Current Sense Amplifier application of MC9S12ZVMC25F1WKK

[wangzhen]

Application background：

We are using MC9S12ZVMC25F1WKK intending to drive a motor (SRM) by its on-chip GDU module. The figure as shown is Current Sense Amplifier circuits configured with the datasheet.

Description:

• Normal：I = 0,in the case of disabling the amplifier, V_AMP ≈ 7mV; When enabled the amplifier V_AMP ≈ 0.96V.
• Abnormal：I = 0, in the case of disabling the amplifier, V_AMP ≈ 73mV; When enabled the amplifier, V_AMP ≈ 1.12V.

In addition, No matter Normal or Abnormal, it has been confirmed that the positive input voltage of the amplifier is 33 mV and V_offset is 0 . 

Questions：

1. When disabled the amplifier, its output is shut down. But where is the “73mV” from? Why the actual value of the output voltage is larger than the calculated value when enabled the amplifier?
2. Is there a fault that includes configuring error and going wrong itself in the integrated amplifier?
3. Is the deviation between Normal and Abnormal only a difference between individuals? If so, what’s the reasons for generating the large deviation?

[pachamatej]

Hi,

Please replace the 200 ohm resistor with 1K. WHy?

1) Gain = 30k/200 = 150 is probably out of specification of the amplifier

2) Since Rp = Rn, then Rp/a = Rn/a. Your opamp configuration is unbalanced, therefore, I'm pretty sure it will not work.

Best regards

Matej