Product category:
Power Supply ICs and Controllers
News Release from: Advanced Analogic Technologies | Subject: AAT2803
Edited by the Electronicstalk Editorial
Team on 21 October 2005
Dual charge pump simplifies handset
power
A novel multifunction high-efficiency dual charge pump supports both white LED backlight and camera flash applications for portable systems that run on lithium batteries.
Many of today's handsets feature two displays, either in a clamshell design with a main display on the inside and a secondary display on the outside or in a bar design with a main display and a keypad backlight By combining independent control of two separate banks of backlight LEDs with flash capability and a light load mode in a single device, AnalogicTech's AAT2803 charge pump helps designers minimise power consumption while reducing component count and package size
This article was originally published on Electronicstalk on 19 Sep 2008 at 8.00am (UK)
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The AAT2803 is a multifunction high-efficiency dual charge pump that supports both white LED backlight and camera flash applications for portable systems that run on lithium-ion/polymer batteries.
The device offers independent control of three separate LED banks (two for backlight and one for camera flash) and features seven channels in total (six for backlight and one for camera flash).
The AAT2803 delivers major power and space savings for handsets featuring two displays, and adds a light load mode to minimise power consumption when the handset display is active in standby mode.
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The backlight charge pump is capable of driving up to six LEDs at a total of 180mA.
The device provides independent control of two groups of four and two LEDs to backlight a primary and secondary display.
The outputs can be operated independently or in parallel.
The AAT2803 uses AnalogicTech's AS2Cwire (Advanced Simple Serial Control) digital interface to enable, disable, and set current for each backlight LED across a 16-level logarithmic scale.
Four low-current settings allow operation in light load mode down to 50uA (typical).
The backlight charge pump maximises power efficiency by operating in 1x, 1.5x and 2x modes.
The mode of operation is automatically selected by comparing the forward voltage of each LED with the input voltage.
Optimised current sinks minimise the voltage headroom required to drive each LED and maximise power efficiency by increasing the amount of time the devices stays in 1x mode before transitioning to 1.5x mode.
Unlike most of the integrated solutions available today, AnalogicTech's AAT2803 uses a dedicated charge pump to drive the backlight.
As a result, backlight operation is not affected by the photo flash, which is driven by a separate charge pump engine.
For flash applications, the device integrates a charge pump with a regulated output voltage.
Delivering up to 120mA of continuous current or up to 300mA of pulsed current, the circuit adds an independent enable pin to maximise system flexibility.
Exhibiting versatility, the AAT2803 features built-in thermal protection, an integrated auto-disable capability for load short-circuit conditions, and soft-start circuitry to prevent excessive inrush current during startup.
The use of a 1MHz constant switching frequency allows designers to support the device with extremely small ceramic capacitors.
The AAT2803 is available in a Pb-free thermally enhanced 24-pin QFN44 package and is rated over the -40 to +85C temperature range.
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