DRV201A Datasheet, PDF (10/25 Pages) Texas Instruments – VOICE COIL MOTOR DRIVER FOR CAMERA AUTO FOCUS

DRV201A
SLVSBN6 – JUNE 2013
VCM DRIVER OUTPUT STAGE OPERATION
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Current in the VCM can be controlled with a linear or PWM mode output stage. Output stage is enabled in
ACTIVE mode which can be controlled through VCM_CURRENT control register and the output stage mode is
selected from MODE register bit PWM/LIN.
In linear mode the output PMOS is configured to a high side current source and current can be controlled from a
VCM_CURRENT registers.
In PWM control the VCM is driven with a half bridge driver. With PWM control the VCM current is increased by
connecting the VCM between V_BAT and GND through the high side PMOS and then released to a ‘freewheeling’
mode through the sense resistor and low side NMOS. Current in the VCM is sensed with a 1-Ω sense resistor
which is connected into an error amplifier input where the other input is controlled by the 10-bit DAC output.
PWM mode switching frequency can be selected from 0.5 MHz up to 4 MHz through a CONTROL register. PWM
or linear mode can be selected with the PWM/LIN bit in the MODE register.
RINGING COMPENSATION
VCM current can be controlled via an I²C interface and VCM_CURRENT registers. Lens stack is connected to a
spring which causes a dampened ringing in the lens position when current is changed. This mechanical ringing is
compensated internally by generating an optimized ramp whenever the current value in the VCM_CURRENT
register is changed. This enables a fast auto focus algorithm and pleasant user experience.
Ringing compensation is dependent on the VCM resonance frequency and this can be controlled via
VCM_FREQ register (07h) from 50 Hz up 150 Hz. Table 1 shows the VCM_FREQ register setting for each
resonance frequency in 1-Hz steps. If more accurate resonance frequency is available, the control value can be
calculated with Equation 1.
Ringing compensation is designed in a way that it can tolerate ±30% frequency variation in the VCM resonance
frequency when 2/f_VCM compensation is used and ±10% variation with 1/f_VCM so only statistical data from the
VCM is needed in production.
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