DRV201_15 Datasheet, PDF (9/29 Pages) Texas Instruments – DRV201 Voice Coil Motor Driver for Camera Auto Focus

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7.2 Functional Block Diagram
Cin
VBAT
DRV201
SLVSB25C – AUGUST 2011 – REVISED JUNE 2015
OSCILLATOR
REFERENCE
POR
10-bit
DAC
DIGITAL
REGISTERS
RINGING
SCL
COMPENSATION
I2C
SDA
GND
ISOURCE
VCM
ISINK
Rsense
7.3 Feature Description
7.3.1 VCM Driver Output Stage Operation
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.
7.3.2 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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