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# MPY634 use as divider

My question is about the "10 to 1 denominator range" mentioned in the data sheet on page 7.  What exactly is this denominator range?  Is this with reference to the numerator?

Question springs from the fact that in my current circuit, I am getting low accuracy for Z input closer to 0 keeping X inputs constant.

• Hi,

The MPY634 transfer function in the divider mode is:

Vout = ((10(Z2 - Z1) / (X1 - X2)) + Y1

The Vout accuracy statement is in relation to the difference in the two denominator numbers. It states that the typical accuracy has a range of 1.0 to 2.5%, for a 10 to 1 denominator range. For example, if X1= +5V, and X2= -5V, the denominator has a value of 10. Then, if  X1= +0.5V and X2= -0.5V, the denominator has a value of 1. So for any denominator difference value that is between 1 and 10, the Vout accuracy will typically be between 1.0 and 2.5%.

Regards, Thomas

PA - Linear Applications Engineering

• In reply to Thomas Kuehl:

If I'm following your answer correctly, this means that applying a trimming voltage of +/-3.5mV to the low X input allows for a 100V denominator value (further down the data sheet there is a reference to 100 to 1 denominator range) - is this correct?

Hi,

Well, my lack of familiarity with the MPY634 operating in divider mode may have led me to some incorrect conclusions. So after giving it more thought here is what I have concluded:

Data-sheet Figure 4 shows the X-denominator inputs have a voltage range of 0.1V ≤ X ≤ 10V. The X1 input is required to be more positive than X2 for correct feedback polarity. If we consider the input voltage in terms of a range, the 10:1 range could be 10V:1V, 5V:0.5V, 1V:0.1V, etc, and it is across a 10:1 range that the accuracy is typically 1 to 2.5%.

Indeed the range can be increased to 100:1, such as 10V:0.1V, but the inaccuracy may exceed 2.5% unless the optional trim voltage (+/-3.5mV) is applied to the X2 input.

Regards, Thomas

PA - Linear Applications Engineering

• In reply to Thomas Kuehl:

sir,

How to apply trim voltage to X2. My X1 input is positive always but still I am getting some voltage at output in divider config even when the numerator is 0 volt or Z2-Z1 is 0volt. How to balance this to make output 0 for numerator part 0? Please illustrate with diagram