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A3907

Low Voltage Voice Coil Motor Driver

Allegro MicroSystems 

A3907

Low Voltage Voice Coil Motor Driver

Output Voltage Range

To guarantee the accuracy and linearity of the programmed cur-

rent, the voltage on the IOUT pin, VOUT , should be greater than

350 mV. The output voltage is a function of the battery voltage,

motor resistance, and the programmed load current, IOUT.

Clamp Diode

When the IC output is turned off, the load inductance causes the

output voltage, VOUT , to rise. An internal clamp diode, connected

between the IOUT and VDD pins, is integrated into the IC to

ensure the output voltage remains at a safe level.

¯S¯¯L¯¯E¯¯E¯¯P¯ Pin

The S¯¯L¯¯E¯¯E¯¯P pin is an active low input. A logic low signal disables

all of the internal circuitry and prevents the IC from draining bat-

tery power.

Applications 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 350mV to guarantee normal linear operation. VDD,

ILOAD, and RLOAD can be adjusted to ensure the device operates

in the linear range. When equation 7 is not satisfied, the load

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

the programmed level.

always be positive for each incremental step.

DNL = (IOUT(n+1) – IOUT(n)) / LSB ,

(8)

where (n = 64 to 1023). DNL should be < 1 LSB.

Offset Error The measured output current at Level Control

code 64, compared to the ideal value according to the transfer

function: 6.4 mA.

VDD(min) – RLOAD(max) × IOUT(max) ≥ 350 mV . (7)

IOUT Errors Defined

Relative Accuracy (INL) This error is calculated by measuring

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

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

sured values at Level Control code 63 and 1023 (see figure 2).

Differential Nonlinearity (DNL) A measure of the monoto-

nicity of the DAC (see equation 8). The slope of the line must

Gain Error The difference between the slopes of the ideal

transfer function and the actual transfer function. The gain error

is calculated by subtracting the offset error at Level Control code

16 from the actual transfer function. This calculated value is com-

pared to the ideal transfer function and reported as a percentage

of the ideal full scale value: 102.3 mA (see figure 3).

Gain Error Drift The change in slope of the transfer function

due to temperature, expressed as LSB / °C.

Allegro MicroSystems, LLC

8

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

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