LM3550 Datasheet, PDF (1/29 Pages) Texas Instruments – 5A Flash LED Driver with Automatic VLED and ESR Detection for Mobile Camera Systems

LM3550
February 29, 2012
5A Flash LED Driver with Automatic V_LED and ESR
Detection for Mobile Camera Systems
General Description
LM3550 is a low-noise, switched-capacitor DC/DC converter
designed to operate as a current-limited and adjustable (up
to 5.3V) super-capacitor charger. LM3550 features user-se-
lectable super-capacitor charge-termination voltages and an
optimal charge-termination mode that maximizes flash-ener-
gy efficiency by accounting for flash element losses. Addi-
tionally, the device provides one adjustable constant current
output (up to 200 mA) and one NFET controller ideal for driv-
ing one or more high-current LEDs either in a high-power flash
mode or a low-power torch mode.
The LM3550 can be configured to utilize a proprietary super-
capacitor charging scheme (Optimal Charge Mode), allowing
faster charging times (0 to Target Voltage) and lower current-
source power dissipation. Optimal Charge Mode adapts to
changes in the flash LEDs forward voltage as well as the su-
per-capacitor's ESR ensuring that the super-capacitor is
charged to the ideal voltage required to sustain constant cur-
rent-flash operation.
The LED current and Flash pulse duration of the LM3550 can
be programmed via an I²C-compatible interface. The
STROBE pin allows the Flash to be toggled via a flash-enable
signal from a camera module. The EOC pin sinks current
when the output voltage reaches 95% of the final value.
The ALD/TEMP input pin allows either a light sensor to adjust
the flash-current level based on the ambient light conditions,
or it allows for over-temperature detection and protection of
the LED during high-power operation or high ambient-tem-
perature conditions by connecting an NTC thermistor tem-
perature monitoring circuit to the pin.
Features
■ ^{Up to 5A Flash Current}
■ ^{4 Selectable Super-Capacitor Charge Voltage Levels}
(4.5V, 5.0V, 5.3V, Optimized)
■ ^{Flash Optimized Charge Mode for Optimal Efficiency}
−33% Faster Charge Time Using Optimal Mode
−49% Less Power Dissipated in Current Source using
Optimal Charge Mode
■ ^{Fast Super-Capacitor Charger with 500 mA Input Current}
Limit
■ ^{Adjustable Torch Current (60 mA to 200 mA)}
■ ^{Ambient Light or LED Thermal Sensing with Current}
Scaleback
■ ^{End-of-Charge Output (EOC)}
■ ^{Dedicated Indicator LED Current Source}
■ ^{No Inductor Required}
■ ^{Manual Flash Enable via Strobe Pin Input}
■ ^{Programmable Flash Pulse Duration, and Torch and Flash}
Currents via I²C-compatible Interface
■ ^{True Shutdown (LED Disconnect)}
■ ^{Flash Time-Out Protection}
■ ^{LED Temperature Protection or Ambient Light Sensing Pin}
■ ^{Low Profile 20-Pin LLP Package (3.0 mm × 2.5 mm × 0.8}
mm)
Applications
■ ^{Camera Phones}
■ ^{Digital Still Camera}
■ ^{Voltage Rail Management}
Typical Application Circuit
30059401
© 2012 Texas Instruments Incorporated 300594 SNVS569A
Solution Size
30059459
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