43 Pages) TI1

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SDA

Start Condition

Stop Condition

SCL

LM3554

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SNVS549A – JUNE 2009 – REVISED APRIL 2011

There is a delay of 250µs before the LEDF flag is valid on a LED short. This is the time from when VLED falls

below the LED short threshold of 500mV (typical) to when the fault flag is valid. There is a delay of 2µs from

when the LEDF flag is valid on an LED open. This delay is the time between when the OVP threshold is

triggered and when the fault flag is valid. The LEDF flag can only be reset to (0) by pulling HWEN low, removing

power to the LM3554, or reading the Flags Register.

Flash Timeout

The TO flag (bit [0] of the Flags Register) reads back a (1) if the LM3554 is active in Flash mode and the

Timeout period expires before the Flash pulse is terminated. The flash pulse can be terminated before the

Timeout period expires by pulling the STROBE pin low (with STR bit '0'), or by writing a ‘0’ to bit 0 or 1 of the

Torch Brightness Register or the Flash Brightness Register. The TO flag is reset to (0) by pulling HWEN low,

removing power to the LM3554, reading the Flags Register, or when the next Flash pulse is triggered.

LED Thermal Fault

The NTC flag (bit [5] of the Flags Register) reads back a (1) if the LM3554 is active in Flash or Torch mode, the

device is in NTC mode, and the voltage at LEDI/NTC has fallen below VTRIP (1.05V typical). When this has

happened and the LM3554 has been forced into Torch or LED shutdown (depending on the state of

Configuration Register 2 bit [1], the Flags Register must be read in order to place the device back in normal

operation. (See Thermal Comparator Mode (NTC) section for more details.)

Input Voltage Monitor Fault

The VIN Monitor Flag (bit [6] of the Flag Register) reads back a '1' when the Input Voltage Monitor is enabled and

VIN falls below the programmed VIN Monitor threshold. This flag must be read back in order to resume normal

operation after the LED current has been forced to Torch mode or turned off due to a VIN Monitor event.

TX1 and TX2 Interrupt Flags

The TX1 and TX2 interrupt flags (bits [3] and [4]) indicate a TX event on the TX1/TORCH and ENVM/TX2 pins.

Bit 3 will read back a (1) if TX1/TORCH is in TX1 mode and the pin has changed from low to high since the last

read of the Flags Register. Bit 4 will read back a (1) if ENVM/TX2 is in TX2 mode and the pin has had a TX

event since the last read of the Flags Register. A read of the Flags Register automatically resets these bits.

The ENVM/TX2/GPIO2 pin, when configured in TX2 mode, has a TX event that can be either a high-to-low

transition or a low-to-high transition depending on the setting of the TX2 polarity bit (see Configuration Register 1

Bit [6]).

2C-Compatible Interface

START AND STOP CONDITIONS

The LM3554 is controlled via an I2C-compatible interface. START and STOP conditions classify the beginning

and end of the I2C session. A START condition is defined as SDA transitioning from HIGH to LOW while SCL is

HIGH. A STOP condition is defined as SDA transitioning from LOW to HIGH while SCL is HIGH. The I2C master

always generates the START and STOP conditions.

Figure 16. Start and Stop Sequences

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