Allegro current sensors not matching data sheet

Thread Starter

MikeKulls

Joined Apr 4, 2016
60
I have a few allegro current sensors, some 50A and some 150A. The datasheet says that the output voltage at 0 current for the unidirectional should be around 0.6V give or take. It says the voltage should be 2.5V for the bidirectional. Mine are all unidirectional and the voltage is close to 2.5V for some. Anyone know what is going on? I've checked the datasheet multiple times and it says the voltage should be 0.6V and rise at 60mV/A. If it starts off at 2.5V it will be at 2.5V + 0.06 * 50 = 5.5V. The supply voltage is only 5V so it doesn't seem to make sense. 0.6V + 0.06 * 50 = 3.6V would appear to make a lot more sense. Values I've measured are below. I am feeding it 5V taken off a raspberry pi. With the 3 pins facing down I am feeding the left pin 5V, middle pin gnd and measuring the right pin. Interesting thing is I have a 050U with all the same numbers that is giving the correct output and the 150Us are giving the correct output. I am hooking them up without the caps and resistor as recommended in the datasheet but I don't think that is it. I tried putting a cap on the power supply and that just made it bang on 2.5V. I'm thinking they are either mislabeled or I've fried them.

ACS758 KCB-150U 0.585V
ACS758 LCB-050U 2.546V
ACS758 LCB-050U 2.504V
ACS758 LCB-050U 2.461V
ACS758 KCB-150U 0.587V
ACS758 LCB-050U 0.596V (in circuit)
 

Alec_t

Joined Sep 17, 2013
14,280
The fact that the ones showing ~2.5V are all so close in value suggests that they are in working order (as bidirectional ones) but have simply been mislabelled. Did you buy them from a reputable source rather than an unheard-of online seller?
 
Last edited:

eetech00

Joined Jun 8, 2013
3,858
Hi

If I remember correctly, there will be an output offset of VCC/2. So if the supply is 5.0v, the offset will be 2.5v at 0 amps input. You have to use an opamp at the output to remove the offset if you want 0v output at 0 amps input.

Edit: Yes. Datasheet says 0.6v Quiescent Output Voltage for Unidirectional device. It also says the output is radiometric, so it will vary with the supply voltage.

Can you post schematic?

eT
 
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Thread Starter

MikeKulls

Joined Apr 4, 2016
60
Maybe not a reputable source, possibly ebay. I've had them sitting around for a while. Some could have come from Farnell or Digikey and some from eBay. Do they actually do fake chips like this?
 

Thread Starter

MikeKulls

Joined Apr 4, 2016
60
Schematic will just be from the datasheet. A 1uF cap on the power from a 7805 and a cap and resistor on the output. Going to a ADS1115 for measurement.
 

dendad

Joined Feb 20, 2016
4,451
Just an interesting hack. You can alter the offset if you carefully mount a magnet nearby as they are Hall sensors. So you can make bi-directional ones into uni-directional and vice-versa.
 

Thread Starter

MikeKulls

Joined Apr 4, 2016
60
Just an interesting hack. You can alter the offset if you carefully mount a magnet nearby as they are Hall sensors. So you can make bi-directional ones into uni-directional and vice-versa.
I think I'll just buy some new ones from Farnel, I mean element 14.
 
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