**Part Number:**MPY634

**Other Parts Discussed in Thread:**OPA564, TINA-TI

Hi, I am using MPY634 as a signal conditioning of my DAC output.

I am using the MPY634 in the Basic Multiplier Connection, as the datasheet shows. I connected X1, Y1, and Z2, each to its own DAC output, while X2 and Y2 are connected to GND. The MPY634's output is then connected to OPA564, and the OPA564's output is connected to the load.

In general, my main DAC's output flows through X1 into OPA564 and finally into the load. I ran a measurement test where I swept the voltage I applied to a 120 Ω. The is swept from -10 V to 10 V with a 0.5 V step. As shown below, I derived a linear transfer function from the measurement results that map the DAC's output (x) to the OPA564's output (y).

y=Mx+C

To achieve the desired M=1 and C=0, I tuned the system by modifying Y1 and Z2 voltages with secondary DACs. I reduced Y1 to around 200 mV, reran the measurement test, and obtained the same transfer function (same M and C). I then reduced the Y1 for another 200 mV and reran the measurement test, yet I still obtained the same transfer function. I did this several times until Y1 is 1 V lower than its initial value (before any voltage reduction). Only then did the transfer function (value of M) change. The problem is the value of M jumps too big because it is 1 V lower than its initial value.

It seems that the MPY634 output won't respond to the 200 mV change of Y1. Is this an expected behavior, or am I missing something?