Discussion in 'The Projects Forum' started by TheNewGuy, Apr 4, 2013.

1. ### TheNewGuy Thread Starter New Member

Nov 16, 2012
2
0
I am trying to use the AD8215 current sensing chip, but I am having trouble making it work. I connected it as it shows in the datasheet for high side sensing. I am currently trying to test it out using a power source from our lab. The power source goes from 0-20 volts and has a max current of .4 amps. The shunt resistor that I am using is .042 Ohms. After the sensing I continue my to complete the circuit loop with a 1k Ohm power resistor then back to ground.

The datasheet says that the chip output with have the following equation.
OUTPUT=(Ishunt*Rshunt)*20
Using this eq. we are taking our output voltage and dividing it by (20*.042) which equals .84, so basically we get OUTPUT/.84 .

When we take measurements we get
INPUT Output from chip calculated Ishunt
10 V 9.4 V 11.19A
15 V 14.5 V 17.2A
I know that these are amps are way higher than what my power source can give, but do not see where I am going wrong.
Has anyone had similar issues with this chip. Could someone give me a point in the right direction? Does the amps have to be a certain level before the chip will work. The chip will be doing high side sensing. The input coming from a solar panel so the normal voltage will be around 28V and the current could be as high as 7 amps. I need to sense the current so that I can try to make a MPPT for the solar panel.

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2. ### crutschow Expert

Mar 14, 2008
19,805
5,543
Are you sure the resistor is 0.042 ohms?
Measure the voltage drop directly across the resistor to see if it's correct.
Post a complete circuit diagram of your setup.

3. ### Ron H AAC Fanatic!

Apr 14, 2005
7,049
673
Your amplifier is saturating at the positive rail. It sounds like your sense resistor is much too high, or even not connected. With a 1k load, you should be getting 16.8mV out.