Product category:
Power Supply ICs and Controllers
News Release from: Analog Devices | Subject: ADP1653
Edited by the Electronicstalk Editorial
Team on 17 November 2006
LED driver preserves handset flash power
White LED driver for camera-phone flash uses new portable power management technique to maintain picture quality even when the battery is taxed by multiple phone functions.
As cellphones that integrate cameras have become more commonplace, major improvements in image quality have been realised However, the integration of new features, such as streaming video, MP3, instant messaging, and mobile e-mail, threatens to reverse the trend in better image quality as camera-phone designers struggle to manage multiple features demanding limited battery power
This article was originally published on Electronicstalk on 14 Sep 2001 at 8.00am (UK)
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An output current power management feature reduces battery-current overstress when the camera flash is activated at the same time the phone is receiving an RF (radio frequency) signal.
Under normal operating conditions ADI's new ADP1653 high-efficiency, high-brightness, dual, white LED driver enables a brighter camera flash than single or low-efficiency white LED drivers, which translates into better picture quality in low-light conditions.
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"As camera phones move to resolutions of 2Mpixel and higher, the light level required to take quality photos rises dramatically", said Arcadio Leon, Marketing Director, Portable Power Management Products, Analog Devices.
"For camera phones, both efficiency and system sequencing play a critical role in minimising battery-current overstress".
"Existing charge pump solutions, for example, have a power efficiency rating as low as 40% under low battery voltage conditions, which means that less than half of the input power is converted to output power, thereby further draining the battery".
"The power efficiency of the ADP1653 peaks at 92% and is typically greater than 80% over the full voltage range of a lithium-ion battery".
In addition, unlike standard step-up DC/DC convertors, the ADP1653 features a logic-input pin that reduces the white LED current to its lowest operation level in less than 50us when the phone activates the power amplifier to send an RF transmission.
This current sequencing technology further extends battery life without compromising photo image quality.
A high-efficiency flash driver solution can be developed using the ADP1653 and four small external components - a diode, micro-inductor and two capacitors.
This bill of materials (BOM) reduces the external component cost by as much as 50% over existing high-efficiency solutions.
The ADP1653 drives two series-connected, high-brightness white LEDs with currents up to 500mA, as well as a separate indicator LED.
The ADP1653 uses a dual-mode interface that can support an I2C interface or 2bit logic bus, allowing designers to program the LED strings independently in hardware, with external resistors, or in software, by writing data to the device's registers.
Safety features incorporated into the ADP1653 include soft-start to reduce inrush current at start-up, flash time-out to prevent destruction of the LED caused by overheating, as well as a power NFET current limit and thermal protection function, both of which prevent overheating of the ADP1653.
The ADP1653 is sampling now and will be available in volume production in February 2007.
It is priced at US $1.45 per unit in 1000-piece quantities and is packaged in a 3 x 3mm LFCSP (lead-frame chip-scale package).
The device is specified over the industrial temperature range (-40 to +85C).
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