user38586: I'm driving a stepper rated at 5V/1.7A using an A4988-based driver circuit with a 12V power supply.  An Arduino controls the stepping sequence.
According to the datasheet for my A4988, I should be calculating Vref as:
Imax = Vref / (8 * Rs)  so,
Vref = I * (8 x Rs) (where Rs is 0.1 ohm on this particular board and confirmed with meter).
So, Vref should be (1.7A x .8) or 1.36V to drive 1.7amps.
The problem is, I cannot adjust the A4988 to get Vref up that high. 
With the adjustment pot full swing, the best I can get is .9 to 1V.  When I energize and hold the motor and use an amp meter, the coil is drawing about .9 amps -- which is still less than the 70% of 1.7 Amps I would like (using full-step mode).
Is Vref potential limited by the input voltage of 12 volts?  Is there something else I'm missing?
Thanks in advance.
Added:  This is the circuit I am using:


user68890: You have a 30K resistor divider in series with the trimmer. Change the 30K resistor for one rated at 27K to obtain those higher values. ;)

38586: <p>I'm driving a stepper rated at 5V/1.7A using an A4988-based driver circuit with a 12V power supply.  An Arduino controls the stepping sequence.</p>

<p>According to the datasheet for my A4988, I should be calculating Vref as:</p>

<p>Imax = Vref / (8 * Rs)  so,</p>

<p>Vref = I * (8 x Rs) (where Rs is 0.1 ohm on this particular board and confirmed with meter).</p>

<p>So, Vref should be (1.7A x .8) or 1.36V to drive 1.7amps.</p>

<p>The problem is, I cannot adjust the A4988 to get Vref up that high. </p>

<p>With the adjustment pot full swing, the best I can get is .9 to 1V.  When I energize and hold the motor and use an amp meter, the coil is drawing about .9 amps -- which is still less than the 70% of 1.7 Amps I would like (using full-step mode).</p>

<p>Is Vref potential limited by the input voltage of 12 volts?  Is there something else I'm missing?</p>

<p>Thanks in advance.</p>

<p>Added:  This is the circuit I am using:
<a href="https://i.stack.imgur.com/riJAo.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/riJAo.png" alt="enter image description here"></a></p>
 68890: <p>You have a 30K resistor divider in series with the trimmer. Change the 30K resistor for one rated at 27K to obtain those higher values. ;)</p>
