MAX471 giving too high current readings

Question

I want to measure current using the MAX471 sensor that outputs voltage proportional to the current (1V/A according to the datasheet). To test the module, I connected a 330 ohm resistor to the sensor and powered it from 3.3V arduino. Using ohms law, I was expecting an output voltage of around 10 mV (for ~ 10 mA) in my circuit. However, I am getting an output of around 2.17 volts which seems wrong.

Does anyone see any mistake in my circuit or how I am trying to measure the current?

Here is my circuit:

My Code:

#include <Arduino.h>

void setup()
{
  Serial.begin(115200);
}

void loop()
{
  int adc_val = analogRead(A5);
  float vol = 3.2 / 4095 * adc_val; // using a 12 bit adc

  Serial.println(vol);
  delay(3000);
}

Answer 1

Do you have the same operating circuit that is shown on page 1 of the datasheet? do you have the 2K resistor they specifically from OUT to ground? Also, it may be worth adding the 1 uF capacitor they recommend from OUT to ground too

The other thing to consider is the actual voltage over the resistor. Check an see if the voltage over the resistor is 3.3 and that there isn't a voltage drop from the chip

If the voltage is fine, there may be a problem with the chip or the arduino

Answer 2

I've got a few MAX471 modules and instead of current readings i get around 90% of input voltage on all of them.

With increasing load the output voltage decreases a bit and the MAX471 chip gets very hot (for example 12V 0mAh = 10V, 12V 200mAh = 9,6V).

I guess we are just "lucky" to get a bad batch or counterfeit chips...