BU64987GWZ Datasheet, PDF (9/25 Pages) Rohm – Bi-directional VCM driver for Auto focus

BU64987GWZ
T
Displacem^? e^?nt ^?
?_(µmµm₎ ?
0
Time
(ms)
Figure 9. Actuator Displacement Waveform (ISRC Disabled)
The resonant frequency (Hz) of the actuator can be calculated with Equation 3 using the resonant period observed in
Figure 9.
f0 = (T)^-1
Equation 3. Resonant Frequency vs. Time Period Relationship
After calculating the correct resonant frequency, program the closest value in the three MSBs of the third byte of the
W[2:0] = 0b100 register using the 5-bit rf[4:0] values from Table . When calculating the resonant frequency take care
that different actuator samples’ resonant frequencies might vary slightly and that the frequency tolerance should be taken
into consideration when selecting the correct driver resonant frequency value.
Table 3. Resonant Frequency Settings
rf[4:0]
f0
rf[4:0]
f0
rf[4:0]
f0
rf[4:0]
f0
0b00000
-
0b01000
85 Hz
0b10000
125 Hz
0b11000
-
0b00001
50 Hz
0b01001
90 Hz
0b10001
130 Hz
0b11001
-
0b00010
55 Hz
0b01010
95 Hz
0b10010
135 Hz
0b11010
-
0b00011
60 Hz
0b01011
100 Hz
0b10011
140 Hz
0b11011
-
0b00100
65 Hz
0b01100
105 Hz
0b10100
145 Hz
0b11100
-
0b00101
70 Hz
0b01101
110 Hz
0b10101
150 Hz
0b11101
-
0b00110
75 Hz
0b01110
115 Hz
0b10110
-
0b11110
-
0b00111
80 Hz
0b01111
120 Hz
0b10111
-
0b11111
-
Selecting the Autofocus Algorithm’s Target DAC Codes
The ISRC algorithm is a proprietary technology developed to limit the ringing of an actuator by predicting the magnitude
of ringing created by an actuator and intelligently controlling the output signal of the driver to minimize the ringing effect.
Due to the ringing control behavior of ISRC, it is unable to operate properly unless the lens is floating (lens lifted off of the
mechanical end of the actuator). As such the ringing control behavior is broken into three separate operational areas in
order to provide the most optimally controlled autofocus algorithm. Please note that bidirectional VCM actuators are
inherently in a naturally floating position and as a result only the final target position is required for correct ISRC operation.
Direct Mode
Step Mode
ISRC Mode
Final target DAC
Point C
Bidirectional VCM
Displacement
(µm)
Traditional VCM
Naturally
floating
Point B
Point A
0
A: lens displacement = 0 µm
B: all lenses floating
C: final lens position
DAC code
Figure 10. Lens Displacement vs. DAC Code with a Traditional VCM Actuator
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TSZ22111・15・001
9/21
TSZ02201-0K1K0B601860-1-2
6. Oct.2016 Rev.001