Allegro MicroSystems Inc. introduced 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 to 5.5V. It has a maximum output current of 102mA with an operating temperature range of -40 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 100µA 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 100nA. Logic input levels are I²C compatible and are independent of VDD.
According to the company, 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 200µs 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 781nsec. In the other half of the ramp a programmable delay of between 6.25µs and 200µs is inserted between each of the remaining current steps.
Allegro’s A3907ECGTR is supplied in a small (1.465 Ãƒï¿½ 0.965mm) 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.