A3904 データシートの表示（PDF） - Allegro MicroSystems

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A3904

Low Voltage Voice Coil Motor Driver

Allegro MicroSystems 

A3904

Low Voltage Voice Coil Motor Driver

Application Information

Headroom The current may not reach the programmed level

if there is not adequate headroom in the output circuit. The IC

output voltage must be over 500 mV to guarantee normal linear

operation. VDD, ILOAD, and RLOAD can be adjusted to ensure that

the device operates in the linear range.

be positive for each incremental step, according to the following

formula:

DNL = (IOUT(n+1) – IOUT(n) ) / LSB – 1 (LSB) .

where n is in the range 16 to 255.

If the equation shown below is not satisfied, the load current

will be limited by the series impedance, and may not reach the

programmed level

VDD(min) – RLOAD(max) × IOUT(max) ≥ 500 mV .

IOUT Errors

Relative accuracy (INL) This error is calculated by measuring

the worse case deviation from a straight line, defined from end

points. The straight line end points are defined by the actual mea-

sured values at Code = 16 and Code = 255. See figure 1.

Offset error The measured output current at input Code = 16,

compared to the ideal value according to the transfer function

(8 mA).

Gain Error The difference in the slopes of the ideal transfer

function and the actual transfer function. The gain error is calcu-

lated by subtracting out the offset error, at Code = 16, from the

actual transfer function. This calculated value is compared to the

ideal transfer function and reported as a percentage of the ideal

full scale value (127.5 mA). See figure 2.

Differential nonlinearity (DNL) A measure of the monotonic-

ity of the D-to-A converter. The slope of the line must always

Gain Error Drift The change in slope of the transfer function

due to temperature, expressed as LSB/°C.

127.5

96.0

INL

127.5

Offset

Error

Gain

Error

64.0

32.0

0

0 16

128

255

Code

Straight line between measured Codes 16 and 255

Relative Accuracy ( Codes 16-255), errors exaggerated for clarity

0

0 16

128

255

Code

Ideal DAC

Actual DAC, errors exaggerated for clarity

Calculated Gain Error, Offset Error removed

Figure 1. Relative accuracy error

Figure 2. Gain error

Allegro MicroSystems, Inc.

6

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

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