DRV201A Datasheet, PDF (8/25 Pages) Texas Instruments – VOICE COIL MOTOR DRIVER FOR CAMERA AUTO FOCUS

DRV201A
SLVSBN6 – JUNE 2013
FUNCTIONAL DESCRIPTION
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The DRV201A is intended for high performance autofocus in camera modules. It is used to control the current in
the voice coil motor (VCM). The current in the VCM generates a magnetic field which forces the lens stack
connected to a spring to move. The VCM current and thus the lens position can be controlled via the I²C
interface and an auto focus function can be implemented.
The DRV201A offers a higher level of performance than the DRV201 in two areas. First, the transition between
PWM and linear modes is free of any resonance. This allows faster image capture after achieving focus in the
PWM mode. The other performance enhancement is in the area of EMC performance. When operating in PWM
mode, transitions were significantly slowed down resulting in lower conducted and radiated noise versus the
DRV201.
The device connects to a video processor or image sensor through a standard I²C interface which supports up to
400-kbit/s data rate. The digital interface supports IO levels from 1.8 V to 3.3 V. All pins have 4-kV HBM ESD
rating.
When SCL is low for at least 0.5 ms, the device enters SHUTDOWN mode. If SCL goes from low to high the
driver enters STANDBY mode in less than 100 μs and default register values are set as shown in Figure 5.
ACTIVE mode is entered whenever the VCM_CURRENT register is set to something else than zero.
Vbat
ISC/SCL
t1
t2
t3
t4
DAC
mode SHUTDOWN
=0
STANDBY
0
ACTIVE
=0
STANDBY SHUTDOWN
Figure 5. Power Up and Down Sequence
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 autofocus algorithm and pleasant user experience.
Current in the VCM can be generated with a linear or PWM control. In linear mode the high side PMOS is
configured as a current source and current is set by the VCM_CURRENT control register. 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. 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.
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