BU64241GWZ Datasheet, PDF (17/24 Pages) Rohm – Linear Constant Current VCM Driver

BU64241GWZ
Datasheet
・Step B6 – DAC Code Update Timing Considerations
Settling time is controlled by the resonant frequency of the actuator and the driver’s slew rate speed setting. Depending
on the combination of these parameters, the settling time can be such that updating point C with a new DAC code before
the lens has settled at the original point C DAC code can adversely affect the settling time due to increased ringing
effects. Utilize the slew rate speed parameter in order to modify the settling time so that any updates to the point C
DAC code do not occur before the lens has settled.
Please review the following example based on an actuator with a resonant frequency of 100 Hz:
Table 5. Relationship Between Slew Rate Speed and Settling Time Based on a 100 Hz Actuator
f₀
slew_rate[1:0] Settling Time
00
52 ms
100 Hz
01
42 ms
10
26 ms
11
18 ms
In this example the settling time of the actuator can vary by up to ± 5 % due to the internal oscillator (MCLK) having a
variance of ± 5%. The settling time has a proportionally inverse relationship to the resonant frequency and therefore the
settling time can be estimated as:
Table 6. Relationship Between Slew Rate Speed and Settling Time Based on a General Resonant Frequency f₀’
f₀’
slew_rate[1:0] Settling Time
00
52 * (100 / f₀’) ms
f₀’ Hz
01
42 * (100 / f₀’) ms
10
26 * (100 / f₀’) ms
11
18 * (100 / f₀’) ms
Note that the orientation of the camera module can affect the settling time due to the influence of gravity on the lens.
・Step C1 – Power Save Operation
The BU64241GWZ can be set to enter power save mode either by setting the external power save pin = VPSL (typically
0 V) or by setting the 2-wire serial PS bit = 0. It is recommended to use the external power save pin method since this
will disable the internal MCLK to achieve lower power consumption while in standby mode. Please note that setting the
external power save pin = VPSL will reset all 2-wire serial registers to 0.
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TSZ22111・15・001
17/20
TSZ02201-0H2H0B600460-1-2
01. Jul. 2013 Rev.004