The LM3561 is a 2-MHz fixed-frequency current-mode synchronous boost converter. The
device is designed to operate as a single 600-mA constant current driver for high-current white
LEDs. The high-side current source allows for grounded cathode LED operation while the 250-mV
regulated headroom voltage ensures that the LED current is well regulated and efficiency remains
The main features of the LM3561 include: an I2C-compatible
interface for controlling the LED current, a hardware Flash enable input for direct triggering of
the Flash pulse, dual TX inputs (TX1 and TX2) which force the Flash pulse into a low-current Torch
mode during high battery current instances, an active high hardware enable (HWEN) allowing for fast
hardware shutdown during system software failures, a dual mode pin which serves as either an
indicator LED driver at up to 18mA or as a dedicated comparator input with an internal 1V
reference, designed to monitor the voltage across a negative temperature coefficient thermistor
(NTC), and a programmable input voltage monitor which monitors IN and can reduce the flash current
or shutdown the device during low battery conditions.
Seven fault flags are available for read back over the
I2C-compatible bus. These include: a flash timeout flag indicating the
flash pulse has reached the end of the programmable timeout duration, a thermal shutdown flag
indicating the LM3561's die temperature has exceeded 150°C, an LED fault flag indicating the output
voltage has tripped the over-voltage threshold, or the LED has become shorted, TX1 and TX2
interrupt flags indicating if either of the TX inputs have been triggered, an NTC flag indicating
the LED has experienced an over temperature condition, and a VIN Monitor flag indicating the input
voltage has fallen below the VIN Monitor threshold.
The LM3561 is available in a tiny (1.215mm × 1.615mm × 0.6mm) 12-bump DSBGA and operates
over the temperature range -40°C to +85°C.
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