AD5820 데이터 시트보기 (PDF) - Analog Devices

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AD5820

AD5820 Evaluation System QuickStart Guide

Analog Devices 

Figure 1. Board configuration and jumper setting.

OUTPUT SLEW RATE CONTROL

The AD5820 is designed to drive both spring preloaded and nonspring linear motors used

in applications such as lens autofocus, image stabilization, or optical zoom. The operation

principle of the spring-preloaded motor is that the lens position is controlled by the

balancing of a voice coil and spring.

The requirement to reduce optical module form factors has led to a reduction in the size

of VCM actuators. As VCM actuators reduce in size, the preloaded balance spring

strength also reduces. When large current transitions occur, the momentum of the lens

can often lead to overshoot and VCM can take some time to settle to its final position.

This phenomenon, often described as mechanical ringing, varies with output current step

size and for large lens displacements can lead to unacceptably long auto focus times. The

AD5820’s unique and proprietary output slew rate control design allows the user to

overcome the mechanical limitations associated with reductions in VCM form factor.

The AD5820 uses an innovative and proprietary scheme to provide the user with the

option of three slew rate control modes. These control modes are exercised via the I2C

bus and are controlled by bits S3 to S0 (bit 3 to bit 0) in the data byte. Table 8 describes

the AD5820 slew rate control modes. The AD5820 contains an 20kHz integrated clock

generator and divider circuitry. This clock generator controls the transition step duration

when the Slew Rate Control bits S2 to S0 are used.

Table 9 shows the truth table and current transition step size for the slew rate control

options. The slew rate control mode feature of the AD5820 allows the user to customise

output transition times and where mechanical ringing is an issue the AD5820 output can

be programmed to effectively decelerate the lens movement as it approaches its target

position; thereby reducing the overshoot and minimising mechanical ringing.

Table 1. Slew Rate Control Modes

Mode 0 Direct Load Mode

When S2, S1 and S0 are zero (code 0 and code 8 in the table below), the output will go to the target code

within the AD5820 settling time. This is software compatible with the AD5398 and the AD5821.

S3 has no effect when S2 to S0 are zero.

Mode 1

Linear Ramp Mode

When S3 is zero and S2 to S0 are non-zero (code 1 to code 7 in the table below), the output will

increment/decrement to the target code in single code steps. The code step duration is selected by S2 to

S0 to be 50us to 3.2ms per step

Mode 2

64/16 Ramp Mode

When S3 is 1 and S2 to S0 are non-zero (code 9 to code 15 in the table below), the output will transition

to the new value in multi-code steps.

• If the Target DAC Code is greater than 128 codes from current DAC code, the AD5820 DAC

will increment in 64 DAC code steps.

• When the current position DAC code is between 16 codes and 128 codes from the target

position, the DAC will increment in 16 Code Steps.

• When the current position DAC code is less than 16 codes from the target, it will step directly

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