Motor Driver enables camera phone autofocus and zoom.
April 13, 2009 -
Operating in temperatures from -40°C to +85°C, A3907 Voice Coil Motor Driver features voltage range of 2.3-5.5 V with maximum output current of 102 mA. Output current is programmed via I2C interface in 100 µA increments and unit features input supply current of less than 100 nA in sleep mode. Programmable output current slew rate control minimizes ringing and settling time. When new current level is programmed, driver steps through all current levels between initial/final desired level.
(Archive News Story - Products mentioned in this Archive News Story may or may not be available from the manufacturer.)
Original Press release
Allegro MicroSystems Inc.
115 N.E. Cutoff, P.O. Box 15036
Worcester, MA, 01615
USA
Allegro MicroSystems, Inc. Introduces New Voice Coil Motor Driver
Worcester, MA - March 27, 2009 - Allegro introduces a new voice coil motor (VCM) driver with I2C serial interface designed for camera lens auto focus and zoom applications. The operating voltage range for this new device is 2.3 V to 5.5 V. It has a maximum output current of 102 mA with an operating temperature range of -40°C to +85°C. This new device is targeted at both the consumer and telecommunications markets.
The output current is programmed via the I2C interface in 100 µA increments. I2C inputs set the internal 10-bit DAC output voltage reference for linear current control using an MOSFET output sink transistor and sense resistor feedback. Input supply current in sleep mode is typically less than 100 nA. Logic input levels are I2C compatible and are independent of VDD.
In most auto focus applications the lens is driven by a VCM preloaded with a spring. The lens position is proportional to current in the VCM. When the VCM current is changed the lens has a tendency to overshoot and ring at its final position. The settling time for the ringing will add to the auto focus time thereby increasing the time between photos. In order to reduce the ringing and settling time Allegro's A3907 offers programmable output current slew rate control. When a new current level is programmed the device steps through each possible current level between initial and final desired level. The delay between each of these levels can be programmed to automatically create either a linear ramp, two step ramp or no ramp between initial and final current. The linear ramp can be programmed with delays from 0 (no ramp) to 200 µsec in 7 possible increments. The two-step ramp takes half of the current steps between initial and final current and creates delays between them of 781 nsec. In the other half of the ramp a programmable delay of between 6.25 µsec and 200 µsec is inserted between each of the remaining current steps.
Allegro's A3907ECGTR is supplied in a small (1.465 - 0.965 mm) six-bump wafer level chip scale package (WLCSP) suffix CG package. This package is lead (Pb) free. It is priced at $0.34 in quantities of 1,000 and has a 12-week lead-time to market.
About Allegro
Allegro MicroSystems, Inc. is leader in developing, manufacturing and marketing high-performance power integrated circuits and integrated Hall-effect magnetic sensors. Allegro's innovative solutions serve high-growth applications within the automotive, communications, computer/office automation, consumer and industrial markets. Allegro is headquartered in Worchester, Massachusetts (USA) with design and applications center located in North and South America, Asia, and Europe. Further information about Allegro can be found at www.allegromicro.com.
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