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DETAILED FUNCTIONAL DESCRIPTION
The AW3643 is a high-power white LED flash driver capable of delivering up to 1.5A in either of the two
parallel LEDs. The total allowed LED current during operation is 1.5A (I
LED1
+I
LED2
≤1.5A). The device
incorporates a 2MHz or 4MHz constant frequency-synchronous current-mode PWM boost converter and dual
high-side current sources to regulate the LED current over the 2.7V to 5.5V input voltage range.
The AW3643 PWM DC-DC boost converter switches and boosts the output to maintain at least V
HR
across
each of the current sources (LED1/2). This minimum headroom voltage ensures that both current sources
remain in regulation. If the input voltage is above the LED voltage + current source headroom voltage, the
device would not switch, but turns the PMOS on continuously (Pass mode). In Pass mode the difference
between (V
IN
− I
LED
× R
PMOS
) and the voltage across the LED is dropped across the current source.
The AW3643 has three logic inputs including a hardware Flash Enable (STROBE), a hardware Torch Enable
(TORCH/TEMP, TORCH = default), and a Flash Interrupt input (TX) designed to interrupt the flash pulse
during high battery-current conditions. These logic inputs have internal 300kΩ (typical) pull-down resistors to
GND.
Additional features of the AW3643 include an internal comparator for LED thermal sensing via an external
NTC thermistor and an input voltage monitor that can reduce the Flash current during low V
IN
conditions. It
also has a Hardware Enable (HWEN) pin that can be used to reset the state of the device and the registers by
pulling the HWEN pin to ground.
Control is done via an I
2
C-compatible interface. This includes adjustment of the Flash and Torch current
levels, changing the Flash Timeout Duration, and changing the switch current limit. Additionally, there are flag
and status bits that indicate flash current timeout, LED over-temperature condition, LED failure (open/short),
device thermal shutdown, TX interrupt, and V
IN
under-voltage conditions.
